Energies

Research

15 pages, 3205 KiB

Open AccessArticle

Hybrid HVDC (H²VDC) System Using Current and Voltage Source Converters

by José Rafael Lebre¹, Paulo Max Maciel Portugal²

and Edson Hirokazu Watanabe^1,*

¹ Electrical Engineering Program, COPPE—Federal University of Rio de Janeiro, Athos da Silveira Ramos 149, 68504 Rio de Janeiro, Brazil

² Furnas Centrais Elétricas, Departament of Operation Electrical Studies, Real Grandeza 219, Botafogo, 68504 Rio de Janeiro, Brazil

Energies 2018, 11(6), 1323; https://doi.org/10.3390/en11061323 - 23 May 2018

Cited by 13 | Viewed by 4762

Abstract

This paper presents an analysis of a new high voltage DC (HVDC) transmission system, which is based on current and voltage source converters (CSC and VSC) in the same circuit. This proposed topology is composed of one CSC (rectifier) and one or more [...] Read more.

This paper presents an analysis of a new high voltage DC (HVDC) transmission system, which is based on current and voltage source converters (CSC and VSC) in the same circuit. This proposed topology is composed of one CSC (rectifier) and one or more VSCs (inverters) connected through an overhead transmission line in a multiterminal configuration. The main purpose of this Hybrid HVDC (H²VDC), as it was designed, is putting together the best benefits of both types of converters in the same circuit: no commutation failure and system’s black start capability in the VSC side, high power converter capability and low cost at the rectifier side, etc. A monopole of the H²VDC system with one CSC and two VSCs—here, the VSC is the Modular Multilevel Converter (MMC) considered with full-bridge submodules—in multiterminal configuration is studied. The study includes theoretical analyses, development of the CSC and VSCs control philosophies and simulations. The H²VDC system’s behavior is analyzed by computational simulations considering steady-state operation and short-circuit conditions at the AC and DC side. The obtained results and conclusions show a promising system for very high-power multiterminal HVDC transmission. Full article

(This article belongs to the Special Issue Power Electronics and Power Quality)

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17 pages, 8011 KiB

Open AccessArticle

Gear Ratio Optimization of a Multi-Speed Transmission for Electric Dump Truck Operating on the Structure Route

by Senqi Tan

, Jue Yang^*

, Xinxin Zhao, Tingting Hai and Wenming Zhang

School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China

Energies 2018, 11(6), 1324; https://doi.org/10.3390/en11061324 - 23 May 2018

Cited by 30 | Viewed by 7476

Abstract

Research demonstrated that the application of a multi-speed transmission could improve the dynamic and economic performance of electric vehicles. This paper deals with a novel multi-speed transmission for the electric dump truck (EDT) operating on the structure route (SR), which has a definite [...] Read more.

Research demonstrated that the application of a multi-speed transmission could improve the dynamic and economic performance of electric vehicles. This paper deals with a novel multi-speed transmission for the electric dump truck (EDT) operating on the structure route (SR), which has a definite starting point and end point without complex traffic conditions. To optimize the gear ratio and shift schedule to reduce energy consumption in such conditions, the mathematical model of the transmission and the dynamic model of the EDT are initially required. Following this, the shift schedule is presented according to the motor efficiency map. After that, the gear ratio optimization is carried out by a particle swarm optimization (PSO) algorithm. Moreover, the proposed EDT is compared with an EDT with a single-speed transmission. The simulation results show that the energy consumption is reduced by 6.1%. Full article

(This article belongs to the Collection Electric and Hybrid Vehicles Collection)

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18 pages, 7141 KiB

Open AccessArticle

An Integrated Current-Voltage Compensator Design Method for Stable Constant Voltage and Current Source Operation of LLC Resonant Converters

by Yeong-Jun Choi

, Hwa-Rang Cha

, Sang-Min Jung

and Rae-Young Kim^*

The Department of Electrical and Biomedical Engineering, Hanyang University, Seoul 04763, Korea

Energies 2018, 11(6), 1325; https://doi.org/10.3390/en11061325 - 23 May 2018

Cited by 4 | Viewed by 3904

Abstract

This paper proposes a method to charge a lithium ion battery with an integrated compensator. Unlike the conventional charging method which uses separate voltage/current compensators based on a constant voltage-constant current charge profile, the proposed method uses a single compensator. The conventional method [...] Read more.

This paper proposes a method to charge a lithium ion battery with an integrated compensator. Unlike the conventional charging method which uses separate voltage/current compensators based on a constant voltage-constant current charge profile, the proposed method uses a single compensator. The conventional method requires a complicated design process such as separate plant modeling for compensator design and the compensator tuning process in the frequency domain. Moreover, it has the disadvantage of a transient state between the mode change. However, the proposed method simplifies the complicated process and eliminates the transient response. The proposed compensator is applied to the LLC resonant converter and is designed to provide smooth and reliable performance during the entire charging process. In this paper, for the compensator design, the frequency domain models of the LLC resonant converter at the constant voltage and constant current charging mode are derived including the impedance model of the battery pack. Additionally, the worst condition of the compensator design during the entire charging process is considered. To demonstrate the effectiveness of the proposed method, the theoretical design procedure is presented in this paper, and it is verified through experimental results using a 300 W LLC converter and battery pack. Full article

(This article belongs to the Special Issue Power Electronics 2018)

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23 pages, 8555 KiB

Open AccessArticle

3D Numerical Simulation and Experiment Validation of Dynamic Damage Characteristics of Anisotropic Shale for Percussive-Rotary Drilling with a Full-Scale PDC Bit

by Guangjian Dong^1,2,*

and Ping Chen^1,2,*

¹ State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China

² College of Oil and Gas Engineering, Southwest Petroleum University, Chengdu 610500, China

Energies 2018, 11(6), 1326; https://doi.org/10.3390/en11061326 - 23 May 2018

Cited by 33 | Viewed by 3921

Abstract

The lower rate of penetration (ROP) is one of the key technical difficulties during drilling of shale reservoirs. Percussive-rotary drilling (PRD) is crucial for increasing ROP. One of the core problems of ROP optimization for PRD are the dynamic damage characteristics of rock [...] Read more.

The lower rate of penetration (ROP) is one of the key technical difficulties during drilling of shale reservoirs. Percussive-rotary drilling (PRD) is crucial for increasing ROP. One of the core problems of ROP optimization for PRD are the dynamic damage characteristics of rock fragmentation. By considering the dynamic drilling parameters, a new model for estimating the PRD with a full-scale polycrystalline diamond compact (PDC) bit is established. The mechanical parameters of shale are measured by a wave velocity method. Rock damage characteristics are simulated by using the finite element method. The numerical simulation model is verified by the actual drilling case in LMX shale reservoir in Sichuan (China). The results indicate that rock element damage occurs along the direction of maximum principal stress. The order of decreasing rock damage rate is impact-static load, static load and impact load. When the impact load has the same peak value, and the rock elements in contact with the cutters obtain more energy with load frequency increasing. The rock fragmentation efficiency under a sine wave is higher than rectangular and pulse waves. The rock can obtain more energy to be broken with the increasing impact load duration and peak values. When the impact-static load goes over the rock damage threshold value, the higher the peak value of the impact load is, the more energy the rock will obtain. The higher the lateral vibration amplitude of the drill bit, the lower the efficiency of rock fragmentation. Repetitions of drill bit axial vibration at one indentation point will reduce the ROP, and the axial vibration energy of the drill bit is consumed. Therefore, a small lateral movement and reasonable axial vibration frequency increase the rock breaking efficiency. The ROP was increased through the suppression of drill string and the application of vibration. The study results can be used in the optimization designs of bit trajectory and ROP for PRD tools. Full article

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25 pages, 12638 KiB

Open AccessArticle

ICT Based HIL Validation of Voltage Control Coordination in Smart Grids Scenarios

by Kamal Shahid^1,*

, Lennart Petersen², Rasmus Løvenstein Olsen¹ and Florin Iov²

¹ Department of Electronic Systems, Aalborg University, 9220 Aalborg, Denmark

² Department of Energy Technology, Aalborg University, 9220 Aalborg, Denmark

Energies 2018, 11(6), 1327; https://doi.org/10.3390/en11061327 - 23 May 2018

Cited by 2 | Viewed by 2900

Abstract

This paper aims to validate the capability of renewable generation (ReGen) plants to provide online voltage control coordination ancillary service to the system operators in smart grids. Simulation studies about online coordination concepts from ReGen plants have already been identified in previous publications. [...] Read more.

This paper aims to validate the capability of renewable generation (ReGen) plants to provide online voltage control coordination ancillary service to the system operators in smart grids. Simulation studies about online coordination concepts from ReGen plants have already been identified in previous publications. However, here, the results are validated through a real-time Hardware-In-the-Loop framework using an exemplary benchmark grid area in Denmark as a base case that includes flexible renewable power plants providing voltage control functionality. The provision of voltage control support from ReGen plants is verified on a large-scale power system against the baseline scenario, considering the hierarchical industrial controller platforms used nowadays in power plants. Moreover, the verification of online voltage control support is carried out by taking into account a communication network as well as the associated data traffic patterns obtained from a real network. Based on the sets of recordings, guidelines and recommendations for practical implementation of the developed control algorithms for targeted ancillary service are made. This provides a deep insight for stakeholders, i.e., wind turbine and photo-voltaic system manufacturers and system operators, regarding the existing boundaries for current technologies and requirements for accommodating the new ancillary services in industrial application. Full article

(This article belongs to the Section A: Sustainable Energy)

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27 pages, 2522 KiB

Open AccessArticle

Modified Cuckoo Search Algorithm: A Novel Method to Minimize the Fuel Cost

by Thang Trung Nguyen¹, Dieu Ngoc Vo²

, Nguyen Vu Quynh³

and Le Van Dai^4,5,*

¹ Power System Optimization Research Group, Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam

² Department of Power Systems, Ho Chi Minh City University of Technology, Ho Chi Minh City 700000, Vietnam

³ Department of Electrical Engineering, Lac Hong University, Bien Hoa 810000, Vietnam

⁴ Institute of Research and Development, Duy Tan University, Danang 550000, Vietnam

⁵ Office of Science Research and Development, Lac Hong University, Bien Hoa 810000, Vietnam

Energies 2018, 11(6), 1328; https://doi.org/10.3390/en11061328 - 23 May 2018

Cited by 20 | Viewed by 3771

Abstract

Economic load dispatch (ELD) is an important optimization problem for operating and controlling modern power systems, and if ELD is effectively executed, power systems work stably and economically. The main objective of this paper is to develop a novel method to solve the [...] Read more.

Economic load dispatch (ELD) is an important optimization problem for operating and controlling modern power systems, and if ELD is effectively executed, power systems work stably and economically. The main objective of this paper is to develop a novel method to solve the ELD with the purpose of minimizing the total fuel cost of all available generating units while requirements are to satisfy all constraints regarding thermal units, generators, and transmission power networks. The proposed high performance cuckoo search algorithm (HPCSA) is developed from the efficient technique for the second new solution generation of conventional cuckoo search algorithm (CCSA), called adaptive mutation technique. This proposed technique diversifies the local search ability based on a new comparison criterion. The HPCSA is verified on difference systems under special conditions, namely the 10-unit system with multi fuels, 15-unit system considering prohibited operating zones, and three IEEE systems with 30, 57, and 118 buses considering transmission power network constraints. The specific evaluation of the HPCSA is compared to that of Lagrange optimization-based methods (LMS), neural network-based methods (NNMS), CCSA, and other popular methods such as Particle swarm optimization (PSO) variants, Differential evolution (DE) variants, Genetic Algorithm (GA) variants, and state-of-the-art methods. In comparison with CCSA, the proposed method is always more effective and more robust since the proposed method can find most solutions with better quality and faster convergence speed. In comparison with LMS and NNMS, the proposed method can also find solutions with approximate or equal quality. In comparison with popular methods and state-of-the-art methods, the proposed method has more potential since it can reach faster convergence to valid solutions with approximate or better quality. Consequently, it can be concluded that the proposed HPCSA is an effective optimization tool for dealing with ELD problems. Full article

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26 pages, 3879 KiB

Open AccessArticle

ICT Based Performance Evaluation of Primary Frequency Control Support from Renewable Power Plants in Smart Grids

by Kamal Shahid^1,*

, Müfit Altin²

, Lars Møller Mikkelsen¹, Rasmus Løvenstein Olsen¹ and Florin Iov³

¹ Department of Electronic Systems, Aalborg University, 9220 Aalborg, Denmark

² DTU Wind Energy, 4000 Roskilde, Denmark

³ Department of Energy Technology, Aalborg University, 9220 Aalborg, Denmark

Energies 2018, 11(6), 1329; https://doi.org/10.3390/en11061329 - 23 May 2018

Cited by 6 | Viewed by 3872

Abstract

The increased penetration of Renewable Energy Generation (ReGen) plants in future power systems poses several challenges to the stability of the entire system. In future green energy rich power systems, the responsibility for providing ancillary services will be shifted from conventional power plants [...] Read more.

The increased penetration of Renewable Energy Generation (ReGen) plants in future power systems poses several challenges to the stability of the entire system. In future green energy rich power systems, the responsibility for providing ancillary services will be shifted from conventional power plants towards ReGen plants, such as wind and photovoltaic power plants. Frequency control support from the Wind Power Plants (WPPs) is one of the crucial ancillary services in order to preserve operational stability in case of grid disturbances. Among other requirements, the ability to provide fast frequency control support from ReGen plants will highly depend on the underlying communication infrastructure that allows an exchange of information between different ReGen plants and the control centers. This paper, therefore, focuses on the evaluation of the impact of communication and the related aspects to provide online frequency control support from ReGen (with special focus on WPP). The performance evaluation is based on an aggregated WPP model that is integrated into a generic power system model. This generic power system model is specifically designed to assess the ancillary services in a relatively simple yet relevant environment. Several case studies with different wind speeds at a particular wind-power penetration level and communication scenarios are considered to evaluate the performance of power system frequency response. The article provides the Transmission System Operator (TSO) and other communication engineers insights into the importance and various aspects of communication infrastructure for general service coordination between WPPs and specifically primary frequency control coordination from WPPs in future power systems. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2018)

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10 pages, 5743 KiB

Open AccessArticle

Visualization of Operational Performance of Grid-Connected PV Systems in Selected European Countries

by Bala Bhavya Kausika^*

, Panagiotis Moraitis

and Wilfried G. J. H. M. Van Sark

Copernicus Institute, Utrecht University, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands

Energies 2018, 11(6), 1330; https://doi.org/10.3390/en11061330 - 23 May 2018

Cited by 14 | Viewed by 3441

Abstract

This paper presents the results of the analyses of operational performance of small-sized residential PV systems, connected to the grid, in the Netherlands and some other European countries over three consecutive years. Web scraping techniques were employed to collect detailed yield data at [...] Read more.

This paper presents the results of the analyses of operational performance of small-sized residential PV systems, connected to the grid, in the Netherlands and some other European countries over three consecutive years. Web scraping techniques were employed to collect detailed yield data at high time resolution (5–15 min) from a large number (31,844) of systems with 741 MWp of total capacity, delivering data continuously for at least one year. Annual system yield data was compared from small and medium-sized installations. Cartography and spatial analysis techniques in a geographic information system (GIS) were used to visualize yield and performance ratio, which greatly facilitates the assessment of performance for geographically scattered systems. Variations in yield and performance ratios over the years were observed with higher values in 2015 due to higher irradiation values. The potential of specific yield and performance maps lies in the updating of monitoring databases, quality control of data, and availability of irradiation data. The automatic generation of performance maps could be a trend in future mapping. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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21 pages, 10703 KiB

Open AccessArticle

Research on the Neutral-Point Voltage Balance for NPC Three-Level Inverters under Non-Ideal Grid Conditions

by Jian Guo Lyu^1,2,*

, Ji Dong Wang¹, Wen Bin Hu¹ and Zhao Feng Wu¹

¹ Nanjing University of Science and Technology, Nanjing 210094, China

² Jiangsu Collaborative Innovation Center for Smart Distribution Network, Nanjing 211167, China

Energies 2018, 11(6), 1331; https://doi.org/10.3390/en11061331 - 23 May 2018

Cited by 5 | Viewed by 2474

Abstract

In order to solve the neutral-point voltage unbalancing problem for neutral-point clamped (NPC) three-level inverters under non-ideal grid conditions, a novel zero-sequence component injection method for modulation signals was proposed in this paper. Based on the mathematical expressions of neutral-point voltage unbalancing, the [...] Read more.

In order to solve the neutral-point voltage unbalancing problem for neutral-point clamped (NPC) three-level inverters under non-ideal grid conditions, a novel zero-sequence component injection method for modulation signals was proposed in this paper. Based on the mathematical expressions of neutral-point voltage unbalancing, the fluctuation of the neutral-point voltage under different grid conditions was studied. The proposed method dynamically calculates the zero-sequence component for modulation signals by region selections based on sinusoidal pulse width modulation (DCR-SPWM). Under non-ideal grid conditions, this DCR-SPWM method can control the neutral-point voltage balance for NPC three-level inverters with different grid and output power conditions, and improves the grid current quality. The simulation results verified the correctness of the theoretical analysis in this paper, and the feasibility and effectiveness of this method were verified by the experiments in the experimental platform of the NPC three-level grid-connected inverter based on DSP-CPLD controllers. Full article

(This article belongs to the Section F: Electrical Engineering)

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17 pages, 4475 KiB

Open AccessArticle

Co-Simulation of Smart Distribution Network Fault Management and Reconfiguration with LTE Communication

by Michele Garau^1,2, Emilio Ghiani^1,*

, Gianni Celli¹

, Fabrizio Pilo¹

and Sergio Corti³

¹ Department of Electrical and Electronic Engineering, University of Cagliari, Piazza d’Armi, 09123 Cagliari, Italy

² Department of Information Security and Communication Technology, NTNU—Norwegian University of Science and Technology, O.S. Bragstads plass 2B, 7491 Trondheim, Norway

³ Ricerca sul Sistema Energetico—RSE S.p.A., via R. Rubattino 54, 20134 Milano, Italy

Energies 2018, 11(6), 1332; https://doi.org/10.3390/en11061332 - 23 May 2018

Cited by 28 | Viewed by 5591

Abstract

Transition towards a smart grid requires network modernization based on the deployment of information and communication technologies for managing network operation and coordinating distributed energy resources in distribution systems. The success of the most advanced smart grid functionalities depends on the availability and [...] Read more.

Transition towards a smart grid requires network modernization based on the deployment of information and communication technologies for managing network operation and coordinating distributed energy resources in distribution systems. The success of the most advanced smart grid functionalities depends on the availability and quality of communication systems. Amongst the most demanding functionalities, those related to fault isolation, location and system restoration (FLISR) to obtain a self-healing smart grid are critical and require low latency communication systems, particularly in case of application to weakly-meshed operated networks. Simulation tools capable of capturing the interaction between communication and electrical systems are of outmost utility to check proper functioning of FLISR under different utilization conditions, to assess the expected improvements of Quality of Service, and to define minimum requirements of the communication system. In this context, this paper investigates the use of public mobile telecommunication system 4G Long Term Evolution (LTE) for FLISR applications in both radially and weakly-meshed medium voltage (MV) distribution networks. This study makes use of a co-simulation software platform capable to consider power system dynamics. The results demonstrate that LTE can be used as communication medium for advanced fault location, extinction, and network reconfiguration in distribution networks. Furthermore, this paper shows that the reduction of performances with mobile background usage does not affect the system and does not cause delays higher than 100 ms, which is the maximum allowable for power system protections. Full article

(This article belongs to the Special Issue Methods and Concepts for Designing and Validating Smart Grid Systems)

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14 pages, 1751 KiB

Open AccessFeature PaperArticle

Urban Environment and Solar PV Performance: The Case of the Netherlands

by Panagiotis Moraitis^*

, Bala Bhavya Kausika

, Nick Nortier and Wilfried Van Sark

Utrecht University, Copernicus Institute, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands

Energies 2018, 11(6), 1333; https://doi.org/10.3390/en11061333 - 23 May 2018

Cited by 30 | Viewed by 5702

Abstract

The modern urban landscape creates numerous challenges for the deployment of solar Photovoltaic (PV) technology. The large structures that dominate the skyline of every city create compactness, which, in turn, limits the available rooftop area and creates unpredicted shading patterns. The majority of [...] Read more.

The modern urban landscape creates numerous challenges for the deployment of solar Photovoltaic (PV) technology. The large structures that dominate the skyline of every city create compactness, which, in turn, limits the available rooftop area and creates unpredicted shading patterns. The majority of research today relies on modern applications such as geographical information system (GIS) software to evaluate urban morphology; however, this approach is computationally intensive and therefore it is usually limited to a small geographical area. In this paper, we approach this issue from another perspective, utilizing the enormous amount of high resolution PV yield data that is available for the Netherlands. Our results not only correlate performance losses with urban compactness indicators, but they also reveal a significant seasonality effect that can reach 15% in some cases. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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22 pages, 3972 KiB

Open AccessEditor’s ChoiceArticle

A New Method for Contrasting Energy Performance and Near-Zero Energy Building Requirements in Different Climates and Countries

by Kaiser Ahmed^1,*, Margaux Carlier², Christian Feldmann³ and Jarek Kurnitski^1,4

¹ Department of Civil Engineering, Aalto University, Rakentajanaukio 4 A, FI-02150 Espoo, Finland

² Faculty of Engineering and Architecture, Ghent University, 9000 Ghent, Belgium

³ Association of Engineers in Heating, Ventilation and Air Conditioning AICVF, 75008 Paris, France

⁴ Department of Civil Engineering and Architecture, Tallinn University of Technology, 12616 Tallinn, Estonia

Energies 2018, 11(6), 1334; https://doi.org/10.3390/en11061334 - 23 May 2018

Cited by 27 | Viewed by 4058

Abstract

In this study a robust method enabling one to compare the energy performance in different climates was developed. Derived normalization factors allow “to move” the building from one climate to another with corresponding changes in heating, cooling, and electric lighting energy. Degree days, [...] Read more.

In this study a robust method enabling one to compare the energy performance in different climates was developed. Derived normalization factors allow “to move” the building from one climate to another with corresponding changes in heating, cooling, and electric lighting energy. Degree days, solar-air temperature and economic insulation thickness were used to normalize space heating and cooling needs. Solar-air temperature based degree days resulted in 5% accuracy in space heating and dry-bulb air temperature based cooling degree days were trustworthy in cooling need normalization. To overcome the limitation of the same thermal insulation in all climates, an economic insulation thickness was applied. Existing and nearly zero energy requirements were contrasted in four countries with a reference office building to analyze the impacts of climate and national regulation on primary energy use. By applying standard energy calculation input data and primary energy factors from European standards to buildings with national technical solutions, nearly zero energy building requirements comparison with European Commission benchmarks was possible to conduct. Generally, in Central and North Europe comparison, national input data caused much more difference than the climate. Full article

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17 pages, 4453 KiB

Open AccessArticle

Influence of Single and Multiple Dry Bands on Critical Flashover Voltage of Silicone Rubber Outdoor Insulators: Simulation and Experimental Study

by Arshad^1,2,*, Muhammad Ali Mughal¹

, Azam Nekahi², Mansoor Khan³ and Farhana Umer⁴

¹ Department of Electrical Engineering, Faculty of Engineering and Technology, HITEC University, Taxila 47080, Pakistan

² School of Engineering and Built Environment, Glasgow Caledonian University, G4 0BA Scotland, UK

³ School of Electrical Engineering, Sichuan University, Chengdu 610065, China

⁴ Electrical Engineering Department, Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan

Energies 2018, 11(6), 1335; https://doi.org/10.3390/en11061335 - 24 May 2018

Cited by 12 | Viewed by 2930

Abstract

Dry band formation on the surface of outdoor insulators is one of the main reasons leading to flashover and power outages. In this paper, a dynamic arc model is proposed for single and multiple dry bands configuration to predict the critical flashover voltage [...] Read more.

Dry band formation on the surface of outdoor insulators is one of the main reasons leading to flashover and power outages. In this paper, a dynamic arc model is proposed for single and multiple dry bands configuration to predict the critical flashover voltage for silicone rubber outdoor insulators. An arc is modelled as a time dependent impedance consisting of a Resistor Inductor Capacitor (RLC) circuit. The effect of dry band location and existence of multiple dry bands on critical flashover voltage is investigated. To validate the proposed model, experiments were conducted in a climate chamber under controlled environmental conditions on rectangular silicone rubber sheets polluted using improved solid layer method based on IEC 60,507. Tests were conducted at different dry band configurations and pollution severity levels. A good correlation was found between experimental results and simulation results. This model can provide a good foundation for the development of mathematical models for station post insulators having multiple dry and clean bands and can be used in the design and selection of outdoor insulators for polluted conditions. Full article

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24 pages, 1534 KiB

Open AccessArticle

METATECH: METeorological Data Analysis for Thermal Energy CHaracterization by Means of Self-Learning Transparent Models

by Evelina Di Corso^*

, Tania Cerquitelli^*

and Daniele Apiletti^*

Department of Control and Computer Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24–10129 Torino, Italy

Energies 2018, 11(6), 1336; https://doi.org/10.3390/en11061336 - 24 May 2018

Cited by 15 | Viewed by 3184

Abstract

In the last few years, a large number of smart meters have been deployed in buildings to continuously monitor fine-grained energy consumption. Meteorological data deeply impact energy consumption, and an in-depth analysis of collected and correlated data can uncover interesting and actionable insights [...] Read more.

In the last few years, a large number of smart meters have been deployed in buildings to continuously monitor fine-grained energy consumption. Meteorological data deeply impact energy consumption, and an in-depth analysis of collected and correlated data can uncover interesting and actionable insights to improve the overall energy balance of our communities and to enhance people’s awareness of energy wasting. To effectively extract meaningful and interpretable insights from large collections of energy measurements and multi-dimensional meteorological data, innovative data science methodologies should be devised. Research frontiers are addressing self-learning approaches, which allow non-experts to exploit machine learning techniques more easily, and algorithmic transparency of models, hence providing actionable, explicit, declarative knowledge representation. This paper presents METeorological Data Analysis for Thermal Energy CHaracterization (METATECH), a data mining engine based on both exploratory and unsupervised data analytics algorithms, devised to build transparent models correlating weather conditions and energy consumption in buildings. METATECH exploits a joint approach coupling cluster analysis and generalized association rules to allow a deeper yet human-readable understanding of how meteorological data impact heating consumption. First, a partitional clustering algorithm is applied to weather conditions. Then, resulting clusters are characterized by means of generalized association rules, which provide a self-learning explainable model of the most interesting correlations between energy consumption and weather conditions at different granularity levels. The experimental evaluation performed on real datasets demonstrates the effectiveness of the proposed approach in automatically extracting interesting knowledge from data, and provide it transparently to domain experts. Full article

(This article belongs to the Section D: Energy Storage and Application)

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31 pages, 15099 KiB

Open AccessFeature PaperArticle

Analytical Modeling Approach to Study Harmonic Mitigation in AC Grids with Active Impedance at Selective Frequencies

by Gonzalo Abad^1,*, Aitor Laka², Gabriel Saavedra² and Jon Andoni Barrena¹

¹ Electronics and Computing Department, Mondragon University, 20500 Mondragon, Spain

² Industry and Marine Drives Department, Ingeteam Power Technology S.A., 48170 Zamudio, Spain

Energies 2018, 11(6), 1337; https://doi.org/10.3390/en11061337 - 24 May 2018

Cited by 7 | Viewed by 3105

Abstract

This paper presents an analytical model, oriented to study harmonic mitigation aspects in AC grids. As it is well known, the presence of non-desired harmonics in AC grids can be palliated in several manners. However, in this paper, a power electronic-based active impedance [...] Read more.

This paper presents an analytical model, oriented to study harmonic mitigation aspects in AC grids. As it is well known, the presence of non-desired harmonics in AC grids can be palliated in several manners. However, in this paper, a power electronic-based active impedance at selective frequencies (ACISEF) is used, due to its already proven flexibility and adaptability to the changing characteristics of AC grids. Hence, the proposed analytical model approach is specially conceived to globally consider both the model of the AC grid itself with its electric equivalent impedances, together with the power electronic-based ACISEF, including its control loops. In addition, the proposed analytical model presents practical and useful properties, as it is simple to understand and simple to use, it has low computational cost and simple adaptability to different scenarios of AC grids, and it provides an accurate enough representation of the reality. The benefits of using the proposed analytical model are shown in this paper through some examples of its usefulness, including an analysis of stability and the identification of sources of instability for a robust design, an analysis of effectiveness in harmonic mitigation, an analysis to assist in the choice of the most suitable active impedance under a given state of the AC grid, an analysis of the interaction between different compensators, and so on. To conclude, experimental validation of a 2.15 kA ACISEF in a real 33 kV AC grid is provided, in which real users (household and industry loads) and crucial elements such as wind parks and HVDC systems are near inter-connected. Full article

(This article belongs to the Section F: Electrical Engineering)

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24 pages, 10456 KiB

Open AccessFeature PaperArticle

An Influence of Thermally-Induced Micro-Cracking under Cooling Treatments: Mechanical Characteristics of Australian Granite

by Badulla Liyanage Avanthi Isaka¹, Ranjith Pathegama Gamage^1,*

, Tharaka Dilanka Rathnaweera¹

, Mandadige Samintha Anne Perera^1,2

, Dornadula Chandrasekharam³

and Wanniarachchige Gnamani Pabasara Kumari¹

¹ Department of Civil Engineering, Monash University, Building 60, Melbourne, VIC 3800, Australia

² Department of Infrastructure Engineering, The University of Melbourne, Building 176, Melbourne, VIC 3010, Australia

³ Indian Institute of Technology Hyderabad, Telangana 502285, India

Energies 2018, 11(6), 1338; https://doi.org/10.3390/en11061338 - 24 May 2018

Cited by 98 | Viewed by 5381

Abstract

The aim of this study is to characterise the changes in mechanical properties and to provide a comprehensive micro-structural analysis of Harcourt granite over different pre-heating temperatures under two cooling treatments (1) rapid and (2) slow cooling. A series of uniaxial compression tests [...] Read more.

The aim of this study is to characterise the changes in mechanical properties and to provide a comprehensive micro-structural analysis of Harcourt granite over different pre-heating temperatures under two cooling treatments (1) rapid and (2) slow cooling. A series of uniaxial compression tests was conducted to evaluate the mechanical properties of granite specimens subjected to pre-heating to temperatures ranging from 25–1000 °C under both cooling conditions. An acoustic emission (AE) system was incorporated to identify the fracture propagation stress thresholds. Furthermore, the effect of loading and unloading behaviour on the elastic properties of Harcourt granite was evaluated at two locations prior to failure: (1) crack initiation and (2) crack damage. Scanning electron microscopy (SEM) analyses were conducted on heat-treated thin rock slices to observe the crack/fracture patterns and to quantify the extent of micro-cracking during intense heating followed by cooling. The results revealed that the thermal field induced in the Harcourt granite pore structure during heating up to 100 °C followed by cooling causes cracks to close, resulting in increased mechanical characteristics, in particular, material stiffness and strength. Thereafter, a decline in mechanical properties occurs with the increase of pre-heating temperatures from 100 °C to 800 °C. However, the thermal deterioration under rapid cooling is much higher than that under slow cooling, because rapid cooling appears to produce a significant amount of micro-cracking due to the irreversible thermal shock induced. Multiple stages of loading and unloading prior to failure degrade the elastic properties of Harcourt granite due to the damage accumulated through the coalescence of micro-cracks induced during compression loading. However, this degradation is insignificant for pre-heating temperatures over 400 °C, since the specimens are already damaged due to excessive thermal deterioration. Moreover, unloading after crack initiation tends to cause insignificant irreversible strains, whereas significant permanent strains occur during unloading after crack damage, and this appears to increase with the increase of pre-heating temperature over 400 °C. Full article

(This article belongs to the Special Issue Geothermal Energy: Utilization and Technology 2018)

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16 pages, 7449 KiB

Open AccessArticle

A Predictive Model for Dry-Growth Icing on Composite Insulators under Natural Conditions

by Xingbo Han^*, Xingliang Jiang, Zhongyi Yang and Conglai Bi

State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University, Shapingba District, Chongqing 400044, China

Energies 2018, 11(6), 1339; https://doi.org/10.3390/en11061339 - 25 May 2018

Cited by 11 | Viewed by 2502

Abstract

Icing can adversely influence electric power system security. Two main issues are caused by icing: the overload of transmission lines, and the reduction in the insulation ability of the insulators. Most previous research has focused on the flashover characteristics of ice-covered insulators, but [...] Read more.

Icing can adversely influence electric power system security. Two main issues are caused by icing: the overload of transmission lines, and the reduction in the insulation ability of the insulators. Most previous research has focused on the flashover characteristics of ice-covered insulators, but research on the icing process of the insulator is seriously lacking. Considering the effect of icing shape, the outer airflow field of an insulator was calculated and the local collision efficiencies of water droplets (β₁) were investigated according to the Lagrange algorithm. The simulation showed that the values of β₁ on the insulator edge and rod are much higher than on the insulator surface, and both were significantly influenced by the wind speed and median volume diameter (MVD) of the water droplets. Based on thermal balance equations, a dynamic dry-growth icing model was established. Using the natural icing conditions of Xuefeng Mountain (China) as an example, validation experiments were conducted on a composite insulator and the climate parameters measured by multi-cylinders were used to model the icing shape and mass. The results indicate that high wind speed and low temperature increase icing rate; the icing was mainly concentrated on the windward side and the greatest horizontal thickness was generally on the insulator edge. The dry-growth model had an average error lower than 25% for icing thickness and an average error lower than 20% for icing mass, which were affected by icing roughness. Full article

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15 pages, 4301 KiB

Open AccessArticle

A Fuzzy Logical-Based Variable Step Size P&O MPPT Algorithm for Photovoltaic System

by John Macaulay^*

and Zhongfu Zhou

College of Engineering, Swansea University, Bay Campus, Swansea SA1 8EN, UK

Energies 2018, 11(6), 1340; https://doi.org/10.3390/en11061340 - 25 May 2018

Cited by 78 | Viewed by 8183

Abstract

This paper presents a Modified Perturb & Observe (P&O) Maximum power point tracking (MPPT) algorithm using fuzzy logic-based variable step size to overcome some of the limitations associated with the conventional P&O MPPT tracking method to improve the transient response and reduce the [...] Read more.

This paper presents a Modified Perturb & Observe (P&O) Maximum power point tracking (MPPT) algorithm using fuzzy logic-based variable step size to overcome some of the limitations associated with the conventional P&O MPPT tracking method to improve the transient response and reduce the steady-state terminal voltage oscillations. The proposed MPPT algorithm was implemented and tested on an indoor emulated PV source that is constructed from a conventional solar panel and a DC power supply, a boost DC-DC converter and a dSPACE-based MPPT controller. The advantage of implementing this testing platform for MPPT is easy implementation and indoor testing of MPPT algorithms and DC-DC power converters. Thus, dependency on atmospheric conditions such as irradiance level can be avoided. Details of the emulated PV source mathematical model and electrical characteristics, the proposed MPPT algorithm via dSPACE, simulation and test results were presented in the paper. Full article

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12 pages, 1788 KiB

Open AccessArticle

Biofuel and Biochemical Analysis of Amphora coffeaeformis RR03, a Novel Marine Diatom, Cultivated in an Open Raceway Pond

by Muthu Ganesan Rajaram^1,2, Subramani Nagaraj^1,2

, Manubolu Manjunath³, Annakkili Baskara Boopathy^1,4, Chidambaram Kurinjimalar¹, Ramasamy Rengasamy¹, Thanasekaran Jayakumar², Joen-Rong Sheu^2,* and Jiun-Yi Li^2,5,*

¹ Centre for Advanced Studies in Botany, University of Madras, Guindy Campus, Chennai 600025, Tamil Nadu, India

² Department of Pharmacology, Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei 110, Taiwan

³ Department of Evolution, Ecology and Organismal Biology, Ohio State University, Columbus, OH 43210, USA

⁴ Department of Biochemistry, Caussanel College of Arts and Science, Ramanathapuram 623523, India

⁵ Department of Cardiovascular Surgery, Mackay Memorial Hospital, and Mackay Medical College, Taipei 104, Taiwan

Energies 2018, 11(6), 1341; https://doi.org/10.3390/en11061341 - 25 May 2018

Cited by 11 | Viewed by 2808

Abstract

(1) Background: To increase the biochemical productivity and to reduce the production cost of microalgal biodiesel, this study aimed to investigate the effects of CO₂ on biomass, fatty acids, carbon-hydrogen, and biochemical accumulation of the marine diatom, Amphora coffeaeformis RR03 (A. coffeaeformis [...] Read more.

(1) Background: To increase the biochemical productivity and to reduce the production cost of microalgal biodiesel, this study aimed to investigate the effects of CO₂ on biomass, fatty acids, carbon-hydrogen, and biochemical accumulation of the marine diatom, Amphora coffeaeformis RR03 (A. coffeaeformis) RR03. (2) Methods: Fatty acid composition of the dry biomass of A. coffeaeformis RR03 was analysed using Gas chromatography-mass spectrometry (GC-MS). (3) Results: The results showed that A. coffeaeformis RR03 contained high biomass productivity and biochemical composition in different cultivation conditions. A. coffeaeformis RR03 showed maximum growth of 5.2 × 10⁶/mL on 21st day cultivation under CO₂ supply. The bio-crude oil production from A. coffeaeformis RR03 was 36.19 megajoule (MJ). GC-MS analysis found that the dry biomass of A. coffeaeformis RR03 contained maximum of 47.72% fatty acids of 16-octadecanoic acid methyl ester (10:12) and 19.58% pentadecanoic acid, 13-methyl-, and methyl ester (9.24). (4) Conclusion: The results of this study may suggest that a novel diatom of A. coffeaeformis RR03 could be a suitable candidate for biocrude production in order to meet the future demand of energy. Full article

(This article belongs to the Section L: Energy Sources)

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14 pages, 2540 KiB

Open AccessArticle

Experimental Investigation into the Effect of Oil Injection on the Performance of a Variable Speed Twin-Screw Compressor

by Zhilong He¹

, Tao Wang^1,2,*, Xiaolin Wang³, Xueyuan Peng¹ and Ziwen Xing¹

¹ School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China

² School of Energy and Power Engineering, Zhengzhou University of Light Industry, Zhengzhou 450000, China

³ School of Engineering & ICT, University of Tasmania, Private Bag 65, Hobart TAS 7001, Australia

Energies 2018, 11(6), 1342; https://doi.org/10.3390/en11061342 - 25 May 2018

Cited by 12 | Viewed by 4454

Abstract

In this paper, the effect of oil injection flow rate on the performance of a variable speed twin-screw compressor was investigated experimentally. Comprehensive experiments were conducted at different compressor rotational speeds and oil injection flow rates. As the rotational speed increased from 1000 [...] Read more.

In this paper, the effect of oil injection flow rate on the performance of a variable speed twin-screw compressor was investigated experimentally. Comprehensive experiments were conducted at different compressor rotational speeds and oil injection flow rates. As the rotational speed increased from 1000 to 3000 rpm, the compressor volumetric and adiabatic efficiencies increased while the specific power consumption decreased. However, the oil injection flow rate showed different influences on the compressor performance. As the oil injection flow rate increased from 27 to 50 L/min, the adiabatic and volumetric efficiencies increased while the compressor discharge temperature and specific power decreased. Further increases in the oil injection flow rate had little effect on compressor performance at flow rates above 50 L/min. The analysis indicated that the oil injection flow rate was limited by the discharge temperature at low compressor rotational speeds and was a trade-off among two efficiencies and specific power consumption at high rotational speeds. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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15 pages, 10888 KiB

Open AccessArticle

Influence of Single/Dual Ventilation Path on Fluid Field and Temperature Field of HVLSSR-PMSM with Air-Cooled Hybrid Ventilation Systems

by Zhaobin Cao¹

, Weili Li¹, Xiaochen Zhang¹, Yu Fan¹ and Jianjun Zeng^1,2,*

¹ School of Electrical Engineering, Beijing Jiaotong University, Beijing 100044, China

² School of Electrical and Automation Engineering, East China Jiaotong University, Nanchang 330013, China

Energies 2018, 11(6), 1343; https://doi.org/10.3390/en11061343 - 25 May 2018

Cited by 8 | Viewed by 3549

Abstract

Due to the solid rotor structure, High-Voltage Line-Start Solid Rotor Permanent Magnet Synchronous Motor (HVLSSR-PMSM) operates with high rotor temperature rise. If the ventilation path cannot take the rotor heat away in time, the rotor will overheat or even may led to the [...] Read more.

Due to the solid rotor structure, High-Voltage Line-Start Solid Rotor Permanent Magnet Synchronous Motor (HVLSSR-PMSM) operates with high rotor temperature rise. If the ventilation path cannot take the rotor heat away in time, the rotor will overheat or even may led to the thermal demagnetization for permanent magnet. Therefore, it is of great significance to study the thermal issues of HVLSSR-PMSM. In the paper, the fluid field and temperature field of a 315 kW, 6 kV HVLSSR-PMSM with air-cooled hybrid ventilation systems are investigated. Firstly, the electromagnetic analysis of the machine is done by using the finite-element method, the loss distributions then are obtained, which will be assigned as the heat source for thermal analysis. Then, the three -dimensional (3-D) fluid thermal coupled mathematical model for thermal analysis of HVLSSR-PMSM is established. The temperature field and the fluid flowing state of HVLSSR-PMSM with single ventilation path air-cooled system are investigated by using the established 3D fluid thermal coupled mathematical model. A dual ventilation path air-cooled system for HVLSSR-PMSM is proposed to reduce the operating temperature rise. Then, the temperature field and fluid field of HVLSSR-PMSM with dual ventilation system are analyzed by comparing with single ventilation system. Moreover, the temperature experiments are carried out on the machine with dual ventilation system to validate the accuracy of the established mathematical models. The results show that the proposed dual ventilation path air-cooled system can effectively improve the thermal distribution of HVLSSR-PMSM, whilst it can also reduce the working temperature rise of the machine. Full article

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11 pages, 1157 KiB

Open AccessArticle

Effect of Different Operating Temperatures on the Biological Hydrogen Methanation in Trickle Bed Reactors

by Andreas Lemmer^* and Timo Ullrich^*

State Institute of Agricultural Engineering and Bioenergy, University of Hohenheim, Garbenstraße 9, 70599 Stuttgart, Germany

Energies 2018, 11(6), 1344; https://doi.org/10.3390/en11061344 - 25 May 2018

Cited by 21 | Viewed by 3869

Abstract

To improve the reactor efficiency, this study investigated the influence of temperature on the biological hydrogen methanation (BHM) in trickle-bed reactors (TBR). Rising temperatures increase the metabolic activity of methanogenic microorganisms, thus leading to higher reactor specific methane formation rates (MFR). In order [...] Read more.

To improve the reactor efficiency, this study investigated the influence of temperature on the biological hydrogen methanation (BHM) in trickle-bed reactors (TBR). Rising temperatures increase the metabolic activity of methanogenic microorganisms, thus leading to higher reactor specific methane formation rates (MFR). In order to quantify the potential for improved performance, experiments with four different operating temperatures ranging from 40 to 55 °C were carried out. Methane content increased from 88.29 ± 2.12 vol % at 40 °C to 94.99 ± 0.81 vol % at 55 °C with a stable biological process. Furthermore, a reactor specific methane formation rate (MFR) of up to 8.85 ± 0.45 m³ m⁻³ d⁻¹ was achieved. It could be shown that the microorganisms were able to adapt to higher temperatures within hours. The tests showed that TBR performance with regard to BHM can be significantly increased by increasing the operating temperature. Full article

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17 pages, 338 KiB

Open AccessArticle

Risk Constrained Trading Strategies for Stochastic Generation with a Single-Price Balancing Market

by Jethro Browell

Department of Electronic and Electrical Engineering, University of Strathclyde, Glasgow G1 1XQ, UK

Energies 2018, 11(6), 1345; https://doi.org/10.3390/en11061345 - 25 May 2018

Cited by 17 | Viewed by 3278

Abstract

Trading energy from wind and other forms of stochastic generation in competitive electricity markets is challenging due to the limited predictability of these resources. This paper examines the specific case of single-price balancing markets and derives risk-constrained strategies in a probabilistic framework, going [...] Read more.

Trading energy from wind and other forms of stochastic generation in competitive electricity markets is challenging due to the limited predictability of these resources. This paper examines the specific case of single-price balancing markets and derives risk-constrained strategies in a probabilistic framework, going beyond the trivial zero/max solution, which would have participants offer either zero or their maximum energy production based on a prediction of whether the system will be in net up- or down-regulation. The zero/max approach is unacceptable in reality as it exposes the participant to potentially huge imbalance charges, and would violate price taker assumption for a portfolio of significant size. Here, we propose several trading strategies that control risk by hedging against penalising balancing prices in favour of rewarding ones by contracting forecast generation plus some adjustment. These strategies are formulated in a probabilistic framework to address the presence of forecast uncertainty and asymmetric costs in balancing markets. A case study using data from the Great Britain electricity market is presented and it is shown that the proposed strategies are able to simultaneously increase revenue and reduce risk using risk-constrained strategies. Furthermore, the required forecasts of electricity prices and system length are produced using standard tools and widely available explanatory information and are found to have sufficient skill to increase revenue compared to not hedging. Full article

(This article belongs to the Section A: Sustainable Energy)

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18 pages, 10427 KiB

Open AccessArticle

Comparison of Shell and Solid Finite Element Models for the Static Certification Tests of a 43 m Wind Turbine Blade

by Mathijs Peeters^1,*

, Gilberto Santo²

, Joris Degroote²

and Wim Van Paepegem¹

¹ Department of Materials, Textiles and Chemical Engineering, Ghent University, Tech Lane Ghent Science Park–Campus A, Technologiepark-Zwijnaarde 903, 9052 Zwijnaarde, Belgium

² Department of Flow, Heat and Combustion Mechanics, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Ghent, Belgium

Energies 2018, 11(6), 1346; https://doi.org/10.3390/en11061346 - 25 May 2018

Cited by 26 | Viewed by 9112

Abstract

A commercial 43 m wind turbine blade was tested under static loads. During these tests, loads, displacements, and local strains were recorded. In this work, the blade was modeled using the finite element method. Both a segment of the spar structure and the [...] Read more.

A commercial 43 m wind turbine blade was tested under static loads. During these tests, loads, displacements, and local strains were recorded. In this work, the blade was modeled using the finite element method. Both a segment of the spar structure and the full-scale blade were modeled. In both cases, conventional outer mold layer shell and layered solid models were created by means of an in-house developed software tool. First, the boundary conditions and settings for modeling the tests were explored. Next, the behavior of a spar segment under different modeling methods was investigated. Finally, the full-scale blade tests were conducted. The resulting displacements and longitudinal and transverse strains were investigated. It was found that for the considered load case, the differences between the shell and solid models are limited. Thus, it is concluded that the shell representation is sufficiently accurate. Full article

(This article belongs to the Collection Wind Turbines)

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18 pages, 4194 KiB

Open AccessArticle

Comparative Analysis of 18-Pulse Autotransformer Rectifier Unit Topologies with Intrinsic Harmonic Current Cancellation

by Shahbaz Khan^1,*

, Xiaobin Zhang¹, Muhammad Saad², Husan Ali¹

, Bakht Muhammad Khan³ and Haider Zaman¹

¹ School of Automation, Northwestern Polytechnical University, Xi’an 710129, China

² School of Traffic and Control Signal, Chang’an University, Xi’an 710072, China

³ School of Electronics and Information, Northwestern Polytechnical University, Xi’an 710129, China

Energies 2018, 11(6), 1347; https://doi.org/10.3390/en11061347 - 25 May 2018

Cited by 22 | Viewed by 4208

Abstract

With the evolution of the More Electric Aircraft (MEA) concept, high pulse converters have gained the attention of researchers due to their higher power quality. Among the high pulse converters, 18-pulse autotransformer rectifier unit (ATRU) offers better power quality level with small size, [...] Read more.

With the evolution of the More Electric Aircraft (MEA) concept, high pulse converters have gained the attention of researchers due to their higher power quality. Among the high pulse converters, 18-pulse autotransformer rectifier unit (ATRU) offers better power quality level with small size, weight and medium complexity. The conventional topologies of autotransformers that require the use of extra elements such as Inter Phase Transformers (IPT) or Zero Sequence Blocking Transformers (ZSBT), adding to the complexity, weight and size of the overall system, are not considered in the analysis. For 18-pulse rectification, only those topologies of autotransformers which have the intrinsic current harmonic cancellation capabilities are presented here for comparison. These topologies offer current harmonic levels within limits specified by IEEE 519 with reduced weight and size as compared to the conventional multi-pulse converters. A comparison of different differential delta/fork configured 18-pulse autotransformer rectifier units is presented so as to come up with the best among available topologies with respect to weight, size and power quality. Experimental prototypes of each topology were designed and their results are displayed along with the simulation results for comparison. Full article

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17 pages, 1152 KiB

Open AccessArticle

Scheduling Distributed Energy Resource Operation and Daily Power Consumption for a Smart Building to Optimize Economic and Environmental Parameters

by Zahra Pooranian^1,*

, Jemal H. Abawajy²

, Vinod P¹

and Mauro Conti¹

¹ Department of Mathematics, University of Padua, Padua 35131, Italy

² School of Information Technology, Deakin University, Geelong, VIC 3125, Australia

Energies 2018, 11(6), 1348; https://doi.org/10.3390/en11061348 - 25 May 2018

Cited by 45 | Viewed by 5114

Abstract

In this paper, we address the problem of minimizing the total daily energy cost in a smart residential building composed of multiple smart homes with the aim of reducing the cost of energy bills and the greenhouse gas emissions under different system constraints [...] Read more.

In this paper, we address the problem of minimizing the total daily energy cost in a smart residential building composed of multiple smart homes with the aim of reducing the cost of energy bills and the greenhouse gas emissions under different system constraints and user preferences. As the household appliances contribute significantly to the energy consumption of the smart houses, it is possible to decrease electricity cost in buildings by scheduling the operation of domestic appliances. In this paper, we propose an optimization model for jointly minimizing electricity costs and CO₂ emissions by considering consumer preferences in smart buildings that are equipped with distributed energy resources (DERs). Both controllable and uncontrollable tasks and DER operations are scheduled according to the real-time price of electricity and a peak demand charge to reduce the peak demand on the grid. We formulate the daily energy consumption scheduling problem in multiple smart homes from economic and environmental perspectives and exploit a mixed integer linear programming technique to solve it. We validated the proposed approach through extensive experimental analysis. The results of the experiment show that the proposed approach can decrease both CO₂ emissions and the daily energy cost. Full article

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12 pages, 1694 KiB

Open AccessArticle

Cross Test Comparison in Transformer Windings Frequency Response Analysis

by Szymon Banaszak^* and Wojciech Szoka

Department of Electrotechnology and Diagnostics, West Pomeranian University of Technology in Szczecin, ul. Sikorskiego 37, 70-313 Szczecin, Poland

Energies 2018, 11(6), 1349; https://doi.org/10.3390/en11061349 - 25 May 2018

Cited by 17 | Viewed by 3556

Abstract

Frequency Response Analysis (FRA) is an important tool used for diagnostic measurements of power transformers. Standard test configuration applied in the industry is the end-to-end open test setup; however, an interwinding capacitive configuration is also used. This paper presents a method—Cross Test Comparison [...] Read more.

Frequency Response Analysis (FRA) is an important tool used for diagnostic measurements of power transformers. Standard test configuration applied in the industry is the end-to-end open test setup; however, an interwinding capacitive configuration is also used. This paper presents a method—Cross Test Comparison (CTC)—for simultaneous analysis of results coming from both the mentioned test setups. Such an approach could offer a more sensitive tool for detecting some faults; moreover, it takes into consideration the influence of both voltage sides of a transformer in a one test result. The authors have used several indices to quantitatively assess the test results and proposed new approach to data interpretation. CTC method was tested using data from measurements performed in three cases: a unit tested in laboratory with introduced controlled deformations; transformers measured under industrial conditions; and a transformer with FRA changes resulting from tap-changer operations. The results showed that CTC method is more effective at detecting faults on the basis of FRA measurements. Full article

(This article belongs to the Section F: Electrical Engineering)

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16 pages, 2850 KiB

Open AccessArticle

A Study on Coordinated Optimization of Electric Vehicle Charging and Charging Pile Selection

by Lixing Chen^1,*, Xueliang Huang², Hong Zhang^1,* and Yinsheng Luo¹

¹ School of Electrical & Information Engineering, Jiangsu University of Technology, Changzhou 213001, China

² School of Electrical Engineering, Southeast University, Nanjing 210096, China

Energies 2018, 11(6), 1350; https://doi.org/10.3390/en11061350 - 25 May 2018

Cited by 15 | Viewed by 4441

Abstract

This paper was intended to explore the mutual influences between electric vehicle (EV) charging and charging facility planning, to establish a two-stage model for optimizing the EVs’ charging and charging piles’ selection. In the first stage, the distribution pattern of the demands for [...] Read more.

This paper was intended to explore the mutual influences between electric vehicle (EV) charging and charging facility planning, to establish a two-stage model for optimizing the EVs’ charging and charging piles’ selection. In the first stage, the distribution pattern of the demands for EV charging, and various EVs were effectively grouped, in order to reduce the amount of computation for solving the second stage model. The goal of the second stage was to minimize the annual investment and electricity purchasing costs on the charging piles, and the coordinated optimization was carried out for EV charging and charging pile selection. The CPLEX and IP_SOLVE packages were used in MATLAB (R2014a/64 bits) to solve the established optimization model. The simulation results showed that, compared with the scheme for selecting the charging pile under the typical charging pattern (TCP), the total cost of the charging pile could be reduced by 6.32% with a scheme under the optimized charging pattern (OCP), thereby promoting the coordinated development of both the EVs and charging facilities. Full article

(This article belongs to the Special Issue Energy Management in Vehicle–Grid–Traffic Nexus)

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17 pages, 10798 KiB

Open AccessArticle

A Multifunctional Dynamic Voltage Restorer for Power Quality Improvement

by Dung Vo Tien¹, Radomir Gono¹

and Zbigniew Leonowicz^2,*

¹ Department of Electrical Power Engineering, FEECS, VSB, Technical University of Ostrava, 70800 Ostrava, Czech Republic

² Faculty of Electrical Engineering, Wroclaw University of Science and Technology, 50370 Wroclaw, Poland

Energies 2018, 11(6), 1351; https://doi.org/10.3390/en11061351 - 25 May 2018

Cited by 37 | Viewed by 5367

Abstract

Power quality is a major concern in electrical power systems. The power quality disturbances such as sags, swells, harmonic distortion and other interruptions have an impact on the electrical devices and machines and in severe cases can cause serious damages. Therefore it is [...] Read more.

Power quality is a major concern in electrical power systems. The power quality disturbances such as sags, swells, harmonic distortion and other interruptions have an impact on the electrical devices and machines and in severe cases can cause serious damages. Therefore it is necessary to recognize and compensate all types of disturbances at an earliest time to ensure normal and efficient operation of the power system. To solve these problems, many types of power devices are used. At the present time, one of those devices, Dynamic Voltage Restorer (DVR) is the most efficient and effective device used in power distribution systems. In this paper, design and modeling of a new structure and a new control method of multifunctional DVRs for voltage quality correction are presented. The new control method was built in the stationary frame by combining Proportional Resonant controllers and Sequence-Decouple Resonant controllers. The performance of the device and this method under different conditions such as voltage swell, voltage sag due to symmetrical and unsymmetrical short circuit, starting of motors, and voltage distortion are described. Simulation result show the superior capability of the proposed DVR to improve power quality under different operating conditions and the effectiveness of the proposed method. The proposed new DVR controller is able to detect the voltage disturbances and control the converter to inject appropriate voltages independently for each phase and compensate to load voltage through three single-phase transformers. Full article

(This article belongs to the Special Issue 17TH International Conference on Environment and Electrical Engineering)

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17 pages, 6133 KiB

Open AccessFeature PaperArticle

Reversible Heat Pump–Organic Rankine Cycle Systems for the Storage of Renewable Electricity

by Sebastian Staub^1,*

, Peter Bazan², Konstantinos Braimakis³, Dominik Müller¹, Christoph Regensburger⁴, Daniel Scharrer², Bernd Schmitt⁵, Daniel Steger⁴, Reinhard German², Sotirios Karellas³, Marco Pruckner², Eberhard Schlücker⁴, Stefan Will⁵ and Jürgen Karl¹

¹ Institute of Energy Process Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Fürther Strasse 244f, D-90429 Nürnberg, Germany

² Computer Networks and Communication Systems, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Martensstr 3, 91058 Erlangen, Germany

³ Laboratory of Steam Boilers and Thermal Plants, National Technical University of Athens, 9 Heroon Polytechniou, 15780 Athens, Greece

⁴ Institute of Process Machinery and Systems Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Cauerstr. 4, 91058 Erlangen, Germany

⁵ Institute of Engineering Thermodynamics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Am Weichselgarten 8, 91058 Erlangen-Tennenlohe, Germany

Energies 2018, 11(6), 1352; https://doi.org/10.3390/en11061352 - 25 May 2018

Cited by 61 | Viewed by 14092

Abstract

Storage of electricity from fluctuating renewable energy sources has become one of the predominant challenges in future energy systems. A novel system comprises the combination of a heat pump and an Organic Rankine Cycle (ORC) with a simple hot water storage tank. The [...] Read more.

Storage of electricity from fluctuating renewable energy sources has become one of the predominant challenges in future energy systems. A novel system comprises the combination of a heat pump and an Organic Rankine Cycle (ORC) with a simple hot water storage tank. The heat pump upgrades low temperature heat with excess power. The upgraded heat can drive an Organic Rankine Process using the heat pump in reverse operation mode. This approach allows a comparably efficient storage of excess electricity. Waste heat sources usually do not qualify for electricity production even with ORC processes due to low temperatures. Upgrading the temperature of the waste heat by means of excess electricity makes the use of an ORC feasible in order to recover the electricity input. Thermodynamic cycle simulations with IPSEpro software outline that the process provides power-to-power efficiencies in a range of 50% for small-scale applications based on commercially available heat pump components. The isentropic efficiency of compressors/expanders plays a crucial role on the system performance. Applications of the proposed cycle in the megawatt range with more efficient turbines and dynamic compressors will therefore increase the power-to-power efficiency to above 70%. Full article

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22 pages, 7651 KiB

Open AccessArticle

Assessment of Explicit Models for Different Photovoltaic Technologies

by Santiago Pindado^1,2,*

, Javier Cubas^1,2

, Elena Roibás-Millán^1,2

, Francisco Bugallo-Siegel² and Félix Sorribes-Palmer¹

¹ Instituto Universitario de Microgravedad “Ignacio Da Riva” (IDR/UPM), Universidad Politécnica de Madrid, ETSI Aeronáutica y del Espacio, Pza. del Cardenal Cisneros 3, 28040 Madrid, Spain

² Departamento of Sistemas Aeroespaciales, Transporte Aéreo y Aeropuertos (SATAA), Universidad Politécnica de Madrid, ETSI Aeronáutica y del Espacio, Pza. del Cardenal Cisneros 3, 28040 Madrid, Spain

Energies 2018, 11(6), 1353; https://doi.org/10.3390/en11061353 - 25 May 2018

Cited by 33 | Viewed by 3654

Abstract

Accurate and simple mathematical models are usually required to assess the performances of photovoltaic devices. In particular, it is common practice to use explicit models to evaluate the current–voltage (I–V) performance curves, mainly based on simple analytical expressions that [...] Read more.

Accurate and simple mathematical models are usually required to assess the performances of photovoltaic devices. In particular, it is common practice to use explicit models to evaluate the current–voltage (I–V) performance curves, mainly based on simple analytical expressions that enable the parameters determination with a little computational effort. Six different explicit photovoltaic models (i.e., explicit I–V equations) by different authors (Akbaba & Alattawi; El-Tayyan; Karmalkar & Haneefa; Das/Saetre et al.; Das; and Pindado & Cubas) are analyzed and compared. This comparison is carried out by fitting these models to eight I–V curves for different technologies, including Si, Si polycrystalline, Ga–As, and plastic solar cells. The accuracy of each model depends on the photovoltaic technology to which it is applied. The best fit to each I–V curve studied is normally obtained with a different model, with an average deviation under 2% in terms of short-circuit current (normalized RMSE). In general, the model proposed by Karmalkar & Haneefa shows the highest level of accuracy, and is a good fit for all I–V curves studied. Full article

(This article belongs to the Section L: Energy Sources)

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23 pages, 9320 KiB

Open AccessArticle

Near-Wall Thermal Processes in an Inclined Impinging Jet: Analysis of Heat Transport and Entropy Generation Mechanisms

by Florian Ries^1,*

, Yongxiang Li¹

, Dario Klingenberg¹, Kaushal Nishad¹

, Johannes Janicka^1,2 and Amsini Sadiki^1,2,3

¹ Institute of Energy and Power Plant Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany

² Darmstadt Graduate School of Energy Science and Engineering, Technische Universität Darmstadt, 64287 Darmstadt, Germany

³ Laboratoire de Génies des Procédés et Thermodynamique, Institut Supérieur des Sciences et Techniques Appliquées, B.P. 6534 Kinshasa 31 NDOLO, D.R. Congo

Energies 2018, 11(6), 1354; https://doi.org/10.3390/en11061354 - 25 May 2018

Cited by 24 | Viewed by 3644

Abstract

In this work, near-wall thermal transport processes and entropy generation mechanisms in a turbulent jet impinging on a

45^{\circ}

-inclined heated surface are investigated using a direct numerical simulation (DNS). The objectives are to analyze the subtle mechanisms of heat transport in [...] Read more.

In this work, near-wall thermal transport processes and entropy generation mechanisms in a turbulent jet impinging on a

45^{\circ}

-inclined heated surface are investigated using a direct numerical simulation (DNS). The objectives are to analyze the subtle mechanisms of heat transport in the vicinity of an inclined impinged wall, to determine the causes of irreversibilities that are responsible for the reduction of performance of impingement cooling applications and to provide a comprehensive dataset for model development and validation. Results for near-wall thermal characteristics including heat fluxes are analyzed. An entropy production map is provided from the second law analysis. The following main outcomes can be drawn from this study: (1) the location of peak heat transfer occurs not directly at the stagnation point; instead, it is slightly shifted towards the compression side of the jet, while at this region, the heat is transported counter to the temperature gradient; (2) turbulent thermal and fluid flow transport processes around the stagnation point are considerably different from those found in other near-wall-dominated flows and are strongly non-equilibrium in nature; (3) heat fluxes appear highly anisotropic especially in the vicinity of the impinged wall; (4) in particular, the heated wall acts as a strong source of irreversibility for both entropy production related to viscous dissipation and to heat conduction. All these findings imply that a careful design of the impinged plate is particularly important in order to use energy in such a thermal arrangement effectively. Finally, this study confirms that the estimation of the turbulent part of the entropy production based on turbulence dissipation rates in non-reacting, non-isothermal fluid flows represents a reliable approximate approach within the second law analysis, likewise in the context of computationally less expensive simulation techniques like RANS and/or LES. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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18 pages, 1109 KiB

Open AccessArticle

Critical Lines Identification for Skeleton-Network of Power Systems under Extreme Weather Conditions Based on the Modified VIKOR Method

by Chang Han¹

, Yuxuan Zhao¹, Zhenzhi Lin^1,*, Yi Ding¹, Li Yang¹, Guanqiang Lin², Tianwen Mo² and Xiaojun Ye²

¹ School of Electrical Engineering, Zhejiang University, Hangzhou 310027, China

² Electric Power Dispatching and Control Center, Huizhou Power Supply Bureau of Guangdong Power Grid Co., Ltd., Huizhou 516000, China

Energies 2018, 11(6), 1355; https://doi.org/10.3390/en11061355 - 25 May 2018

Cited by 12 | Viewed by 2672

Abstract

Identifying and preferentially reinforcing critical lines for skeleton-network of power systems is significant in improving the secure and stable operation of power systems under extreme weather conditions. Under this background, in this paper, six indexes are first presented for identifying critical lines for [...] Read more.

Identifying and preferentially reinforcing critical lines for skeleton-network of power systems is significant in improving the secure and stable operation of power systems under extreme weather conditions. Under this background, in this paper, six indexes are first presented for identifying critical lines for skeleton-network with the power elements’ parameters and the impact of extreme weather conditions, the network topology and the operation state of power systems considered. Then, the modified Vise Kriterijumska Optimizacija I Kompromisno Resenje in Serbian (VIKOR) method, in which the synthetic weights of indexes determined by the combination weighting method are adopted, is utilized to identify the importance degrees of lines in a given power system. Both the overall performance and the outstanding individual performance of lines are considered, which is beneficial for the critical lines identification for skeleton-network. Finally, the proposed multi-indexes and methods are applied to part of the actual Guangdong power system in China. The numerical results are compared with those obtained by single-attribute and multi-attribute evaluation methods and other evaluation methods. Full article

(This article belongs to the Section F: Electrical Engineering)

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24 pages, 4630 KiB

Open AccessArticle

On the Optimal Pole Width for Direct Drive Linear Wave Power Generators Using Ferrite Magnets

by Anders Hagnestål

Department of Electric Power and Energy Systems, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Teknikringen 33, 100 44 Stockholm, Sweden

Energies 2018, 11(6), 1356; https://doi.org/10.3390/en11061356 - 25 May 2018

Cited by 5 | Viewed by 3070

Abstract

In this work, ferrite magnet linear generators for wave power applications are considered. These machines operate at unusually low speeds, around and even below 1 m/s, at which the optimal geometry differs from standard machines, since the copper loss and the force density [...] Read more.

In this work, ferrite magnet linear generators for wave power applications are considered. These machines operate at unusually low speeds, around and even below 1 m/s, at which the optimal geometry differs from standard machines, since the copper loss and the force density become considerably more important. The focus is on translator design, and analytical two-dimensional (2D) expressions for the optimal 2D geometry are derived. Finite Element Analysis (FEA) is also applied to verify the analytical expressions and to determine effects from leakage fluxes and iron saturation. Demagnetization of ferrite magnets is also discussed and calculations are made to show the demagnetization situation for the magnets in different geometries. Finally, an example generator design is made to illustrate the findings. This generator is compared to three other generator concepts. It is concluded that ferrite magnet generators can have at least nearly the same shear stress as surface mounted neodymium magnet generators at low speed if the airgap is 3 mm or less, provided that a proper pole length is chosen, and that they can be economically competitive to neodymium magnet generators for wave power. It is also concluded that the demagnetization situation for the magnets can be severe, and that the choice of magnet grade and pole length is crucial in this respect. Full article

(This article belongs to the Section A: Sustainable Energy)

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18 pages, 2818 KiB

Open AccessArticle

A Decision Support System for Public Funding of Experimental Development in Energy Research

by Simon Hirzel^1,*

, Tim Hettesheimer¹, Peter Viebahn²

and Manfred Fischedick²

¹ Fraunhofer Institute for Systems and Innovation Research ISI, Breslauer Str. 48, 76139 Karlsruhe, Germany

² Wuppertal Institut für Klima, Umwelt, Energie, Döppersberg 19, 42103 Wuppertal, Germany

Energies 2018, 11(6), 1357; https://doi.org/10.3390/en11061357 - 26 May 2018

Cited by 6 | Viewed by 3203

Abstract

New energy technologies may fail to make the transition to the market once research funding has ended due to a lack of private engagement to conclude their development. Extending public funding to cover such experimental developments could be one way to improve this [...] Read more.

New energy technologies may fail to make the transition to the market once research funding has ended due to a lack of private engagement to conclude their development. Extending public funding to cover such experimental developments could be one way to improve this transition. However, identifying promising research and development (R&D) proposals for this purpose is a difficult task for the following reasons: Close-to-market implementations regularly require substantial resources while public budgets are limited; the allocation of public funds needs to be fair, open, and documented; the evaluation is complex and subject to public sector regulations for public engagement in R&D funding. This calls for a rigorous evaluation process. This paper proposes an operational three-staged decision support system (DSS) to assist decision-makers in public funding institutions in the ex-ante evaluation of R&D proposals for large-scale close-to-market projects in energy research. The system was developed based on a review of literature and related approaches from practice combined with a series of workshops with practitioners from German public funding institutions. The results confirm that the decision-making process is a complex one that is not limited to simply scoring R&D proposals. Decision-makers also have to deal with various additional issues such as determining the state of technological development, verifying market failures or considering existing funding portfolios. The DSS that is suggested in this paper is unique in the sense that it goes beyond mere multi-criteria aggregation procedures and addresses these issues as well to help guide decision-makers in public institutions through the evaluation process. Full article

(This article belongs to the Section A: Sustainable Energy)

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15 pages, 5728 KiB

Open AccessArticle

A Novel Method for Lithium-Ion Battery Online Parameter Identification Based on Variable Forgetting Factor Recursive Least Squares

by Zizhou Lao¹, Bizhong Xia^1,*, Wei Wang², Wei Sun², Yongzhi Lai² and Mingwang Wang²

¹ Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China

² Sunwoda Electronic Co., Ltd., Shenzhen 518108, China

Energies 2018, 11(6), 1358; https://doi.org/10.3390/en11061358 - 26 May 2018

Cited by 68 | Viewed by 4858

Abstract

For model-based state of charge (SOC) estimation methods, the battery model parameters change with temperature, SOC, and so forth, causing the estimation error to increase. Constantly updating model parameters during battery operation, also known as online parameter identification, can effectively solve this problem. [...] Read more.

For model-based state of charge (SOC) estimation methods, the battery model parameters change with temperature, SOC, and so forth, causing the estimation error to increase. Constantly updating model parameters during battery operation, also known as online parameter identification, can effectively solve this problem. In this paper, a lithium-ion battery is modeled using the Thevenin model. A variable forgetting factor (VFF) strategy is introduced to improve forgetting factor recursive least squares (FFRLS) to variable forgetting factor recursive least squares (VFF-RLS). A novel method based on VFF-RLS for the online identification of the Thevenin model is proposed. Experiments verified that VFF-RLS gives more stable online parameter identification results than FFRLS. Combined with an unscented Kalman filter (UKF) algorithm, a joint algorithm named VFF-RLS-UKF is proposed for SOC estimation. In a variable-temperature environment, a battery SOC estimation experiment was performed using the joint algorithm. The average error of the SOC estimation was as low as 0.595% in some experiments. Experiments showed that VFF-RLS can effectively track the changes in model parameters. The joint algorithm improved the SOC estimation accuracy compared to the method with the fixed forgetting factor. Full article

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10 pages, 2765 KiB

Open AccessArticle

Magnesium Aminoclay-Fe₃O₄ (MgAC-Fe₃O₄) Hybrid Composites for Harvesting of Mixed Microalgae

by Bohwa Kim^1,†, Vu Khac Hoang Bui^2,†, Wasif Farooq³, Sang Goo Jeon⁴, You-Kwan Oh^5,* and Young-Chul Lee^2,*

¹ Advanced Biomass R&D Center, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Korea

² Department of BioNano Technology, Gachon University, 1342 Seongnamdaero, Sujeong-gu, Seongnam-si, Gyeonggi-do 13120, Korea

³ Department of Chemical Engineering, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran 31261, Saudi Arabia

⁴ Biomass and Waste Energy Laboratory, Korea Institute of Energy Research (KIER), Daejeon 34129, Korea

⁵ School of Chemical and Biomolecular Engineering, Pusan National University, Busan 46241, Korea

^† Equally Contributing Authors.

Energies 2018, 11(6), 1359; https://doi.org/10.3390/en11061359 - 26 May 2018

Cited by 13 | Viewed by 3472

Abstract

In this paper, we describe the synthesis of magnesium aminoclay-iron oxide (MgAC-Fe₃O₄) hybrid composites for microalgae-harvesting application. MgAC-templated Fe₃O₄ nanoparticles (NPs) were synthesized in different ratios of MgAC and Fe₃O₄ NPs. The uniform [...] Read more.

In this paper, we describe the synthesis of magnesium aminoclay-iron oxide (MgAC-Fe₃O₄) hybrid composites for microalgae-harvesting application. MgAC-templated Fe₃O₄ nanoparticles (NPs) were synthesized in different ratios of MgAC and Fe₃O₄ NPs. The uniform distribution of Fe₃O₄ NPs in the MgAC matrix was confirmed by transmission electron microscopy (TEM). According to obtained X-ray diffraction (XRD) patterns, increased MgAC loading leads to decreased intensity of the composites’ (311) plane of Fe₃O₄ NPs. For harvesting of Chlorella sp. KR-1, Scenedesmus obliquus and mixed microalgae (Chlorella sp. KR-1/ Scenedesmus obliquus), the optimal pH was 4.0. At higher pHs, the microalgae-harvesting efficiencies fell. Sample #1, which had the highest MgAC concentration, showed the most stability: the harvesting efficiencies for Chlorella sp. KR-1, Scenedesmus obliquus, and mixed microalgae were reduced only to ~50% at pH = 10.0. The electrostatic interaction between MgAC and the Fe₃O₄ NPs in the hybrid samples by microalgae, as confirmed by zeta potential measurements, were attributed to the harvesting mechanisms. Moreover, the zeta potentials of the MgAC-Fe₃O₄ hybrid composites were reduced as pH was increased, thus diminishing the microalgae-harvesting efficiencies. Full article

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24 pages, 3683 KiB

Open AccessArticle

Permanent Magnet Brushless DC Motor and Mechanical Structure Design for the Electric Impact Wrench System

by Chengyuan He^*,†

and Thomas Wu^*

¹ Department of Electrical Engineering and Computer Science, University of Central Florida, Orlando, FL 32816, USA

^† Current Address: 4000 Central Florida Blvd, Orlando, FL 32816, USA.

Energies 2018, 11(6), 1360; https://doi.org/10.3390/en11061360 - 27 May 2018

Cited by 31 | Viewed by 7987

Abstract

This paper presents an analytical method to design an interior permanent magnet brushless DC electric motor (IPMBLDC motor) for a kind of electric impact wrench used for loading and unloading car bolts. It takes into account magnet assembly gap, rotor saturation webs, and [...] Read more.

This paper presents an analytical method to design an interior permanent magnet brushless DC electric motor (IPMBLDC motor) for a kind of electric impact wrench used for loading and unloading car bolts. It takes into account magnet assembly gap, rotor saturation webs, and bridges. Assumed flux leakage coefficient and selected working point of a permanent magnet were used in the initial design. An advanced equivalent magnetic circuit was developed to verify the total flux leakage and the quiescent operating point based on initial design parameters. Key design method points are considered and analyzed. Thermal analysis is given to simulate the temperature rise of all parts of the motor. The new impact wrench mechanical structure is designed, and its working principle analyzed. An electromagnetic field analysis based on MATLAB and the MAXWELL 2D finite element method (FEM) were used in the design to verify the equivalent magnetic circuit and optimize the IPMBLDC motor parameters. Experimental results are obtained to verify the design. The electrical and mechanical designs are combined and an analytical IPMBLDC motor design method is provided. We also show an innovative and reasonable mechanical dynamical calculation method for the impact wrench system, which can be used in whole system design of other functional electric tools. Full article

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25 pages, 3109 KiB

Open AccessArticle

Energy Management Strategy for a Bioethanol Isolated Hybrid System: Simulations and Experiments

by Pablo Gabriel Rullo^1,2,*

, Ramon Costa-Castelló^3,4

, Vicente Roda⁴

and Diego Feroldi^1,5

¹ Grupo de Ingeniería de Sistemas de Procesos (GISP), Centro Franco-Argentino de Ciencias de la Información y de Sistemas (CIFASIS) CONICET-UNR, 27 de Febrero 210 bis, Rosario S2000EZP, Argentina

² Departamento de Ingeniería Eléctrica, Facultad Regional San Nicolás, Universidad Tecnológica Nacional, Colón 332, San Nicolás de Los Arroyos B2900LWH, Argentina

³ Departament d’Enginyeria de Sistemes, Automàtica i Informàtica Industrial, UPC, C/Pau Gargallo 5, 08028 Barcelona, Spain

⁴ Institut de Robòtica i Informàtica Industrial, CSIC-UPC, Llorens i Artigas 4-6, 08028 Barcelona, Spain

⁵ Facultad de Ciencias Exactas, Ingeniería y Agrimensura—Universidad Nacional de Rosario (FCEIA–UNR), Rosario 2000, Argentina

Energies 2018, 11(6), 1362; https://doi.org/10.3390/en11061362 - 28 May 2018

Cited by 9 | Viewed by 3562

Abstract

Renewable energy sources have significant advantages both from the environmental and the economic point of view. Additionally, renewable energy sources can contribute significantly to the development of isolated areas that currently have no connection to the electricity supply network. In order to make [...] Read more.

Renewable energy sources have significant advantages both from the environmental and the economic point of view. Additionally, renewable energy sources can contribute significantly to the development of isolated areas that currently have no connection to the electricity supply network. In order to make efficient use of these energy sources, it is necessary to develop appropriate energy management strategies. This work presents an energy management strategy for an isolated hybrid renewable energy system with hydrogen production from bioethanol reforming. The system is based on wind-solar energy, batteries and a bioethanol reformer, which produces hydrogen to feed a fuel cell system. Bioethanol can contribute to the development of isolated areas with surplus agricultural production, which can be used to produce bioethanol. The energy management strategy takes the form of a state machine and tries to maximize autonomy time while minimizing recharging time. The proposed rule-based strategy has been validated both by simulation and experimentally in a scale laboratory station. Both tests have shown the viability of the proposed strategy complying with the specifications imposed and a good agreement between experimental and simulation results. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 1875 KiB

Open AccessArticle

A Case Study of Presplitting Blasting Parameters of Hard and Massive Roof Based on the Interaction between Support and Overlying Strata

by Ningbo Zhang^1,2,3, Changyou Liu^3,* and Baobao Chen³

¹ School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China

² School of Civil, Mining and Environmental Engineering, Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, NSW 2522, Australia

³ School of Mines, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China

Energies 2018, 11(6), 1363; https://doi.org/10.3390/en11061363 - 28 May 2018

Cited by 7 | Viewed by 2272

Abstract

Due to the existence of a hard and massive roof (HMR), severe ground pressure behaviors have been observed at the working face, resulting in safety issues and the degradation of production effectiveness. Based on the HMR conditions of the Datong Mining Area, the [...] Read more.

Due to the existence of a hard and massive roof (HMR), severe ground pressure behaviors have been observed at the working face, resulting in safety issues and the degradation of production effectiveness. Based on the HMR conditions of the Datong Mining Area, the fracture-related instability of the HMR and its effects on the support selection were investigated by analyzing the interaction between support and overlying strata. Advancefixed-distance presplitting blasting (AFPB) technology was proposed to control the caving interval of HMR, and the influence of the controlled interval on the working load of supports was also analyzed. The working load of the support and the caving interval of the HMR were determined based on the controlled HMR fracture technology, and these were verified by field application tests. The working resistance of the support and the step distance were determined based on controlled roof fracture and were verified by on-site application experiments. The results revealed that cracks emerged after the presplitting blasting, resulting in significantly reduced strata behaviors. Furthermore, the support exhibited good adaptability. Full article

(This article belongs to the Section L: Energy Sources)

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15 pages, 5168 KiB

Open AccessArticle

Study on a Novel Gelled Foam for Conformance Control in High Temperature and High Salinity Reservoirs

by Tong Li^1,†, Jichao Fang^2,†

, Baolei Jiao³, Long He³, Caili Dai^2,* and Qing You^1,*

¹ School of Energy Resources, China University of Geosciences, Beijing 100083, China

² State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, China

³ SINOPEC Northwest Branch Company Technology Research Institute of Petroleum Engineering, Urumqi 830011, China

^† These authors contributed equally to this work.

Energies 2018, 11(6), 1364; https://doi.org/10.3390/en11061364 - 28 May 2018

Cited by 21 | Viewed by 3000

Abstract

A novel gelled foam for conformance control was investigated for its ability to enhance oil recovery (EOR) in high temperature and high salinity reservoirs. The formulation optimization, foaming performance, and core flooding performance of the gelled foam were systematically evaluated under harsh reservoir [...] Read more.

A novel gelled foam for conformance control was investigated for its ability to enhance oil recovery (EOR) in high temperature and high salinity reservoirs. The formulation optimization, foaming performance, and core flooding performance of the gelled foam were systematically evaluated under harsh reservoir conditions. The gelled foam formulation was optimized with 0.4% polymer (hydrolyzed polyacrylamide; HPAM), 0.06% cross-linker (phenolic) and 0.2% foaming agent (sulphobetaine; SB). The addition of the gel improved the stability of the foam system by 3.8 times that of traditional foam. A stabilization mechanism in the gelled foam was proposed to describe the stabilization process of the foam film. The uniformly distributed three-dimensional network structure of the gel provided a thick protective layer for the foam system that maintained the stability of the foam and improved the strength and thickness of the liquid film. The gelled foam exhibited good formation adaptability, profile control, and EOR performance. The foam flowed into the high permeability layer, plugged the dominant channel, and increased the swept volume. Oil recovery was enhanced by 29.4% under harsh high -temperature and high salinity conditions. Full article

(This article belongs to the Section L: Energy Sources)

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16 pages, 638 KiB

Open AccessArticle

Pruning Biomass Potential in Italy Related to Crop Characteristics, Agricultural Practices and Agro-Climatic Conditions

by Luigi Pari¹

, Vincenzo Alfano^1,*

, Daniel Garcia-Galindo², Alessandro Suardi¹

and Enrico Santangelo¹

¹ Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria (CREA), Centro di ricerca Ingegneria e Trasformazioni agroalimentari, Monterotondo, 00016 Rome, Italy

² Research Centre for Energy Resources and Consumption (CIRCE), 50018 Zaragoza, Spain

Energies 2018, 11(6), 1365; https://doi.org/10.3390/en11061365 - 28 May 2018

Cited by 23 | Viewed by 3191

Abstract

This work, developed under the EuroPruning Project, aims to look at relations between pruning biomass production and several factors related both to crop species and management. The aim is to find out mathematical relations that allow improvement of the biomass potential assessment. This [...] Read more.

This work, developed under the EuroPruning Project, aims to look at relations between pruning biomass production and several factors related both to crop species and management. The aim is to find out mathematical relations that allow improvement of the biomass potential assessment. This is generally calculated using biomass production ratios. These ratios are variable due to the influence of several aspects. On the one hand there are crop characteristics—such as species, cultivar, and age—and on the other, crop management, which is often associated to local habits and conditions such as the training system, planting pattern, density, pruning methods, irrigation and climate. This work has been produced by gathering data from literature reviews and surveying. The subset of Italian records in the EuroPruning database consists of 70 records. Each record contains the biomass production ratio and eight agronomic variables. Additionally, a set of six climatic and agro-climatic groups of variables (in total 28 variables) have been added to each record. Moderate to good correlations have been found, especially with few climatic factors. As a result, two regression models are proposed for the evaluation of the vineyard and olive tree pruning biomass ratios for Italy, and applied to assess pruning biomass potential. Full article

(This article belongs to the Section A: Sustainable Energy)

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16 pages, 3039 KiB

Open AccessArticle

Meso-Scale CFD Simulation for Wind Resources: A Case Study of Complex Mountainous Terrain

by Lalit Roy^*

and David MacPhee

Mechanical Engineering, The University of Alabama, Tuscaloosa, AL 35401, USA

Energies 2018, 11(6), 1366; https://doi.org/10.3390/en11061366 - 28 May 2018

Cited by 5 | Viewed by 2960

Abstract

Land based site selection for a wind farm has some challenging criteria, namely, cost for electricity generation and distribution, acquiring ownership of the site, potential barriers from various laws and permits, security concerns, access issues, feasibility of accommodation, etc. However, wind resource assessment [...] Read more.

Land based site selection for a wind farm has some challenging criteria, namely, cost for electricity generation and distribution, acquiring ownership of the site, potential barriers from various laws and permits, security concerns, access issues, feasibility of accommodation, etc. However, wind resource assessment deems the first criterion to rule out a site before other criteria can play roles in the selection process. In this paper, a Computational Fluid Dynamics (CFD) study has been performed on a complex mountainous terrain near a shore in the west coast of the US to assess the wind resource in order to spot potential suitable sites for wind turbines. Average wind speed at a height of 10 m at the centre (44°22

^{'}

12.0

^{'}

^{'}

N, 123°59

^{'}

24.0

^{'}

^{'}

W) of the chosen region under study has been compared with the simulated data for validation. Results from the study, which yields a continuous map of flow field variables, have revealed much more detailed features than the available state-wise wind maps. For example, it has revealed as high as 147% variation in wind speeds and 438% in wind power, making it possible to choose suitable sites without the need for, or perhaps in advance of, expensive direct measurements. This type of analysis may help in preliminary assessments and expedite the site selection process. Full article

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17 pages, 429 KiB

Open AccessArticle

Achieving Cost Minimization and Fairness in Multi-Supplier Smart Grid Environment

by Amna Malik¹, Zain Ali², Ahmed Bilal Awan³

, Ahmed G. Abo-Khalil^3,4 and Guftaar Ahmad Sardar Sidhu^2,*

¹ Department of Physics, Govt. Sadiq College Women University, 63100 Bahawalpur, Pakistan

² Department of Electrical Engineering, COMSATS University Islamabad, 45500 Islamabad, Pakistan

³ Department of Electrical Engineering, College of Engineering, Majmaah University, 15341 Al Majmaah, Saudi Arabia

⁴ Electrical Engineering Department, Faculty of Engineering, Assiut University, University Street, Assiut 71515, Egypt

Energies 2018, 11(6), 1367; https://doi.org/10.3390/en11061367 - 28 May 2018

Cited by 2 | Viewed by 3339

Abstract

In this paper, we study the energy management techniques in the smart grid with multiple energy providers. We seek to minimize the electricity cost. In this paper, the desired objectives are achieved through scheduling of different consumers to different utilities at different time [...] Read more.

In this paper, we study the energy management techniques in the smart grid with multiple energy providers. We seek to minimize the electricity cost. In this paper, the desired objectives are achieved through scheduling of different consumers to different utilities at different time slots. We consider a practical system where multiple users can be allocated to a single utility, but, a user cannot be assigned to more than one utility. As a first goal, we formulate a sum cost minimization problem subject to independent generation capacity of each utility. A dual decomposition approach is exploited to find an efficient solution where the sub-gradient approach is adopted to update the dual variables. Later, a min-max based optimization framework is adopted to achieve the fairness among different customers. Moreover, suboptimal schemes are also designed to reduce the computational complexity. Simulation results are presented to validate the performance of the proposed solutions. Full article

(This article belongs to the Collection Smart Grid)

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18 pages, 6721 KiB

Open AccessArticle

Research on Unbalance Fault-Tolerant Control Strategy of Modular Multilevel Photovoltaic Grid-Connected Inverter

by Yiqi Liu^1,*

, Danhua Li², Yu Jin³, Qingbo Wang¹ and Wenlong Song¹

¹ College of Mechanical and Electrical Engineering, Northeast Forestry University, Harbin 150040, China

² Maintenance Branch Company, State Grid Chongqing Electric Power Company, Chongqing 400039, China

³ School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China

Energies 2018, 11(6), 1368; https://doi.org/10.3390/en11061368 - 28 May 2018

Cited by 4 | Viewed by 2661

Abstract

The average switching model of modular multilevel converter (MMC) is built in this paper when the hot reserved strategy is adopted as a fault-tolerant control. When the MMC SM faults, the rest of the SMs cannot support the DC-link voltage, which results in [...] Read more.

The average switching model of modular multilevel converter (MMC) is built in this paper when the hot reserved strategy is adopted as a fault-tolerant control. When the MMC SM faults, the rest of the SMs cannot support the DC-link voltage, which results in interruption of the inverter. To tackle this issue, a novel fault-tolerant control strategy is proposed to bypass the SM under fault and re-regulate the SM capacitor voltage and carrier phase-shift angle to maintain the main components of circulating current, and reduce the Total Harmonic Distortion (THD) of grid connected current to enable the stable operation of the photovoltaic inverter. The maximum power tracking control is improved to solve the problem of long restoration time when faults occur, based on a constant voltage startup method combined with a fix-step incremental conductance method. Simulations in MATLAB/Simulink and experimental results have verified the feasibility and effectiveness of the proposed control strategy. Full article

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20 pages, 1910 KiB

Open AccessArticle

Service Continuity of PV Synchronous Buck/Buck-Boost Converter with Energy Storage^†

by Saima Siouane, Slaviša Jovanović and Philippe Poure^*

¹ Institut Jean Lamour (UMR7198), Université de Lorraine Vandoeuvre lès Nancy, Campus Artem - BP 50840, F-54511 Nancy, France

^† This paper is an extended version of our paper published in EEEIC 2017: Service Continuity of PV Synchronous buck/buck-boost Converter with Energy Storage.

Energies 2018, 11(6), 1369; https://doi.org/10.3390/en11061369 - 28 May 2018

Cited by 12 | Viewed by 4947

Abstract

Numerous advantages offered by Photovoltaic (PV) generation systems coupled with the increasing power demands for clean energy put PV systems in the front of many research works. For stand-alone applications powered with PV systems, the reliability of the power conversion stage is essential [...] Read more.

Numerous advantages offered by Photovoltaic (PV) generation systems coupled with the increasing power demands for clean energy put PV systems in the front of many research works. For stand-alone applications powered with PV systems, the reliability of the power conversion stage is essential to ensure the continuous supply of energy. Therefore, in the case of any failure occurring in the power conversion stage, it is mandatory to provide remedial actions to guarantee the service continuity of the produced electrical power. This paper analyses the service continuity of a two-stage buck/buck-boost converter with energy storage, driven with synchronous control. The initial two-stage converter is made fault-tolerant and robust to failures of its two switches by adding only one additional switch associated with two diodes. In this study, only open-circuit switch faults are considered. The proposed fault-tolerant circuit and the initial one have the same electrical behavior when synchronous control is used. The applied synchronous control in both healthy conditions and post-fault operation ensures the same functionalities without degrading the system’s performances. The proposed two-stage synchronously-controlled circuit is validated through simulation in the cases of open circuit faults on the two switches of the initial converter. The obtained results show the feasibility of the proposed functional redundancy and the continuity of operation at full power after switch fault diagnosis. Full article

(This article belongs to the Special Issue 17TH International Conference on Environment and Electrical Engineering)

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23 pages, 1570 KiB

Open AccessFeature PaperArticle

Method for Assessing the Development of Underground Hard Coal Mines on a Regional Basis: The Concept of Measurement and Research Results

by Izabela Jonek-Kowalska

Faculty of Organization and Management, The Silesian University of Technology, Zabrze 41-800, Poland

Energies 2018, 11(6), 1370; https://doi.org/10.3390/en11061370 - 28 May 2018

Cited by 11 | Viewed by 3564

Abstract

The functioning and development of the extractive industry depends on many unusual conditions that are not found in other industries, such as the size of deposits, the level of natural and technical hazards, geographic location, or the method of mineral extraction (open pit [...] Read more.

The functioning and development of the extractive industry depends on many unusual conditions that are not found in other industries, such as the size of deposits, the level of natural and technical hazards, geographic location, or the method of mineral extraction (open pit or underground). Therefore, it is difficult to use universal development assessment methods for such specific production units. As a result, the research undertaken in this article aims to develop an indicator method for evaluating the development potential of underground hard coal mines. This method is based on a theoretical and practical analysis of the conditions of functioning of hard coal mines, expert research, and multiple case studies verifying the operation of the presented development indicator. The first part of the article is devoted to identifying and analyzing the criteria for assessing the functioning of underground hard coal mines. Next, the essence and methodology of creating and interpreting the proposed indicator was presented. The second part of the article is empirical, and contains the results of the assessment carried out using the developed indicators for five Polish hard coal mines for the years 2011–2015. The results of the research indicate that the most important factors in the development of hard coal mines relate to the geological and mining conditions, and those concerning natural hazard levels. However, during the functioning, the financial conditions and related production conditions, which ultimately determine the survival and development of underground mining plants, gain in significance. Full article

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15 pages, 4190 KiB

Open AccessArticle

Optimal Scheduling and Real-Time Control Schemes of Battery Energy Storage System for Microgrids Considering Contract Demand and Forecast Uncertainty

by Hong-Chao Gao¹, Joon-Ho Choi¹, Sang-Yun Yun^1,*

, Hak-Ju Lee² and Seon-Ju Ahn^1,*

¹ Department of Electrical Engineering, Chonnam National University, 77, Yongbong-ro, Buk-gu, Gwangju 61186, Korea

² Energy System Group Energy New Business Laboratory, Korea Electric Power Research Institute, Daejeon 34056, Korea

Energies 2018, 11(6), 1371; https://doi.org/10.3390/en11061371 - 28 May 2018

Cited by 33 | Viewed by 3523

Abstract

Optimal operation of the battery energy storage system (BESS) is very important to reduce the running cost of a microgrid. Rolling horizon-based scheduling, which updates the optimal decision based on the latest information, is widely applied to microgrid operation. In this paper, the [...] Read more.

Optimal operation of the battery energy storage system (BESS) is very important to reduce the running cost of a microgrid. Rolling horizon-based scheduling, which updates the optimal decision based on the latest information, is widely applied to microgrid operation. In this paper, the optimal scheduling of a microgrid, considering the energy cost, demand charge, and the battery wear-cost, is formulated as a mixed integer linear programming (MILP) problem. This paper also deals with two practical and important issues when applying the rolling-horizon strategy to BESS scheduling. First, to mitigate the high dependency of the load forecast on the latest information, a confidence weight parameter method is proposed. Second, a new target state of charge (SOC) assignment method is proposed to avoid the depletion of BESS and to reduce the wear-cost of the battery. In addition to the optimal scheduling, a novel real-time control scheme is proposed to mitigate the effect of the forecast uncertainty. The performance of the proposed methods is tested with data measured from a campus microgrid. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 668 KiB

Open AccessArticle

The Conductive and Predictive Effect of Oil Price Fluctuations on China’s Industry Development Based on Mixed-Frequency Data

by Jian Chai^1,2,4

, Puju Cao^1,*, Xiaoyang Zhou¹

, Kin Keung Lai³, Xiaofeng Chen⁴ and Siping (Sue) Su⁴

¹ School of Economics and Management, Xidian University, Xi’an 710126, China

² Nanjing University of Information Science & Technology, Jiangsu Talents Research Base, Nanjing 210044, China

³ Department of Management Sciences, City University of Hong Kong, Hong Kong 999077, China

⁴ Department of Decision Sciences, College of Business and Economics, Western Washington University, Bellingham, WA 98225, USA

Energies 2018, 11(6), 1372; https://doi.org/10.3390/en11061372 - 28 May 2018

Cited by 6 | Viewed by 4631

Abstract

Presently, the total supply of crude oil is sufficient, but short-term supply and demand imbalances and regional imbalances still exist. The effect of crude oil supply security and price impact cannot be ignored. As the world’s largest oil importer, China is highly dependent [...] Read more.

Presently, the total supply of crude oil is sufficient, but short-term supply and demand imbalances and regional imbalances still exist. The effect of crude oil supply security and price impact cannot be ignored. As the world’s largest oil importer, China is highly dependent on foreign oil. Therefore, the fluctuation of international oil prices may impact the development of China’s various industries in a significant and differential way. However, because the available data have different frequencies, much of the recent research that addresses the effect of oil prices on industry development need to replace, split, or merge the original data, resulting in loss of the information from the original data. Using the mixed data sampling model (MIDAS(m,K,h)-AR(1)) with the first-order lag autoregressive terms of the interpreted variables, this study builds a mixed data model to investigate the effect of oil price volatility on the output of China's industries. This study expands the extant research by financial market fluctuations and macroeconomic analysis, and at the same time makes short-term predictions on the output of China’s seven main industries. The analysis results show that the mixed data regression model brings the original information contained in different frequency data into the model analysis, and utilizes the latest high frequency data of the explanatory variables to perform real-time short-term prediction of low-frequency interpreted variables. This method improves the timeliness of forecasting macroeconomic indicators and the accuracy of short-term forecasts. The empirical results show that the spot price of international crude oil has a significant and differential impact on the outputs of the seven industries in China. Among them, oil price fluctuation has the greatest impact on the output of China’s financial industry. Full article

(This article belongs to the Special Issue Energy Economy, Sustainable Energy and Energy Saving)

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16 pages, 4757 KiB

Open AccessArticle

Spatial and Temporal Optimization Strategy for Plug-In Electric Vehicle Charging to Mitigate Impacts on Distribution Network

by Lili Gong¹, Wu Cao¹, Kangli Liu¹

, Jianfeng Zhao^1,* and Xiang Li²

¹ School of Electrical Engineering, Southeast University, Nanjing 210096, China

² LiuZhou Power Supply Bureau, GuangXi Power Grid Co., Ltd., Liuzhou 545006, China

Energies 2018, 11(6), 1373; https://doi.org/10.3390/en11061373 - 29 May 2018

Cited by 16 | Viewed by 3136

Abstract

The large deployment of plug-in electric vehicles (PEVs) challenges the operation of the distribution network. Uncoordinated charging of PEVs will cause a heavy load burden at rush hour and lead to increased power loss and voltage fluctuation. To overcome these problems, a novel [...] Read more.

The large deployment of plug-in electric vehicles (PEVs) challenges the operation of the distribution network. Uncoordinated charging of PEVs will cause a heavy load burden at rush hour and lead to increased power loss and voltage fluctuation. To overcome these problems, a novel coordinated charging strategy which considers the moving characteristics of PEVs is proposed in this paper. Firstly, the concept of trip chain is introduced to analyze the spatial and temporal distribution of PEVs. Then, a stochastic optimization model for PEV charging is established to minimize the distribution network power loss (DNPL) and maximal voltage deviation (MVD). After that, the particle swarm optimization (PSO) algorithm with an embedded power flow program is adopted to solve the model, due to its simplicity and practicality. Last, the feasibility and efficiency of the proposed strategy is tested on the IEEE 33 distribution system. Simulation results show that the proposed charging strategy not only reduces power loss and the peak valley difference, but also improves voltage profile greatly. Full article

(This article belongs to the Section F: Electrical Engineering)

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12 pages, 2216 KiB

Open AccessArticle

Solar Radiation Estimation Algorithm and Field Verification in Taiwan

by Ping-Huan Kuo¹

, Hsin-Chuan Chen² and Chiou-Jye Huang^3,*

¹ Computer and Intelligent Robot Program for Bachelor Degree, National Pingtung University, Pingtung 90004, Taiwan

² School of Computer Engineering, University of Electronic Science and Technology of China Zhongshan Institute, Zhongshan 528402, China

³ School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou 341000, China

Energies 2018, 11(6), 1374; https://doi.org/10.3390/en11061374 - 29 May 2018

Cited by 8 | Viewed by 3661

Abstract

The power generation potential of a solar photovoltaic (PV) power generation system is closely related to the on-site solar radiation, and sunshine conditions are an important reference index for evaluating the installation of a solar PV system. Meanwhile, the long-term operation and maintenance [...] Read more.

The power generation potential of a solar photovoltaic (PV) power generation system is closely related to the on-site solar radiation, and sunshine conditions are an important reference index for evaluating the installation of a solar PV system. Meanwhile, the long-term operation and maintenance of a PV system needs solar radiation information as a reference for system performance evaluation. Obtaining solar radiation information through the installation of irradiation monitoring stations is often very costly, and the cost of sustaining the reliability of the monitoring system, Internet stability and subsequent operation and maintenance can often be alarming. Therefore, the establishment of a solar radiation estimation model can reduce the installation of monitoring stations and decrease the cost of obtaining solar radiation information. In this study, we use an inverse distance weighting algorithm to establish the solar radiation estimation model. The model was built by obtaining information from 20 solar radiation monitoring stations in central and southern Taiwan, and field verification was implemented at Yuan Chang Township town hall and the Tainan Liujia campus. Furthermore, a full comparison between Inverse Distance Weighting (IDW) and the Kriging method is also given in this paper. The estimation results demonstrate the performance of the IDW method. In the experiment, the performance of the IDW method is better than the Ordinary Kriging (OK) method. The Mean Absolute Percentage Error (MAPE) values of the solar radiation estimation model by IDW at the two field verifications were 4.30% and 3.71%, respectively. Full article

(This article belongs to the Special Issue Selected Papers from the IEEE ICASI 2018)

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18 pages, 5214 KiB

Open AccessArticle

A Communication-Free Decentralized Control for Grid-Connected Cascaded PV Inverters

by Mei Su¹, Chao Luo¹, Xiaochao Hou¹

, Wenbin Yuan¹, Zhangjie Liu^1,*, Hua Han¹ and Josep M. Guerrero²

¹ School of Information Science and Engineering, Central South University, Changsha 410083, China

² Department of Energy Technology, Aalborg University, DK-9220 Aalborg East, Denmark

Energies 2018, 11(6), 1375; https://doi.org/10.3390/en11061375 - 29 May 2018

Cited by 12 | Viewed by 3949

Abstract

This paper proposes a communication-free decentralized control for grid-connected cascaded PV inverter systems. The cascaded PV inverter system is an AC-stacked architecture, which promotes the integration of low voltage (LV) distributed photovoltaic (PV) generators into the medium/high voltage (MV/HV) power grid. The proposed [...] Read more.

This paper proposes a communication-free decentralized control for grid-connected cascaded PV inverter systems. The cascaded PV inverter system is an AC-stacked architecture, which promotes the integration of low voltage (LV) distributed photovoltaic (PV) generators into the medium/high voltage (MV/HV) power grid. The proposed decentralized control is fully free of communication links and phase-locked loop (PLL). All cascaded inverters are controlled as current controlled voltage sources locally and independently to achieve maximum power point tracking (MPPT) and frequency self-synchronization with the power grid. As a result, control complexity as well as communication costs are reduced, and the system’s reliability is greatly enhanced compared with existing communication-based methods. System stability and dynamic performance are evaluated by small-signal analysis to guide the design of system parameters. The feasibility and effectiveness of the proposed solution are verified by simulation tests. Full article

(This article belongs to the Special Issue Microgrids-2018)

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17 pages, 1730 KiB

Open AccessArticle

Hybrid Decomposition-Reconfiguration Models for Long-Term Solar Radiation Prediction Only Using Historical Radiation Records

by Si-Ya Wang¹, Jun Qiu^2,3,* and Fang-Fang Li^1,3,*

¹ College of Water Resources & Civil Engineering, China Agricultural University; Beijing 100083, China

² State Key Laboratory of Hydroscience & Engineering, Tsinghua University, Beijing 100084, China

³ State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Xining 810016, China

Energies 2018, 11(6), 1376; https://doi.org/10.3390/en11061376 - 29 May 2018

Cited by 15 | Viewed by 2458

Abstract

Solar radiation prediction is significant for solar energy utilization. This paper presents hybrid methods following the decomposition-prediction-reconfiguration paradigm using only historical radiation records with different combination of decomposition methods, Ensemble Empirical Mode Decomposition (EEMD) and Wavelet Analysis (WA), and the reconfiguration methods, regression [...] Read more.

Solar radiation prediction is significant for solar energy utilization. This paper presents hybrid methods following the decomposition-prediction-reconfiguration paradigm using only historical radiation records with different combination of decomposition methods, Ensemble Empirical Mode Decomposition (EEMD) and Wavelet Analysis (WA), and the reconfiguration methods, regression model (RE) and Artificial Neural Network (ANN). The application in west China indicates that these hybrid decomposition-reconfiguration models perform well for monthly prediction, while the comparisons of the daily prediction show that the hybrid EEMD-RE model has a higher degree of fitting and a better prediction effect in long-term prediction of solar radiation intensity, which verifies (1) decomposition of original solar radiation data results in components with regular characteristics; (2) the relationship between the original solar radiation sequence and the derived intrinsic mode functions (IMFs) is linear; and (3) EEMD has strong adaptivity for non-linear and non-stationary series. The proposed hybrid decomposition-reconfiguration models have great application prospect for monthly long-term prediction of solar radiation intensity, especially in the areas where complex climate data is difficult to obtain, and the EEMD-RE model is recommended for the daily long-term prediction. Full article

(This article belongs to the Section A: Sustainable Energy)

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22 pages, 9044 KiB

Open AccessArticle

Energy Performance of Liquid Desiccant and Evaporative Cooling-Assisted 100% Outdoor Air Systems under Various Climatic Conditions

by Shiying Li and Jae-Weon Jeong^*

Department of Architectural Engineering, College of Engineering, Hanyang University, 222 Wangsimni-Ro, Seongdong-Gu, Seoul 04763, Korea

Energies 2018, 11(6), 1377; https://doi.org/10.3390/en11061377 - 29 May 2018

Cited by 11 | Viewed by 3578

Abstract

The main purpose of this study is to evaluate the applicability of a liquid desiccant and evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS) in six typical cities in China. The six cities are located in different climatic zones in China and are selected [...] Read more.

The main purpose of this study is to evaluate the applicability of a liquid desiccant and evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS) in six typical cities in China. The six cities are located in different climatic zones in China and are selected because they are comparable owing to the outdoor air conditions. Many studies have shown that the annual operating energy consumption of LD-IDECOAS is nearly half compared with the conventional variable air volume (VAV) system. Because the climate characteristics of the six selected cities were different, the appropriate mode of operation of the LD-IDECAOS was applied to each studied city, and energy simulations were performed. Based on the design conditions of each region, the required cooling and heating loads were calculated for office buildings using transient system simulations (TRNSYS) 17, and the performance of the LD-IDECOAS and its energy consumption were simulated with a commercial engineering equation solver (EES) program. Depending on the climate characteristics of each city, adequate modifications were evaluated with simulations in terms of energy consumption. The proposed system was compared with the VAV system and the evaporative cooling assisted 100% outdoor air-conditioning system (IDECOAS) for detailed simulation results in the effort to evaluate the energy-saving potential. Finally, the results show that the proposed system saves considerable energy over conventional VAV systems and, in summer, the applications save even more energy than IDECOAS. However, there is a slight difference between the different geographical regions in terms of the annual operating energy consumption. In summary, the proposed system can yield significant energy-saving benefits in hot and humid regions whereas, in dry regions, the proposed system is more applicable in the summer. Consequently, LD-IDECOAS can be adopted for different climatic zones as a heating, ventilating, and air-conditioning (HVAC) system by introducing 100% outdoor air. Full article

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10 pages, 1153 KiB

Open AccessArticle

Methodical Aspects of Biogas Production in Small-Volume Bioreactors in Laboratory Investigations

by Agnieszka Kasprzycka^* and Jan Kuna

Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, 20-290 Lublin, Poland

Energies 2018, 11(6), 1378; https://doi.org/10.3390/en11061378 - 29 May 2018

Cited by 7 | Viewed by 3392

Abstract

The aim of this study was to develop a methodology to investigate the biofermentation process in small-volume fermenters. Dark serum bottles with a volume of 100–120 mL, tightly sealed with a rubber septum, were used as bioreactors. The optimum measurement conditions in this [...] Read more.

The aim of this study was to develop a methodology to investigate the biofermentation process in small-volume fermenters. Dark serum bottles with a volume of 100–120 mL, tightly sealed with a rubber septum, were used as bioreactors. The optimum measurement conditions in this type of bioreactor comprise: (i) filling two-thirds of the maximum volume with a suspension; (ii) a 2% bioreactor loading (on a dry basis) and; (iii) the daily equalization of pressure by removing the biogas through the septum pierced with a syringe needle and the intensive mixing of the remaining suspension. The methane yield (quantity and dynamics) obtained in this type of bioreactor is analogous to that of industrial bioreactors or large-scale laboratory bioreactors. The use of small-volume bioreactors that can be incubated will facilitate the preliminary selection of analysed systems and provide an indication of those that should be investigated in large-scale bioreactors. Full article

(This article belongs to the Special Issue BioEnergy and BioChemicals Production from Biomass and Residual Resources)

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19 pages, 6554 KiB

Open AccessFeature PaperArticle

In Deep Analysis on the Behavior of Grape Marc Constituents during Hydrothermal Carbonization

by Daniele Basso¹

, Elsa Weiss-Hortala²

, Francesco Patuzzi¹, Marco Baratieri^1,*

and Luca Fiori³

¹ Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, 39100 Bolzano, Italy

² IMT Mines Albi, Centre RAPSODEE, UMR CNRS 5302, Campus Jarlard, F-81013 Albi CEDEX 09, France

³ DICAM, Department of Civil, Environmental and Mechanical Engineering, University of Trento—Via Mesiano 77, 38123 Trento, Italy

Energies 2018, 11(6), 1379; https://doi.org/10.3390/en11061379 - 29 May 2018

Cited by 35 | Viewed by 3935

Abstract

Grape marc is a residue of the wine-making industry, nowadays not always effectively valorized. It consists of grape seeds (mostly lignocellulosic) and grape skins (mostly holocellulosic). In order to understand possible correlations between seeds and skins in forming hydrochar for it to be [...] Read more.

Grape marc is a residue of the wine-making industry, nowadays not always effectively valorized. It consists of grape seeds (mostly lignocellulosic) and grape skins (mostly holocellulosic). In order to understand possible correlations between seeds and skins in forming hydrochar for it to be used as a solid biofuel, hydrothermal carbonization (HTC) was applied separately to grape marc and its constituents. HTC was performed at several process conditions (temperature: 180, 220 and 250 °C; reaction time: 0.5, 1, 3 and 8 h), in order to collect data on the three phases formed downstream of the process: solid (hydrochar), liquid and gas. An in deep analytical characterization was performed: ultimate analysis and calorific value for hydrochar, Total Organic Carbon (TOC) and Inductively Coupled Plasma (IPC) analyses for liquid phase, composition for gas phase. In previous works, the same experimental apparatus was used to treat residual biomass, obtaining interesting results in terms of possible hydrochar exploitation as a solid biofuel. Thus, the main objectives of this work were both to get results for validating the hypothesis to apply HTC to this feedstock, and to collect data for subsequent theoretical investigations. Moreover, a severity model was developed to allow a predictive description of the hydrochar yield as a function of a unique parameter condensing both temperature and reaction time effects. The results obtained demonstrate that this process can upgrade wet residues into a solid biofuel ad that the process can be satisfactorily described in terms of a severity factor. Full article

(This article belongs to the Special Issue Thermo Fluid Conversion of Biomass)

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21 pages, 7100 KiB

Open AccessArticle

Geothermal-Related Thermo-Elastic Fracture Analysis by Numerical Manifold Method

by Jun He^1,2, Quansheng Liu^1,2, Zhijun Wu^1,2,* and Yalong Jiang^1,2

¹ The Key Laboratory of Safety for Geotechnical and Structural Engineering of Hubei Province, School of Civil Engineering, Wuhan University, Wuhan 430072, China

² Stake Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China

Energies 2018, 11(6), 1380; https://doi.org/10.3390/en11061380 - 29 May 2018

Cited by 10 | Viewed by 3143

Abstract

One significant factor influencing geothermal energy exploitation is the variation of the mechanical properties of rock in high temperature environments. Since rock is typically a heterogeneous granular material, thermal fracturing frequently occurs in the rock when the ambient temperature changes, which can greatly [...] Read more.

One significant factor influencing geothermal energy exploitation is the variation of the mechanical properties of rock in high temperature environments. Since rock is typically a heterogeneous granular material, thermal fracturing frequently occurs in the rock when the ambient temperature changes, which can greatly influence the geothermal energy exploitation. A numerical method based on the numerical manifold method (NMM) is developed in this study to simulate the thermo-elastic fracturing of rocklike granular materials. The Voronoi tessellation is incorporated into the pre-processor of NMM to represent the grain structure. A contact-based heat transfer model is developed to reflect heat interaction among grains. Based on the model, the transient thermal conduction algorithm for granular materials is established. To simulate the cohesion effects among grains and the fracturing process between grains, a damage-based contact fracture model is developed to improve the contact algorithm of NMM. In the developed numerical method, the heat interaction among grains as well as the heat transfer inside each solid grain are both simulated. Additionally, as damage evolution and fracturing at grain interfaces are also considered, the developed numerical method is applicable to simulate the geothermal-related thermal fracturing process. Full article

(This article belongs to the Special Issue Geothermal Energy: Utilization and Technology 2018)

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16 pages, 3977 KiB

Open AccessArticle

Applications of Complex Network Analysis in Electric Power Systems

by Mahmoud Saleh¹, Yusef Esa¹ and Ahmed Mohamed^1,2,*

¹ Department of Electrical Engineering, The City University of The City College of New York, New York, NY 10031, USA

² Department of Electrical Engineering (on leave), Menia University, Menia 61512, Egypt

Energies 2018, 11(6), 1381; https://doi.org/10.3390/en11061381 - 29 May 2018

Cited by 62 | Viewed by 13229

Abstract

This paper provides a review of the research conducted on complex network analysis (CAN) in electric power systems. Moreover, a new approach is presented to find optimal locations for microgrids (MGs) in electric distribution systems (EDS) utilizing complex network analysis. The optimal placement [...] Read more.

This paper provides a review of the research conducted on complex network analysis (CAN) in electric power systems. Moreover, a new approach is presented to find optimal locations for microgrids (MGs) in electric distribution systems (EDS) utilizing complex network analysis. The optimal placement in this paper points to the location that will result in enhanced grid resilience, reduced power losses and line loading, better voltage stability, and a supply to critical loads during a blackout. The criteria used to point out the optimal placement of the MGs were predicated on the centrality analysis selected from the complex network theory, the center of mass (COM) concept from physics, and the recently developed controlled delivery grid (CDG) model. An IEEE 30 bus network was utilized as a case study. Results using MATLAB (MathWorks, Inc., Nattick, MA, USA) and PowerWorld (PowerWorld Corporation, Champaign, IL, USA) demonstrate the usefulness of the proposed approach for MGs placement. Full article

(This article belongs to the Collection Smart Grid)

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15 pages, 1026 KiB

Open AccessArticle

A Robust Suboptimal Current Control of an Interlink Converter for a Hybrid AC/DC Microgrid

by Ismi Rosyiana Fitri, Jung-Su Kim^*

and Hwachang Song^*

Department of Electrical and Information Engineering, Seoul National University of Science and Technology, Seoul 01811, Korea

Energies 2018, 11(6), 1382; https://doi.org/10.3390/en11061382 - 29 May 2018

Cited by 15 | Viewed by 3080

Abstract

A hybrid AC/DC microgrid is established with the aim of exploiting numerous types of renewable energy to meet the needs of different loads. The microgrid is decomposed by AC DC sub-grids which are connected by an interlink converter (IC). To maintain the security [...] Read more.

A hybrid AC/DC microgrid is established with the aim of exploiting numerous types of renewable energy to meet the needs of different loads. The microgrid is decomposed by AC DC sub-grids which are connected by an interlink converter (IC). To maintain the security and reliability of the microgrid, an automatic controller for the interlink converter is needed. In this paper, we propose a Linear Matrix Inequalities (LMI)-based current control method for the interlink converter. As the main features here, the interlink converter permits bidirectional power exchange between both sub-grids when a power–demand imbalance occurs in one sub-grid regardless of the converter system parameters. Simulations with various filter parameters are performed using the Matlab/Simulink software to validate the effectiveness of the proposed controller. In comparison with the existing Linear Quadratic Regulator (LQR)-based current control, the proposed method is more robust against unknown system parameters and high load perturbation. Full article

(This article belongs to the Special Issue 18th International Symposium on Advanced Intelligent Systems (ISIS2017))

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17 pages, 928 KiB

Open AccessArticle

Multi-Objective Optimization of the Envelope of Building with Natural Ventilation

by Krzysztof Grygierek¹ and Joanna Ferdyn-Grygierek^2,*

¹ Faculty of Civil Engineering, The Silesian University of Technology, 44-100 Gliwice, Poland

² Faculty of Energy and Environmental Engineering, The Silesian University of Technology, 44-100 Gliwice, Poland

Energies 2018, 11(6), 1383; https://doi.org/10.3390/en11061383 - 29 May 2018

Cited by 38 | Viewed by 3821

Abstract

A properly designed house should provide occupants with the high level of thermal comfort at low energy demand. On many occasions investors choose to add additional insulation to the buildings to reduce heat demand. This may lead to overheating of the building without [...] Read more.

A properly designed house should provide occupants with the high level of thermal comfort at low energy demand. On many occasions investors choose to add additional insulation to the buildings to reduce heat demand. This may lead to overheating of the building without a cooling system in summer periods (these prevail in Poland). Additionally, it affects the deterioration of thermal comfort, which can only be improved by increasing ventilation. The paper presents the multi-objective optimization of the selected design parameters in a single-family building in temperate climate conditions. The influence of four types of windows, their size, building orientation, insulation of external wall, roof and ground floor and infiltration on the life cycle costs and thermal comfort is analyzed for the building without cooling. Infiltration changes during the simulation and is controlled by a special controller. Its task is to imitate the behavior of occupants in changing the supply airflow. Optimal selection of the design parameters is carried out using Non-dominated Sorting Genetic Algorithm II (NSGA-II) by coupling the building performance simulation program EnergyPlus with optimization environment. For the single-family house, optimal values of design variables for three different criteria are presented. Full article

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12 pages, 3420 KiB

Open AccessArticle

Investigation on Gas Hydrate Slurry Pressure Drop Properties in a Spiral Flow Loop

by Yongchao Rao^1,2,3, Ziwen Wang^2,3, Shuli Wang^2,3,* and Minguan Yang¹

¹ School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China

² Jiangsu Key Laboratory of Oil-Gas Storage and Transportation Technology, Changzhou 213016, China

³ School of Petroleum Engineering, Changzhou University, Changzhou 213016, China

Energies 2018, 11(6), 1384; https://doi.org/10.3390/en11061384 - 29 May 2018

Cited by 5 | Viewed by 2754

Abstract

Although many studies have been conducted to investigate the hydrates formation and slurry flow during the transportation, studies on the hydrates slurry pressure drop properties using spiral flow in a loop are still almost blank. In the current work, a series of experiments [...] Read more.

Although many studies have been conducted to investigate the hydrates formation and slurry flow during the transportation, studies on the hydrates slurry pressure drop properties using spiral flow in a loop are still almost blank. In the current work, a series of experiments about hydrate formation process and pressure drop properties were conducted in a spiral flow loop. The experiments in this work were conducted in a spiral flow loop, the loop is 97 ms, and the internal diameter is 25 mms. The experimental results showed that characteristics of hydrate formation process in a spiral loop, and the twist rate of twist tape had an influence on hydrate slurry pressure. Finally, the pressure drop model of hydrate slurry in a spiral flow loop was established, and the relative error were within 10%. This work helped to understand the effects of spiral flow on the gas hydrate formation process and slurry pressure drop, and provide an insight into the mechanism of how spiral flow affect gas transportation. Full article

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24 pages, 11393 KiB

Open AccessArticle

Performance Analysis of Permanent Magnet Motors for Electric Vehicles (EV) Traction Considering Driving Cycles

by Thanh Anh Huynh¹

and Min-Fu Hsieh^2,*

¹ Department of Systems and Naval Mechatronic Engineering, National Cheng Kung University, Tainan 70101, Taiwan

² Department of Electrical Engineering, National Cheng Kung University, Tainan 70101, Taiwan

Energies 2018, 11(6), 1385; https://doi.org/10.3390/en11061385 - 29 May 2018

Cited by 91 | Viewed by 14929

Abstract

This paper evaluates the electromagnetic and thermal performance of several traction motors for electric vehicles (EVs). Two different driving cycles are employed for the evaluation of the motors, one for urban and the other for highway driving. The electromagnetic performance to be assessed [...] Read more.

This paper evaluates the electromagnetic and thermal performance of several traction motors for electric vehicles (EVs). Two different driving cycles are employed for the evaluation of the motors, one for urban and the other for highway driving. The electromagnetic performance to be assessed includes maximum motor torque output for vehicle acceleration and the flux weakening capability for wide operating range under current and voltage limits. Thermal analysis is performed to evaluate the health status of the magnets and windings for the prescribed driving cycles. Two types of traction motors are investigated: two interior permanent magnet motors and one permanent magnet-assisted synchronous reluctance motor. The analysis results demonstrate the benefits and disadvantages of these motors for EV traction and provide suggestions for traction motor design. Finally, experiments are conducted to validate the analysis. Full article

(This article belongs to the Collection Electric and Hybrid Vehicles Collection)

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16 pages, 2814 KiB

Open AccessArticle

Computing Active Power Losses Using a Mathematical Model of a Regulated Street Luminaire

by Roman Sikora^*

, Przemysław Markiewicz and Wiesława Pabjańczyk

Institute of Electrical Power Engineering, Lodz University of Technology, 90-924 Lodz, Poland

Energies 2018, 11(6), 1386; https://doi.org/10.3390/en11061386 - 29 May 2018

Cited by 9 | Viewed by 2507

Abstract

Before the use of regulated street luminaires with variable power and luminous flux, computations were performed using constant values for their electrical and photometric parameters. At present, where such lighting is in use, it is no longer possible to base calculations on such [...] Read more.

Before the use of regulated street luminaires with variable power and luminous flux, computations were performed using constant values for their electrical and photometric parameters. At present, where such lighting is in use, it is no longer possible to base calculations on such assumptions. Computations of energy and power losses, for example, need to be performed for all dimming levels and based on the applied regulation algorithm. Based on measurements carried out on regulated luminaires, it was found that certain electrical parameters have a nonlinear dependence on the dimming level. Electrical parameters were also observed to depend on the value of the supply voltage. The results of the measurements are presented in this article. Failure to take account of power losses in computations of the energy efficiency of street lighting in accordance with the applicable EN 13201 standard causes values of energy efficiency indicators to be overstated. Power loss computations are presented in this article for a sample street lighting system with regulated luminaires, for the whole range of dimming levels and additionally for fluctuations of ±10% in the supply voltage. In addition, a mathematical model of a regulated luminaire is constructed with the use of regression methods, and a practical application of that model is described. Full article

(This article belongs to the Section F: Electrical Engineering)

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18 pages, 2122 KiB

Open AccessArticle

Improved Genetic Algorithm-Based Unit Commitment Considering Uncertainty Integration Method

by Kyu-Hyung Jo and Mun-Kyeom Kim^*

Department of Energy System Engineering, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Korea

Energies 2018, 11(6), 1387; https://doi.org/10.3390/en11061387 - 29 May 2018

Cited by 17 | Viewed by 3510

Abstract

In light of the dissemination of renewable energy connected to the power grid, it has become necessary to consider the uncertainty in the generation of renewable energy as a unit commitment (UC) problem. A methodology for solving the UC problem is presented by [...] Read more.

In light of the dissemination of renewable energy connected to the power grid, it has become necessary to consider the uncertainty in the generation of renewable energy as a unit commitment (UC) problem. A methodology for solving the UC problem is presented by considering various uncertainties, which are assumed to have a normal distribution, by using a Monte Carlo simulation. Based on the constructed scenarios for load, wind, solar, and generator outages, a combination of scenarios is found that meets the reserve requirement to secure the power balance of the power grid. In those scenarios, the uncertainty integration method (UIM) identifies the best combination by minimizing the additional reserve requirements caused by the uncertainty of power sources. An integration process for uncertainties is formulated for stochastic unit commitment (SUC) problems and optimized by the improved genetic algorithm (IGA). The IGA is composed of five procedures and finds the optimal combination of unit status at the scheduled time, based on the determined source data. According to the number of unit systems, the IGA demonstrates better performance than the other optimization methods by applying reserve repairing and an approximation process. To account for the result of the proposed method, various UC strategies are tested with a modified 24-h UC test system and compared. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2018)

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12 pages, 3077 KiB

Open AccessArticle

Microgrids Real-Time Pricing Based on Clustering Techniques

by Hao Liu¹

, Nadali Mahmoudi² and Kui Chen^2,*

¹ Jiangsu Province Laboratory of Mining Electric and Automation, China University of Mining and Technology, Xuzhou 221000, China

² Ernst & Young, Brisbane QLD 4000, Australia

Energies 2018, 11(6), 1388; https://doi.org/10.3390/en11061388 - 30 May 2018

Cited by 13 | Viewed by 3230

Abstract

Microgrids are widely spreading in electricity markets worldwide. Besides the security and reliability concerns for these microgrids, their operators need to address consumers’ pricing. Considering the growth of smart grids and smart meter facilities, it is expected that microgrids will have some level [...] Read more.

Microgrids are widely spreading in electricity markets worldwide. Besides the security and reliability concerns for these microgrids, their operators need to address consumers’ pricing. Considering the growth of smart grids and smart meter facilities, it is expected that microgrids will have some level of flexibility to determine real-time pricing for at least some consumers. As such, the key challenge is finding an optimal pricing model for consumers. This paper, accordingly, proposes a new pricing scheme in which microgrids are able to deploy clustering techniques in order to understand their consumers’ load profiles and then assign real-time prices based on their load profile patterns. An improved weighted fuzzy average k-means is proposed to cluster load curve of consumers in an optimal number of clusters, through which the load profile of each cluster is determined. Having obtained the load profile of each cluster, real-time prices are given to each cluster, which is the best price given to all consumers in that cluster. Full article

(This article belongs to the Special Issue Distribution System Operation and Control)

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20 pages, 2063 KiB

Open AccessArticle

Impact of Risk Aversion on the Operation of Hydroelectric Reservoirs in the Presence of Renewable Energy Sources

by Nenad Jovanović¹, Javier García-González^1,*, Santiago Cerisola¹ and Julián Barquín²

¹ Instituto de Investigación Tecnológica (IIT), Escuela Técnica Superior de Ingeniería (ICAI), Universidad Pontificia Comillas, c/Alberto Aguilera 23, 28015 Madrid, Spain

² Endesa (ENEL Group), 60 Rivera del Loira, 28042 Madrid, Spain

Energies 2018, 11(6), 1389; https://doi.org/10.3390/en11061389 - 30 May 2018

Cited by 3 | Viewed by 3390

Abstract

The increasing share of renewable energy sources, such as wind and solar generation, has a direct impact on the planning and operation of power systems. In addition, the consideration of risk criteria within the decision support tools used by market participants (generation companies, [...] Read more.

The increasing share of renewable energy sources, such as wind and solar generation, has a direct impact on the planning and operation of power systems. In addition, the consideration of risk criteria within the decision support tools used by market participants (generation companies, energy services companies, and arbitrageurs) is becoming a common activity given the increasing level of uncertainties faced by them. As a consequence, the behavior of market participants is affected by their level of risk aversion, and the application of equilibrium-based models is a common technique used in order to simulate their behavior. This paper presents a multi-stage market equilibrium model of risk-averse agents in order to analyze up to what extent the operation of hydro reservoirs can be affected by the risk-averse profile of market participants in a context of renewable energy source penetration and fuel price volatility. Full article

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17 pages, 4773 KiB

Open AccessArticle

A Comprehensive Study of Dynamic and Heat Transfer Characteristics of Droplet Impact on Micro-Scale Rectangular Grooved Surface

by Zhe Yan and Yan Li^*

College of Engineering, Ocean University of China, Qingdao 266100, China

Energies 2018, 11(6), 1390; https://doi.org/10.3390/en11061390 - 30 May 2018

Cited by 10 | Viewed by 2808

Abstract

Micro-scale structure of impact surface has a significant effect on the droplet impact. In this study, a three-dimensional numerical model of the droplet impact on micro-scale rectangular grooved surface was established based on coupled level set and volume of fluid (CLSVOF) method. Furthermore, [...] Read more.

Micro-scale structure of impact surface has a significant effect on the droplet impact. In this study, a three-dimensional numerical model of the droplet impact on micro-scale rectangular grooved surface was established based on coupled level set and volume of fluid (CLSVOF) method. Furthermore, the evolution of droplet morphology was experimentally studied and the validation of numerical model was carried out. The effects of groove width, contact angle, impact velocity and surface temperature on dynamic and heat transfer characteristics of droplet impact at low Weber numbers were numerically investigated. The anisotropy coefficient is defined to investigate the anisotropy of droplet morphology caused by the micro-scale grooved structure. The numerical results show that vertical spreading diameter is less than parallel spreading diameter, and the anisotropy of droplet morphology tends to reduce gradually with increasing contact angle. Both dynamic and heat transfer characteristics of droplet impact are the coupling effect of contact angle and groove width. The analysis of wettability state is utilized to illuminate the heat transfer characteristics of grooved surface. The maximum heat transfer rate of grooved surface increases with increasing impact velocity and surface temperature, and it decreases with increasing contact angle. Full article

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20 pages, 7814 KiB

Open AccessArticle

NPC Based Design Optimization for a Net Zero Office Building in Hot Climates with PV Panels as Shading Device

by Muhammad Zubair^1,*

, Ahmed Bilal Awan¹

, Abdullah Al-Ahmadi¹ and Ahmed G. Abo-Khalil^1,2

¹ Department of Electrical Engineering, College of Engineering, Majmaah University, Majmaah 11952, Saudi Arabia

² Electrical Engineering Department, Faculty of Engineering, Assiut University, University Street, Assiut 71515, Egypt

Energies 2018, 11(6), 1391; https://doi.org/10.3390/en11061391 - 30 May 2018

Cited by 28 | Viewed by 3466

Abstract

Hot areas of the world receive a high amount of solar radiation. As a result, buildings in those areas consume more energy to maintain a comfortable climate for their inhabitants. In an effort to design net-zero energy building in hot climates, PV possesses [...] Read more.

Hot areas of the world receive a high amount of solar radiation. As a result, buildings in those areas consume more energy to maintain a comfortable climate for their inhabitants. In an effort to design net-zero energy building in hot climates, PV possesses the unique advantage of generating electrical energy while protecting the building from solar irradiance. In this work, to form a net-zero energy building (NZEB), renewable resources such as solar and wind available onsite for an existing building have been analyzed in a hot climate location. PV and wind turbines in various configurations are studied to form a NZEB, where PV-only systems offer better performance than Hybrid PV Wind systems, based on net present cost (NPC). The self-shading losses in PV placed on rooftop areas are analyzed by placing parallel arrays of PV modules at various distances in between them. The effect on building cooling load by rooftop PV panels as shading devices is investigated. Furthermore, self-shading losses of PV are compared by the savings in cooling loads using PV as shading. In the case study, 12.3% saving in the cooling load of the building is observed when the building rooftop is completed shaded by PV panels; annual cooling load decreased from 3.417 GWh to 2.996 GWh, while only 1.04% shaded losses are observed for fully shaded (FS) buildings compared to those with no shading (NS), as PV generation decreases from 594.39 kWh/m² to 588.21 kWh/m². The net present cost of the project has been decreased from US$4.77 million to US$4.41 million by simply covering the rooftop completely with PV panels, for a net-zero energy building. Full article

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19 pages, 6758 KiB

Open AccessArticle

Reactive Power and Current Harmonic Control Using a Dual Hybrid Power Filter for Unbalanced Non-Linear Loads

by Leonardo Rodrigues Limongi

, Fabricio Bradaschia

, Calebe Hermann de Oliveira Lima

and Marcelo Cabral Cavalcanti^*

Department of Electrical Engineering, Federal University of Pernambuco, Recife 50740-550, Brazil

Energies 2018, 11(6), 1392; https://doi.org/10.3390/en11061392 - 30 May 2018

Cited by 8 | Viewed by 2980

Abstract

An important power quality issue is related to current harmonic components demanded by non-linear loads. A solution to mitigate this issue is to use hybrid power filters (HPFs), that apply low power active filters with passive filters. Some dual-converter topologies have been shown [...] Read more.

An important power quality issue is related to current harmonic components demanded by non-linear loads. A solution to mitigate this issue is to use hybrid power filters (HPFs), that apply low power active filters with passive filters. Some dual-converter topologies have been shown to be attractive due to a better compensation performance compared with single filters, where the HPFs give a reactive power support (an extra feature) together with harmonic compensation. On the other hand, the drawback of dual converters is the high number of active switches. Besides that, due to the high number of unbalanced non-linear loads connected to the electrical grid, triplen harmonics can appear. However, traditional HPFs do not compensate triplen harmonics, which usually have considerable values. Therefore, in this paper, a dual HPF based on the nine-switch inverter (DHPF-NSI) is proposed to compensate current harmonics and to provide reactive power support. The NSI presents a reduced number of switches when compared with classical dual topologies. The compensation of the third harmonic caused by unbalanced nonlinear loads was also inserted in the control system. Experimental results are presented for the DHPF-NSI in order to demonstrate the reactive power and harmonic compensation performances. Full article

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20 pages, 4330 KiB

Open AccessArticle

Multiple Fuel Machines Power Economic Dispatch Using Stud Differential Evolution

by Naila¹, Shaikh Saaqib Haroon²

, Shahzad Hassan^1,*

, Salman Amin², Intisar Ali Sajjad²

, Asad Waqar¹

, Muhammad Aamir¹, Muneeb Yaqoob¹ and Imtiaz Alam¹

¹ Department of Electrical Engineering, Bahria University, Islamabad 44000, Pakistan

² Department of Electrical Engineering, University of Engineering & Technology, Taxila 47050, Pakistan

Energies 2018, 11(6), 1393; https://doi.org/10.3390/en11061393 - 30 May 2018

Cited by 10 | Viewed by 2981

Abstract

This paper presents an optimization method for solving the Power Economic Dispatch (PED) problem of thermal generation units with multiple fuels and valve point loadings. The proposed optimizer is a variant of Differential Evolution (DE) characterized as a Stud Differential Evolution (SDE), which [...] Read more.

This paper presents an optimization method for solving the Power Economic Dispatch (PED) problem of thermal generation units with multiple fuels and valve point loadings. The proposed optimizer is a variant of Differential Evolution (DE) characterized as a Stud Differential Evolution (SDE), which has been proposed earlier and implemented on a hydrothermal energy system. In SDE, an operator named Stud Crossover (SC) is introduced in the conventional DE during the trial vector updating process. In SC operator, a best vector gives its optimal information to all other population members through mating. The proposed algorithm’s effectiveness to solve Multiple Fuel PED problem, with and without Valve Point Loading Effects (VPLEs), has been validated by testing it on 10 machine multiple fuel standard test systems having 2400 MW, 2500 MW, 2600 MW, and 2700 MW load demands. The results depict the strength of SDE over various other methods in the literature. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 6802 KiB

Open AccessArticle

Effect of Initial Wettability on Performance of Smart Water Flooding in Carbonate Reservoirs—An Experimental Investigation with IOR Implications

by Kholood Al-Nofli¹, Peyman Pourafshary^2,*

, Nader Mosavat³

and Ali Shafiei^2,*

¹ Petroleum Development Oman, Muscat 100, Oman

² Department of Petroleum Engineering, School of Mining and Geosciences, Nazarbayev University, 53 Kabanbay Batyr Avenue, Astana 010000, Kazakhstan

³ Department of Engineering and Technology, Muscat University, Muscat 130, Oman

Energies 2018, 11(6), 1394; https://doi.org/10.3390/en11061394 - 30 May 2018

Cited by 26 | Viewed by 4067

Abstract

In this paper, the effects of salinity and active ions on wettability alteration in carbonate reservoirs with different initial wettability conditions with implications in smart water flood design, optimization, and performance analysis are experimentally investigated. Contact angle measurement was used as the main [...] Read more.

In this paper, the effects of salinity and active ions on wettability alteration in carbonate reservoirs with different initial wettability conditions with implications in smart water flood design, optimization, and performance analysis are experimentally investigated. Contact angle measurement was used as the main tool to study the alteration in wettability. Other analytical techniques such as pH measurements along with energy-dispersive X-ray spectroscopy (EDS) were used to support the analysis. Initial wettability of the tested carbonate samples ranges from strongly water wet to preferentially water wet, neutral wet, oil wet, and strongly oil wet (5 cases or groups) condition. Four different synthetic brines, namely high salinity (Hsal), low salinity (Lsal), and smart waters 1 and 2 (SW1 = a Mg brine, and SW2 = a Mg and sulfate brine) were prepared and used by adjusting the salinity and ion concentration to study their effects on wettability alteration. Low-salinity brine (Lsal) proved to be more effective than high-salinity brine (Hsal) for the wettability alteration of calcite surfaces at intermediate (neutral) or oil-wet conditions. The smart brine containing only the Mg²⁺ ion (SW1) was able to alter the wettability of calcite surfaces in intermediate or oil-wet states. The sulfate ion played a catalytic role in wettability alteration by the magnesium ion, and the process was faster, as indicated by higher wettability alteration index values. High-salinity brine (Hsal) is a good choice for design of water floods in reservoir rocks with initial wettability in the range of strongly water wet to neutral wet conditions. In the wettability alteration process of oil-wet samples, brine with a high magnesium ion concentration was slower than brine containing high concentrations of both magnesium and sulfate ions. This can be attributed to the catalytic role of the sulfate ion compared to that of the magnesium ion. Finally, the results showed that the initial wettability of the reservoir rock plays a major role in design of a proper water flood to maximize oil recovery from carbonate reservoirs. The results obtained from this research work suggests that some effective smart water flooding scenarios can be developed and executed incorporating different smart brines to manage the reservoir rock wettability and maximize the oil recovery from carbonate oil reservoirs. Full article

(This article belongs to the Section L: Energy Sources)

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20 pages, 3321 KiB

Open AccessArticle

Modeling and Control of a Combined Heat and Power Unit with Two-Stage Bypass

by Yaokui Gao¹, Yong Hu^1,*, Deliang Zeng¹, Jizhen Liu¹ and Feng Chen²

¹ School of Control and Computer Engineering, North China Electric Power University, Beijing 102206, China

² Beijing Guodian Zhishen Control Technology CO., Ltd., Beijing 102200, China

Energies 2018, 11(6), 1395; https://doi.org/10.3390/en11061395 - 30 May 2018

Cited by 14 | Viewed by 3375

Abstract

This paper presents a non-linear dynamic model of a combined heat and power (CHP) unit with two-stage bypass for the first time. This model is derived through an analysis of the material and energy balance of the CHP unit. The static parameters are [...] Read more.

This paper presents a non-linear dynamic model of a combined heat and power (CHP) unit with two-stage bypass for the first time. This model is derived through an analysis of the material and energy balance of the CHP unit. The static parameters are determined via the design data of the CHP unit, and the dynamic parameters refer to model parameters of same type of units in other references. Based on the model, an optimized control scheme for the coordination system of the unit is proposed. This scheme introduces a stair-like feedforward-feedback predictive control algorithm to solve the control problem of large delays in boiler combustion, and integrates decoupling control to reduce the effect of external disturbance on the main steam pressure. Simulation results indicate that the model effectively reflects the dynamics of the CHP unit and can be used for designing and verifying its coordinated control system; the control scheme can achieve decoupling control of the CHP unit; the fluctuation of main steam pressure is considerably reduced; and the adjustment of coal feed flow is stable. In this case, the proposed scheme can guarantee the safe, stable and flexible operation of the unit and lay the foundation for decoupling the heat load-based constraint of CHP units, thereby expanding the access space of wind power in northern China. Full article

(This article belongs to the Special Issue Control and Nonlinear Dynamics on Energy Conversion Systems)

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16 pages, 1941 KiB

Open AccessArticle

Optimal Configuration of Energy Storage System Coordinating Wind Turbine to Participate Power System Primary Frequency Regulation

by Junhui Li^1,*, Yunbao Ma¹, Gang Mu¹, Xichao Feng², Gangui Yan¹, Gan Guo¹ and Tianyang Zhang¹

¹ Department of Electrical Engineering, Northeast Electric Power University, Jilin 132012, China

² Shenyang Power Supply Bureau, State Grid Liaoning Electric Power Company Limited, Shenyang 110811, China

Energies 2018, 11(6), 1396; https://doi.org/10.3390/en11061396 - 30 May 2018

Cited by 33 | Viewed by 3143

Abstract

Large scale wind power integration has a negative influence on the frequency response. Assistant measurement improves the frequency stability of power systems under high wind penetration. The Proportional Curtailment Strategy (PCS) for wind turbines provides a primary frequency reserve for power systems. To [...] Read more.

Large scale wind power integration has a negative influence on the frequency response. Assistant measurement improves the frequency stability of power systems under high wind penetration. The Proportional Curtailment Strategy (PCS) for wind turbines provides a primary frequency reserve for power systems. To solve the worthless curtailed wind power, the PCS is used to improve the utilization of wind power curtailment. Then the wind turbine and the lithium battery Energy Storage System (ESS) provide primary frequency reserves together. Different control strategies of ESS have been proposed based on the different methods for selecting valid reserves. The economic benefits of different control strategies have been compared based on the same frequency regulation reserve. The optimal control strategy is the maximum method. The economic benefit of the maximum value method is ¥4,445,300. Full article

(This article belongs to the Section D: Energy Storage and Application)

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10 pages, 4353 KiB

Open AccessArticle

Efficient Planar Hybrid n-Si/PEDOT:PSS Solar Cells with Power Conversion Efficiency up to 13.31% Achieved by Controlling the SiO_x Interlayer

by Chenxu Zhang¹, Yuming Zhang^1,*, Hui Guo¹, Qubo Jiang², Peng Dong¹ and Chunfu Zhang^1,*

¹ Wide Bandgap Semiconductor Technology Disciplines State Key Laboratory, School of Microelectronics, Xidian University, Xi’an 710071, China

² School of Electronic Engineering and Automation, Guilin University of Electronic Technology, No. 1 Jinji Road, Guilin 541004, China

Energies 2018, 11(6), 1397; https://doi.org/10.3390/en11061397 - 30 May 2018

Cited by 19 | Viewed by 3705

Abstract

In this work, the effects of the SiO_x interface layer grown by exposure in air on the performance of planar hybrid n-Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells are investigated. Compared to the cell with a hydrogen-terminated Si surface, the cell with an oxygen-terminated Si [...] Read more.

In this work, the effects of the SiO_x interface layer grown by exposure in air on the performance of planar hybrid n-Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells are investigated. Compared to the cell with a hydrogen-terminated Si surface, the cell with an oxygen-terminated Si surface reveals improved characteristics in power conversion efficiency, increased from 10.44% to 13.31%. By introducing the SiO_x, the wettability of the Si surface can be improved, allowing an effective spread of the PEDOT:PSS solution and thus a good contact between the PEDOT:PSS film and Si. More importantly, it can change the polarity of the Si surface from a negative dipole to a positive dipole, owing to the introduction of the SiO_x interface. The Si energy band will bend up and give rise to a favorable band alignment between Si and PEDOT:PSS to promote carrier separation. These results could be potentially employed to further development of this simple, low-cost heterojunction solar cell. Full article

(This article belongs to the Special Issue Solar Photovoltaics Trilemma: Efficiency, Stability and Cost Reduction 2018)

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18 pages, 10045 KiB

Open AccessArticle

On the Heat Transfer Enhancement of Plate Fin Heat Exchanger

by Yuan Xue¹, Zhihua Ge^1,*, Xiaoze Du^2,*

and Lijun Yang¹

¹ Key Laboratory of Condition Monitoring and Control for Power Plant Equipment, Ministry of Education, North China Electric Power University, Beijing 102206, China

² School of Energy and Power Engineering, Lanzhou University of Technology, Lanzhou 730050, China

Energies 2018, 11(6), 1398; https://doi.org/10.3390/en11061398 - 30 May 2018

Cited by 46 | Viewed by 6460

Abstract

The plate fin heat exchanger is a compact heat exchanger applied in many industries because of its high thermal performance. To enhance the heat transfer of plate fin heat exchanger further, three new kinds of wavy plate fins, namely perforated wavy fin, staggered [...] Read more.

The plate fin heat exchanger is a compact heat exchanger applied in many industries because of its high thermal performance. To enhance the heat transfer of plate fin heat exchanger further, three new kinds of wavy plate fins, namely perforated wavy fin, staggered wavy fin and discontinuous wavy fin, are proposed and investigated by computational fluid dynamics (CFD) simulations. The effects of key design parameters, including that of waviness aspect ratios, perforation diameters, staggered ratios and breaking distance are investigated, respectively, with Reynolds number changes from 500 to 4500. It is found that due to the swirl flow and efficient mixing of the fluid, the proposed heat transfer enhancement techniques all have advantages over the traditional wavy fin. At the same time, serration is beneficial to reduce the friction factor, and the breaking technique can reduce heat transfer area. Through the performance evaluation criteria, the staggered wavy fin has an advantage over the small waviness aspect ratio; with increasing waviness aspect ratio, this predominance is gradually surpassed by the perforated wavy fin, and the advantage of the discontinuous fin is the smallest and almost invariable. A maximum performance evaluation criteria (PEC) as high as 1.24 can be obtained for the perforated wavy fin at the waviness aspect ratio γ = 0.45. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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17 pages, 4471 KiB

Open AccessArticle

Voltage Regulation and Power Loss Minimization in Radial Distribution Systems via Reactive Power Injection and Distributed Generation Unit Placement

by Ghaeth Fandi^1,2,*

, Ibrahim Ahmad¹, Famous O. Igbinovia¹, Zdenek Muller¹, Josef Tlusty^1,3 and Vladimir Krepl²

¹ Department of Electrical Power Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, Technická 2, 166 27 Prague 6, Czech Republic

² Department of Sustainable Technologies, Faculty of Tropical AgriSciences, Czech University of Life Sciences Prague, Kamýcká 961/129, 165 00 Prague 6, Czech Republic

³ Department of Health Care Disciplines and Population Protection, Faculty of Biomedical Engineering, Czech Technical University in Prague, Sportovců 2311, 272 01 Kladno, Czech Republic

Energies 2018, 11(6), 1399; https://doi.org/10.3390/en11061399 - 30 May 2018

Cited by 16 | Viewed by 3288

Abstract

Distributed Generation (DG) has become an essential part of the smart grids due to the widespread integration of renewable energy sources. Reactive power compensation is still one of most important research topics in smart grids. DG units can be used for reactive power [...] Read more.

Distributed Generation (DG) has become an essential part of the smart grids due to the widespread integration of renewable energy sources. Reactive power compensation is still one of most important research topics in smart grids. DG units can be used for reactive power compensation purposes, therefore we can improve the voltage profile and minimize power losses in order to improve the power quality. In this paper two methods will be used to accomplish the mentioned tasks; the first technique depends on the reactive power demand change of the proposed network loads, whereas the second technique uses an algorithm to control DG units according to the measured voltage values in the feeders to generate the needed reactive power. Both methods were applied to different scenarios of DG unit positions and different reactive power values of loads. The chosen DG unit is made up of a Type-4 wind farm which could be used as a general unit where it is able to control reactive power generation in a wider range separately from active power. The simulation results show that using these two methods, the voltage profile could be improved, power losses reduced and the power factor increased according to the placement of DG units. Full article

(This article belongs to the Section F: Electrical Engineering)

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20 pages, 1743 KiB

Open AccessArticle

Piling up or Packaging Policies? An Ex-Post Analysis of Modal Shift in Four Cities

by Marc Dijk^1,*, Moshe Givoni^2,*

and Karen Diederiks¹

¹ International Center for Integrated Assessment and Sustainable Development (ICIS), Maastricht University, 6200 MD Maastricht, The Netherlands

² Transport Research Unit, Department of Geography and the Human Environment, Tel Aviv University, Tel Aviv 6997801, Israel

Energies 2018, 11(6), 1400; https://doi.org/10.3390/en11061400 - 30 May 2018

Cited by 7 | Viewed by 3249

Abstract

Recently, there has been wider acknowledgement that sustainable urban mobility will not be triggered by one ‘silver bullet’ policy, or by piling up various policies, but requires a deliberate package of policies. Until recently, studies on policy instrument (or measure) interaction have been [...] Read more.

Recently, there has been wider acknowledgement that sustainable urban mobility will not be triggered by one ‘silver bullet’ policy, or by piling up various policies, but requires a deliberate package of policies. Until recently, studies on policy instrument (or measure) interaction have been primarily ex-ante studies, estimating interactions in the future. However, from an evidence-based policy-making perspective, ex-ante evaluations need to use knowledge gained through ex-post evaluations, a crucial link in the policy cycle. To contribute to the strengthening of this poor link, this paper provides an ex-post analysis of instrument interaction in four northwest European, medium-sized cities: Bruges, Ghent, Jena & Erfurt. By exposing the relationships between the range of mobility policies implemented in relation to modal shift achieved, we offer insight into the crucial difference between ‘piling up policies’ and deliberate policy packages. As such, the paper offers evidence to inform ex-ante analysis for urban mobility policy-making and contributes to policy learning as part of effective governance. Full article

(This article belongs to the Special Issue The Governance of Sustainable Cities and Innovative Transport)

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13 pages, 1450 KiB

Open AccessArticle

Robust Smart Meter Data Analytics Using Smoothed ALS and Dynamic Time Warping

by Zhen Jiang¹, Di Shi^2,*

, Xiaobin Guo¹, Guangyue Xu², Li Yu¹ and Chaoyang Jing²

¹ Southern China Power Grid EPRI, 11 Kexiang Rd., Guangzhou 510663, China

² eMIT, LLC., 125 N Lake Ave., Pasadena, CA 91101, USA

Energies 2018, 11(6), 1401; https://doi.org/10.3390/en11061401 - 30 May 2018

Cited by 8 | Viewed by 2261

Abstract

This paper presents a robust data-driven framework for clustering large-scale daily chronological load curves from smart meters, with a focus on the challenges encountered in practice. The first challenge is the low data quality issue due to bad and missing data, which has [...] Read more.

This paper presents a robust data-driven framework for clustering large-scale daily chronological load curves from smart meters, with a focus on the challenges encountered in practice. The first challenge is the low data quality issue due to bad and missing data, which has been a major obstacle for various in-depth analyses of smart meter data. A novel Smoothed Alternating Least Squares (SALS) approach is proposed to recover missing/bad smart meter data by taking advantage of their low-rank property. The second challenge is brought by different data reporting rates of smart meters. A Dynamic Time Warping (DTW)-based approach is proposed that is more efficient and eliminates the need for data interpolation or measurement downsampling. The proposed approach enables flexible data collection strategies and gateway locations to meet various smart grid performance requirements. The proposed framework is tested through experiments using real-world smart meter data. Full article

(This article belongs to the Section F: Electrical Engineering)

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13 pages, 2658 KiB

Open AccessArticle

A Pressurized Vitiated Co-Flow Burner and Its Preliminary Application for a Methane Lifted Flame

by Qiushi Qin, Zhijun Wu, Qing Zhang, Wei Xie, Liguang Li and Jun Deng^*

School of Automotive Studies, Tongji University, Shanghai 201804, China

Energies 2018, 11(6), 1402; https://doi.org/10.3390/en11061402 - 30 May 2018

Cited by 2 | Viewed by 3092

Abstract

A new pressurized vitiated co-flow burner (PVCB) was designed and built for the investigation of lifted flame properties and was supported by a vitiated co-flow of hot combustion products from a lean H₂/air flame at a controllable pressure; its preliminary application [...] Read more.

A new pressurized vitiated co-flow burner (PVCB) was designed and built for the investigation of lifted flame properties and was supported by a vitiated co-flow of hot combustion products from a lean H₂/air flame at a controllable pressure; its preliminary application for a methane lifted flame was tested. The distribution of the co-flow temperature, oxygen mole fraction, flow rate, and pressure of the PVCB was measured and calculated. The research results show that the co-flow temperature range is from 300 to 1300 K, the background pressure range is from 1 to 1.5 bar, the stable temperature field of the PVCB is wider, and the background pressure of the PVCB can be controlled. The simulation results show that the PVCB provides a controllable, pressurized co-flow of hot and vitiated gases, which makes it possible to investigate flame stabilization mechanisms. The PVCB has the advantages of controllable background pressure and a stable temperature field. The well-defined uniform boundary conditions and simplified flow of the PVCB simplify the establishment of a numerical model and decouple the turbulent chemical kinetics from the complex recirculating flow. It can be widely used in the research on lifted flames. A lifted flame of methane was recorded under conditions of a co-flow temperature of 1133 K and pressure from 1 to 1.043 bar. The lift-off height decreased and stabilized with the increase in the background pressure. The laminar flame speed and the autoignition delay time were tested and simulated at the same time by Chemkin; the influence of background pressure on the lift-off height, laminar flame speed, and autoignition delay were analyzed. The results show that the autoignition, as well as the flame propagation, dominated the stabilization mechanism of the lifted flame in the PVCB. Full article

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18 pages, 9308 KiB

Open AccessFeature PaperArticle

Numerical Investigation of Gas-Liquid Two-Phase Flow inside PEMFC Gas Channels with Rectangular and Trapezoidal Cross Sections

by Jin Hyun Kim

and Woo Tae Kim^*

Department of Mechanical and Automotive Engineering, Kongju National University, 1223-24 Cheonan Daero, Seobuk-gu, Cheonan 31080, Chungnam, Korea

Energies 2018, 11(6), 1403; https://doi.org/10.3390/en11061403 - 30 May 2018

Cited by 24 | Viewed by 3628

Abstract

The dynamics of liquid water in the gas channels with rectangular sections (REC), trapezoidal sections with open angles of 60 degrees (T60), and trapezoidal sections with open angles of 72 degrees (T72) are numerically investigated via the volume of fluid method. The effects [...] Read more.

The dynamics of liquid water in the gas channels with rectangular sections (REC), trapezoidal sections with open angles of 60 degrees (T60), and trapezoidal sections with open angles of 72 degrees (T72) are numerically investigated via the volume of fluid method. The effects of the contact angle of the top and side walls (CATS), the water inlet configuration, and the air inlet velocity are studied based on the temporal evolution of gas-liquid interface, the water volume fraction (WVF), the water coverage ratio of the gas diffusion layer (GDL) surface (GWCR), and the pressure drop between the air inlet and the outlet. For the hydrophobic GDL surface and the hydrophilic top and side walls, the T72 provides the lowest WVF and GWCR of around 7 percent due to periodic pressure spikes. The REC and T60 show a higher WVF and a lower GWCR as most of liquid water moves along the channel while attached to the top wall. As the CATS increases from 60 to 120 degrees, the behaviors of liquid water become similar for the three cross-sectional shapes. The T72 shows especially similar results irrespective of the CATS. When the liquid water emergence is concentrated along the side wall, the T72 shows the best water removal characteristics. For all the three channel cross-sectional shapes, water slugs move faster and have smaller sizes as the air inlet velocity increases. Full article

(This article belongs to the Section L: Energy Sources)

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16 pages, 2606 KiB

Open AccessArticle

Biomass Feedstock and Climate Change in Agroforestry Systems: Participatory Location and Integration Scenario Analysis of Biomass Power Facilities

by Jin Su Jeong

Departamento de Ingeniería Mecánica, Química y Diseño Industrial, Escuela Técnica Superior de Ingeniería y Diseño Industrial, Universidad Politécnica de Madrid, Ronda de Valencia 3, 28012 Madrid, Spain

Energies 2018, 11(6), 1404; https://doi.org/10.3390/en11061404 - 31 May 2018

Cited by 6 | Viewed by 2418

Abstract

Producing energy with biomass feedstocks as a renewable energy source can contribute to the mitigation of climate change through direct CO₂ sequestration and higher CO₂-emitting fuel replacement. Here, the correct location of a biomass power facility can be considered as [...] Read more.

Producing energy with biomass feedstocks as a renewable energy source can contribute to the mitigation of climate change through direct CO₂ sequestration and higher CO₂-emitting fuel replacement. Here, the correct location of a biomass power facility can be considered as a critical position due to their geographical and spatial characteristic. This research presents a novel approach involving a geographic information system (GIS) location and its integration scenario analysis with the consideration of biomass feedstocks and climate change in agroforestry systems, the agro-silvo-pastoral system (ASPS), of a Spanish case study. A combined participatory operative approach, that is, fuzzy-decision-making trial and evaluation laboratory (F-DEMATEL) with simple additive weighting (SAW) and sensitivity analysis in various disciplines and criteria, is applied by professionals. In particular, an analysis of five biomass power facilities in the area assessed by the methodology found that only one facility (BPF4) is located in the suitable area. Among five integration scenarios (A to E) as the likelihood test by the stakeholders, scenario E (suitability layer) was most supported—that is, it was selected as the most suitability map—while scenario D (general geophysical layer) was least supported, in that the results encapsulated foreseeable problems derived from the effects. Hence, the validation of the methodology proposed can be employed as a decision-making tool to support proper sustainable planning and development of a biomass power facility under the impact of climate change. Full article

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18 pages, 12130 KiB

Open AccessArticle

Real-Time Temperature Estimation of Three-Core Medium-Voltage Cable Joint Based on Support Vector Regression

by Jiangjun Ruan, Qinghua Zhan, Liezheng Tang^* and Ke Tang

School of Electrical Engineering, Wuhan University, Wuhan 430072, China

Energies 2018, 11(6), 1405; https://doi.org/10.3390/en11061405 - 31 May 2018

Cited by 19 | Viewed by 3115

Abstract

The joint is the weakest link in three-core medium-voltage power cable systems and the temperature is an essential indicator to its insulation condition. Therefore, a model to estimate the temperature inside the three-core cable joint was built based on support vector regression (SVR) [...] Read more.

The joint is the weakest link in three-core medium-voltage power cable systems and the temperature is an essential indicator to its insulation condition. Therefore, a model to estimate the temperature inside the three-core cable joint was built based on support vector regression (SVR) with two fixed cable surface temperatures as inputs. The samples for model training were obtained from 3-D transient thermal analyses through finite element method (FEM) under different single-step currents. A temperature-rise test of 15 kV three-core cable joint was carried out and the estimated temperature based on SVR agrees well with the measured result with a maximum error of about 4 °C. Besides, the proposed model could accurately estimate the joint temperature even though the thermal conductivity of armor wrap used in thermal analysis for model training differs from its real value. The accuracies and calculation speed of the proposed model were compared with those of FEM, showing a better generality of our model. A temperature-rise test under unbalanced three-phase currents was performed and the temperature estimation errors are within 6 °C, indicating the applicability of the method. The effect of contact resistance was briefly discussed in the end. This approach helps improve cable operation and maintenance. Full article

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19 pages, 7829 KiB

Open AccessFeature PaperArticle

Evaluating Molecular Evolution of Kerogen by Raman Spectroscopy: Correlation with Optical Microscopy and Rock-Eval Pyrolysis

by Seyedalireza Khatibi^1,*

, Mehdi Ostadhassan¹

, David Tuschel², Thomas Gentzis³

and Humberto Carvajal-Ortiz³

¹ Department of Petroleum Engineering, University of North Dakota, Grand Forks, ND 58203, USA

² Raman Application Department, HORIBA Scientific, Edison, NJ 08820, USA

³ Geology and Petrology department, Core Laboratories, Houston, TX 77040, USA

Energies 2018, 11(6), 1406; https://doi.org/10.3390/en11061406 - 31 May 2018

Cited by 36 | Viewed by 6433

Abstract

Vitrinite maturity and programmed pyrolysis are conventional methods to evaluate organic matter (OM) regarding its thermal maturity. Moreover, vitrinite reflectance analysis can be difficult if prepared samples have no primary vitrinite or dispersed widely. Raman spectroscopy is a nondestructive method that has been [...] Read more.

Vitrinite maturity and programmed pyrolysis are conventional methods to evaluate organic matter (OM) regarding its thermal maturity. Moreover, vitrinite reflectance analysis can be difficult if prepared samples have no primary vitrinite or dispersed widely. Raman spectroscopy is a nondestructive method that has been used in the last decade for maturity evaluation of organic matter by detecting structural transformations, however, it might suffer from fluorescence background in low mature samples. In this study, four samples of different maturities from both shale formations of Bakken (the upper and lower members) Formation were collected and analyzed with Rock-Eval (RE) and Raman spectroscopy. In the next step, portions of the same samples were then used for the isolation of kerogen and analyzed by Raman spectroscopy. Results showed that Raman spectroscopy, by detecting structural information of OM, could reflect thermal maturity parameters that were derived from programmed pyrolysis. Moreover, isolating kerogen will reduce the background noise (fluorescence) in the samples dramatically and yield a better spectrum. The study showed that thermal properties of OM could be precisely reflected in Raman signals. Full article

(This article belongs to the Section L: Energy Sources)

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18 pages, 3633 KiB

Open AccessArticle

Development of Reclosing Method in a Distribution System with Distributed Generation and Battery Energy Storage System

by Hun-Chul Seo

School of IT Engineering, Yonam Institute of Technology, Jinju, Korea

Energies 2018, 11(6), 1407; https://doi.org/10.3390/en11061407 - 31 May 2018

Cited by 4 | Viewed by 3783

Abstract

The connection of distributed generation (DG) and a battery energy storage system (BESS) in distribution systems has recently been increasing. However, little research has been conducted on the reclosing of the distribution system when both the DG and BESS are connected. Therefore, this [...] Read more.

The connection of distributed generation (DG) and a battery energy storage system (BESS) in distribution systems has recently been increasing. However, little research has been conducted on the reclosing of the distribution system when both the DG and BESS are connected. Therefore, this paper proposes a new reclosing method for a distribution system with a DG and BESS. The proposed method also has a circuit breaker (CB) installed in the distribution line. A CB close to the DG and BESS is first reclosed after a fixed dead time and, then, the fault clearance is detected using the current flowing to the fault point. Once the fault is cleared, the reclosing of the CB at the source side is attempted after completing a synchronism check. The proposed method is modeled using an electromagnetic transient program. We perform various simulations according to the capacities of the DG and the fault clearance time, and analyze the simulation results. The simulation results show that steady-state power is supplied to the load from the DG and BESS before reclosing to prevent outage, and that the reclosing is successfully performed. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2018)

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10 pages, 1951 KiB

Open AccessArticle

Electric Field Distribution and Switching Impulse Discharge under Shield Ball Surface Scratch Defect in an UHVDC Hall

by Jianghai Geng^1,*, Yuchen Qin¹, Fangcheng Lv¹, Xiuyuan Yao² and Yujian Ding²

¹ Hebei Provincial Key Laboratory of Power Transmission Equipment Security Defense, North China Electric Power University, Baoding 071003, China

² China Electric Power Research Institute, Beijing 100192, China

Energies 2018, 11(6), 1408; https://doi.org/10.3390/en11061408 - 31 May 2018

Cited by 9 | Viewed by 2660

Abstract

The dimension and surface state of shielding fittings in ultra high voltage direct current (UHVDC) converter station valve halls have a great influence on their surface electric field and switching impulse characteristics, which are important parameters confirming the air gap distance in the [...] Read more.

The dimension and surface state of shielding fittings in ultra high voltage direct current (UHVDC) converter station valve halls have a great influence on their surface electric field and switching impulse characteristics, which are important parameters confirming the air gap distance in the valve hall. The characteristics of impulse discharge under different lengths, dent degrees and burrs around the scratches of Φ1.3 m shield balls with a 2 m sphere-plane gap length were tested, in the UHVDC testing base of the Hebei Electric Power Research Institute. The discharge characteristics under the influence of the surface scratches of the shield ball were obtained. The results demonstrate that the discharge voltage of sphere-plane gap decreases obviously when there are unpolished scratches on the surface of the shield ball. However, when the scratches are polished, the discharge voltage has no significant impact. At the same time, a 1:1 full-scale impulse test model was established based on the finite element method. The electric field intensity and the space electric field distribution of the shield ball were obtained under the influence of scratches with or without burrs. The results of the simulation show that when the surface of the shield ball is smooth, the electric field distribution around it is even. The electric field intensity on the surface of the shield ball increases obviously when there are burrs around the scratches. When there is no burr around the scratches, the length and depth of the scratches have no obvious effect on its electric field distribution. Meanwhile, calculation results are consistent with test results. The results can provide an important basis for the design and optimization of shielding fittings, and technical support for its localization. Full article

(This article belongs to the Section L: Energy Sources)

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18 pages, 9153 KiB

Open AccessArticle

Mechanical Property Measurements and Fracture Propagation Analysis of Longmaxi Shale by Micro-CT Uniaxial Compression

by Minyue Zhou^1,2,3, Yifei Zhang^1,2,3, Runqing Zhou^1,2, Jin Hao^1,2 and Jijin Yang^1,2,3,*

¹ Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

² Institution of Earth Science, Chinese Academy of Science, Beijing 100029, China

³ College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China

Energies 2018, 11(6), 1409; https://doi.org/10.3390/en11061409 - 31 May 2018

Cited by 37 | Viewed by 4503

Abstract

The mechanical properties and fracture propagation of Longmaxi shale loading under uniaxial compression were measured using eight cylindrical shale specimens (4 mm in diameter and 8 mm in height), with the bedding plane oriented at 0° and 90° to the axial loading direction, [...] Read more.

The mechanical properties and fracture propagation of Longmaxi shale loading under uniaxial compression were measured using eight cylindrical shale specimens (4 mm in diameter and 8 mm in height), with the bedding plane oriented at 0° and 90° to the axial loading direction, respectively, by micro computed tomography (micro-CT). Based on the reconstructed three-dimensional (3-D) CT images of cracks, different stages of the crack growth process in the 0° and 90° orientation specimen were revealed. The initial crack generally occurred at relatively smaller loading force in the 0° bedding direction specimen, mainly in the form of tensile splitting along weak bedding planes. Shear sliding fractures were dominant in the specimens oriented at 90°, with a small number of parallel cracks occurring on the bedding plane. The average thickness and volume of cracks in the 90° specimen is higher than those for the specimen oriented at 0°. The geometrical characterization of fractures segmented from CT scan binary images shows that a specific surface area correlates with tortuosity at the different load stages of each specimen. The 3-D box-counting dimension (BCD) calculations can accurately reflect crack evolution law in the shale. The results indicate that the cracks have a more complex pattern and rough surface at an orientation of 90°, due to crossed secondary cracks and shear failure. Full article

(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries 2018)

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18 pages, 7149 KiB

Open AccessArticle

An Experimental Investigation on the NO and CO Emission Characteristics of a Swirl Convergent-Divergent Nozzle at Elevated Pressure

by Zhongya Xi^*, Zhongguang Fu, Xiaotian Hu, Syed Waqas Sabir

and Yibo Jiang

National Thermal Power Engineering & Technology Research Center, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(6), 1410; https://doi.org/10.3390/en11061410 - 31 May 2018

Cited by 5 | Viewed by 3362

Abstract

The behavior of the pollutants NO and CO at elevated combustor pressure are of special importance due to the continuing trend toward developing engines operating at higher pressure ratios to yield higher thermal efficiency. An experiment was performed to examine the NO and [...] Read more.

The behavior of the pollutants NO and CO at elevated combustor pressure are of special importance due to the continuing trend toward developing engines operating at higher pressure ratios to yield higher thermal efficiency. An experiment was performed to examine the NO and CO emissions for a swirl convergent-divergent nozzle at elevated pressure. The NO and CO correlations were obtained. Meanwhile, the flame length, exhaust gas oxygen concentration, exit temperature and global flame residence time were also determined to analyze the NO and CO emission characteristics. The results showed that, with the increase in combustor pressure P, flame length decreased proportionally to P^−0.49; exit O₂ volume fraction increased and exit temperature was reduced. The global flame residence time decreased proportionally to P^−0.43. As pressure increased, The NO and Emission Index of NO (EINO) levels decreased proportionally to P^−0.53 and P^−0.6 respectively, which is mainly attributed to the influence of global flame residence time; the NO and EINO increased almost proportionally with the increase in global flame residence time. The EINO scaling EINO (ρu_e/d) was proportional to Fr^0.42, which indicated that compared with pure fuel, the fuel diluted with primary air can cause a decrease in the exponent of the Fr power function. At higher pressure, the CO and Emission Index of CO (EICO) decreased proportionally to P^−0.35 and P^−0.4, respectively, due to the increased unburned methane and high pressure which accelerated chemical reaction kinetics to promote the conversion of CO to CO₂. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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20 pages, 2610 KiB

Open AccessArticle

Time-Domain Voltage Sag State Estimation Based on the Unscented Kalman Filter for Power Systems with Nonlinear Components

by Rafael Cisneros-Magaña¹, Aurelio Medina^1,* and Olimpo Anaya-Lara²

¹ División de Estudios de Posgrado, Facultad de Ingeniería Eléctrica, Universidad Michoacana de San Nicolás de Hidalgo, Av. Francisco J. Múgica S/N, Morelia, Michoacán 58030, Mexico

² Institute for Energy and Environment, Department of Electronic and Electrical Engineering, University of Strathclyde, 204 George Street, Glasgow G1 1RX, UK

Energies 2018, 11(6), 1411; https://doi.org/10.3390/en11061411 - 1 Jun 2018

Cited by 10 | Viewed by 3225

Abstract

This paper proposes a time-domain methodology based on the unscented Kalman filter to estimate voltage sags and their characteristics, such as magnitude and duration in power systems represented by nonlinear models. Partial and noisy measurements from the electrical network with nonlinear loads, used [...] Read more.

This paper proposes a time-domain methodology based on the unscented Kalman filter to estimate voltage sags and their characteristics, such as magnitude and duration in power systems represented by nonlinear models. Partial and noisy measurements from the electrical network with nonlinear loads, used as data, are assumed. The characteristics of voltage sags can be calculated in a discrete form with the unscented Kalman filter to estimate all the busbar voltages; being possible to determine the rms voltage magnitude and the voltage sag starting and ending time, respectively. Voltage sag state estimation results can be used to obtain the power quality indices for monitored and unmonitored busbars in the power grid and to design adequate mitigating techniques. The proposed methodology is successfully validated against the results obtained with the time-domain system simulation for the power system with nonlinear components, being the normalized root mean square error less than 3%. Full article

(This article belongs to the Special Issue Power Quality in Microgrids Based on Distributed Generators)

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14 pages, 1212 KiB

Open AccessArticle

Carbon Footprint of Electricity Generation in Brazil: An Analysis of the 2016–2026 Period

by Murillo Vetroni Barros^*, Cassiano Moro Piekarski

and Antonio Carlos De Francisco

Sustainable Production Systems Laboratory (LESP), Postgraduate Program in Production Engineering (PPGEP), Federal University of Technology—Paraná (UTFPR), 84016-210 Ponta Grossa, Parana, Brazil

Energies 2018, 11(6), 1412; https://doi.org/10.3390/en11061412 - 1 Jun 2018

Cited by 41 | Viewed by 7261

Abstract

The present paper aims to evaluate the past and future environmental performance of the electricity generation in Brazil in terms of Global Warming Potential (GWP) and Global Temperature Potential (GTP). To that end, the Life Cycle Assessment (LCA) tool was used to evaluate [...] Read more.

The present paper aims to evaluate the past and future environmental performance of the electricity generation in Brazil in terms of Global Warming Potential (GWP) and Global Temperature Potential (GTP). To that end, the Life Cycle Assessment (LCA) tool was used to evaluate the system’s environmental performance, based on ISO 14040 and ISO 14044, using the Ecoinvent v 3.3 database. This study provides data on global warming by the GWP and GTP 100 years impact category. The functional unit and reference flow is kWh. The model was applied to the electricity generation in Brazil for the years 2016–2026 using Umberto NXT Universal software. The results indicate that the greatest environmental impacts lie on generation sources such as oil, natural gas, hydropower and hard coal. Carbon dioxide was the main contributor to atmospheric emissions in the life cycle of the Brazilian electricity matrix in 2016 and 2026. The total potential impact (and per kWh) is expected to decrease until 2021. The Brazilian electricity matrix is expected to be less pollutant in terms of carbon footprint until 2021. The study can contribute to directing public policies, promoting development actions and encouraging different electricity matrices. Full article

(This article belongs to the Section L: Energy Sources)

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14 pages, 13578 KiB

Open AccessArticle

Influence of Grain Size Heterogeneity and In-Situ Stress on the Hydraulic Fracturing Process by PFC^2D Modeling

by Zhenhua Han^1,2,3, Jian Zhou^1,2,*

and Luqing Zhang^1,2

¹ Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Science, Beijing 100029, China

² Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China

³ College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China

Energies 2018, 11(6), 1413; https://doi.org/10.3390/en11061413 - 1 Jun 2018

Cited by 26 | Viewed by 3645

Abstract

A modified fluid-mechanically coupled algorithm in PFC^2D was adopted in this article to study the influence of grain size heterogeneity and in-situ stress on hydraulic fracturing behavior. Simulated results showed that the in-situ stress and grain size heterogeneity significantly affect the initiation, [...] Read more.

A modified fluid-mechanically coupled algorithm in PFC^2D was adopted in this article to study the influence of grain size heterogeneity and in-situ stress on hydraulic fracturing behavior. Simulated results showed that the in-situ stress and grain size heterogeneity significantly affect the initiation, growth, and spatial distribution of the hydraulic fractures: (1) the initiation and breakdown pressure are gradually reduced with the increase of the grain size heterogeneity; (2) with increased in-situ stress, the initiation and breakdown pressure increase, and the reduction effect of grain size heterogeneity on the breakdown pressure becomes more obvious; (3) in grain size homogeneous rock, the initiation pressure decreases with increasing in-situ stress ratio, however, the initiation pressure of grain size heterogeneous rock is almost unaffected by the in-situ stress ratio; (4) The in-situ stress ratio and grain size heterogeneity affect the spatial distribution of hydraulic fractures simultaneously. When the in-situ stress ratio is larger than 1, the hydraulic fractures propagate substantially along the direction of the maximum principal stress. When the in-situ stress ratio is 1, the initiation position and extension direction of hydraulic fractures are random and complex fracture networks can easily develop in a grain size homogeneous model. Full article

(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries 2018)

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16 pages, 2687 KiB

Open AccessArticle

Experimental Investigation on Influence Factors of Acoustic Emission Activity in Coal Failure Process

by Huiming Yang^1,2,*, Guangcai Wen^1,2, Qianting Hu³, Yuanyuan Li^4,* and Linchao Dai^1,2

¹ State Key Laboratory of Gas Disaster Detecting, Preventing and Emergency Controlling, China Coal Technology Engineering Group Chongqing Research Institute, Chongqing 400037, China

² Gas Research Branch, China Coal Technology Engineering Group Chongqing Research Institute, Chongqing 400037, China

³ State Key Laboratory of Coal Mine Disaster Dynamics and CONTROL, Chongqing University, Chongqing 400044, China

⁴ Department of Basic Courses, Chongqing Jianzhu College, Chongqing 400072, China

Energies 2018, 11(6), 1414; https://doi.org/10.3390/en11061414 - 1 Jun 2018

Cited by 26 | Viewed by 2912

Abstract

Stress-dominated coal and gas outburst disaster has become one of the main safety problems in deep coal mines. Acoustic emission (AE) or microseismic technology has been viewed as a promising method that can effectively reflect the stress and stability status of rock mass. [...] Read more.

Stress-dominated coal and gas outburst disaster has become one of the main safety problems in deep coal mines. Acoustic emission (AE) or microseismic technology has been viewed as a promising method that can effectively reflect the stress and stability status of rock mass. The AE activity precursor of coal failure is the theoretical basis of this technology. In this study, AE experiments in failure process of coal specimens with different properties and under different stress conditions were performed in laboratory to explore influence factors and their effect of AE activity, and AE activity pattern classification was proposed based on the failure type of coal. The results indicate that the AE activity of different coals under loading are associated with the failure phase, and the evolution pattern of AE activity depends on the failure type of stressed coal. Both the mechanical property and the external stress condition have an important influential effect on the failure type and AE activity pattern in coal failure process. The internal mechanical property decides the inherent tendency of stressed coals to perform brittle or ductile behavior, and the responded AE activity pattern. The contrast of fissure distribution of specimens suggested that fissure structure in coal significantly affects the fracturing mode of coal in uniaxial compression and the AE activity pattern. The external stress condition has a transition effect on AE event energy distribution and AE activity pattern. Under the effect of external stress condition, the energy distribution of AE events was transforming between relative disperse and relative concentration, the failure type and AE activity evolution pattern of coal could appear the brittle-ductile transition. Based on the view of failure type, the pattern of AE activity of coal failure can be classified into three types, i.e., ductile, brittle, and semi-brittle pattern. It is suggested that the high-level AE activity can be viewed as the precursor of brittle instability of coal, and relative quiet phenomenon of AE activity as the precursor of ductile or semi-brittle instability. The research achievement can provide a theoretical base for the prewarning criteria establishment of coal and rock dynamic disasters at depth and improve the insight of AE activity in the coal failure process. Full article

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14 pages, 2280 KiB

Open AccessArticle

New Energy Corridors in the Euro-Mediterranean Area: The Pivotal Role of Sicily

by Salvatore Favuzza¹

, Mariano Giuseppe Ippolito¹, Fabio Massaro^1,*

, Liliana Mineo¹, Rossano Musca² and Gaetano Zizzo¹

¹ Department of Energy, Information Engineering and Mathematical Models, DEIM, University of Palermo, 90128 Palermo (Pa), Italy

² Neplan AG, Oberwachtstrasse 2, CH-8700 Küsnacht (ZH), Switzerland

Energies 2018, 11(6), 1415; https://doi.org/10.3390/en11061415 - 1 Jun 2018

Cited by 14 | Viewed by 3886

Abstract

The present paper deals with the new opportunities deriving from the interconnections of the European and North African transmission systems. In order to achieve a single international market for electricity exchanges, interconnections between networks in different countries are becoming increasingly important and Sicily, [...] Read more.

The present paper deals with the new opportunities deriving from the interconnections of the European and North African transmission systems. In order to achieve a single international market for electricity exchanges, interconnections between networks in different countries are becoming increasingly important and Sicily, for its geographical position in the middle of the Mediterranean Sea, will undoubtedly play an important role as an electrical bridge between Europe and the North Africa in the near future. The paper, presenting the actual electro-energetic context of Tunisia, reports the new important interconnection already realized in South Italy (in particular in Sicily) and describe the planned interventions of the near future. In the second part of the paper, using the Neplan software package (10.7.4, NEPLAN AG, CH-8700 Küsnacht (ZH), Switzerland) for simulating the grid, some load flows are carried out to check some operating scenarios (2020 and 2025) considering energy flows from north to south, avoiding system violations. Full article

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12 pages, 363 KiB

Open AccessArticle

Optimal Charging of Electric Vehicles with Trading on the Intraday Electricity Market

by Ilham Naharudinsyah¹

and Steffen Limmer^2,*

¹ Department of Systems and Control, Graduate School of Engineering, Tokyo Institute of Technology, Tokyo 152-8552, Japan

² Honda Research Institute Europe GmbH, Offenbach/Main 63073, Germany

Energies 2018, 11(6), 1416; https://doi.org/10.3390/en11061416 - 1 Jun 2018

Cited by 22 | Viewed by 3335

Abstract

Trading on the energy market is a possible way to reduce the electricity costs of charging electric vehicles at public charging stations. In many European countries, it is possible to trade electricity until shortly before the period of delivery on so called intraday [...] Read more.

Trading on the energy market is a possible way to reduce the electricity costs of charging electric vehicles at public charging stations. In many European countries, it is possible to trade electricity until shortly before the period of delivery on so called intraday electricity markets. In the present work, the potential for reducing the electricity costs by trading on the intraday market is investigated using the example of the German market. Based on simulations, the authors reveal that by optimizing the charging schedule together with the trading on the intraday electricity market, the costs can be reduced by around 8% compared to purchasing all the required energy from the energy supplier. By allowing the charging station operator to resell the energy to the intraday electricity market, an additional cost reduction of around 1% can be achieved. Besides the potential cost savings, the impacts of the trading unit and of the lead time of the intraday electricity market on the costs are investigated. The authors reveal that the achievable electricity costs can be strongly affected by the lead time, while the trading unit has only a minor effect on the costs. Full article

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21 pages, 24785 KiB

Open AccessArticle

Experimental Investigation of Static Stall Hysteresis and 3-Dimensional Flow Structures for an NREL S826 Wing Section of Finite Span

by Hamid Sarlak^1,*

, Ariane Frère^2,3, Robert Mikkelsen¹ and Jens N. Sørensen¹

¹ Section of Fluid Mechanics, Department of Wind Energy, Technical University of Denmark, 2800 Lyngby, Denmark

² Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, 1348 Louvain-la-Neuve, Belgium

³ Research Center En Aeronautique (Cenaero), 6041 Gosselies, Belgium

Energies 2018, 11(6), 1418; https://doi.org/10.3390/en11061418 - 1 Jun 2018

Cited by 9 | Viewed by 4709

Abstract

Flow characteristics of an S826 airfoil at different Reynolds numbers, ranging from 40,000–400,000 (based on airfoil chord length) and angles of attack from −10–25 degrees are thoroughly investigated in a low-speed wind tunnel. The airfoil’s lift and drag polars are first measured, and [...] Read more.

Flow characteristics of an S826 airfoil at different Reynolds numbers, ranging from 40,000–400,000 (based on airfoil chord length) and angles of attack from −10–25 degrees are thoroughly investigated in a low-speed wind tunnel. The airfoil’s lift and drag polars are first measured, and with a focus on pitching the airfoil in upstroke and downstroke orders, static stall hysteresis is identified in selected experiments at Reynolds numbers below 100,000 near the stall angle and subsequently investigated. Experiments using wire-generated free stream turbulence are conducted, and the hysteresis effects are shown to disappear when introducing a free stream turbulence of less than 2.5%. Further, spanwise flow is detected by comparing lift and drag values measured using both surface pressure integration at one cross section as well as integral force gauge measurement, and the surface oil flow visualization technique is subsequently used to study the 3D flow topologies formed on the airfoil. The formation of distinct stall cells on the suction side of the airfoil is observed at Reynolds numbers above 100,000 near the stall angle. By repeating the experiments, stall cells are proven to be reproduceable, although the identical geometries are necessarily not retained in abscence of surface impurities such as tapes. The effect of disturbances on the stall cells is investigated by utilizing roughness elements on the airfoil surface, and it is found that while such disturbances tend to change the shape of the stall cells, they do not contribute to the creation, nor destruction of the cells. Polar and visualisation measurements are also used to study flow separation, and it is observed that the separation location, as well as the laminar separation bubble, moves towards the leading edge when increasing the angle of attack. Full article

(This article belongs to the Collection Wind Turbines)

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20 pages, 5483 KiB

Open AccessArticle

A Simple Fractal-Based Model for Soil-Water Characteristic Curves Incorporating Effects of Initial Void Ratios

by Gaoliang Tao¹

, Yin Chen¹

, Lingwei Kong²

, Henglin Xiao¹, Qingsheng Chen^1,* and Yuxuan Xia³

¹ Hubei Provincial Ecological Road Engineering Technology Research Center, Hubei University of Technology, Wuhan 430068, China

² State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China

³ Hubei Subsurface Multi-Scale Imaging Key Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China

Energies 2018, 11(6), 1419; https://doi.org/10.3390/en11061419 - 1 Jun 2018

Cited by 29 | Viewed by 4119

Abstract

In this paper, a simple and efficient fractal-based approach is presented for capturing the effects of initial void ratio on the soil-water characteristic curve (SWCC) in a deformable unsaturated soil. In terms of testing results, the SWCCs (expressed by gravimetric water content) of [...] Read more.

In this paper, a simple and efficient fractal-based approach is presented for capturing the effects of initial void ratio on the soil-water characteristic curve (SWCC) in a deformable unsaturated soil. In terms of testing results, the SWCCs (expressed by gravimetric water content) of the unsaturated soils at different initial void ratios were found to be mainly controlled by the air-entry value (Ψ_a), while the fractal dimension (D) could be assumed to be constant. As a result, in contrast to the complexity of existing models, a simple and efficient model with only two parameters (i.e., D and Ψ_a) was established for predicting the SWCC considering the effects of initial void ratio. The procedure for determining the model parameters with clear physical meaning were then elaborated. The applicability and accuracy of the proposed model were well demonstrated by comparing its predictions with four sets of independent experimental data from the tests conducted in current work, as well as the literature on a wide range of soils, including Wuhan Clay, Hefei and Guangxi expansive soil, Saskatchewan silt, and loess. Good agreements were obtained between the experimental data and the model predictions in all of the cases considered. Full article

(This article belongs to the Special Issue Emerging Advances in Petrophysics: Porous Media Characterization and Modeling of Multiphase Flow)

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20 pages, 2872 KiB

Open AccessArticle

Lithium-Ion Battery Prognostics with Hybrid Gaussian Process Function Regression

by Yu Peng, Yandong Hou, Yuchen Song, Jingyue Pang and Datong Liu^*

Department of Automatic Test and Control, Harbin Institute of Technology, Harbin 150080, China

Energies 2018, 11(6), 1420; https://doi.org/10.3390/en11061420 - 1 Jun 2018

Cited by 59 | Viewed by 4368

Abstract

The accurate prognostics of lithium-ion battery state of health (SOH) and remaining useful life (RUL) have great significance for reducing the costs of maintenance. The methods based on the physical models cannot perform satisfactorily as the systems become more and more complex. With [...] Read more.

The accurate prognostics of lithium-ion battery state of health (SOH) and remaining useful life (RUL) have great significance for reducing the costs of maintenance. The methods based on the physical models cannot perform satisfactorily as the systems become more and more complex. With the development of digital acquisition and storage technology, the data of battery cells can be obtained. This makes the data-driven methods get more and more attention. In this paper, to overcome the problem that the trend fitting deteriorates rapidly when test data are far from the training data for multiple-step-ahead estimation, a prognostic method fusing the wavelet de-noising (WD) method and the hybrid Gaussian process function regression (HGPFR) model for predicting the RUL of the lithium-ion battery is proposed. Gaussian process regression (GPR) is a typical representative for the Bayesian structure with non-parameter expression and uncertainty presentation. In this case, the effects on predictive results are compared and analyzed using the proposed method and the HGPFR model with different lengths of training data. Besides, in consideration of the degradation characteristics for the lithium-ion battery data set, the selections of the wavelet de-noising method are performed with corresponding experimental analyses. Furthermore, we set the hype-parameter for the mean function and co-variance function, and then develop a method for parameter optimization to make the proposed model suitable for the data. Moreover, a numerical simulation based on the data repository of Department of Engineering Science (DES) university of Oxford and Center for Advanced Life Cycle Engineering (CALCE) of University of Maryland is carried out, and the results are analyzed. For the data repository, an accuracy of 2.2% is obtained compared with the same value of 6.7% for the HGPFR model. What is more, the applicability and stability are verified with the prognostic results by the proposed method. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 1296 KiB

Open AccessArticle

Capacitive Emulation Using Predictive Current Control in LCL-Filtered Grid-Connected Converters to Mitigate Grid Current Distortion

by Jose Miguel Espi

and Jaime Castello^*

Department of Electrical Engineering, University of Valencia, Avd. Universitat S/N, 46100 Burjassot-Valencia, Spain

Energies 2018, 11(6), 1421; https://doi.org/10.3390/en11061421 - 1 Jun 2018

Cited by 2 | Viewed by 2668

Abstract

This paper presents an improvement of the capacitive emulation (CE) method to reduce the line current distortion caused by grid-tied LCL-filtered converters. In these cases, the grid voltage is applied to the LCL’s capacitor, which generates a distorted capacitor current that pollutes the [...] Read more.

This paper presents an improvement of the capacitive emulation (CE) method to reduce the line current distortion caused by grid-tied LCL-filtered converters. In these cases, the grid voltage is applied to the LCL’s capacitor, which generates a distorted capacitor current that pollutes the line. The CE method consists in controlling the converter currents instead of the grid currents, while the converter generates a copy of the distorted capacitor current, so that both the copy and the distorted currents cancel each other in the grid. Therefore, we can say that the converter emulates a negative capacitance connected to the grid, while at the same time delivers its active and reactive powers at the fundamental frequency. The CE method is achieved by adding an estimation of the distorted capacitor current to the converter current reference. However, an effective capacitive emulation requires a current control capable of accurately tracking all harmonics added to the current reference. In this sense, this paper proposes the use of a new integral predictive current control (IPCC), a dead-beat type of control that ensures a constant closed-loop group delay in a wide bandwidth. Unlike a PI control where the closed-loop delay varies with the frequency of the tracked harmonic, the constant control delay of the IPCC can be effectively compensated with a buffer-based advanced current reference. The effectiveness of the proposed CE method with IPCC control to reduce the total harmonic distortion (THD) of the line currents has been proved experimentally on a 10 kVA transformerless grid-connected three-phase inverter. Full article

(This article belongs to the Section F: Electrical Engineering)

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12 pages, 5001 KiB

Open AccessArticle

Area-Saving and High-Efficiency RGB LED Driver with Adaptive Driving Voltage and Energy-Saving Technique

by Yi-Chieh Hsu¹, Jing-Yuan Lin^2,* and Charlie Chung-Ping Chen¹

¹ Graduate Institute of Electronics Engineering, and Department of Electrical Engineering, National Taiwan University, Taipei 10607, Taiwan

² Department of Electronic and Computer Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan

Energies 2018, 11(6), 1422; https://doi.org/10.3390/en11061422 - 1 Jun 2018

Cited by 3 | Viewed by 3421

Abstract

The red-green-blue light-emitting diode (RGBLED) driver with adaptive driving voltage and energy-saving (ADVE) technique is presented in this paper. To obtain the proper driving voltage, a dynamic output voltage selector is proposed. This approach tracks the reference voltage of a boost converter to [...] Read more.

The red-green-blue light-emitting diode (RGBLED) driver with adaptive driving voltage and energy-saving (ADVE) technique is presented in this paper. To obtain the proper driving voltage, a dynamic output voltage selector is proposed. This approach tracks the reference voltage of a boost converter to achieve the appropriate output voltage of the boost converter. Hence, the power loss of the linear current regulator is reduced to improve the efficiency of whole system. Moreover, the chip area is saved by the proposed switching linear current regulator. This chip was fabricated using TSMC 0.35 μm 2P4M complementary metal-oxide-semiconductor (CMOS) technology. The active chip area is 0.3 mm². The maximum driving current and operating frequency are 100 mA and 100 kHz, respectively. Compared with a conventional LED driver with fixed output voltage, the experimental results demonstrate that the power loss of the proposed LED driver with ADVE technique is reduced by over 58%. Full article

(This article belongs to the Section F: Electrical Engineering)

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17 pages, 4092 KiB

Open AccessArticle

An Optimal Scheduling Dispatch of a Microgrid under Risk Assessment

by Whei-Min Lin¹, Chung-Yuen Yang¹, Chia-Sheng Tu² and Ming-Tang Tsai^3,*

¹ Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung 807, Taiwan

² College of Intelligence Robot, Fuzhou Polytechnic, Fuzhou 350108, China

³ Department of Electrical Engineering, Cheng-Shiu University, Kaohsiung 833, Taiwan

Energies 2018, 11(6), 1423; https://doi.org/10.3390/en11061423 - 2 Jun 2018

Cited by 7 | Viewed by 2644

Abstract

This paper presents the scheduling dispatch of a microgrid (MG), while considering renewable energy, battery storage systems, and time-of-use price. For the risk evaluation of an MG, the Value-at-Risk (VAR) is calculated by using the Historical Simulation Method (HSM). By considering the various [...] Read more.

This paper presents the scheduling dispatch of a microgrid (MG), while considering renewable energy, battery storage systems, and time-of-use price. For the risk evaluation of an MG, the Value-at-Risk (VAR) is calculated by using the Historical Simulation Method (HSM). By considering the various confidence levels of the VAR, a scheduling dispatch model of the MG is formulated to achieve a reasonable trade-off between the risk and cost. An Improved Bee Swarm Optimization (IBSO) is proposed to solve the scheduling dispatch model of the MG. In the IBSO procedure, the Sin-wave Weight Factor (SWF) and Forward-Backward Control Factor (FBCF) are embedded in the bee swarm of the BSO to improve the movement behaviors of each bee, specifically, its search efficiency and accuracy. The effectiveness of the IBSO is demonstrated via a real MG case and the results are compared with other methods. In either a grid-connected scenario or a stand-alone scenario, an optimal scheduling dispatch of MGs is carried out, herein, at various confidence levels of risk. The simulation results provide more information for handling uncertain environments when analyzing the VAR of MGs. Full article

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14 pages, 3994 KiB

Open AccessArticle

Design, Analysis, and Evaluation of a Compact Electromagnetic Energy Harvester from Water Flow for Remote Sensors

by Tao Wang^*

and Yunce Zhang

Ocean College, Zhejiang University, Zhoushan 316000, China

Energies 2018, 11(6), 1424; https://doi.org/10.3390/en11061424 - 2 Jun 2018

Cited by 9 | Viewed by 2993

Abstract

This paper develops an electromagnetic energy harvester, which can generate small-scale electricity from non-directional water flow in oceans or rivers for remote sensors. The energy harvester integrates a Tesla disk turbine, a miniature axial-flux permanent magnet generator, and a ring cover with symmetrical [...] Read more.

This paper develops an electromagnetic energy harvester, which can generate small-scale electricity from non-directional water flow in oceans or rivers for remote sensors. The energy harvester integrates a Tesla disk turbine, a miniature axial-flux permanent magnet generator, and a ring cover with symmetrical grooves which are utilized to rectify flow direction. A compact structure is achieved by mounting the permanent magnets of the generator directly on the end surfaces of the turbine rotor. Theoretical analysis is implemented to illustrate the energy conversion process between flow kinetic form and electrical form. Additionally, a mathematical model is developed to investigate the magnetic field distribution produced by the cubical permanent magnets as well as parametric effect. Plastic prototypes with a diameter of 65 mm and a height of 46 mm are fabricated by using a 3D printing technique. The effect of the groove angle is experimentally investigated and compared under a no-load condition. The prototype with the optimal groove angle can operate at flow velocity down to 0.61 m/s and can induce peak-to-peak electromotive force of 2.64–11.92 V at flow velocity of 0.61–1.87 m/s. It can be observed from the results that the analytical and the measured curves are in good accordance. Loaded experiments show that the output electrical power is 23.1 mW at flow velocity of 1.87 m/s when the load resistance is approximately equal to the coil resistance. The advantages and disadvantages of the proposed energy harvester are presented through comparison with existing similar devices. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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14 pages, 5702 KiB

Open AccessArticle

Study on Reduced Cost of Non-Salient Machine System Using MTPA Angle Pre-Compensation Method Based on EEMF Sensorless Control

by Kyoung Jin Joo¹

, Joon Sung Park²

and Ju Lee^1,*

¹ Department of Electrical Engineering, Hanyang University, Seoul 04763, Korea

² Intelligent Mechatronics Research Center, Korea Electronics Technology Institute, Gyeonggi-do 13509, Korea

Energies 2018, 11(6), 1425; https://doi.org/10.3390/en11061425 - 2 Jun 2018

Cited by 5 | Viewed by 4230

Abstract

When a consumer chooses a product, one of the most important considerations is price. Therefore, cost reduction is the most important factor when manufacturing a product. This paper has applied the sensorless method to remove the position sensor in an interior permanent magnet [...] Read more.

When a consumer chooses a product, one of the most important considerations is price. Therefore, cost reduction is the most important factor when manufacturing a product. This paper has applied the sensorless method to remove the position sensor in an interior permanent magnet synchronous motor (IPMSM) system and examined the way to reduce the use of the trigonometric function in order to lower the dependency on a high-end CPU. A sensorless method has been studied to use an extended electromotive force (EEMF) that can increase the degree of freedom of the motor in the IPMSM system. In addition, an observer is applied to the estimated position to stabilize the system. Furthermore, many trigonometric functions are used for driving the IPMSM. Since this trigonometric function requires decimal point operations, that requires a lot of computation time and a high-performance CPU. Therefore, this paper proposes a new method to pre-compensate the maximum torque per ampere (MTPA) angle as a way to reduce the use of the trigonometric functions which makes a high-spec CPU unnecessary. Simulations and experiments are conducted to verify the proposed control algorithm. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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25 pages, 2340 KiB

Open AccessArticle

Exploiting Game Theoretic Based Coordination Among Appliances in Smart Homes for Efficient Energy Utilization

by Muhammad Hassan Rahim¹, Adia Khalid¹

, Nadeem Javaid^1,*

, Mahmood Ashraf²

, Khursheed Aurangzeb³

and Abdulaziz Saud Altamrah³

¹ COMSATS Institute of Information Technology, Islamabad 44000, Pakistan

² Department of Computer Science, Federal Urdu University of Arts, Science and Technology, Islamabad 44000, Pakistan

³ College of Computer and Information Sciences, King Saud University, Riyadh 11543, Saudi Arabia

Energies 2018, 11(6), 1426; https://doi.org/10.3390/en11061426 - 2 Jun 2018

Cited by 8 | Viewed by 3745

Abstract

In this paper, a demand side management (DSM) scheme is used to make energy utilization more efficient. The DSM scheme encourages the consumer to change energy utilization patterns which benefit the utility. In return, the consumer gets some incentives from the utility. The [...] Read more.

In this paper, a demand side management (DSM) scheme is used to make energy utilization more efficient. The DSM scheme encourages the consumer to change energy utilization patterns which benefit the utility. In return, the consumer gets some incentives from the utility. The objectives of the proposed DSM system include: electricity bill reduction, reduced peak to average ratio (PAR), and maximization of consumer comfort. In the proposed system, the electrical devices are scheduled by using elephant herding optimization (EHO) and adaptive cuckoo search (ACS) algorithms. Moreover, a new algorithm called hybrid elephant adaptive cuckoo (HEAC) is proposed which uses the features of both former algorithms. A comparison of these algorithms is also presented in terms of three performance parameters. The HEAC shows better performance as compared to EHO and ACS which is evident from the simulation results. Different electricity tariffs are introduced by the utility to provide incentives to the consumers. A regional based time of use (ToU) tariff is used to make the system effective for different types of regions. Moreover, this enables the consumers to act according to the regional environment. The coordination can play a very important role in cost reduction as well as in consumer comfort maximization. The coordination is incorporated among the electrical devices by using cooperative game theory (GT) and dynamic programming (DP). Extensive simulations are performed to show the effectiveness of the proposed scheme in terms of electricity utilization cost, PAR reduction, and consumer comfort maximization. Full article

(This article belongs to the Special Issue Energy Economy, Sustainable Energy and Energy Saving)

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23 pages, 4897 KiB

Open AccessArticle

Quantitative Resilience Assessment under a Tri-Stage Framework for Power Systems

by Han Zhang, Hanjie Yuan, Gengfeng Li^* and Yanling Lin

The State Key Laboratory of Electrical Insulation and Power Equipment, the Shaanxi Key Laboratory of Smart Grid, Xi’an Jiaotong University, Xi’an 710049, China

Energies 2018, 11(6), 1427; https://doi.org/10.3390/en11061427 - 3 Jun 2018

Cited by 35 | Viewed by 3276

Abstract

The frequent occurrence of natural disasters and malicious attacks has exerted unprecedented disturbances on power systems, accounting for the extensive attention paid to power system resilience. Combined with the evolving nature of general disasters, this paper proposes resilience assessment approaches for power systems [...] Read more.

The frequent occurrence of natural disasters and malicious attacks has exerted unprecedented disturbances on power systems, accounting for the extensive attention paid to power system resilience. Combined with the evolving nature of general disasters, this paper proposes resilience assessment approaches for power systems under a tri-stage framework. The pre-disaster toughness is proposed to quantify the robustness of power systems against potential disasters, where the thinking of area division and partitioned multi-objective risk method (PMRM) is introduced. In the case of information deficiency caused by disasters, the during-disaster resistance to disturbance is calculated to reflect the real-time system running state by state estimation (SE). The post-disaster restoration ability consists of response ability, restoration efficiency and restoration economy, which is evaluated by Sequential Monte-Carlo Simulation to simulate the system restoration process. Further, a synthetic metric system is presented to quantify the resilience performance of power systems from the above three aspects. The proposed approaches and framework are validated on the IEEE RTS 79 system, and helpful conclusions are drawn from extensive case studies. Full article

(This article belongs to the Section F: Electrical Engineering)

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16 pages, 6761 KiB

Open AccessArticle

Comparative Investigation of Hybrid Excitation Flux Switching Machines

by Yi Du^*

, Wei Lu, Qi Wang, Xiaoyong Zhu and Li Quan

School of Electrical and Information Engineering, Jiangsu University, Zhenjiang 212013, China

Energies 2018, 11(6), 1428; https://doi.org/10.3390/en11061428 - 3 Jun 2018

Cited by 2 | Viewed by 2383

Abstract

In this paper, the effect of partitioned stator (PS) structure and iron flux bridges in hybrid excitation flux switching (HEFS) machines is comprehensively discussed and compared. Firstly, the operating principles of four HEFS machines with single stator and PS respectively with and without [...] Read more.

In this paper, the effect of partitioned stator (PS) structure and iron flux bridges in hybrid excitation flux switching (HEFS) machines is comprehensively discussed and compared. Firstly, the operating principles of four HEFS machines with single stator and PS respectively with and without iron flux bridges are described. Then an equivalent lumped parameter magnetic circuit model is developed to analyze the characteristics of PS structure and iron flux bridges. In order to achieve a fair comparison among different HEFS machines, the multi-level design optimization method is used to obtain the optimal parameters efficiently, based on which the electromagnetic performances of four machines are comprehensively evaluated by using 2D finite element analysis (2D-FEA). The results reveal that the machines with PS structure can exhibit not only a better flux regulation capability but also a higher torque density than conventional HEFS machines. Moreover, by adopting iron flux bridges, enlarged wide constant power speed region (CPSR) can be achieved, but the PM utilization will be slightly sacrificed. Full article

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17 pages, 1293 KiB

Open AccessArticle

Dual Enhancement of Power System Monitoring: Improved Probabilistic Multi-Stage PMU Placement with an Increased Search Space & Mathematical Linear Expansion to Consider Zero-Injection Bus

by Ziad M. Ali^1,2

, Seyed-Ehsan Razavi^3,*, Mohammad Sadegh Javadi⁴

, Foad H. Gandoman^5,6 and Shady H.E. Abdel Aleem⁷

¹ Electrical Engineering Department, College of Engineering at Wadi Addawaser, Prince Sattam bin Abdulaziz University, 11991 Wadi Addawaser, Saudi Arabia

² Electrical Engineering Department, Aswan Faculty of Engineering, Aswan University, 81542 Aswan, Egypt

³ Faculty of Electrical and Computer Engineering, University of Birjand, 97175-615 Birjand, Iran

⁴ Department of Electrical Engineering, Shiraz Branch, Islamic Azad University, 71993-4 Shiraz, Iran

⁵ ETEC Department & MOBI Research Group, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussel, Belgium

⁶ Flanders Make, 3001 Heverlee, Belgium

⁷ Mathematical, Physical and Engineering Sciences, 15th of May Higher Institute of Engineering, 11731 Cairo, Egypt

Energies 2018, 11(6), 1429; https://doi.org/10.3390/en11061429 - 3 Jun 2018

Cited by 7 | Viewed by 3108

Abstract

This paper presents a mathematical linear expansion model for the probabilistic Multistage Phasor Measurement Unit (PMU) Placement (MPP) in which zero-injection buses (ZIBs), as well as communication channel limitations, are taken into consideration. From the linearization perspective, presenting a model formulizing the probabilistic [...] Read more.

This paper presents a mathematical linear expansion model for the probabilistic Multistage Phasor Measurement Unit (PMU) Placement (MPP) in which zero-injection buses (ZIBs), as well as communication channel limitations, are taken into consideration. From the linearization perspective, presenting a model formulizing the probabilistic concept of observability while modelling the ZIB is of great significance, and has been done in this paper for the first time. More importantly, the proposed probabilistic MPP utilizes a technique disregarding the prevalent subsidiary optimizations for each planning stage. Although this technique, in turn, increases the problem complexity with manifold variables, it guarantees the global optimal solution in a wider and thorough search space; while in the prevalent methods, some parts of the search space might be missed. Furthermore, the proposed model indicates more realistic aspects of the MPP where system operators are allowed to follow their intention about the importance of buses such as strategic ones based on monitoring the priority principles. In addition, the model is capable of considering the network topology changes due to long-term expansions over the planning horizon. Finally, in order to demonstrate the effectiveness of the proposed formulation, the model is conducted on the IEEE 57-bus standard test system and the large scale 2383-bus Polish power system. Full article

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15 pages, 6629 KiB

Open AccessArticle

Analysis and Improvement of Adaptive Coefficient Third Harmonic Voltage Differential Stator Grounding Protection

by Ying Zhu^1,*

, Yuping Li², Jianbin Sang², Minglei Bao² and Haixiang Zang¹

¹ College of Energy and Electrical Engineering, Hohai University, Nanjing 211100, China

² Nanjing SAC Power Grid Automation Co., Ltd., Nanjing 211100, China

Energies 2018, 11(6), 1430; https://doi.org/10.3390/en11061430 - 3 Jun 2018

Cited by 2 | Viewed by 3177

Abstract

This paper presents a novel third harmonic voltage differential stator grounding protection (THV-DSGP) method combining the adaptive coefficient and fixed coefficient. It can solve the protection sensitivity degradation problem when the insulation resistance of stator winding to ground is slowly declining. This protection [...] Read more.

This paper presents a novel third harmonic voltage differential stator grounding protection (THV-DSGP) method combining the adaptive coefficient and fixed coefficient. It can solve the protection sensitivity degradation problem when the insulation resistance of stator winding to ground is slowly declining. This protection method retains the advantages of the adaptive coefficient, which is to maintain high sensitivity in case of an instantaneous ground fault. Moreover, the fixed coefficient can remember the initial insulation state of the stator winding and prevent relay failure when the stator insulation is slowly declining. In addition, due to zero-sequence voltage disconnection (ZSVD) often leading to malfunctioning of the THV stator ground protection, the existing criterion of the ZSVD was improved according to the electrical characteristics of the generator when ZSVD happens. THV-DSGP with both adaptive coefficient and fixed coefficient was simulated in the Matlab/Simulink. The simulation results show that the proposed protection can be applied to the slow ground fault of the stator winding. Furthermore, the improved criterion of ZSVD can effectively distinguish the stator metal earth fault and the secondary loop break of the zero-sequence voltage. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2018)

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14 pages, 3307 KiB

Open AccessArticle

Reliability Assessment of Power Systems with Photovoltaic Power Stations Based on Intelligent State Space Reduction and Pseudo-Sequential Monte Carlo Simulation

by Wenxia Liu, Dapeng Guo^*

, Yahui Xu, Rui Cheng, Zhiqiang Wang and Yueqiao Li

School of Electrical and Electronic Engineering, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(6), 1431; https://doi.org/10.3390/en11061431 - 3 Jun 2018

Cited by 29 | Viewed by 3035

Abstract

As the number and capacity of photovoltaic (PV) power stations increase, it is of great significance to evaluate the PV-connected power systems in an effective, reasonable, and quick way. In order to overcome the challenge of PV’s time-sequential characteristic and improve upon the [...] Read more.

As the number and capacity of photovoltaic (PV) power stations increase, it is of great significance to evaluate the PV-connected power systems in an effective, reasonable, and quick way. In order to overcome the challenge of PV’s time-sequential characteristic and improve upon the computational efficiency, this paper presents a new methodology to evaluate the reliability of the power system with photovoltaic power stations, which combines intelligent state space reduction and a pseudo-sequential Monte Carlo simulation (PMCS). First, a non-aggregate Markov model of photovoltaic output is established, which effectively retains some time-sequential representation of the PV output. Then, the differential evolution algorithm (DE) is introduced into the sampling stage of PMCS to carry out an intelligent state space reduction (ISSR). By using the DE algorithm, success states are searched out and removed, thus the state space is reduced and formed with a high density of loss-of-load. Hence, unnecessary samplings are avoided, which optimizes the PMCS sampling mechanism and improves the computational efficiency. Finally, the proposed method is tested in the modified IEEE RTS-79 system. The results indicate that this new method has a better computational efficiency than the time-sequential Monte Carlo simulation method (TMCS) and pure PMCS. In addition, the effectiveness and feasibility of this method are also verified. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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15 pages, 5518 KiB

Open AccessArticle

Numerical Study on the Transient Thermal Performance of a Two-Phase Closed Thermosyphon

by Zhongchao Zhao^*, Yong Zhang, Yanrui Zhang, Yimeng Zhou and Hao Hu

School of Energy and Power, Jiangsu University of Science and Technology, Zhenjiang 212000, China

Energies 2018, 11(6), 1433; https://doi.org/10.3390/en11061433 - 3 Jun 2018

Cited by 18 | Viewed by 4176

Abstract

The transient thermal performance of phase change and heat and mass transfer in a two-phase closed thermosyphon are studied with computational fluid dynamics (CFD). A CFD model based on the volume of fluid technique is built. Deionized water is specified as the working [...] Read more.

The transient thermal performance of phase change and heat and mass transfer in a two-phase closed thermosyphon are studied with computational fluid dynamics (CFD). A CFD model based on the volume of fluid technique is built. Deionized water is specified as the working fluid of this thermosyphon. The CFD model reproduces evaporation and condensation in the thermosyphon at different heating inputs. The average wall temperatures are also analyzed. Variations of average wall temperatures indicate that this thermosyphon reaches a steady state after 19 s, and starts to work in advance when the heating input increases. Moreover, thermal resistance is decreased until a minimum (0.552 K/W) by increasing the heating input, and the effective thermal conductivity is elevated to a maximum (2.07 × 106 W/m∙K). Full article

(This article belongs to the Special Issue Engineering Fluid Dynamics 2018)

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17 pages, 1712 KiB

Open AccessArticle

Thermodynamic, Economic and Environmental Evaluation of an Improved Ventilation Air Methane-Based Hot Air Power Cycle Integrated with a De-Carbonization Oxy-Coal Combustion Power Plant

by Cheng Xu^*, Yachi Gao, Qiang Zhang, Guoqiang Zhang and Gang Xu

National Thermal Power Engineering and Technology Research Center, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(6), 1434; https://doi.org/10.3390/en11061434 - 4 Jun 2018

Cited by 4 | Viewed by 2437

Abstract

Efficient utilization of ventilation air methane (VAM) as well as improving the energy efficiency of de-carbonization oxy-coal combustion power plants are intensively studied for achieving energy savings and greenhouse gas (GHG) emission control. Here, an improved VAM-coal hybrid power generation system, which integrates [...] Read more.

Efficient utilization of ventilation air methane (VAM) as well as improving the energy efficiency of de-carbonization oxy-coal combustion power plants are intensively studied for achieving energy savings and greenhouse gas (GHG) emission control. Here, an improved VAM-coal hybrid power generation system, which integrates a VAM-based hot air power cycle with a de-carbonization oxy-coal combustion circulating fluid bed (CFB) power plant was proposed. In the proposed system, part of the boiler flue gas was bypassed to feed the VAM auto-oxidation, and the whole VAM oxidation heat was efficiently utilized to drive a hot air power cycle. Meanwhile, the turbine exhaust air was utilized to heat the feed/condensed water within the regenerative heating trains in a cascade way, which was in turn beneficial to de-carbonization oxy-coal combustion plant. The mass and energy balance of the proposed system were determined using the simulation process. The thermodynamic benefits, economic viability and the environmental impacts were discussed. Results showed that energy efficiency of the proposed system reached 27.1% with the energy saving ratio at 0.9%. The cost of electricity (COE) was $118.15/MWh with the specific CO₂ emission as low as 17.46 kg CO₂/MWh. Full article

(This article belongs to the Section F: Electrical Engineering)

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18 pages, 5915 KiB

Open AccessArticle

Design and Control of Small DC-Link Capacitor-Based Three-Level Inverter with Neutral-Point Voltage Balancing

by Hyo-Chul In¹, Seok-Min Kim² and Kyo-Beum Lee^2,*

¹ Green Energy Research and Development Center, EGTRONICS Company, Innoplex B/D 502, 304 Sinwon-ro, Yeongtong-gu, Suwon 16675, Korea

² Department of Electrical and Computer Engineering, Ajou University, 206, World cup-ro, Yeongtong-gu, Suwon 16499, Korea

Energies 2018, 11(6), 1435; https://doi.org/10.3390/en11061435 - 4 Jun 2018

Cited by 15 | Viewed by 5145

Abstract

This paper presents a method to improve the quality of input-output currents in a three-level neutral-point clamped (NPC) inverter with small direct current-link (DC-link) capacitor systems. The inverter systems with the small DC-link capacitors have several advantages in terms of cost, volume, life-time, [...] Read more.

This paper presents a method to improve the quality of input-output currents in a three-level neutral-point clamped (NPC) inverter with small direct current-link (DC-link) capacitor systems. The inverter systems with the small DC-link capacitors have several advantages in terms of cost, volume, life-time, and reliability when compared to inverters that use large DC-link capacitors. However, there are problems with respect to the deterioration of the input current quality and a severe ripple of neutral-point voltage (NPV), which can cause an aggravated output current. To mitigate these issues, an additional circuit is applied for the input current shaping and a compensation algorithm is applied to reduce the ripple voltage of NPV. The effectiveness of the proposed design and control method is verified with various simulation and experimental results. Full article

(This article belongs to the Special Issue Power Electronics 2018)

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21 pages, 10878 KiB

Open AccessFeature PaperArticle

An Adaptive Frequency Strategy for Variable Speed Wind Turbines: Application to High Wind Integration Into Power Systems

by Ana Fernández-Guillamón^1,*

, Jorge Villena-Lapaz², Antonio Vigueras-Rodríguez³

, Tania García-Sánchez⁴ and Ángel Molina-García¹

¹ Department of Electrical Engineering, Universidad Politécnica de Cartagena, 30202 Cartagena, Spain

² Alberta Electric System Operator, Calgary, AB T2P 0L4, Canada

³ Department of Civil Engineering, Universidad Politécnica de Cartagena, 30203 Cartagena, Spain

⁴ Department of Electrical Engineering, Universidad Politécnica de Valencia, 46022 Valencia, Spain

Energies 2018, 11(6), 1436; https://doi.org/10.3390/en11061436 - 4 Jun 2018

Cited by 19 | Viewed by 3415

Abstract

This paper presents a new frequency controller for variable speed wind turbines connected to the grid under power imbalance conditions. It is based on the fast power reserve emulation technique, having two different operation modes: overproduction and recovery mode. In the first mode, [...] Read more.

This paper presents a new frequency controller for variable speed wind turbines connected to the grid under power imbalance conditions. It is based on the fast power reserve emulation technique, having two different operation modes: overproduction and recovery mode. In the first mode, the active power provided by wind turbines is set over the mechanical power, reducing their rotational speed. This overproduction power is estimated according to the frequency excursion. In the second mode, the active power is established under the mechanical power to recover the initial rotational speed through a smooth trajectory. The power system considered for simulation purposes includes thermal, hydro-power and wind-power plants. The controller proposed has been evaluated under different mix-generation scenarios implemented in Matlab/Simulink. Extensive results and comparison to previous proposals are also included in the paper. Full article

(This article belongs to the Section F: Electrical Engineering)

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17 pages, 1559 KiB

Open AccessArticle

Optimization of Inventory Routing Problem in Refined Oil Logistics with the Perspective of Carbon Tax

by Songyi Wang¹

, Fengming Tao^1,2,* and Yuhe Shi³

¹ College of Mechanical Engineering, Chongqing University, Chongqing 400044, China

² School of Economics and Business Administration, Chongqing University, Chongqing 400044, China

³ School of Transportation and Logistics, Southwest Jiaotong University, Chengdu 610031, China

Energies 2018, 11(6), 1437; https://doi.org/10.3390/en11061437 - 4 Jun 2018

Cited by 22 | Viewed by 3850

Abstract

In order to solve the optimization problem of the refined oil distribution system from the perspectives of low-carbon and environmental protection, this paper focuses on the characteristics of the secondary distribution of refined oil and combines it with the integrated optimization concept of [...] Read more.

In order to solve the optimization problem of the refined oil distribution system from the perspectives of low-carbon and environmental protection, this paper focuses on the characteristics of the secondary distribution of refined oil and combines it with the integrated optimization concept of refined oil distribution network, where a low-carbon inventory routing problem (LCIRP) model is constructed with the minimum total costs as the objective function on the basis of considering carbon emissions. An adaptive genetic algorithm combined with greedy algorithm is designed to solve the model, and an example is given to verify the effectiveness of the algorithm. Then, this paper solves the model with two parts by introducing a practical numerical example: in the first part, the LCIRP models with different carbon tax values are solved, which verifies the effectiveness of the model and proves that carbon tax policies can effectively reduce the carbon emissions in the secondary distribution network of refined oil; in the second part, the LCIRP models with the different maximum load capacity of oil tank trucks are solved, which provides the economic and environmentally friendly distribution schemes for refined oil distribution enterprises under the premise of carbon tax policies and load limitation. Finally, the emission reduction proposals that take into account both economic and environmental benefits are given respectively from the aspect of government environmental protection agencies and from the aspect of refined oil distribution enterprises. Full article

(This article belongs to the Special Issue Modeling and Simulation of Carbon Emission Related Issues)

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24 pages, 10439 KiB

Open AccessArticle

A Modularized Discharge-Type Balancing Topology for Series-Connected Super Capacitor String

by Shaogui Fan¹

, Li Sun¹, Jiandong Duan^1,* and Dong Zhang²

¹ School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China

² State Grid Heilongjiang Electric Power Company Limited, Qiqihar Power Supply Company Power Dispatching Center, Qiqihar 161005, China

Energies 2018, 11(6), 1438; https://doi.org/10.3390/en11061438 - 4 Jun 2018

Cited by 2 | Viewed by 3004

Abstract

This paper proposed a modularized discharge-type topology for the voltage balance of series-connected super capacitor (SC) string. The proposed topology consists of cascaded converter modules and a boost converter. The cascaded converter modules discharge the higher voltage SCs directly with the ideal output [...] Read more.

This paper proposed a modularized discharge-type topology for the voltage balance of series-connected super capacitor (SC) string. The proposed topology consists of cascaded converter modules and a boost converter. The cascaded converter modules discharge the higher voltage SCs directly with the ideal output current to realize a fast balancing speed and the boost converter feedbacks the extra energy from the higher voltage SCs to the super capacitor energy storage system (SCESS). The modular design of the cascaded converter modules makes the balancing system suitable for different voltage levels of SCESS. Unlike the charge-type topologies which discharge the higher voltage SCs indirectly, the proposed topology discharges the higher voltage SCs directly with a big current, and the over voltage phenomenon of SCs is then avoided, which means the reliability of the SCESS can be improved. The voltage stress of the switches inside the cascaded converter modules is low, which is different from the existing modularized discharge-type balancing topology. What is more, the control of cascaded converter modules and the boost converter can be implemented by analog devices which will simplify the control of the whole system. The control degree of freedom is high and the voltage of each cell can be controlled. An in-depth comparison analysis with the charge-type balancing topology is performed from the perspective of balancing speed and round-trip energy efficiency. The proposed topology and the balancing performance are confirmed by experimental results. Full article

(This article belongs to the Special Issue Power Electronics for Energy Storage)

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25 pages, 10509 KiB

Open AccessArticle

Power and Capacity Consensus Tracking of Distributed Battery Storage Systems in Modular Microgrids

by Xianyong Zhang^1,*, Yaohong Huang¹, Li Li¹ and Wei-Chang Yeh²

¹ School of Automation, Guangdong Polytechnic Normal University, Guangzhou 510665, China

² Integration and Collaboration Laboratory, Department of Industrial Engineering and Engineering Management, National Tsing Hua University, Hsinchu 46804804, Taiwan

Energies 2018, 11(6), 1439; https://doi.org/10.3390/en11061439 - 4 Jun 2018

Cited by 13 | Viewed by 2430

Abstract

Conventional microgrids have a specific system configuration and a complex hierarchical control structure, which has resulted in difficulties in their economic development. A modular microgrid based on distributed battery storage has been proposed to realize the rapid economic development of small-to-medium microgrids. Control [...] Read more.

Conventional microgrids have a specific system configuration and a complex hierarchical control structure, which has resulted in difficulties in their economic development. A modular microgrid based on distributed battery storage has been proposed to realize the rapid economic development of small-to-medium microgrids. Control of modular microgrids is simplified to voltage control within modules and exchange power control among modules. Battery power has great influence on battery performance. Space-time complementary power characteristics among modules help to alleviate power fluctuations, prolong the service life and realize the unified maintenance of distributed batteries. Leader-following consensus theory of multi-agent systems is adopted to realize the power and capacity consensus tracking of distributed battery storage in a modular microgrid. Sufficient and necessary conditions for continuous-time and sampled-data bounded power and capacity consensus tracking of distributed battery storages are deduced by a matrix analytical method. Steady regions of sampling period and sampling delay for sampled-data bounded power and capacity consensus tracking are determined by analytical or numerical solutions. Simulations and experiments on a modular microgrid demonstration project located on DongAo Island (China) show the effectiveness and robustness of the proposed power and capacity consensus tracking strategy for distributed storage systems. The power and capacity consensus tracking strategy determines the exchange power among modules and improves the control technology of modular microgrids. Full article

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17 pages, 5463 KiB

Open AccessArticle

Single-Ended Protection Scheme for VSC-Based DC Microgrid Lines

by Cheng Lv¹, Xiaodong Zheng^1,*, Nengling Tai¹ and Shi Chen²

¹ Department of Electrical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China

² Power Grid Technology Centre, State Grid Jiangsu Electric Power Company Research Institute, Nanjing 211103, China

Energies 2018, 11(6), 1440; https://doi.org/10.3390/en11061440 - 4 Jun 2018

Cited by 3 | Viewed by 3475

Abstract

With the promotion of distributed energy and direct current (DC) loads, the DC microgrid is able to provide a higher power quality and improve the grid efficiency. Various technical issues in DC microgrids are still to be addressed, particularly a proper protection scheme [...] Read more.

With the promotion of distributed energy and direct current (DC) loads, the DC microgrid is able to provide a higher power quality and improve the grid efficiency. Various technical issues in DC microgrids are still to be addressed, particularly a proper protection scheme for fault detection and isolation in DC microgrids utilizing voltage source converters (VSCs). In this paper, the pole-to-pole DC fault transient behavior of the VSC-based microgrids is firstly analyzed with four successive stages, and then the exact requirements for protections are presented. Furthermore, a novel single-ended protection scheme based on local transient signals is proposed, which needs no data transmission or synchronization between two ends, ensuring the speed. A four-terminal DC microgrid model was built in PSCAD/EMTDC. Numerous simulations have demonstrated the validity of the proposed scheme. Full article

(This article belongs to the Special Issue Power Electronics in DC-Microgrid Systems)

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14 pages, 6196 KiB

Open AccessArticle

3D Numerical Study of Multiphase Counter-Current Flow within a Packed Bed for Post Combustion Carbon Dioxide Capture

by Li Yang^1,2, Fang Liu², Zhengchang Song^2,*, Kunlei Liu³ and Kozo Saito^3,*

¹ Key Laboratory of Coal-Based CO₂ Capture and Geological Storage, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China

² School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China

³ Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506, USA

Energies 2018, 11(6), 1441; https://doi.org/10.3390/en11061441 - 4 Jun 2018

Cited by 6 | Viewed by 4493

Abstract

The hydrodynamics within counter-current flow packed beds is of vital importance to provide insight into the design and operational parameters that may impact reactor and reaction efficiencies in processes used for post combustion CO₂ capture. However, the multiphase counter-current flows in random [...] Read more.

The hydrodynamics within counter-current flow packed beds is of vital importance to provide insight into the design and operational parameters that may impact reactor and reaction efficiencies in processes used for post combustion CO₂ capture. However, the multiphase counter-current flows in random packing used in these processes are complicated to visualize. Hence, this work aimed at developing a computational fluid dynamics (CFD) model to study more precisely the complex details of flow inside a packed bed. The simulation results clearly demonstrated the development of, and changes in, liquid distributions, wetted areas, and film thickness under various gas and liquid flow rates. An increase in values of the We number led to a more uniform liquid distribution, and the flow patterns changed from droplet flow to film flow and trickle flow as the We number was increased. In contrast, an increase in gas flow rate had no significant effect on the wetted areas and liquid holdup. It was also determined that the number of liquid inlets affected flow behavior, and the liquid surface tension had an insignificant influence on pressure drop or liquid holdup; however, lower surface tension provided a larger wetted area and a thinner film. An experimental study, performed to enable comparisons between experimentally measured pressure drops and simulation-determined pressure drops, showed close correspondence and similar trends between the experimental data and the simulation data; hence, it was concluded that the simulation model was validated and could reasonably predict flow dynamics within a counter-current flow packed bed. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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15 pages, 3954 KiB

Open AccessArticle

Interaction of Wind Turbine Wakes under Various Atmospheric Conditions

by Sang Lee^*

, Peter Vorobieff and Svetlana Poroseva

Department of Mechanical Engineering, University of New Mexico, Albuquerque, NM 87131, USA

Energies 2018, 11(6), 1442; https://doi.org/10.3390/en11061442 - 4 Jun 2018

Cited by 5 | Viewed by 3476

Abstract

We present a numerical study of two utility-scale 5-MW turbines separated by seven rotor diameters. The effects of the atmospheric boundary layer flow on the turbine performance were assessed using large-eddy simulations. We found that the surface roughness and the atmospheric stability states [...] Read more.

We present a numerical study of two utility-scale 5-MW turbines separated by seven rotor diameters. The effects of the atmospheric boundary layer flow on the turbine performance were assessed using large-eddy simulations. We found that the surface roughness and the atmospheric stability states had a profound effect on the wake diffusion and the Reynolds stresses. In the upstream turbine case, high surface roughness increased the wind shear, accelerating the decay of the wake deficit and increasing the Reynolds stresses. Similarly, atmospheric instabilities significantly expedited the wake decay and the Reynolds stress increase due to updrafts of the thermal plumes. The turbulence from the upstream boundary layer flow combined with the turbine wake yielded higher Reynolds stresses for the downwind turbine, especially in the streamwise component. For the downstream turbine, diffusion of the wake deficits and the sharp peaks in the Reynolds stresses showed faster decay than the upwind case due to higher levels of turbulence. This provides a physical explanation for how turbine arrays or wind farms can operate more efficiently under unstable atmospheric conditions, as it is based on measurements collected in the field. Full article

(This article belongs to the Collection Wind Turbines)

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23 pages, 2028 KiB

Open AccessFeature PaperArticle

Impacts of the Allocation Mechanism Under the Third Phase of the European Emission Trading Scheme

by Wolfgang Eichhammer^1,2,*

, Nele Friedrichsen³, Sean Healy⁴ and Katja Schumacher⁴

¹ Fraunhofer Institute for Systems and Innovation Research ISI, 76139 Karlsruhe, Germany

² Copernicus Institute of Sustainable Development, Utrecht University, 3584 CB Utrecht, The Netherlands

³ Fraunhofer Institute for Systems and Innovation Research ISI, Now with: DB Energie GmbH, 60326 Frankfurt a.M., Germany

⁴ Öko-Institut e.V.—Institute for Applied Ecology, 10179 Berlin, Germany

Energies 2018, 11(6), 1443; https://doi.org/10.3390/en11061443 - 4 Jun 2018

Cited by 1 | Viewed by 3307

Abstract

This paper focuses on the following two key research questions in the context of the change in allocation rules in the move from Phase I/II (2005–2012) to Phase III (2013–2020) of the European Emission Trading Scheme (EU ETS): First, how do allocations compare [...] Read more.

This paper focuses on the following two key research questions in the context of the change in allocation rules in the move from Phase I/II (2005–2012) to Phase III (2013–2020) of the European Emission Trading Scheme (EU ETS): First, how do allocations compare with actual installation-verified emissions in Phase III? For that purpose we analyse changes in sector-country allocations and verified emissions between Phase II and Phase III. The analysis is based on a selection of 2150 installations present in all phases of the EU ETS, taken from the European Union Transaction Log (EUTL) The results show that over-allocation has been considerably reduced in Phase III. Overall, allocation for the selected sectors decreased by 20% in 2013 compared to 2008 but varying across installations. Second, we investigate, whether the introduction of benchmarks in Phase III may have triggered carbon-reducing measures for industrial processes. For that purpose, we analyse for four product groups (cement clinker, pig iron, ammonia and nitric acid) the specific emissions (per tonne of product). Care was taken to define a data set with a similar delimitation of emission and production data. The findings were cross-checked through selected expert interviews. Our findings indicate that there is no evidence so far for improving specific emissions, though the strong improvement for nitric acid, as well as some improvement linked to ammonia occurring before the start of Phase III may have been supported by the introduction of Phase III. Full article

(This article belongs to the Special Issue Lessons from the Evaluation of Existing Emission Trading Schemes)

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21 pages, 9854 KiB

Open AccessArticle

Impeller Optimized Design of the Centrifugal Pump: A Numerical and Experimental Investigation

by Xiangdong Han^1,2,3, Yong Kang^1,2,3,4,*, Deng Li^1,2,3

and Weiguo Zhao⁵

¹ Key Laboratory of Hydraulic Machinery Transients, Ministry of Education, Wuhan University, Wuhan 430072, China

² Hubei Key Laboratory of Waterjet Theory and New Technology, Wuhan University, Wuhan 430072, China

³ School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, China

⁴ Collaborative Innovation Center of Geospatial Technology, Wuhan 430079, China

⁵ School of Energy and Power Engineering, Lanzhou University of Technology, Lanzhou 730050, China

Energies 2018, 11(6), 1444; https://doi.org/10.3390/en11061444 - 4 Jun 2018

Cited by 24 | Viewed by 8435

Abstract

Combined numerical simulation with experiment, blade wrap angle, and blade exit angle are varied to investigate the optimized design of the impeller of centrifugal pump. Blade wrap angles are 122°, 126°, and 130°. Blade exit angles are 24°, 26°, and 28°. Based on [...] Read more.

Combined numerical simulation with experiment, blade wrap angle, and blade exit angle are varied to investigate the optimized design of the impeller of centrifugal pump. Blade wrap angles are 122°, 126°, and 130°. Blade exit angles are 24°, 26°, and 28°. Based on numerical simulation, internal flow of the centrifugal pump with five different impellers under 0.6, 0.8, 1.0, 1.2, and 1.5 Q_d are simulated. Variations of static pressure, relative velocity, streamline, and turbulent kinetic energy are analyzed. The impeller with blade wrap angle 126° and blade exit angle 24° are optimal. Distribution of static pressure is the most uniform and relative velocity sudden changes do not exist. Streamlines are the smoothest. Distribution scope of turbulent kinetic energy is the smallest. Based on performance experiments, head and efficiency of the centrifugal pump with the best impeller are tested. The values of head and efficiency are higher than that of the original pump. Centrifugal pump with the best impeller has better hydraulic performance than the original centrifugal pump. Full article

(This article belongs to the Special Issue Engineering Fluid Dynamics 2018)

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17 pages, 3882 KiB

Open AccessArticle

Economic and Technical Aspects of Flexible Storage Photovoltaic Systems in Europe

by Henrik Zsiborács¹, Nóra Hegedűsné Baranyai^1,*, András Vincze², István Háber³ and Gábor Pintér¹

¹ Department of Economic Methodology, University of Pannonia, Georgikon Faculty, 8360 Keszthely, Hungary

² Department of Foreign Languages, University of Pannonia, Georgikon Faculty, 8360 Keszthely, Hungary

³ Department of Mechanical Engineering, University of Pécs, Faculty of Engineering and Information Technology, 7624 Pécs, Hungary

Energies 2018, 11(6), 1445; https://doi.org/10.3390/en11061445 - 4 Jun 2018

Cited by 57 | Viewed by 6459

Abstract

Solar energy has an increasing role in the global energy mix. The need for flexible storage photovoltaic systems and energy storage in electricity networks is becoming increasingly important as more generating capacity uses solar and wind energy. This paper is a study on [...] Read more.

Solar energy has an increasing role in the global energy mix. The need for flexible storage photovoltaic systems and energy storage in electricity networks is becoming increasingly important as more generating capacity uses solar and wind energy. This paper is a study on the economic questions related to flexible storage photovoltaic systems of household size in 2018. The aim is to clarify whether it is possible in the European Union to achieve a payback of the costs of flexible storage photovoltaic system investments for residential customers considering the technology-specific storage aspects prevalent in 2018. We studied seven different flexible storage photovoltaic investments with different battery technologies in Germany, France, Italy, and Spain because, in Europe, these countries have a prominent role with regard to the spread of photovoltaic technology. These investment alternatives are studied with the help of economic indicators for the different cases of the selected countries. At the end of our paper we come to the conclusion that an investment of a flexible storage photovoltaic (PV) system with Olivine-type-LiFePO₄, Lithium-Ion, Vented lead-acid battery (OPzS), Sealed lead-acid battery (OPzV), and Aqueous Hybrid Ion (AHI) batteries can have a positive net present value due to the high electricity prices in Germany and in Spain. The most cost-effective technology was the Olivine-type-LiFePO₄ and the Lithium-Ion at the time of the study. We suggest the provision of governmental support and uniform European modifications to the regulatory framework, especially concerning grid fees and tariffs, which would be necessary in the beginning to help to introduce these flexible storage PV systems to the market. Full article

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18 pages, 7452 KiB

Open AccessFeature PaperArticle

Feedback-Oriented Intelligent Monitoring of a Storage-Based Solar Photovoltaic (PV)-Powered Microgrid with Mesh Networks

by Ahmad Almadhor

Electrical and Computer Engineering Department, University of Denver, Denver, CO 80210, USA

Energies 2018, 11(6), 1446; https://doi.org/10.3390/en11061446 - 4 Jun 2018

Cited by 8 | Viewed by 2894

Abstract

This paper proposes a mesh network-based communication architecture that can be used to monitor and control different elements in a microgrid. A solar Photovoltaic (PV) and storage-based, off-grid, microgrid model is designed using MATLAB Simulink. The communication mechanism between every element [...] Read more.

This paper proposes a mesh network-based communication architecture that can be used to monitor and control different elements in a microgrid. A solar Photovoltaic (PV) and storage-based, off-grid, microgrid model is designed using MATLAB Simulink. The communication mechanism between every element of the microgrid is also represented and simulated in the model developed. Basic features of monitoring and regulating the generation, and demand-side of the grid are discussed along with feedback-based measures for effective performance monitoring in the microgrid. Finally, the paper also points out a unique cloud infrastructure that can be used to store data, perform data analysis and assist in decision making in case of extreme situations. Overall, this paper proposes a simple feedback based mechanism for proactive monitoring of PV generation in a microgrid using a communication architecture powered by mesh networks. Full article

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21 pages, 7842 KiB

Open AccessArticle

The Effect of Unbalanced Impedance Loads on the Short-Circuit Current

by Insu Kim

School of Electrical Engineering, Inha University, Incheon 22212, Korea

Energies 2018, 11(6), 1447; https://doi.org/10.3390/en11061447 - 4 Jun 2018

Cited by 7 | Viewed by 4039

Abstract

Conventional short-circuit studies often neglect the load current because the short-circuit current (SCC) flowing from generators is much greater than the SCC that is affected by various loading conditions. As distributed or clustered loads that are unbalanced in phases are connected to the [...] Read more.

Conventional short-circuit studies often neglect the load current because the short-circuit current (SCC) flowing from generators is much greater than the SCC that is affected by various loading conditions. As distributed or clustered loads that are unbalanced in phases are connected to the grid, they can also change the magnitude and phase angle of the SCC, despite their small capacities. Thus, the objective of this study is to present algorithms that are able to analyze such an impedance unbalanced load. For this purpose, this study initially derives an SCC model of the unbalanced impedance load in phases. Since the proposed SCC model requires the pre-fault voltage, it uses a power-flow analysis algorithm that iteratively calculates the current that is to be injected and the pre-fault voltage, using the bus impedance matrix. Then, the proposed SCC calculation algorithm transforms the unbalanced loads into equivalent impedances, using the pre-fault voltage, and adds them to sequence networks as input data, using the proposed SCC model. The proposed algorithms are verified in various case studies. As a result, the proposed SCC calculation algorithms are more accurate, because they do not neglect unbalanced loads. Full article

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13 pages, 1670 KiB

Open AccessArticle

Electrical Properties of Polyethylene/Polypropylene Compounds for High-Voltage Insulation

by Sameh Ziad Ahmed Dabbak¹, Hazlee Azil Illias^1,*

, Bee Chin Ang², Nurul Ain Abdul Latiff¹ and Mohamad Zul Hilmey Makmud^1,3,*

¹ Department of Electrical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

² Department of Chemical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

³ Complex of Science and Technology, Faculty of Science and Natural Resources, University Malaysia Sabah, Kota Kinabalu 88400, Malaysia

Energies 2018, 11(6), 1448; https://doi.org/10.3390/en11061448 - 4 Jun 2018

Cited by 62 | Viewed by 8682

Abstract

In high-voltage insulation systems, the most commonly used material is polymeric material because of its high dielectric strength, high resistivity, and low dielectric loss in addition to good chemical and mechanical properties. In this work, various polymer compounds were prepared, consisting of low-density [...] Read more.

In high-voltage insulation systems, the most commonly used material is polymeric material because of its high dielectric strength, high resistivity, and low dielectric loss in addition to good chemical and mechanical properties. In this work, various polymer compounds were prepared, consisting of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), HDPE/PP, and LDPE/PP polymer blends. The relative permittivity and breakdown strength of each sample types were evaluated. In order to determine the physical properties of the prepared samples, the samples were also characterized using differential scanning calorimetry (DSC). The results showed that the dielectric constant of PP increased with the increase of HDPE and LDPE content. The breakdown measurement data for all samples were analyzed using the cumulative probability plot of Weibull distribution. From the acquired results, it was found that the dielectric strengths of LDPE and HDPE were higher than that of PP. Consequently, the addition of LDPE and HDPE to PP increased the breakdown strength of PP, but a variation in the weight ratio (30%, 50% and 70%) did not change significantly the breakdown strength. The DSC measurements showed two exothermic crystallization peaks representing two crystalline phases. In addition, the DSC results showed that the blended samples were physically bonded, and no co-crystallization occurred in the produced blends. Full article

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18 pages, 5019 KiB

Open AccessArticle

Short-Term Load Forecasting for Electric Bus Charging Stations Based on Fuzzy Clustering and Least Squares Support Vector Machine Optimized by Wolf Pack Algorithm

by Xing Zhang

Department of Economic Management, North China Electric Power University, Baoding 071003, China, [email protected]

Energies 2018, 11(6), 1449; https://doi.org/10.3390/en11061449 - 4 Jun 2018

Cited by 40 | Viewed by 3405

Abstract

Accurate short-term load forecasting is of momentous significance to ensure safe and economic operation of quick-change electric bus (e-bus) charging stations. In order to improve the accuracy and stability of load prediction, this paper proposes a hybrid model that combines fuzzy clustering (FC), [...] Read more.

Accurate short-term load forecasting is of momentous significance to ensure safe and economic operation of quick-change electric bus (e-bus) charging stations. In order to improve the accuracy and stability of load prediction, this paper proposes a hybrid model that combines fuzzy clustering (FC), least squares support vector machine (LSSVM), and wolf pack algorithm (WPA). On the basis of load characteristics analysis for e-bus charging stations, FC is adopted to extract samples on similar days, which can not only avoid the blindness of selecting similar days by experience, but can also overcome the adverse effects of unconventional load data caused by a sudden change of factors on training. Then, WPA with good global convergence and computational robustness is employed to optimize the parameters of LSSVM. Thus, a novel hybrid load forecasting model for quick-change e-bus charging stations is built, namely FC-WPA-LSSVM. To verify the developed model, two case studies are used for model construction and testing. The simulation test results prove that the proposed model can obtain high prediction accuracy and ideal stability. Full article

(This article belongs to the Special Issue Short-Term Load Forecasting by Artificial Intelligent Technologies)

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16 pages, 5046 KiB

Open AccessArticle

Investigation of Water Hammer Protection in Water Supply Pipeline Systems Using an Intelligent Self-Controlled Surge Tank

by Wuyi Wan^*

and Boran Zhang

Department of Hydraulic Engineering, College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China

Energies 2018, 11(6), 1450; https://doi.org/10.3390/en11061450 - 4 Jun 2018

Cited by 36 | Viewed by 4377

Abstract

A surge tank is a common pressure control device in long pressurized pipelines. The performance is greatly influenced by the location, cross area, and the characteristics of the connector. In order to improve the property of the surge tank, the effect of the [...] Read more.

A surge tank is a common pressure control device in long pressurized pipelines. The performance is greatly influenced by the location, cross area, and the characteristics of the connector. In order to improve the property of the surge tank, the effect of the connector is numerically analyzed by the method of characteristics (MOC). A hysteretic effect can occur when the discharge capacity is limited. Therefore, the performance of the surge tank can be improved if the discharge capacity of the connector is appropriately controlled according to the different conditions. For the adjustability of the connector’s discharge capacity, a kind of intelligent self-controlled surge tank (IST) is proposed. In addition, through simulations and analysis, IST is proved to have advantages in pressure control and applicability compared to normal surge tanks. Full article

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17 pages, 2622 KiB

Open AccessArticle

Design of a Path-Tracking Steering Controller for Autonomous Vehicles

by Chuanyang Sun¹, Xin Zhang^1,*, Lihe Xi¹ and Ying Tian²

¹ Beijing Key Laboratory of Powertrain for New Energy Vehicle, School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China

² Beijing Jiaotong University Yangtze River Delta Research Institute, Zhenjiang 212009, China

Energies 2018, 11(6), 1451; https://doi.org/10.3390/en11061451 - 4 Jun 2018

Cited by 58 | Viewed by 7145

Abstract

This paper presents a linearization method for the vehicle and tire models under the model predictive control (MPC) scheme, and proposes a linear model-based MPC path-tracking steering controller for autonomous vehicles. The steering controller is designed to minimize lateral path-tracking deviation at high [...] Read more.

This paper presents a linearization method for the vehicle and tire models under the model predictive control (MPC) scheme, and proposes a linear model-based MPC path-tracking steering controller for autonomous vehicles. The steering controller is designed to minimize lateral path-tracking deviation at high speeds. The vehicle model is linearized by a sequence of supposed steering angles, which are obtained by assuming the vehicle can reach the desired path at the end of the MPC prediction horizon and stay in a steady-state condition. The lateral force of the front tire is directly used as the control input of the model, and the rear tire’s lateral force is linearized by an equivalent cornering stiffness. The course-direction deviation, which is the angle between the velocity vector and the path heading, is chosen as a control reference state. The linearization model is validated through the simulation, and the results show high prediction accuracy even in regions of large steering angle. This steering controller is tested through simulations on the CarSim-Simulink platform (R2013b, MathWorks, Natick, MA, USA), showing the improved performance of the present controller at high speeds. Full article

(This article belongs to the Special Issue Selected Papers from SDEWES 2017: The 12th Conference on Sustainable Development of Energy, Water and Environment Systems)

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18 pages, 2643 KiB

Open AccessArticle

Impact of Demand Response Programs on Optimal Operation of Multi-Microgrid System

by Anh-Duc Nguyen¹, Van-Hai Bui¹, Akhtar Hussain¹

, Duc-Huy Nguyen²

and Hak-Man Kim^1,3,*

¹ Department of Electrical Engineering, Incheon National University, 12-1 Songdo-dong, Yeonsu-gu, Incheon 406840, Korea

² Department of Electrical Engineering, Hanoi University of Science and Technology, Hanoi 112400, Vietnam

³ Research Institute for Northeast Asian Super Grid, Incheon National University, 12-1 Songdo-dong, Yeonsu-gu, Incheon 406840, Korea

Energies 2018, 11(6), 1452; https://doi.org/10.3390/en11061452 - 4 Jun 2018

Cited by 35 | Viewed by 4721

Abstract

The increased penetration of renewables is beneficial for power systems but it poses several challenges, i.e., uncertainty in power supply, power quality issues, and other technical problems. Backup generators or storage system have been proposed to solve this problem but there are limitations [...] Read more.

The increased penetration of renewables is beneficial for power systems but it poses several challenges, i.e., uncertainty in power supply, power quality issues, and other technical problems. Backup generators or storage system have been proposed to solve this problem but there are limitations remaining due to high installation and maintenance cost. Furthermore, peak load is also an issue in the power distribution system. Due to the adjustable characteristics of loads, strategies on demand side such as demand response (DR) are more appropriate in order to deal with these challenges. Therefore, this paper studies how DR programs influence the operation of the multi-microgrid (MMG). The implementation is executed based on a hierarchical energy management system (HiEMS) including microgrid EMSs (MG-EMSs) responsible for local optimization in each MG and community EMS (C-EMS) responsible for community optimization in the MMG. Mixed integer linear programming (MILP)-based mathematical models are built for MMG optimal operation. Five scenarios consisting of single DR programs and DR groups are tested in an MMG test system to evaluate their impact on MMG operation. Among the five scenarios, some DR programs apply curtailing strategies, resulting in a study about the influence of base load value and curtailable load percentage on the amount of curtailed load and shifted load as well as the operation cost of the MMG. Furthermore, the impact of DR programs on the amount of external and internal trading power in the MMG is also examined. In summary, each individual DR program or group could be handy in certain situations depending on the interest of the MMG such as external trading, self-sufficiency or operation cost minimization. Full article

(This article belongs to the Special Issue Microgrids-2018)

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17 pages, 1453 KiB

Open AccessArticle

Convex Programming and Bootstrap Sensitivity for Optimized Electricity Bill in Healthcare Buildings under a Time-Of-Use Pricing Scheme

by Rodolfo Gordillo-Orquera^1,2,*

, Sergio Muñoz-Romero^2,3, Diego Arcos-Aviles¹

, Rafael Chillón⁴, Luis M. Lopez-Ramos^2,5

, Antonio G. Marques²

and José Luis Rojo-Álvarez^2,3

¹ WICOM Energy Research Group, Departamento de Electrica y Electronica, Universidad de las Fuerzas Armadas ESPE, Sangolquí 171-5-231B, Ecuador

² Department of Signal Theory and Communications, Rey Juan Carlos University, 28943 Fuenlabrada, Spain

³ Center for Computational Simulation, Universidad Politécnica de Madrid, Boadilla, 28223 Madrid, Spain

⁴ Hospital Universitario de Fuenlabrada, 28492 Fuenlabrada, Spain

⁵ Wisenet Signal Processing & Wireless Networks Laboratory, University of Agder, 4876 Grimstad, Norway

Energies 2018, 11(6), 1454; https://doi.org/10.3390/en11061454 - 5 Jun 2018

Cited by 2 | Viewed by 3239

Abstract

Efficient energy management is strongly dependent on determining the adequate power contracts among the ones offered by different electricity suppliers. This topic takes special relevance in healthcare buildings, where noticeable amounts of energy are required to generate an adequate health environment for patients [...] Read more.

Efficient energy management is strongly dependent on determining the adequate power contracts among the ones offered by different electricity suppliers. This topic takes special relevance in healthcare buildings, where noticeable amounts of energy are required to generate an adequate health environment for patients and staff. In this paper, a convex optimization method is scrutinized to give a straightforward analysis of the optimal power levels to be contracted while minimizing the electricity bill cost in a time-of-use pricing scheme. In addition, a sensitivity analysis is carried out on the constraints in the optimization problems, which are analyzed in terms of both their empirical distribution and their bootstrap-estimated statistical distributions to create a simple-to-use tool for this purpose, the so-called mosaic-distribution. The evaluation of the proposed method was carried out with five-year consumption data on two different kinds of healthcare buildings, a large one given by Hospital Universitario de Fuenlabrada, and a primary care center, Centro de Especialidades el Arroyo, both located at Fuenlabrada (Madrid, Spain). The analysis of the resulting optimization shows that the annual savings achieved vary moderately, ranging from −0.22 % to +27.39%, depending on the analyzed year profile and the healthcare building type. The analysis introducing mosaic-distribution to represent the sensitivity score also provides operative information to evaluate the convenience of implementing energy saving measures. All this information is useful for managers to determine the appropriate power levels for next year contract renewal and to consider whether to implement demand response mechanisms in healthcare buildings. Full article

(This article belongs to the Special Issue Building Energy Use: Modeling and Analysis)

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11 pages, 2390 KiB

Open AccessArticle

Research into an Online Calibration System for the Errors of Voltage Transformers Based on Open–Closed Capacitor

by Zhenhua Li^1,2,*

, Qiuhui Li¹

, Zhengtian Wu³

and Zhenxing Li¹

¹ College of Electrical Engineering & New Energy, China Three Gorges University College, Yichang 443002, China

² Hubei Provincial Collaborative Innovation Center for New Energy Microgrid, China Three Gorges University, Yichang 443002, China

³ School of Electronic and Information Engineering, Suzhou University of Science and Technology, Suzhou 215009, China

Energies 2018, 11(6), 1455; https://doi.org/10.3390/en11061455 - 5 Jun 2018

Cited by 10 | Viewed by 2211

Abstract

Periodical calibration is necessary to ensure the accuracy and reliability of voltage transformers. The traditional calibration method requires the power to be off, and the calibration period for this method is too long, meaning that problems with the transformer cannot be found in [...] Read more.

Periodical calibration is necessary to ensure the accuracy and reliability of voltage transformers. The traditional calibration method requires the power to be off, and the calibration period for this method is too long, meaning that problems with the transformer cannot be found in time. In this paper, a voltage transformer error online calibration system based on open–closed capacitors is proposed. Two open–closed capacitors and other auxiliary devices are utilized to construct the standard voltage sensor. The outputs of the open–closed capacitors are compared with each other to realize accurate self-checking. The average value of the output is used as the final output, which can improve the system’s accuracy and reliability. An improved algorithm based on a hybrid convolution window is proposed to extract the fundamental and harmonic signals. Test results show that the variation of the ratio error is less than 0.037%, and the variation of the angle error is less than 0.45’. Full article

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15 pages, 1313 KiB

Open AccessArticle

Esterification of Jatropha Oil with Isopropanol via Ultrasonic Irradiation

by Chia-Chi Chang¹, Syuan Teng¹, Min-Hao Yuan², Dar-Ren Ji¹, Ching-Yuan Chang^1,3,*, Yi-Hung Chen⁴, Je-Lueng Shie⁵, Chungfang Ho⁶, Sz-Ying Tian¹, Cesar Augusto Andrade-Tacca¹

, Do Van Manh⁷, Min-Yi Tsai¹, Mei-Chin Chang¹, Yen-Hau Chen¹, Michael Huang¹

and Bo-Liang Liu¹

¹ Graduate Institute of Environmental Engineering, National Taiwan University, Taipei 106, Taiwan

² Department of Occupational Safety and Health, China Medical University, Taichung 404, Taiwan

³ Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan

⁴ Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei 106, Taiwan

⁵ Department of Environmental Engineering, National I-Lan University, I-Lan 260, Taiwan

⁶ Department of International Business, Chung Yuan Christian University, Chung-Li 320, Taiwan

⁷ Institute of Environmental Technology, Vietnam Academy of Science and Technology, Hanoi 1000000, Vietnam

Energies 2018, 11(6), 1456; https://doi.org/10.3390/en11061456 - 5 Jun 2018

Cited by 11 | Viewed by 2832

Abstract

The reduction of high acid value (AV) of inedible jatropha oil (JO) by esterification with isopropanol (IPA), which is a common alcohol solvent waste in Taiwan’s high-tech industry, was studied. The decrease of AV is beneficial for the subsequent transesterification to produce JO [...] Read more.

The reduction of high acid value (AV) of inedible jatropha oil (JO) by esterification with isopropanol (IPA), which is a common alcohol solvent waste in Taiwan’s high-tech industry, was studied. The decrease of AV is beneficial for the subsequent transesterification to produce JO biodiesel (i.e., biodiesel of fatty acid isopropyl ester (FAIE)). Acid catalyst (H₂SO₄) and a novel mixing/emulsion technique using ultrasound irradiation (UI) were applied to promote and facilitate the esterification process. The results showed that increased IPA/oil molar ratio (M_IOE) can significantly reduce the AV, kinematic viscosity (KV), density (ρ_LO), and water content (M_W) of esterified JO, while also providing the benefit of enhancing the yield (Y_F) of biodiesel of FAIE. For example, with M_IOE = 5 at esterification temperature (T_E) = 394.2 K (393.8–394.7 K), a reduction of AV of 99.25% with Y_F of 67.15% can be achieved. Free fatty acid (FFA) was reduced from 18.06 wt.% to 0.14 wt.%, indicating 17.92 wt.% out of 18.06 wt.% of FFA was esterified to FAIE. As a result, among the Y_F of 67.15%, 49.23% (= 67.15 wt.% deducting 17.92 wt.%) was contributed by the transesterification of triglycerides. By esterification of high FFA-containing raw JO with acid catalyst, one can not only avoid saponification, but also reduce the loading of the subsequent alkali-catalyzed transesterification. Moreover, increasing T_E from 394.2 to 454.4 K further reduced AV (from 0.27 to 0.084 mg KOH/g) and M_W (from 0.27 to 0.043 wt.%), but, on the other hand, it increased KV (from 14.62 to 25.2 mm²/s) and ρ_LO (from 901.6 to 913.3 kg/m³), while it decreased Y_F (from 67.15 to 25.84%). In sum, IPA was successfully used as a replacement for methanol in the esterification of JO while UI provided mixing/emulsion along with heating resulting from cavitation for the system. Full article

(This article belongs to the Section A: Sustainable Energy)

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25 pages, 5085 KiB

Open AccessArticle

Optimal Planning Method of On-load Capacity Regulating Distribution Transformers in Urban Distribution Networks after Electric Energy Replacement Considering Uncertainties

by Yu Su¹, Niancheng Zhou¹, Qianggang Wang^1,*

, Chao Lei² and Jian Fang³

¹ State Key Laboratory of Power Transmission Equipment & System Security and New Technology; Chongqing University, Chongqing 400044, China

² State Grid Sichuan Electric Power Company Tianfu Power Supply Company, Chengdu 610000, China

³ China Southern Power Grid Guangzhou Power Supply Co., Ltd., Guangzhou 510000, China

Energies 2018, 11(6), 1457; https://doi.org/10.3390/en11061457 - 5 Jun 2018

Cited by 6 | Viewed by 2805

Abstract

Electric energy replacement is the umbrella term for the use of electric energy to replace oil (e.g., electric automobiles), coal (e.g., electric heating), and gas (e.g., electric cooking appliances), which increases the electrical load peak, causing greater valley/peak differences. On-load capacity regulating distribution [...] Read more.

Electric energy replacement is the umbrella term for the use of electric energy to replace oil (e.g., electric automobiles), coal (e.g., electric heating), and gas (e.g., electric cooking appliances), which increases the electrical load peak, causing greater valley/peak differences. On-load capacity regulating distribution transformers have been used to deal with loads with great valley/peak differences, so reasonably replacing conventional distribution transformers with on-load capacity regulating distribution transformers can effectively cope with load changes after electric energy replacement and reduce the no-load losses of distribution transformers. Before planning for on-load capacity regulating distribution transformers, the nodal effective load considering uncertainties within the life cycle after electric energy replacement was obtained by a Monte Carlo method. Then, according to the loss relation between on-load capacity regulating distribution transformers and conventional distribution transformers, three characteristic indexes of annual continuous apparent power curve and replacement criteria for on-load capacity regulating distribution transformers were put forward in this paper, and a set of distribution transformer replaceable points was obtained. Next, based on cost benefit analysis, a planning model of on-load capacity regulating distribution transformers which consists of investment profitability index within the life cycle, investment cost recouping index and capacity regulating cost index was put forward. The branch and bound method was used to solve the planning model within replaceable point set to obtain upgrading and reconstruction scheme of distribution transformers under a certain investment. Finally, planning analysis of on-load capacity regulating distribution transformers was carried out for electric energy replacement points in one urban distribution network under three scenes: certain load, uncertain load and nodal effective load considering uncertainties. Results showed that the planning method of on-load capacity regulating distribution transformers proposed in this paper was very feasible and is of great guiding significance to distribution transformer planning after electric energy replacement and the popularization of on-load capacity regulating distribution transformers. Full article

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17 pages, 1985 KiB

Open AccessArticle

Adaptive Higher-Order Sliding Mode Control for Islanding and Grid-Connected Operation of a Microgrid

by Yaozhen Han^1,2,*, Ronglin Ma¹

and Jinghan Cui^2,3

¹ School of Information Science and Electrical Engineering, Shandong Jiaotong University, Jinan 250357, China

² State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China

³ Department of Chemical & Materials Engineering Faculty of Engineering, University of Alberta, Edmonton, AB T5J4P6, Canada

Energies 2018, 11(6), 1459; https://doi.org/10.3390/en11061459 - 5 Jun 2018

Cited by 19 | Viewed by 2630

Abstract

Grid-connected and islanding operations of a microgrid are often influenced by system uncertainties, such as load parameter variations and unmodeled dynamics. This paper proposes a novel adaptive higher-order sliding mode (AHOSM) control strategy to enhance system robustness and handle an unknown uncertainty upper [...] Read more.

Grid-connected and islanding operations of a microgrid are often influenced by system uncertainties, such as load parameter variations and unmodeled dynamics. This paper proposes a novel adaptive higher-order sliding mode (AHOSM) control strategy to enhance system robustness and handle an unknown uncertainty upper bounds problem. Firstly, microgrid models with uncertainties are established under islanding and grid-connected modes. Then, adaptive third-order sliding mode and adaptive second-order sliding mode control schemes are respectively designed for the two modes. Microgrid models’ descriptions are divided into nominal part and uncertain part, and higher-order sliding mode (HOSM) control problems are transformed into finite time stability problems. Again, a scheduled law is proposed to increase or decrease sliding mode control gain adaptively. Real higher-order sliding modes are established, and finite time stability is proven based on the Lyapunov method. In order to achieve smooth mode transformation, an islanding mode detection algorithm is also adopted. The proposed control strategy accomplishes voltage control and current control of islanding mode and grid-connected mode. Control voltages are continuous, and uncertainty upper bounds are not required. Furthermore, adjustable control gain can further whittle control chattering. Simulation experiments verify the validity and robustness of the proposed control scheme. Full article

(This article belongs to the Section F: Electrical Engineering)

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18 pages, 2031 KiB

Open AccessArticle

Forecasting Electricity Market Price for End Users in EU28 until 2020—Main Factors of Influence

by Simon Pezzutto^1,*, Gianluca Grilli^2,3, Stefano Zambotti¹ and Stefan Dunjic⁴

¹ Institute for Renewable Energy, European Academy of Bozen/Bolzano (EURAC Research), Viale Druso 1, 39100 Bolzano, Italy

² Economic and Social Research Institute, Sir John Rogerson’s Quay, Dublin Dublin 2, Ireland

³ Trinity College Dublin, the University of Dublin, Dublin Dublin 2, Ireland

⁴ Joule Assets Europe Group SRL, Via Cesare Battisti 56, 41121 Modena, Italy

Energies 2018, 11(6), 1460; https://doi.org/10.3390/en11061460 - 5 Jun 2018

Cited by 29 | Viewed by 4782

Abstract

The scope of the present investigation is to provide a description of final electricity prices development in the context of deregulated electricity markets in EU28, up to 2020. We introduce a new methodology to predict long-term electricity market prices consisting of two parts: [...] Read more.

The scope of the present investigation is to provide a description of final electricity prices development in the context of deregulated electricity markets in EU28, up to 2020. We introduce a new methodology to predict long-term electricity market prices consisting of two parts: (1) a self-developed form of Porter’s five forces analysis (PFFA) determining that electricity markets are characterized by a fairly steady price increase. Dominant driving factors come out to be: (i) uncertainty of future electricity prices; (ii) regulatory complexity; and (iii) generation overcapacities. Similar conclusions derive from (2) a self-developed form of multiple-criteria decision analysis (MCDA). In this case, we find that the electricity market particularly depends on (i) market liberalization and (ii) the European Union (EU)’s economy growth. The applied methodologies provide a novel contribution in forecasting electricity price trends, by analyzing the sentiments, expectations, and knowledge of industry experts, through an assessment of factors influencing the market price and goals of key market participants. An extensive survey was conducted, interviewing experts all over Europe showed that the electricity market is subject to a future slight price increase. Full article

(This article belongs to the Special Issue Forecasting Models of Electricity Prices 2018)

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22 pages, 20426 KiB

Open AccessArticle

Three-Dimensional Peridynamic Model for Predicting Fracture Evolution during the Lithiation Process

by Hanlin Wang, Erkan Oterkus^* and Selda Oterkus

Department of Naval Architecture, Ocean and Marine Engineering, University of Strathclyde, Glasgow G4 0LZ, UK

Energies 2018, 11(6), 1461; https://doi.org/10.3390/en11061461 - 5 Jun 2018

Cited by 22 | Viewed by 3580

Abstract

Due to its large electric capacity, silicon has become one of the most promising electrode materials for lithium ion batteries. However, silicon undergoes large volumetric expansion and material stiffness reduction during the charging process. This can lead to fracture and failure of lithium-ion [...] Read more.

Due to its large electric capacity, silicon has become one of the most promising electrode materials for lithium ion batteries. However, silicon undergoes large volumetric expansion and material stiffness reduction during the charging process. This can lead to fracture and failure of lithium-ion batteries. Damage formation and evolution inside the electrode are influenced by the lithium ion concentration and electrode material. High stress gradients induced by heterogeneous deformation can lead to massive migration of lithium ions towards high geometrical singularity regions, such as crack edge regions, which increases the lithium ion concentration. Fully coupled mechanical diffusion equations are important in describing the mechanics of this problem. In this study, the three-dimensional peridynamic theory is presented to solve the coupled field problem. In addition, the newly developed peridynamic differential operator concept is utilized to convert partial differential equations into peridynamic form for the diffusion equation. Spherical and cylindrical shaped energy storage structures with different pre-existing penny-shaped cracks are considered to demonstrate the capability of the developed framework. It is shown that peridynamic theory is a suitable tool for predicting crack evolution during the lithiation process. Full article

(This article belongs to the Special Issue Computational Methods of Multi-Physics Problems)

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19 pages, 6626 KiB

Open AccessArticle

Loading History Effect on Creep Deformation of Rock

by Wendong Yang^1,*

, Ranjith Pathegama Gamage²

, Chenchen Huang¹, Guangyu Luo¹, Jingjing Guo¹ and Shugang Wang³

¹ College of Pipeline and Civil Engineering, China University of Petroleum, Qingdao 266580, China

² Deep Earth Energy Research Laboratory, Department of Civil Engineering, Monash University, 3800 Melbourne, VIC, Australia

³ Research Center of Geotechnical and Structural Engineering, Shandong University, Jinan 250061, China

Energies 2018, 11(6), 1462; https://doi.org/10.3390/en11061462 - 6 Jun 2018

Cited by 14 | Viewed by 3287

Abstract

The creep characteristics of rocks are very important for assessing the long-term stability of rock engineering structures. Two loading methods are commonly used in creep tests: single-step loading and multi-step loading. The multi-step loading method avoids the discrete influence of rock specimens on [...] Read more.

The creep characteristics of rocks are very important for assessing the long-term stability of rock engineering structures. Two loading methods are commonly used in creep tests: single-step loading and multi-step loading. The multi-step loading method avoids the discrete influence of rock specimens on creep deformation and is relatively time-efficient. It has been widely accepted by researchers in the area of creep testing. However, in the process of multi-step loading, later deformation is affected by earlier loading. This is a key problem in considering the effects of loading history. Therefore, we intend to analyze the deformation laws of rock under multi-step loading and propose a method to correct the disturbance of the preceding load. Based on multi-step loading creep tests, the memory effect of creep deformation caused by loading history is discussed in this paper. A time-affected correction method for the creep strains under multi-step loading is proposed. From this correction method, the creep deformation under single-step loading can be estimated by the super-position of creeps obtained by the dissolution of a multistep creep. We compare the time-affected correction method to the coordinate translation method without considering loading history. The results show that the former results are more consistent with the experimental results. The coordinate translation method produces a large error which should be avoided. Full article

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28 pages, 768 KiB

Open AccessArticle

Day Ahead Real Time Pricing and Critical Peak Pricing Based Power Scheduling for Smart Homes with Different Duty Cycles

by Nadeem Javaid^1,*

, Adnan Ahmed¹, Sohail Iqbal²

and Mahmood Ashraf³

¹ Department of Computer Science, COMSATS University Islamabad, Islamabad 44000, Pakistan

² School of Electrical Engineering and Computer Science, National University of Sciences and Technology, Islamabad 44000, Pakistan

³ Department of Computer Science, Federal Urdu University of Arts, Science and Technology, Islamabad 44000, Pakistan

Energies 2018, 11(6), 1464; https://doi.org/10.3390/en11061464 - 6 Jun 2018

Cited by 48 | Viewed by 4390

Abstract

In this paper, we propose a demand side management (DSM) scheme in the residential area for electricity cost and peak to average ratio (PAR) alleviation with maximum users’ satisfaction. For this purpose, we implement state-of-the-art algorithms: enhanced differential evolution (EDE) and teacher learning-based [...] Read more.

In this paper, we propose a demand side management (DSM) scheme in the residential area for electricity cost and peak to average ratio (PAR) alleviation with maximum users’ satisfaction. For this purpose, we implement state-of-the-art algorithms: enhanced differential evolution (EDE) and teacher learning-based optimization (TLBO). Furthermore, we propose a hybrid technique (HT) having the best features of both aforementioned algorithms. We consider a system model for single smart home as well as for a community (multiple homes) and each home consists of multiple appliances with different priorities. The priority is assigned (to each appliance) by electricity consumers and then the proposed scheme finds an optimal solution according to the assigned priorities. Day-ahead real time pricing (DA-RTP) and critical peak pricing (CPP) are used for electricity cost calculation. To validate our proposed scheme, simulations are carried out and results show that our proposed scheme efficiently achieves the aforementioned objectives. However, when we perform a comparison with existing schemes, HT outperforms other state-of-the-art schemes (TLBO and EDE) in terms of electricity cost and PAR reduction while minimizing the average waiting time. Full article

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13 pages, 4923 KiB

Open AccessArticle

Impact of Low Molecular Weight Acids on Oil Impregnated Paper Insulation Degradation

by Kakou D. Kouassi¹, Issouf Fofana^2,*

, Ladji Cissé¹, Yazid Hadjadj³, Kouba M. Lucia Yapi² and K. Ambroise Diby¹

¹ Ufr-SSMT Laboratory of Physics Condensed Matter and Technology, Université Félix Houphouet Boigny de Cocody-Abidjan, 22 BP 582 Abidjan 22, Côte d’Ivoire

² Research Chair on the Aging of Power Network Infrastructure (ViAHT), Université du Québec à Chicoutimi, Chicoutimi, QC G7H 2B1, Canada

³ Measurement Sciences and Standards, National Research Council Canada (NRC), Ottawa, ON K1A 0R6, Canada

Energies 2018, 11(6), 1465; https://doi.org/10.3390/en11061465 - 6 Jun 2018

Cited by 24 | Viewed by 4013

Abstract

Aging of a power transformer’s insulation system produces carboxylic acids. These acids—acetic, formic and levulinic—are absorbed by the paper insulating material, thus accelerating the degradation of the whole insulation system. In this contribution, the effect of these acids on the aging of oil-impregnated [...] Read more.

Aging of a power transformer’s insulation system produces carboxylic acids. These acids—acetic, formic and levulinic—are absorbed by the paper insulating material, thus accelerating the degradation of the whole insulation system. In this contribution, the effect of these acids on the aging of oil-impregnated paper insulation used in power transformer is reported. A laboratory aging experiment considering different concentrations of these three acids was performed to assess their effect on the insulation system’s degradation. Each acid was individually mixed with virgin oil, and a mixture of acids was also blended with oil. The paper’s degradation was assessed by the degree of polymerization (DPv). It was found that the DPv of paper aged with formic acid decreased much faster in comparison to the other acids. Full article

(This article belongs to the Special Issue Engineering Dielectric Liquid Applications)

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13 pages, 3315 KiB

Open AccessArticle

Biogas from Fresh Spring and Summer Grass: Effect of the Harvesting Period

by Alessandro Chiumenti¹, Davide Boscaro², Francesco Da Borso¹, Luigi Sartori² and Andrea Pezzuolo^2,*

¹ Department of Agricultural, Food, Animal and Environmental Sciences (DI4A), University of Udine, 33100 Udine, Italy

² Department of Agroforesty and Landscape, University of Padua, 35020 Legnaro, Italy

Energies 2018, 11(6), 1466; https://doi.org/10.3390/en11061466 - 6 Jun 2018

Cited by 38 | Viewed by 4425

Abstract

Yard trimmings, landscape management and agricultural practices determine the collection of biomass currently destined mainly to the production of a valuable soil amendant by composting. While composting requires energy, especially for the turning/aeration phases and for air treatment (i.e., biofilters in the case [...] Read more.

Yard trimmings, landscape management and agricultural practices determine the collection of biomass currently destined mainly to the production of a valuable soil amendant by composting. While composting requires energy, especially for the turning/aeration phases and for air treatment (i.e., biofilters in the case of enclosed systems), anaerobic digestion represents an energy positive process that results in production of biogas and digestate, which can be used as fuel and fertilizer, respectively. The focus of the present research was the evaluation of biogas and methane potential of grass collected in two different periods of the year (spring and summer) from riverbanks located in Northern Italy. The conversion to biogas of feedstocks is greatly influenced by the composition of the organic matter, content of cellulose, and lignin in particular. The production of biomass per hectare and the consequent biogas production were also evaluated. The experimental tests were performed on both samples of fresh grass in laboratory scale batch reactors, characterized by 4.0 L of volume and operated in mesophilic conditions (38 °C), for 40 days per cycle. The anaerobic digestion process was performed on a mixture of inoculum and grass, characterized by inoculum:substrate VS (volatile solids) ratio equal to 2. The inoculum was represented by digestate from a full-scale anaerobic digestion plant fed with dairy cow manure. The results in terms of biogas production, biogas quality (CH₄, CO₂, H₂S), and emissions from digestates (NH₃, CO₂ and CH₄) are presented in the paper. Total solids (TS), volatile solids (VS), pH, volatile fatty acids (VFA), alkalinity, acidity vs. alkalinity ratio, fibers (cellulose, lignin), and total Kjieldahl nitrogen (TKN) were determined both on input and output of the process. The biogas yield obtained from grass resulted higher than expected, quite similar to the yield obtained from energy crops, with Biomethane Potential (BMP) of 340.2 NL·kg⁻¹VS and of 307.7 NL·kg⁻¹VS, respectively, for spring and summer grass. Biogas quality was slightly lower for summer grass, perhaps in relation to the higher content of fibers (lignin). Alternatively, the yield of grass per surface was significantly different between spring and summer with the highest production in the summer. In fact, the results revealed a methane yield of 263 Nm³·ha⁻¹ and of 1181 Nm³·ha⁻¹, respectively for spring and summer grass. Full article

(This article belongs to the Special Issue Production and Utilization of Biogas)

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14 pages, 2630 KiB

Open AccessArticle

Monte Carlo-Based Comprehensive Assessment of PV Hosting Capacity and Energy Storage Impact in Realistic Finnish Low-Voltage Networks

by Ammar Arshad^*

, Verner Püvi

and Matti Lehtonen

Department of Electrical Engineering and Automation, Aalto University, Maarintie 8, 02150 Espoo, Finland

Energies 2018, 11(6), 1467; https://doi.org/10.3390/en11061467 - 6 Jun 2018

Cited by 28 | Viewed by 3271

Abstract

The direction taken towards sustainable power system and renewable energy generation is now irreversible. The power grid needs to host more renewable energy sources, such as solar power, and tackle power quality problems that come along with it. In this paper, firstly, the [...] Read more.

The direction taken towards sustainable power system and renewable energy generation is now irreversible. The power grid needs to host more renewable energy sources, such as solar power, and tackle power quality problems that come along with it. In this paper, firstly, the Hosting Capacities (HCs), of Photo-Voltaic (PV), were found for various regions and their limiting constraints were defined. Afterwards, comparison was made with the HC values obtained for different voltage value standards defined by various countries. Next, single-phase PV connection percentages in the network were defined that makes the voltage unbalance the limiting factor for HC. Lastly, the HC of the solar generation coupled with a Battery Energy Storage System (BESS) was assessed for the Finnish Low-Voltage (LV) grids. Different BESS-based scenarios were employed and their impact on voltage unbalance and HCs were observed. Finally, also the load voltage unbalance was incorporated to make the approach realistic and its impact on HC was analyzed. Results reveal that, depending on the connection strategy, the BESS can increase as well as decrease the HC based on voltage unbalance criteria. However, the load voltage unbalance has little effect on the solar HC values. Full article

(This article belongs to the Section F: Electrical Engineering)

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16 pages, 7666 KiB

Open AccessArticle

Improvement of Transient State Response through Feedforward Compensation Method of AC/DC Power Conversion System (PCS) Based on Space Vector Pulse Width Modulation (SVPWM)

by Seok-Jin Hong¹

, Seung-Wook Hyun¹, Kyung-Min Kang¹, Jung-Hyo Lee² and Chung-Yuen Won^1,*

¹ Information and Communication Engineering, Sungkyunkwan University, Suwon 16419, Korea

² Department of Electrical Engineering, Kunsan National University, Gunsan, Jeollabuk-do 54150, Korea

Energies 2018, 11(6), 1468; https://doi.org/10.3390/en11061468 - 6 Jun 2018

Cited by 5 | Viewed by 3939

Abstract

In a DC distribution system configured by AC/DC power conversion system (PCS), the voltage control performance of the AC/DC PCS determines the stability and reliability of the DC distribution grid. The DC voltage of grid is maintained by capacitor, thus transient voltage is [...] Read more.

In a DC distribution system configured by AC/DC power conversion system (PCS), the voltage control performance of the AC/DC PCS determines the stability and reliability of the DC distribution grid. The DC voltage of grid is maintained by capacitor, thus transient voltage is an inevitable problem when a grid is connected with a high amount of load or renewable energy. Space vector pulse width modulation (SVPWM) is well known as a stable modulation method and is used in AC/DC PCS and many types of topologies, but a solution for the transient states issue of DC link has not clearly been studied. In this paper, a feedforward compensation method based on the mathematical model of SVPWM is proposed to solve the transient state problem in a DC distribution system. The proposed method is verified by simulation and experiment. AC/DC PCS with the proposed feedforward compensation method has more robust DC voltage control characteristics. Full article

(This article belongs to the Special Issue Power Electronics 2018)

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13 pages, 587 KiB

Open AccessArticle

Passivity-Based Robust Output Voltage Tracking Control of DC/DC Boost Converter for Wind Power Systems

by Seok-Kyoon Kim

Department of Creative Convergence Engineering, Hanbat National University, Daejeon 341-58, Korea

Energies 2018, 11(6), 1469; https://doi.org/10.3390/en11061469 - 6 Jun 2018

Cited by 7 | Viewed by 3338

Abstract

This paper exhibits a passivity-based robust output voltage controller for DC/DC boost converters for wind power system applications. The proposed technique has two features. The first one is to introduce a nonlinear disturbance observer for estimating the disturbances arising from the load and [...] Read more.

This paper exhibits a passivity-based robust output voltage controller for DC/DC boost converters for wind power system applications. The proposed technique has two features. The first one is to introduce a nonlinear disturbance observer for estimating the disturbances arising from the load and parameter variations. The second one is to derive a proportional-type passivity-based output voltage tracking controller incorporating the disturbance observer output, which simplifies the control algorithm by removing the use of tracking error integrators and an anti-windup algorithm. These two features constitute the useful closed-loop properties called the performance recovery and offset-free properties. Numerical simulation results confirm the efficacy of the proposed scheme, where a wind power system including the proposed controller is emulated using the PowerSIM software. Full article

(This article belongs to the Special Issue Control and Nonlinear Dynamics on Energy Conversion Systems)

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12 pages, 2015 KiB

Open AccessArticle

Reaction Mechanism Reduction for Ozone-Enhanced CH₄/Air Combustion by a Combination of Directed Relation Graph with Error Propagation, Sensitivity Analysis and Quasi-Steady State Assumption

by Yingzu Liu¹, Zhihua Wang^1,*, Liang Li^2,*

, Kaidi Wan¹ and Kefa Cen¹

¹ State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China

² School of Engineering and Technology, University of Hertfordshire, Herts AL10 9AB, UK

Energies 2018, 11(6), 1470; https://doi.org/10.3390/en11061470 - 6 Jun 2018

Cited by 8 | Viewed by 3260

Abstract

In this study, an 18-steps, 22-species reduced global mechanism for ozone-enhanced CH₄/air combustion processes was derived by coupling GRI-Mech 3.0 and a sub-mechanism for ozone decomposition. Three methods, namely, direct relation graphics with error propagation, (DRGRP), sensitivity analysis (SA), and quasi-steady-state [...] Read more.

In this study, an 18-steps, 22-species reduced global mechanism for ozone-enhanced CH₄/air combustion processes was derived by coupling GRI-Mech 3.0 and a sub-mechanism for ozone decomposition. Three methods, namely, direct relation graphics with error propagation, (DRGRP), sensitivity analysis (SA), and quasi-steady-state assumption (QSSA), were used to downsize the detailed mechanism to the global mechanism. The verification of the accuracy of the skeletal mechanism in predicting the laminar flame speeds and distribution of the critical components showed that that the major species and the laminar flame speeds are well predicted by the skeletal mechanism. However, the pollutant NO was predicated inaccurately due to the precursors for generating NO were removed as redundant components. The laminar flame speeds calculated by the global mechanism fit the experimental data well. The comparisons of simulated results between the detailed mechanism and global mechanism were investigated and showed that the global mechanism could accurately predict the major and intermediate species and significantly reduced the time cost by 72%. Full article

(This article belongs to the Special Issue Fuels of the Future)

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12 pages, 1049 KiB

Open AccessArticle

Towards Efficient Sink Mobility in Underwater Wireless Sensor Networks

by Aqeb Yahya¹, Saif Ul Islam¹, Adnan Akhunzada¹, Ghufran Ahmed¹

, Shahaboddin Shamshirband^2,3,*

and Jaime Lloret⁴

¹ COMSATS Institute of Information Technology, Islamabad 45550, Pakistan

² Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam

³ Faculty of Information Technology, Ton Duc Thang University, Ho Chi Minh City, Vietnam

⁴ Integrated Management Coastal Research Institute, Universitat Politecnica de Valencia, 46022 Valencia, Spain

Energies 2018, 11(6), 1471; https://doi.org/10.3390/en11061471 - 6 Jun 2018

Cited by 33 | Viewed by 3499

Abstract

The unique characteristics of underwater environment such as long propagation delay, limited bandwidth, energy-constraint and non-uniform topology are big challenges in designing a routing protocol for underwater wireless sensor networks (UWSNs). In this paper, a novel routing scheme is proposed through which two [...] Read more.

The unique characteristics of underwater environment such as long propagation delay, limited bandwidth, energy-constraint and non-uniform topology are big challenges in designing a routing protocol for underwater wireless sensor networks (UWSNs). In this paper, a novel routing scheme is proposed through which two mobile sinks are used for efficient collection of sensed data packets. Moreover, a new metric “Mobile Sink Utility Ratio (MUR)” is also introduced that helps in measuring the usage of mobile sink in the collection of data packets. The proposed scheme is rigorously evaluated and compared with current state-of-the-art routing protocols. The simulation of the proposed scheme shows promising results in terms of throughput, network lifetime, packet drop ratio and MUR. Full article

(This article belongs to the Special Issue Energy Efficient and Smart Cities)

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16 pages, 7080 KiB

Open AccessArticle

Dual-Side Independent Switched Capacitor Control for Wireless Power Transfer with Coplanar Coils

by Chong Han, Bo Zhang^*, Zanfeng Fang, Dongyuan Qiu, Yanfeng Chen and Wenxun Xiao

School of Electric Power Engineering, South China University of Technology, Guangzhou 510641, China

Energies 2018, 11(6), 1472; https://doi.org/10.3390/en11061472 - 6 Jun 2018

Cited by 4 | Viewed by 2776

Abstract

The transfer coils of traditional Magnetic Coupling Resonant Wireless Power Transfer (MCR-WPT) systems are generally arranged coaxially. Coplanar coils can be an alternative scheme that can save more space in some applications, such as mobile phone wireless charging. However, the inductances of coplanar [...] Read more.

The transfer coils of traditional Magnetic Coupling Resonant Wireless Power Transfer (MCR-WPT) systems are generally arranged coaxially. Coplanar coils can be an alternative scheme that can save more space in some applications, such as mobile phone wireless charging. However, the inductances of coplanar coils are sensitive to foreign objects, which leads to a reduction in transfer efficiency and output power. A MCR-WPT system with coplanar coils and its control strategy are proposed in this paper. First, the characteristic of the mutual inductance and the magnetic field distribution between the coplanar coils are analyzed. A formula to calculate mutual inductance between the coplanar coils is proposed in this part. Secondly, the effect of inductance offset and frequency detuning on transfer efficiency and output power are analyzed. Then, the control strategy to eliminate frequency detuning is proposed. The proposed method implements switched capacitor to take place of constant compensation capacitor. The equivalent capacitance of switched capacitor is adjusted when the frequency detuning occurred. Thus, the inherent frequency of the resonant tank tracks the source frequency all the time. Since the switched capacitor of each side is controlled based on the quantity of their own, the control process is independent and does not require wireless communication. The complexity and the cost of the system are reduced. At the end of the article, the veracity of mutual inductance formula and the effectiveness of the proposed control strategy are verified by experiments. The experimental coils are placed in in an environment full of interference. The inductances of the coils are reduced from 224 μH to about 214 μH. The transfer efficiency and output power of MCR-WPT system with closed-loop control are higher than the one without control. At a distance of 5 cm from edge to edge, the transfer efficiency is 76.37% under the proposed control and 72.21% under no control. The output power is 285.66 W under the proposed control and 271.37 W under no control. Full article

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17 pages, 1411 KiB

Open AccessArticle

Cooperation or Localization in European Capacity Markets? A Coalitional Game over Graph Approach

by Giorgos Stamtsis^*,† and Haris Doukas^†

¹ Decision Support Systems Laboratory, School of Electrical and Computer Engineering, National Technical University of Athens, Iroon Politechniou 9, 157 80 Athens, Greece

^† The views and opinions expressed in this article are solely those of the authors.

Energies 2018, 11(6), 1473; https://doi.org/10.3390/en11061473 - 6 Jun 2018

Cited by 5 | Viewed by 2795

Abstract

Capacity markets, as a means to address the capacity adequacy issue, are constantly becoming an important part of the European internal electricity market. The debate focuses on how the capacity markets will be smoothly integrated in one Pan-European power market, without resulting in [...] Read more.

Capacity markets, as a means to address the capacity adequacy issue, are constantly becoming an important part of the European internal electricity market. The debate focuses on how the capacity markets will be smoothly integrated in one Pan-European power market, without resulting in multiple national fragmentations and consequently in economic efficiency losses. Cross-border participation and regional cooperation are considered as two sine qua non conditions in this respect. The present paper provides a coalitional game theoretical approach aiming to facilitate the cooperation of neighboring countries, when it comes to the security of electricity supply and the necessity of establishing a capacity market. Such an approach can support respective decisions about capacity markets cooperation as well as stress-test the benefits considering all cooperation possibilities. Full article

(This article belongs to the Section F: Electrical Engineering)

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17 pages, 11083 KiB

Open AccessArticle

Analysis of Pressure Fluctuations in a Prototype Pump-Turbine with Different Numbers of Runner Blades in Turbine Mode

by Deyou Li¹

, Yuekun Sun², Zhigang Zuo^2,*, Shuhong Liu^2,*, Hongjie Wang¹

and Zhenggui Li^1,3

¹ School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China

² State Key Laboratory of HydroScience and Engineering, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China

³ Key Laboratory of Fluid and Power Machinery (Xihua University), Ministry of Education Sichuan, Chengdu 610039, China

Energies 2018, 11(6), 1474; https://doi.org/10.3390/en11061474 - 6 Jun 2018

Cited by 22 | Viewed by 2968

Abstract

In pump-turbines, high pressure fluctuation is one of the crucial instabilities, which is harmful to the stable and effective operation of the entire unit. Extensive studies have been carried out to investigate pressure fluctuations (amplitude and frequency) at specific locations. However, limited research [...] Read more.

In pump-turbines, high pressure fluctuation is one of the crucial instabilities, which is harmful to the stable and effective operation of the entire unit. Extensive studies have been carried out to investigate pressure fluctuations (amplitude and frequency) at specific locations. However, limited research was conducted on the distribution of pressure fluctuations in turbine mode in a pump-turbine, as well as the influence of the number of runner blades on pressure fluctuations. Hence, in this study, three dimensional numerical simulations were performed to predict the distribution of pressure fluctuations with different numbers of runner blades in a prototype pump-turbine in turbine mode using the shear stress transport (SST) k-ω turbulence model. Three operating points with the same hydraulic head and different mass flow rates were simulated. The distribution of pressure fluctuation components of blade passing frequency and its harmonics in the direction along the whole flow path, as well as along the circumferential direction, was presented. The mass flow rate and number of runner blades have great influence on the distribution of pressure fluctuations, especially at blade passing frequency along circumferential direction. The mass flow rate mainly affects the position of peak pressure fluctuations, while the number of runner blades mainly changes the number of peak pressure fluctuations. Additionally, the number of runner blades influences the dominant frequencies of pressure fluctuations especially in the spiral casing and draft tube. Full article

(This article belongs to the Section D: Energy Storage and Application)

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18 pages, 3063 KiB

Open AccessArticle

Feasibility Study of Self-Sufficient Solar Cooling Façade Applications in Different Warm Regions

by Alejandro Prieto^1,*

, Ulrich Knaack¹, Thomas Auer² and Tillmann Klein¹

¹ Façade Research Group, Department of Architectural, Faculty of Architecture and the Built Environment, Engineering + Technology, Delft University of Technology, Julianalaan 134, 2628BL Delft, The Netherlands

² Department of Architecture, Technical University of Munich, Arcisstraße 21, 80333 Munich, Germany

Energies 2018, 11(6), 1475; https://doi.org/10.3390/en11061475 - 6 Jun 2018

Cited by 7 | Viewed by 3181

Abstract

Small-scale systems and integrated concepts are currently being explored to promote the widespread application of solar cooling technologies in buildings. This article seeks to expand application possibilities by exploring the feasibility of solar cooling integrated façades, as decentralized self-sufficient cooling modules on different [...] Read more.

Small-scale systems and integrated concepts are currently being explored to promote the widespread application of solar cooling technologies in buildings. This article seeks to expand application possibilities by exploring the feasibility of solar cooling integrated façades, as decentralized self-sufficient cooling modules on different warm regions. The climate feasibility of solar electric and solar thermal concepts is evaluated based on solar availability and local cooling demands to be met by current technical possibilities. Numerical calculations are employed for the evaluation, considering statistical climate data; cooling demands per orientation from several simulated scenarios; and state-of-the-art efficiency values of solar cooling technologies, from the specialized literature. The main results show that, in general, warm-dry climates and east/west orientations are better suited for solar cooling façade applications, compared to humid regions and north/south orientations. Results from the base scenario show promising potential for solar thermal technologies, reaching a theoretical solar fraction of 100% in several cases. Application possibilities expand when higher solar array area and lower tilt angle on panels are considered, but these imply aesthetical and constructional constraints for façade design. Finally, recommendations are drafted considering prospects for the exploration of suitable technologies for each location, and façade design considerations for the optimization of the solar input per orientation. Full article

(This article belongs to the Special Issue Building renewable energy and thermal energy storage system 2018)

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25 pages, 3912 KiB

Open AccessArticle

Economic Evaluation of Actively Consuming Wind Power for an Integrated Energy System Based on Game Theory

by Xiaojuan Han^1,*, Feng Wang¹, Chunguang Tian², Kai Xue³ and Junfeng Zhang³

¹ School of Control and Computer Engineering, North China Electric Power University, Beijing 102206, China

² Electrical Power Research Institute of Jilin Electric Power Corporation, Changchun 130021, China

³ Jilin Provincial Electric Power Training Center, Changchun 130021, China

Energies 2018, 11(6), 1476; https://doi.org/10.3390/en11061476 - 6 Jun 2018

Cited by 18 | Viewed by 2403

Abstract

Facing the growing problem of the curtailed wind during winter heating periods in the north of China, a flexible control method of wind power heating using the integrated energy system to consume the curtailed wind is proposed. Energy storage technology is introduced to [...] Read more.

Facing the growing problem of the curtailed wind during winter heating periods in the north of China, a flexible control method of wind power heating using the integrated energy system to consume the curtailed wind is proposed. Energy storage technology is introduced to coordinate regenerative electric boilers to match the fast fluctuation of wind power. The consuming model of the curtailed wind for the integrated energy system is established under three models through the study of the consumption mechanisms for the curtailed wind. The “wind power-energy storage system” and “wind power-regenerative electric boiler” are regarded as the game’s participants, and the maximum daily benefit of the system is regarded as the objective function, an economic evaluation model of the integrated energy system to consume the curtailed wind based on game theory is established. For comparative analysis, the model is respectively solved by particle swarm optimization (PSO) and the firefly algorithm (FA). The effectiveness of the model is verified by the actual operation data of a wind power heating demonstration project in China. The simulation results show that the most economy benefits of the overall system can be obtained by using energy storage systems to coordinate regenerative electric boilers, which provides a theoretical basis for the consumption of the curtailed wind. Full article

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20 pages, 1710 KiB

Open AccessArticle

A Dynamic Model for Indoor Temperature Prediction in Buildings

by Petri Hietaharju^*

, Mika Ruusunen and Kauko Leiviskä

Control Engineering, University of Oulu, P.O. Box 4300, FI-90014 Oulu, Finland

Energies 2018, 11(6), 1477; https://doi.org/10.3390/en11061477 - 6 Jun 2018

Cited by 42 | Viewed by 5226

Abstract

A novel dynamic model for the temperature inside buildings is presented, aiming to improve energy efficiency by providing predictive information on the heat demand. To analyse the performance and generalizability of the modelling approach, real measurement data was gathered from five different types [...] Read more.

A novel dynamic model for the temperature inside buildings is presented, aiming to improve energy efficiency by providing predictive information on the heat demand. To analyse the performance and generalizability of the modelling approach, real measurement data was gathered from five different types of buildings. Easily available data from various sources was utilized. The chosen model structure leads to a minimal number of input variables and free parameters. Simulations with real data from five buildings, and applying the identical model structure showed that the average modelling error during the 28-h prediction horizon was constantly below 5%. The results thus demonstrate that the model structure can be standardized and easily applied to predict the indoor temperatures of large buildings. This would finally enable demand side management and the predictive optimization of the heat demand at city level. Full article

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12 pages, 3611 KiB

Open AccessArticle

The Influence of LED Lighting Sources on the Nature of Power Factor

by Miroslaw Wlas¹

and Stanislaw Galla^2,*

¹ Departments of Electric Drivers and Energy Conversions, Faculty of Electrical and Control Engineering, Gdansk University of Technology, ul. G. Narutowicza 11/12, 80-288 Gdansk, Poland

² Departments of Metrology and Optoelectronics, Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, ul. G. Narutowicza 11/12, 80-288 Gdansk, Poland

Energies 2018, 11(6), 1479; https://doi.org/10.3390/en11061479 - 6 Jun 2018

Cited by 12 | Viewed by 2902

Abstract

This article presents measurements of electric power absorbed by a newly built facility for office and scientific research activities. These measurements highlighted the need for compensation of capacitive reactive power—not predicted by the designer—due to the vast use of LED lighting in the [...] Read more.

This article presents measurements of electric power absorbed by a newly built facility for office and scientific research activities. These measurements highlighted the need for compensation of capacitive reactive power—not predicted by the designer—due to the vast use of LED lighting in the facility. The article also describes a reactive power compensation system, designed on the basis of the above-mentioned measurements, and the introduced control and measurement system that enables on-site monitoring and online analysis of consumed energy and power. The research was carried out using popular LED lighting sources available on the local market (Poland). Basic electrical parameters of the locally available LEDs were measured as a function of the changes in harmonic levels occurring in the supply voltage. The test illustrated that samples were characterized by a very low power factor, which decreased as the level of harmonic disturbances increased. On the basis of the measurements, the authors suggest that obligatory requirements should be introduced in regard to the minimum power factor at the level of 0.9 for popular LED lighting sources (below 25 W). Full article

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13 pages, 2231 KiB

Open AccessArticle

Decoupling Greenhouse Gas Emissions from Crop Production: A Case Study in the Heilongjiang Land Reclamation Area, China

by Yu Zhang

, Xiaojiao Zou, Caifen Xu and Qingshan Yang^*

School of Geographical Science, Northeast Normal University, Changchun 130024, China

Energies 2018, 11(6), 1480; https://doi.org/10.3390/en11061480 - 6 Jun 2018

Cited by 17 | Viewed by 3053

Abstract

Modern agriculture contributes significantly to greenhouse gas emissions in several ways. From the perspective of sustainability assessment, it is not enough to evaluate mitigation measures that rely only on emissions reductions. In this article, we use the method of decoupling analysis to construct [...] Read more.

Modern agriculture contributes significantly to greenhouse gas emissions in several ways. From the perspective of sustainability assessment, it is not enough to evaluate mitigation measures that rely only on emissions reductions. In this article, we use the method of decoupling analysis to construct a decoupling index based on carbon footprint and crop yield and evaluate the relationship between crop production and greenhouse gas emissions using the most modern grain production base in China as a case study. The results indicate that a weak but variable decoupling trend occurred from 2001 to 2015 and that each branch achieved on average a weak decoupling across the study period. In addition, rice production constituted 80% of the regional carbon footprint in a crop’s life cycle. The results of our analysis of rice production show that weak decoupling was the most common outcome but was not consistent because a weak coupling occurred in 2015. Each branch on average achieved a weak decoupling except for the SH branch. Our research indicates that high agricultural material inputs with low utilization efficiency contributed to the poor relationship between crop production and greenhouse gas emissions in the study area. Fertilizer, especially N fertilizer, was an important contributor to the total greenhouse gas emissions of crop production. As a supplement to carbon footprint assessment, this decoupling analysis helps local decision-makers diagnose the level of green growth, identify key options to mitigate greenhouse gas emissions from agriculture, and adopt more targeted interventions towards sustainable agriculture. Full article

(This article belongs to the Special Issue Modeling and Simulation of Carbon Emission Related Issues)

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20 pages, 5534 KiB

Open AccessArticle

Strong Tracking of a H-Infinity Filter in Lithium-Ion Battery State of Charge Estimation

by Bizhong Xia¹, Zheng Zhang^1,*, Zizhou Lao¹, Wei Wang², Wei Sun², Yongzhi Lai² and Mingwang Wang²

¹ Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, Guangdong, China

² Sunwoda Electronic Co. Ltd., Shenzhen 518108, Guangdong, China

Energies 2018, 11(6), 1481; https://doi.org/10.3390/en11061481 - 6 Jun 2018

Cited by 34 | Viewed by 3700

Abstract

The accuracy of state-of-charge (SOC) estimation, one of the most important functions of a battery management system (BMS), is the basis for the proper operation of an electric vehicle. This study proposes a method for accurate SOC estimation. To achieve a balance between [...] Read more.

The accuracy of state-of-charge (SOC) estimation, one of the most important functions of a battery management system (BMS), is the basis for the proper operation of an electric vehicle. This study proposes a method for accurate SOC estimation. To achieve a balance between accuracy and simplicity, a second-order resistor–capacitor equivalent circuit model is applied before the algorithm is deduced, and the parameters of the established model are determined using a fitting technique. Battery state space equations are then described. A strong tracking H-infinity filter (STHF) is proposed based on an H-infinity filter (HF) and a strong tracking filter. By introducing a suboptimal fading factor, the STHF approach can use the relevant information in the estimation residual sequence to update the estimation results. To verify the robustness of this approach, battery test experiments are performed at different temperatures on lithium-ion batteries. Finally, the SOC estimation results obtained using the STHF suggest that the STHF method exhibits high robustness against the measured noises and initial error. For comparison, the estimation results of the commonly used extended Kalman filter (EKF) and HF methods are also displayed. It is suggested that the proposed STHF approach obtains a more accurate SOC estimation. Full article

(This article belongs to the Section D: Energy Storage and Application)

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20 pages, 14447 KiB

Open AccessArticle

An Efficient Controlled Islanding Strategy for Large-Scale AC/DC Power Systems

by Changcheng Song¹, Xiaodong Chu^1,*, Linlin Ma², Xiaobo Wang², Xin Li², Liang Wang², Bing Zhang² and Cheng Wu²

¹ Key Laboratory of Power System Intelligent Dispatch and Control of Ministry of Education, Shandong University, 17923 Jingshi Road, Jinan 250061, China

² Shandong Electric Power Dispatching and Control Center, Jinan 250001, China

Energies 2018, 11(6), 1483; https://doi.org/10.3390/en11061483 - 6 Jun 2018

Cited by 2 | Viewed by 2558

Abstract

A controlled islanding strategy should be carefully designed to prevent power systems from overall collapse caused by extremely serious faults, which is of high computational complexity for large-scale AC/DC power systems. An efficient controlled islanding strategy for large-scale AC/DC power systems is proposed [...] Read more.

A controlled islanding strategy should be carefully designed to prevent power systems from overall collapse caused by extremely serious faults, which is of high computational complexity for large-scale AC/DC power systems. An efficient controlled islanding strategy for large-scale AC/DC power systems is proposed in this paper. The original power system is first reduced to decrease the computational complexity. The reduced power system is then partitioned into a number of dispatch areas by using the breadth-first search algorithm. Next, the reduced power system is recovered to obtain the detailed information of the dispatch areas. The spectral clustering algorithm is used to cluster the large number of dispatch areas into a small number of islanding areas. Finally, the controlled islanding strategy is verified by assessing the steady and dynamic performance of the power system. The feasibility, efficacy, and adaptability of the controlled islanding strategy are demonstrated by the case study of a large-scale multi-infeed AC/DC power system in China. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 4829 KiB

Open AccessArticle

Evaluation of a Distributed Photovoltaic System in Grid-Connected and Standalone Applications by Different MPPT Algorithms

by Ru-Min Chao^1,2,*, Shih-Hung Ko¹, Hung-Ku Lin¹ and I-Kai Wang¹

¹ Department of Systems and Naval Mechatronics Engineering, NCKU, Tainan 701, Taiwan

² Research Center for Energy Technology and Strategy, NCKU, Tainan 701, Taiwan

Energies 2018, 11(6), 1484; https://doi.org/10.3390/en11061484 - 7 Jun 2018

Cited by 13 | Viewed by 4078

Abstract

Due to the shortage of fossil fuel and the environmental pollution problem, solar energy applications have drawn a lot of attention worldwide. This paper reports the use of the latest patented distributed photovoltaic (PV) power system design, including the two possible maximum power [...] Read more.

Due to the shortage of fossil fuel and the environmental pollution problem, solar energy applications have drawn a lot of attention worldwide. This paper reports the use of the latest patented distributed photovoltaic (PV) power system design, including the two possible maximum power point tracking (MPPT) algorithms, a power optimizer, and a PV power controller, in grid-connected and standalone applications. A distributed PV system with four amorphous silicon thin-film solar panels is used to evaluate both the quadratic maximization (QM) and the Steepest descent (SD) MPPT algorithms. The system’s design is different for the QM or the SD MPPT algorithm being used. The test result for the grid-connected silicon-based PV panels will also be reported. Considering the settling time for the power optimizer to be 20 ms, the test result shows that the tracking time for the QM method is close to 200 ms, which is faster when compared with the SD method whose tracking time is 500 ms. Besides this, the use of the QM method provides a more stable power output since the tracking is restricted by a local power optimizer rather than the global tracking the SD method uses. For a standalone PV application, a solar-powered boat design with 18 PV panels using a cascaded MPPT controller is introduced, and it provides flexibility in system design and the effective use of photovoltaic energy. Full article

(This article belongs to the Special Issue Selected Papers from the IEEE ICASI 2018)

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13 pages, 22838 KiB

Open AccessArticle

Computational Fluid Dynamics (CFD) Investigation of Wind Turbine Nacelle Separation Accident over Complex Terrain in Japan

by Takanori Uchida

Research Institute for Applied Mechanics (RIAM), Kyushu University, 6-1 Kasuga-kouen, Kasuga, Fukuoka 816-8580, Japan

Energies 2018, 11(6), 1485; https://doi.org/10.3390/en11061485 - 7 Jun 2018

Cited by 11 | Viewed by 4972

Abstract

We have developed an unsteady and non-linear wind synopsis simulator called RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over Complex Terrain) to simulate the airflow on a micro scale, i.e., a few tens of km or less. In [...] Read more.

We have developed an unsteady and non-linear wind synopsis simulator called RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over Complex Terrain) to simulate the airflow on a micro scale, i.e., a few tens of km or less. In RIAM-COMPACT, the large-eddy simulation (LES) has been adopted for turbulence modeling. LES is a technique in which the structures of relatively large eddies are directly simulated and smaller eddies are modeled using a sub-grid scale model. In the present study, we conducted numerical wind diagnoses for the Taikoyama Wind Farm nacelle separation accident in Japan. The simulation results suggest that all six wind turbines at Taikoyama Wind Farm are subject to significant influence from separated flow (terrain-induced turbulence) which is generated due to the topographic irregularities in the vicinity of the wind turbines. A proposal was also made on reconstruction of the wind farm. Full article

(This article belongs to the Collection Wind Turbines)

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16 pages, 2515 KiB

Open AccessArticle

Small-Signal Performance of Type 4 Wind Turbine Generator-Based Clusters in Power Systems

by Wuhui Chen^1,*

, Zaixing Teng¹, Junhua Zhao^2,*

and Jing Qiu^3,*

¹ School of Electrical and Information Engineering, The Jiangsu University, Zhenjiang 212013, China

² School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen 518100, China

³ School of Electrical and Information Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Energies 2018, 11(6), 1486; https://doi.org/10.3390/en11061486 - 7 Jun 2018

Cited by 7 | Viewed by 2912

Abstract

The impact of Type 4 wind turbine generator (WTG)-based 10 million megawatt clusters (TMMC) on small-signal dynamics of power systems was investigated using the second-generation generic models (GM) of Western Electricity Coordinating Council (WECC). A WTG participation index (WTG PI) was defined to [...] Read more.

The impact of Type 4 wind turbine generator (WTG)-based 10 million megawatt clusters (TMMC) on small-signal dynamics of power systems was investigated using the second-generation generic models (GM) of Western Electricity Coordinating Council (WECC). A WTG participation index (WTG PI) was defined to investigate the impact of Type 4 WTGs on the traditional interarea electromechanical modes. To identify the new electromechanical modes dominated by Type 4 WTGs, an identification factor (IF) was also defined using participation factors. Given the increasing penetration of Type 4 WTGs replacing synchronous generators, the changed law of damping and frequencies of the traditional interarea modes was also investigated using the WTG PI. One new type of electromechanical mode dominated by Type 4 WTGs was identified by using the defined IF. These new modes can be divided into two categories: strong-interaction modes and weak-interaction modes, depending on the number of participating WTGs. The strong-interaction modes dominated by Type 4 WTGs can result in widely spread power oscillations in power systems. The results of small-signal analysis were validated by time domain simulation and mode detection. Full article

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16 pages, 1008 KiB

Open AccessArticle

Computational Intelligence Techniques Applied to the Day Ahead PV Output Power Forecast: PHANN, SNO and Mixed

by Emanuele Ogliari^*

, Alessandro Niccolai^*

, Sonia Leva

and Riccardo E. Zich

Dipartimento di Energia, Politecnico di Milano, Via Lambruschini 4, 20156 Milano, Italy

Energies 2018, 11(6), 1487; https://doi.org/10.3390/en11061487 - 7 Jun 2018

Cited by 33 | Viewed by 3326

Abstract

An accurate forecast of the exploitable energy from Renewable Energy Sources is extremely important for the stability issues of the electric grid and the reliability of the bidding markets. This paper presents a comparison among different forecasting methods of the photovoltaic output power [...] Read more.

An accurate forecast of the exploitable energy from Renewable Energy Sources is extremely important for the stability issues of the electric grid and the reliability of the bidding markets. This paper presents a comparison among different forecasting methods of the photovoltaic output power introducing a new method that mixes some peculiarities of the others: the Physical Hybrid Artificial Neural Network and the five parameters model estimated by the Social Network Optimization. In particular, the day-ahead forecasts evaluated against real data measured for two years in an existing photovoltaic plant located in Milan, Italy, are compared by means both new and the most common error indicators. Results reported in this work show the best forecasting capability of the new “mixed method” which scored the best forecast skill and Enveloped Mean Absolute Error on a yearly basis (47% and 24.67%, respectively). Full article

(This article belongs to the Special Issue Solar and Wind Energy Forecasting)

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19 pages, 2294 KiB

Open AccessArticle

Optimal Dispatch of a Virtual Power Plant Considering Demand Response and Carbon Trading

by Zuoyu Liu¹, Weimin Zheng², Feng Qi¹, Lei Wang³, Bo Zou³, Fushuan Wen^4,5,*

and You Xue¹

¹ School of Electrical Engineering, Zhejiang University, No. 38 Zheda Rd., Hangzhou 310027, China

² State Grid Zhejiang Electric Power Co., Ltd., No. 8 Huanglong Rd., Hangzhou 310007, China

³ State Grid Zhejiang Economic Research Institute, No.1 Nanfu Road, Hangzhou 310008, China

⁴ Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam

⁵ Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam

Energies 2018, 11(6), 1488; https://doi.org/10.3390/en11061488 - 7 Jun 2018

Cited by 47 | Viewed by 4674

Abstract

The implementation of demand response (DR) could contribute to significant economic benefits meanwhile simultaneously enhancing the security of the concerned power system. A well-designed carbon emission trading mechanism provides an efficient way to achieve emission reduction targets. Given this background, a virtual power [...] Read more.

The implementation of demand response (DR) could contribute to significant economic benefits meanwhile simultaneously enhancing the security of the concerned power system. A well-designed carbon emission trading mechanism provides an efficient way to achieve emission reduction targets. Given this background, a virtual power plant (VPP) including demand response resources, gas turbines, wind power and photovoltaics with participation in carbon emission trading is examined in this work, and an optimal dispatching model of the VPP presented. First, the carbon emission trading mechanism is briefly described, and the framework of optimal dispatching in the VPP discussed. Then, probabilistic models are utilized to address the uncertainties in the predicted generation outputs of wind power and photovoltaics. Demand side management (DSM) is next implemented by modeling flexible loads such as the chilled water thermal storage air conditioning systems (CSACSs) and electric vehicles (EVs). On this basis, a mixed integer linear programming (MILP) model for the optimal dispatching problem in the VPP is established, with an objective of maximizing the total profit of the VPP considering the costs of power generation and carbon emission trading as well as charging/discharging of EVs. Finally, the developed dispatching model is solved by the commercial CPLEX solver based on the YALMIP/MATLAB (version 8.4) toolbox, and sample examples are served for demonstrating the essential features of the proposed method. Full article

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17 pages, 1260 KiB

Open AccessArticle

Scenario Analysis of Carbon Emissions of Beijing-Tianjin-Hebei

by Jianguo Zhou, Baoling Jin^*, Shijuan Du and Ping Zhang

Department of Economics and Management, North China Electric Power University, Baoding 071003, China

Energies 2018, 11(6), 1489; https://doi.org/10.3390/en11061489 - 7 Jun 2018

Cited by 19 | Viewed by 2740

Abstract

This paper utilizes the generalized Fisher index (GFI) to decompose the factors of carbon emission and exploits improved particle swarm optimization-back propagation (IPSO-BP) neural network modelling to predict the primary energy consumption CO₂ emissions in different scenarios of Beijing-Tianjin-Hebei region. The results [...] Read more.

This paper utilizes the generalized Fisher index (GFI) to decompose the factors of carbon emission and exploits improved particle swarm optimization-back propagation (IPSO-BP) neural network modelling to predict the primary energy consumption CO₂ emissions in different scenarios of Beijing-Tianjin-Hebei region. The results show that (1) the main factors that affect the region are economic factors, followed by population size. On the contrary, the factors that mainly inhibit the carbon emissions are energy structure and energy intensity. (2) The peak year of carbon emission changes with the different scenarios. In a low carbon scenario, the carbon emission will have a decline stage between 2015 and 2018, then the carbon emission will be in the ascending phase during 2019–2030. In basic and high carbon scenarios, the carbon emission will peak in 2025 and 2028, respectively. Full article

(This article belongs to the Section L: Energy Sources)

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15 pages, 2967 KiB

Open AccessArticle

Comparative Analysis of Lithium-Ion Battery Resistance Estimation Techniques for Battery Management Systems

by Manoj Mathew¹

, Stefan Janhunen², Mahir Rashid¹, Frank Long¹ and Michael Fowler^1,*

¹ Department of Chemical Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada

² Nuvation Energy, 40 Bathurst Dr, Waterloo, ON N2V 1V6, Canada

Energies 2018, 11(6), 1490; https://doi.org/10.3390/en11061490 - 7 Jun 2018

Cited by 49 | Viewed by 5768

Abstract

Safe and efficient operation of a battery pack requires a battery management system (BMS) that can accurately predict the pack state-of-heath (SOH). Although there is no universal definition for battery SOH, it is often defined based on the increase in the battery’s internal [...] Read more.

Safe and efficient operation of a battery pack requires a battery management system (BMS) that can accurately predict the pack state-of-heath (SOH). Although there is no universal definition for battery SOH, it is often defined based on the increase in the battery’s internal resistance. Techniques such as extended Kalman filter (EKF) and recursive least squares (RLS) are two frequently used approaches for online estimation of this resistance. These two methods can, however, be computationally expensive, especially in the case of a battery pack composed of hundreds of cells. In addition, both methods require a battery model as well as chemistry specific parameters. Therefore, this paper investigates the performance of a direct resistance estimation (DRE) technique that requires minimal computational resources and can be implemented without any training data. This approach estimates the ohmic resistance only when the battery experiences sharp pulses in current. Comparison of results from the three algorithms shows that the DRE algorithm can accurately identify a degraded cell under various operating conditions while significantly reducing the required computational complexity. The findings will further advance diagnostic techniques for the identification of a weak cell in a large battery pack. Full article

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13 pages, 5042 KiB

Open AccessArticle

Fault Detection and Location of IGBT Short-Circuit Failure in Modular Multilevel Converters

by Bin Jiang^*, Yanfeng Gong and Yan Li

Department of Electrical and Electronic Engineering, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(6), 1492; https://doi.org/10.3390/en11061492 - 7 Jun 2018

Cited by 7 | Viewed by 4910

Abstract

A single fault detection and location for Modular Multilevel Converter (MMC) is of great significance, as numbers of sub-modules (SMs) in MMC are connected in series. In this paper, a novel fault detection and location method is proposed for MMC in terms of [...] Read more.

A single fault detection and location for Modular Multilevel Converter (MMC) is of great significance, as numbers of sub-modules (SMs) in MMC are connected in series. In this paper, a novel fault detection and location method is proposed for MMC in terms of the Insulated Gate Bipolar Translator (IGBT) short-circuit failure in SM. The characteristics of IGBT short-circuit failures are analyzed, based on which a Differential Comparison Low-Voltage Detection Method (DCLVDM) is proposed to detect the short-circuit fault. Lastly, the faulty IGBT is located based on the capacitor voltage of the faulty SM by Continuous Wavelet Transform (CWT). Simulations have been done in the simulation software PSCAD/EMTDC and the results confirm the validity and reliability of the proposed method. Full article

(This article belongs to the Special Issue Multilevel Converters: Analysis, Modulation, Topologies, and Applications)

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16 pages, 3931 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

An Assessment of the Sustainability of Lignocellulosic Bioethanol Production from Wastes in Iceland

by Sahar Safarian^* and Runar Unnthorsson^*

Department of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland, Hjardarhagi 6, 107 Reykjavik, Iceland

Energies 2018, 11(6), 1493; https://doi.org/10.3390/en11061493 - 7 Jun 2018

Cited by 39 | Viewed by 5934

Abstract

This paper describes the development of a model to comprehensively assess the sustainability impacts of producing lignocellulosic bioethanol from various types of municipal organic wastes (MOWs) in Iceland: paper and paperboard, timber and wood and garden waste. The tool integrates significant economic, energy, [...] Read more.

This paper describes the development of a model to comprehensively assess the sustainability impacts of producing lignocellulosic bioethanol from various types of municipal organic wastes (MOWs) in Iceland: paper and paperboard, timber and wood and garden waste. The tool integrates significant economic, energy, environmental and technical aspects to analyse and rank twelve systems using the most common pretreatment technologies: dilute acid, dilute alkali, hot water and steam explosion. The results show that among the MOWs, paper and paperboard have higher positive rankings under most assessments. Steam explosion is also ranked at the top from the economic, energy and environmental perspectives, followed by the hot water method for paper and timber wastes. Finally, a potential evaluation of total wastes and bioethanol production in Iceland is carried out. The results show that the average production of lignocellulosic bioethanol in 2015 could be 12.5, 11 and 3 thousand tons from paper, timber and garden wastes, respectively, and that production could reach about 15.9, 13.7 and 3.7 thousand tons, respectively, by 2030. Full article

(This article belongs to the Special Issue BioEnergy and BioChemicals Production from Biomass and Residual Resources)

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20 pages, 3340 KiB

Open AccessArticle

The Effect of Oil Properties on the Supercritical CO₂ Diffusion Coefficient under Tight Reservoir Conditions

by Chao Zhang^†

, Chenyu Qiao^†

, Songyan Li^* and Zhaomin Li

¹ College of Petroleum Engineering, China University of Petroleum, Qingdao 266580, China

^† These authors contributed equally to this work.

Energies 2018, 11(6), 1495; https://doi.org/10.3390/en11061495 - 8 Jun 2018

Cited by 29 | Viewed by 4610

Abstract

In this paper, a generalized methodology has been developed to determine the diffusion coefficient of supercritical CO₂ in cores that are saturated with different oil samples, under reservoir conditions. In theory, a mathematical model that combines Fick’s diffusion equation and the Peng-Robinson [...] Read more.

In this paper, a generalized methodology has been developed to determine the diffusion coefficient of supercritical CO₂ in cores that are saturated with different oil samples, under reservoir conditions. In theory, a mathematical model that combines Fick’s diffusion equation and the Peng-Robinson equation of state has been established to describe the mass transfer process. In experiments, the pressure decay method has been employed, and the CO₂ diffusion coefficient can be determined once the experimental data match the computational result of the theoretical model. Six oil samples with different compositions (oil samples A to F) are introduced in this study, and the results show that the supercritical CO₂ diffusion coefficient decreases gradually from oil samples A to F. The changing properties of oil can account for the decrease in the CO₂ diffusion coefficient in two aspects. First, the increasing viscosity of oil slows down the speed of the mass transfer process. Second, the increase in the proportion of heavy components in oil enlarges the mass transfer resistance. According to the results of this work, a lower viscosity and lighter components of oil can facilitate the mass transfer process. Full article

(This article belongs to the Special Issue Emerging Advances in Petrophysics: Porous Media Characterization and Modeling of Multiphase Flow)

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12 pages, 6138 KiB

Open AccessArticle

The Mechanism and Diagnosis of Insulation Deterioration Caused by Moisture Ingress into Oil-Impregnated Paper Bushing

by Bo Qi^1,*

, Quanmin Dai¹

, Chengrong Li¹, Zipeng Zeng¹, Mingli Fu² and Ran Zhuo²

¹ State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Chang Ping District, Beijing 102206, China

² Electric Power Research Institute of China Southern Power Grid, Guangzhou 510530, China

Energies 2018, 11(6), 1496; https://doi.org/10.3390/en11061496 - 8 Jun 2018

Cited by 17 | Viewed by 4736

Abstract

The healthy state of insulation in oil-impregnated bushings is traditionally evaluated by tanδ and capacitance at power frequency and mostly at 10 kV in the test standard. However, there has frequently been insulation accidents induced by moisture ingress (MI) for bushings that have [...] Read more.

The healthy state of insulation in oil-impregnated bushings is traditionally evaluated by tanδ and capacitance at power frequency and mostly at 10 kV in the test standard. However, there has frequently been insulation accidents induced by moisture ingress (MI) for bushings that have passed the standard. The mechanism and new diagnostic features for MI into bushings were not distinct enough and an accurate test method is urgently needed research. To address this technical gap, a bushing model with a transparent sheath was designed and an ultrasonic humidifier device was adopted to simulate the environment of MI in bushings and recorded by digital camera. The parameters of dielectric dissipation factor, capacitance, partial discharge (PD), frequency domain response, and moisture content in oil were measured at room temperature with time. The results presented that both the increment dissipation factor at low frequency of 0.001 Hz and the increment dissipation factor of 1.2 U_m could be used for detecting the earlier insulation defect of oil-impregnated paper (OIP) bushings. The phase resolved partial discharge (PRPD) can serve as the diagnostic basis of the severe state (S₃) of insulation deterioration caused by MI into bushings around the phases of 0–117°, 151–303°, and 325–360°. The research findings would provide a useful reference for the condition diagnosis and maintenance of OIP bushings. Especially, the increment detection of Frequency Domain Spectroscopy (FDS) at the frequency of 1 mHz and 10 kHz was recommended firstly for the operative bushings in real sites. Full article

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13 pages, 575 KiB

Open AccessArticle

Preventive Security-Constrained DCOPF Formulation Using Power Transmission Distribution Factors and Line Outage Distribution Factors

by Victor H. Hinojosa^1,*

and Francisco Gonzalez-Longatt²

¹ Department of Electrical Engineering, Universidad Técnica Federico Santa María, Valparaíso 2390123, Chile

² School of Electric, Electronic and System Engineering, Loughborough University, Loughborough LE11 3TU, UK

Energies 2018, 11(6), 1497; https://doi.org/10.3390/en11061497 - 8 Jun 2018

Cited by 20 | Viewed by 3260

Abstract

This study proposes a very effective formulation to carry out the security-constrained direct current (DC)-based optimal power flow (OPF) problem using two linear factors: (i) the power transmission distribution factors (PTDF) and (ii) the line outage distribution factors (LODF). The security-constrained (SC) DCOPF [...] Read more.

This study proposes a very effective formulation to carry out the security-constrained direct current (DC)-based optimal power flow (OPF) problem using two linear factors: (i) the power transmission distribution factors (PTDF) and (ii) the line outage distribution factors (LODF). The security-constrained (SC) DCOPF problem has been reformulated using these linear distribution factors, and mainly the pre- and post-contingency constraints have been added into the optimization problem based on the active power unit generation (decision variables). The main advantage of this formulation is the reduction of decision variables as well as equality and inequality constraints. To validate the introduced formulation, several experiments have been conducted using MatPower, DIgSILENT Power Factory and Gurobi. Simulation results demonstrate both the feasibility to carry out the SCOPF problem and the potential applicability of the proposed formulation to medium and large-scale power systems. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 1563 KiB

Open AccessArticle

Power Generation Expansion Optimization Model Considering Multi-Scenario Electricity Demand Constraints: A Case Study of Zhejiang Province, China

by Peng Wang¹

, Chunsheng Wang^1,*, Yukun Hu², Liz Varga²

and Wei Wang³

¹ School of Information Science and Engineering, Central South University, Changsha 410083, China

² School of Management, Cranfield University, Bedford MK43 0AL, UK

³ College of Electrical Engineering, Guangxi University, Nanning 530004, China

Energies 2018, 11(6), 1498; https://doi.org/10.3390/en11061498 - 8 Jun 2018

Cited by 12 | Viewed by 3447

Abstract

Reasonable and effective power planning contributes a lot to energy efficiency improvement, as well as the formulation of future economic and energy policies for a region. Since only a few provinces in China have nuclear power plants so far, nuclear power plants were [...] Read more.

Reasonable and effective power planning contributes a lot to energy efficiency improvement, as well as the formulation of future economic and energy policies for a region. Since only a few provinces in China have nuclear power plants so far, nuclear power plants were not considered in many provincial-level power planning models. As an extremely important source of power generation in the future, the role of nuclear power plants can never be overlooked. In this paper, a comprehensive and detailed optimization model of provincial-level power generation expansion considering biomass and nuclear power plants is established from the perspective of electricity demand uncertainty. This model has been successfully applied to the case study of Zhejiang Province. The findings suggest that the nuclear power plants will contribute 9.56% of the total installed capacity, and it will become the second stable electricity source. The lowest total discounted cost is 1033.28 billion RMB and the fuel cost accounts for a large part of the total cost (about 69%). Different key performance indicators (KPI) differentiate electricity demand in scenarios that are used to test the model. Low electricity demand in the development mode of the comprehensive adjustment scenario (COML) produces the optimal power development path, as it provides the lowest discounted cost. Full article

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15 pages, 2558 KiB

Open AccessArticle

Numerical Investigation of Small-Scale Adsorption Cooling System Performance Employing Activated Carbon-Ethanol Pair

by Marzia Khanam^1,2, Skander Jribi^3,*

, Takahiko Miyazaki^1,2,*, Bidyut Baran Saha²

and Shigeru Koyama^1,2

¹ Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga-koen 6-1, Kasuga-shi, Fukuoka 816-8580, Japan

² International Institute for Carbon-Neutral Energy Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka-shi, Fukuoka 819-0395, Japan

³ Laboratory of Electro-Mechanical Systems, National Engineering School of Sfax, University of Sfax, Route Soukra km 3.5, Sfax 3038, Tunisia

Energies 2018, 11(6), 1499; https://doi.org/10.3390/en11061499 - 8 Jun 2018

Cited by 16 | Viewed by 4551

Abstract

Adsorber heat exchanger design has great importance in increasing the performance of the adsorption-based cooling system. In this study, a transient two-dimensional axisymmetric Computational Fluid Dynamics (CFD) model has been developed for the performance investigation of finned tube type adsorber using activated carbon [...] Read more.

Adsorber heat exchanger design has great importance in increasing the performance of the adsorption-based cooling system. In this study, a transient two-dimensional axisymmetric Computational Fluid Dynamics (CFD) model has been developed for the performance investigation of finned tube type adsorber using activated carbon and ethanol as the working pair. The operating conditions of the cooling system were 15, 20 and 80 for evaporation, cooling and heating temperatures, respectively. The simulated temperature profiles for different adsorbent thicknesses were validated with those from experimental data measured in our laboratory. Moreover, the error in mass and energy balance were 3% and 7.88%, respectively. Besides, the performance investigation has been performed for cycle time ranging from 600 s to 1400 s. The optimum cycle time was 800 s and the corresponding evaluated specific cooling power (SCP) and coefficient of performance (COP) were found to be 488 W/kg and 0.61, respectively. The developed CFD model will be used for fin height and fin pitch optimization and can be extended to other adsorbent-adsorbate based adsorption cooling system. Full article

(This article belongs to the Section A: Sustainable Energy)

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22 pages, 8418 KiB

Open AccessArticle

Energy Optimization Strategies for Eco-Friendly Cellular Base Stations

by Mohammed H. Alsharif^*

, Jeong Kim and Jin Hong Kim

Department of Electrical Engineering, College of Electronics and Information Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 05006, Korea

Energies 2018, 11(6), 1500; https://doi.org/10.3390/en11061500 - 8 Jun 2018

Cited by 10 | Viewed by 2771

Abstract

This study focuses on the economic and environmental impacts of the deployment of cellular base stations (BSs) in remote/rural areas of South Korea. The optimal system, energy production, and operational costs of various renewable energy systems (RESs), such as solar power systems and [...] Read more.

This study focuses on the economic and environmental impacts of the deployment of cellular base stations (BSs) in remote/rural areas of South Korea. The optimal system, energy production, and operational costs of various renewable energy systems (RESs), such as solar power systems and hybrid solar power/wind power systems, in supplying third-generation cellular BSs with their required energy are discussed in this paper. To highlight the economic feasibility of the proposed RESs, a comparison between their economic feasibilities is presented. In addition, a comparison between the economic feasibilities of the proposed RESs and the classic energy solution of using a diesel generator (DG) is provided. Results show that the total operating expenses that can be saved can reach up to 56.13% if DG is replaced with the hybrid solar power/wind power system. Moreover, the operating expense savings are increased to 56.99% when a stand-alone solar power system is used. These results can be considered a valuable reference for mobile operators to show that shifting toward renewable energy technology is an attractive option. Full article

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16 pages, 5522 KiB

Open AccessArticle

Network Features of the EU Carbon Trade System: An Evolutionary Perspective

by Yinpeng Liu¹, Xiangyun Gao² and Jianfeng Guo^1,3,*

¹ Institute of Science and Development, Chinese Academy of Sciences, Beijing 100190, China

² School of Humanities and Economic Management, China University of Geosciences, Beijing 100083, China

³ School of Public Policy and Management, University of Chinese Academy of Sciences, Beijing 100049, China

Energies 2018, 11(6), 1501; https://doi.org/10.3390/en11061501 - 8 Jun 2018

Cited by 6 | Viewed by 2655

Abstract

In this paper, a network model is constructed using real trading data from the EU carbon market. Metric indicators are then introduced to measure the network, and the economic meanings of the indicators are discussed. By integrating time windows with the network model, [...] Read more.

In this paper, a network model is constructed using real trading data from the EU carbon market. Metric indicators are then introduced to measure the network, and the economic meanings of the indicators are discussed. By integrating time windows with the network model, three types of network features are examined: growth features, structural features, and scale-free features. The growth pattern of the carbon trading network is then analyzed. As the market grow, the geodesic distances become shorter and the clustering coefficients become larger. The trends of these two indicators suggest that the market is evolving towards efficiency; however, their tiny changes are insufficient to have significant impact. By modeling the heterogeneity of the carbon trading network, we find that the trading relationships between firms obey a broken power law model, which consists of two power law models. The broken power law model can be approximately defined as a traditional power law but with a longer tail in distribution. Furthermore, we find that the model is valid for most of the time of both phases, the model only invalid when the market approaches a high growth rate. Full article

(This article belongs to the Special Issue Lessons from the Evaluation of Existing Emission Trading Schemes)

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14 pages, 10218 KiB

Open AccessArticle

Surface Properties and Pore Structure of Anthracite, Bituminous Coal and Lignite

by Zhenjian Liu¹, Zhenyu Zhang^1,*

, Sing Ki Choi² and Yiyu Lu¹

¹ State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China

² Australian Commonwealth Scientific and Research Organization (CSIRO), Locked Bag 10, Clayton South VIC 3169, Australia

Energies 2018, 11(6), 1502; https://doi.org/10.3390/en11061502 - 12 Jun 2018

Cited by 37 | Viewed by 6605

Abstract

Properties of coal surface and pore structure are important aspects to be investigated in coal preparation and utilization. In order to investigate the limits of different probe methods, a comprehensive approach was comparatively used to probe surface properties and pore structure of anthracite, [...] Read more.

Properties of coal surface and pore structure are important aspects to be investigated in coal preparation and utilization. In order to investigate the limits of different probe methods, a comprehensive approach was comparatively used to probe surface properties and pore structure of anthracite, bituminous coal and lignite. Surface morphology of the three coal samples was analyzed by scanning electron microscopy (SEM). Combining mercury intrusion porosimetry (MIP), physisorption method with carbon dioxide (CO₂) at 273 K and nitrogen (N₂) at 77 K was used to quantify a broad pore size distribution of coals, while FT-IR and water vapor sorption methods were used to study the coal surface properties. The results show that wedge-shaped pores develop with the increase of coal rank due to compression effect. The determined specific surface area (SSA) and pore volume of N₂ decrease with the increase of coal rank, while CO₂ SSA and pore volume are of a kind of U-shaped function of coal rank. MIP results indicate that that the pore size of 10–100 nm accounted for 70.7–97.5% of the total volume in the macropore range. Comparison of different methods indicates that micropores cannot be fully covered by the standard probes. CO₂ adsorption technique can only probe micropores in the range of 0.5 nm to 0.9 nm. Water vapor is not an effective probe to detect the micropores in coals, due to that the water clusters is mainly filled in mesopores and macropores. The results also show that both water vapor adsorption and FT-IR analysis can provide qualitative information of coal surface, rather than qualification of functional groups. Full article

(This article belongs to the Section L: Energy Sources)

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20 pages, 2690 KiB

Open AccessArticle

An Optimization Method for Local Consumption of Photovoltaic Power in a Facility Agriculture Micro Energy Network

by Yuzhu Wang¹, Huanna Niu^1,*, Lu Yang¹, Weizhou Wang² and Fuchao Liu²

¹ College of Information and Electrical Engineering China Agricultural University, Beijing 100083, China

² State Grid Gansu Electric Power Research Institute, Lanzhou 730000, China

Energies 2018, 11(6), 1503; https://doi.org/10.3390/en11061503 - 8 Jun 2018

Cited by 13 | Viewed by 2618

Abstract

In order to solve the problem of optimal dispatching of photovoltaic power for local consumption to the greatest degree in a photovoltaic greenhouse, this paper proposes a multiform energy optimal dispatching model and a solution algorithm. First, an input-output power model is established [...] Read more.

In order to solve the problem of optimal dispatching of photovoltaic power for local consumption to the greatest degree in a photovoltaic greenhouse, this paper proposes a multiform energy optimal dispatching model and a solution algorithm. First, an input-output power model is established for energy storages which are reservoir, biogas digester, and block wall with phase-change thermal storage. Based on it, multiform energy storages play a bridging role of energy transfer in optimal energy dispatching. Subsequently, an optimal energy dispatching model is proposed with the objective of minimizing the sum of the squares of the difference between the loads and the photovoltaic generation in dispatching periods. Control variables are working state quantities of the time-shiftable loads and input-output state quantities of energy storages in dispatching periods. Finally, a genetic algorithm with matrix binary coding is used to solve the energy optimal dispatching model. Simulation results of a practical photovoltaic greenhouse facility agricultural micro energy network system in three typical weather conditions showed that the method could fully utilize the energy transfer function of the multiform energy storage and the time-shiftable characteristics of the agricultural load to achieve the maximum effect of increasing the local consumption of the photovoltaic power. Full article

(This article belongs to the Section F: Electrical Engineering)

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27 pages, 2408 KiB

Open AccessArticle

Multi-Criteria Decision Making (MCDM) Approaches for Solar Power Plant Location Selection in Viet Nam

by Chia-Nan Wang^1,2,*, Van Thanh Nguyen^1,3,*

, Hoang Tuyet Nhi Thai³ and Duy Hung Duong³

¹ Department of Industrial Engineering and Management, National Kaohsiung University of Science and Technology, Kaohsiung 80778, Taiwan

² Department of Industrial Engineering and Management, Fortune Institute of Technology, Kaohsiung 83160, Taiwan

³ Department of Industrial Systems Engineering, CanTho University of Technology, Can Tho 900000, Viet Nam

Energies 2018, 11(6), 1504; https://doi.org/10.3390/en11061504 - 8 Jun 2018

Cited by 105 | Viewed by 7861

Abstract

The ongoing industrialization and modernization period has increased the demand for energy in Viet Nam. This has led to over-exploitation and exhausts fossil fuel sources. Nowadays, Viet Nam’s energy mix is primarily based on thermal and hydro power. The Vietnamese government is trying [...] Read more.

The ongoing industrialization and modernization period has increased the demand for energy in Viet Nam. This has led to over-exploitation and exhausts fossil fuel sources. Nowadays, Viet Nam’s energy mix is primarily based on thermal and hydro power. The Vietnamese government is trying to increase the proportion of renewable energy. The plan will raise the total solar power capacity from nearly 0 to 12,000 MW, equivalent to about 12 nuclear reactors, by 2030. Therefore, the construction of solar power plants is needed in Viet Nam. In this study, the authors present a multi-criteria decision making (MCDM) model by combining three methodologies, including fuzzy analytical hierarchy process (FAHP), data envelopment analysis (DEA), and the technique for order of preference by similarity to ideal solution (TOPSIS) to find the best location for building a solar power plant based on both quantitative and qualitative criteria. Initially, the potential locations from 46 sites in Viet Nam were selected by several DEA models. Then, AHP with fuzzy logic is employed to determine the weight of the factors. The TOPSIS approach is then applied to rank the locations in the final step. The results show that Binh Thuan is the optimal location to build a solar power plant because it has the highest ranking score in the final phase of this study. The contribution of this study is the proposal of a MCDM model for solar plant location selection in Viet Nam under fuzzy environment conditions. This paper also is part of the evolution of a new approach that is flexible and practical for decision makers. Furthermore, this research provides useful guidelines for solar power plant location selection in many countries as well as a guideline for location selection of other industries. Full article

(This article belongs to the Special Issue Energy Economy, Sustainable Energy and Energy Saving)

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20 pages, 1861 KiB

Open AccessArticle

A New Hybrid Approach Using the Simultaneous Perturbation Stochastic Approximation Method for the Optimal Allocation of Electrical Energy Storage Systems

by Guido Carpinelli¹

, Fabio Mottola¹

, Christian Noce², Angela Russo^3,*

and Pietro Varilone⁴

¹ Department of Electrical Engineering and Information Technology, University of Naples Federico II, 80125 Napoli, Italy

² ENEL Global Infrastructure and Networks Srl, Italy

³ Dipartimento Energia “Galileo Ferraris”, Politecnico di Torino, 10129 Torino, Italy

⁴ Dipartimento di Ingegneria Elettrica e dell′Informazione “Maurizio Scarano”, Università di Cassino e del Lazio Meriodionale, 03043 Cassino, Italy

Energies 2018, 11(6), 1505; https://doi.org/10.3390/en11061505 - 8 Jun 2018

Cited by 9 | Viewed by 2334

Abstract

This paper deals with the optimal allocation (siting and sizing) of distributed electrical energy storage systems in unbalanced electrical distribution systems. This problem is formulated as a mixed, non-linear, constrained minimization problem, in which the objective function involves economic factors and constraints address [...] Read more.

This paper deals with the optimal allocation (siting and sizing) of distributed electrical energy storage systems in unbalanced electrical distribution systems. This problem is formulated as a mixed, non-linear, constrained minimization problem, in which the objective function involves economic factors and constraints address the technical limitations of both network and distributed resources. The problem is cumbersome from the computational point of view due to the presence of both constraints of an intertemporal nature and a great number of state variables. In order to guarantee reasonable accuracy-although limiting the computational efforts-a new approach is proposed in this paper: it is based on a Simultaneous Perturbation Stochastic Approximation (SPSA) method and on an innovative inner algorithm, which allows it to quickly carry out the daily scheduling (charging/discharging) of the electrical energy storage systems. The proposed method is applied to a medium voltage (Institute of Electrical and Electronics Engineers) IEEE unbalanced test network, to demonstrate the effectiveness of the procedure in terms of computational effort while preserving the accuracy of the solution. The obtained results are also compared with the results of a Genetic Algorithm and of an exhaustive procedure. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 1924 KiB

Open AccessArticle

Analytical Calculation for Multi-Infeed Interaction Factors Considering Control Modes of High Voltage Direct Current Links

by Chengjun Xia

, Xia Hua^*, Zhen Wang and Zhenlin Huang

School of Electric Power, South China University of Technology, Guangzhou 510640, China

Energies 2018, 11(6), 1506; https://doi.org/10.3390/en11061506 - 8 Jun 2018

Cited by 4 | Viewed by 3734

Abstract

The multi-infeed interaction factor (MIIF) is used extensively in indicating the degree of interaction among high-voltage direct current (HVDC) converters and is currently calculated by simulation methods according to the definition, or by using the equivalent impedance ratio method. The first method is [...] Read more.

The multi-infeed interaction factor (MIIF) is used extensively in indicating the degree of interaction among high-voltage direct current (HVDC) converters and is currently calculated by simulation methods according to the definition, or by using the equivalent impedance ratio method. The first method is an experimental calculation method and the second method does not account for the effects of HVDC control modes. An analytical calculation method for MIIF considering control modes of HVDC links is proposed in this paper. First, the voltage variation of converter bus in the context of small disturbance is equated by using the bus impedance matrix. In this way the equations for the solution of MIIF considering HVDC control mode are obtained. Subsequently, based on two rational assumptions, the practical analytical calculation expression of MIIF is deduced in detail. The MIIF calculation method proposed in this paper is an improvement of the equivalent impedance ratio method and reflects the main influencing factors of voltage interaction including HVDC control modes. Moreover, the derived analytical expression can give a fundamental insight into parameter dependencies of voltage interaction. Finally, the validity and accuracy of the proposed approach are demonstrated in both dual-infeed HVDC system and actual large-scale power grid. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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16 pages, 3438 KiB

Open AccessArticle

Reducing Irradiation Damage in a Long-Life Fast Reactor with Spectral Softening

by Andrew G. Osborne^1,2 and Mark R. Deinert^1,2,*

¹ Department of Mechanical Engineering, The Colorado School of Mines, Golden, CO 80401, USA

² Nuclear Science and Engineering, The Colorado School of Mines, Golden, CO 80401, USA

Energies 2018, 11(6), 1507; https://doi.org/10.3390/en11061507 - 9 Jun 2018

Cited by 5 | Viewed by 2704

Abstract

Long-life fast reactors receive considerable attention for their potential of using uranium efficiently, and because they can operate for extended periods without refueling. However, the main obstacle to achieving maximum operating times and fuel burnup is the neutron radiation damage that accumulates in [...] Read more.

Long-life fast reactors receive considerable attention for their potential of using uranium efficiently, and because they can operate for extended periods without refueling. However, the main obstacle to achieving maximum operating times and fuel burnup is the neutron radiation damage that accumulates in the cladding and structural materials. Simulations of metal-fueled high-burnup fast reactors showed that the damage in these reactors’ cladding material reached 200 displacements per atom (dpa) long before the maximum burnup was achieved. One possibility for overcoming this problem is spectral softening, which would reduce the kinetic energy imparted to reactor materials when neutrons collide with them. In this work, we compared the peak irradiation damage in metal- and oxide-fueled fast reactors with that in equivalent reactors containing beryllium in the fuel and reflectors. We showed that the peak damage to the cladding in a metal-fueled reactor was reduced from 273 dpa to 230 dpa when beryllium was included in the core. In an oxide-fueled reactor, the peak damage to the cladding was reduced from 225 dpa to 203 dpa. All four reactors were operated with a core-average burnup of 112 MWd/kg of initial heavy metal (IHM), without reshuffling or refueling, and contained the same initial actinide mass profiles. Full article

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14 pages, 3993 KiB

Open AccessArticle

A New Diagnostic Algorithm for Multiple IGBTs Open Circuit Faults by the Phase Currents for Power Inverter in Electric Vehicles

by Hongqian Wei¹

, Youtong Zhang^1,*, Lei Yu¹, Mengzhu Zhang² and Khaled Teffah¹

¹ Laboratory of Low Emission Vehicle, Beijing Institute of Technology, Beijing 100081, China

² National Lab of Auto Performance and Emission Test, Beijing Institute of Technology, Beijing 100081, China

Energies 2018, 11(6), 1508; https://doi.org/10.3390/en11061508 - 10 Jun 2018

Cited by 23 | Viewed by 3455

Abstract

In order to simplify the application and improve diagnostic speed of the diagnostics, a novel method to diagnose multiple open circuit faults in insulated gate bipolar transistors (IGBTs) by three-phase currents for power inverter in electric vehicles is presented. The summation of currents [...] Read more.

In order to simplify the application and improve diagnostic speed of the diagnostics, a novel method to diagnose multiple open circuit faults in insulated gate bipolar transistors (IGBTs) by three-phase currents for power inverter in electric vehicles is presented. The summation of currents with semi-period phase-difference is described in diagnostic variables with exploration of the current information in faulty condition. In contrast with plentiful existing methods which rely on the motor models and control parameters, this algorithm merely requires phase currents. Meanwhile, the normalized way based on the absolute phase currents and variable parameter moving average method are applied to improve the diagnostic speed and independence of load variation, which contributes to the real-time application in the electric vehicles. Experimental results, using a vector-controlled permanent magnet synchronous motor (PMSM) and digital signal processor MC56F8346, are presented to verify the algorithm effectiveness, showing many features, such as applicability for multiple open circuit faults, well-robustness against false alarms, briefness and agility for the diagnosis function. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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14 pages, 2798 KiB

Open AccessArticle

Development Strategy for Sustainable Solar Home System in the Akha Upland Community of Thailand

by Pimnapat Bhumkittipich^1,* and Hideaki Ohgaki²

¹ Department of Social Sciences and Humanities, Faculty of Liberal Arts, Rajamangala University of Technology Thanyaburi, Thanyaburi, Pathumtani 12110, Thailand

² Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan

Energies 2018, 11(6), 1509; https://doi.org/10.3390/en11061509 - 10 Jun 2018

Cited by 2 | Viewed by 3812

Abstract

With the growing effects of global warming and carbon pollution, environmental protection has become an urgent necessity. In addition, solar energy has been accepted worldwide for the generation of electricity. However, remote areas in Thailand have not had effective solar home system (SHS) [...] Read more.

With the growing effects of global warming and carbon pollution, environmental protection has become an urgent necessity. In addition, solar energy has been accepted worldwide for the generation of electricity. However, remote areas in Thailand have not had effective solar home system (SHS) development. This paper aims to explore the problems of SHS development and analyze the external factors that could have an impact on their operation in the Akha upland community of Thailand. The result of the survey indicates that about 79.38% of the respondents displayed a high-level lack of information and repair work. Moreover, many respondents presented low-level satisfaction in developing SHS. There are four strategies for sustainable SHS development using a factor analysis process, these include creating approval of SHS technologies 24.93%, developing SHS management 22.64%, promoting SHS technologies 14.29%, and supporting SHS policies 10.97%. In particular, this study considered the public views on the role of an organization that could lead to sustainable development of SHS. Furthermore, these should be managed suitably for each community. As a result, this study has provided some valuable references for SHS promotion in Thailand. Full article

(This article belongs to the Special Issue Toward Sustainable Energy Systems for Smart Grids and Smart Societies)

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10 pages, 3214 KiB

Open AccessArticle

Synergistic Enhancement of Ternary Poly(3,4-ethylenedioxythiophene)/Graphene Oxide/Manganese Oxide Composite as a Symmetrical Electrode for Supercapacitors

by Nur Hawa Nabilah Azman¹, Hong Ngee Lim^1,2

, Md Shuhazlly Mamat³ and Yusran Sulaiman^1,4,*

¹ Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, Serdang 43400 UPM, Selangor, Malaysia

² Functional Devices Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, Serdang 43400 UPM, Selangor, Malaysia

³ Department of Physics, Faculty of Science, Universiti Putra Malaysia, Serdang 43400 UPM, Selangor, Malaysia

⁴ Materials Synthesis and Characterization Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, Serdang 43400 UPM, Selangor, Malaysia

Energies 2018, 11(6), 1510; https://doi.org/10.3390/en11061510 - 11 Jun 2018

Cited by 23 | Viewed by 3030

Abstract

A novel facile preparation of poly(3,4-ethylenedioxythiophene)/graphene oxide/manganese oxide (PEDOT/GO/MnO₂) ternary composite as an electrode material for a supercapacitor was evaluated. The ternary composite was sandwiched together and separated by filter paper soaked in 1 M KCl in order to investigate the [...] Read more.

A novel facile preparation of poly(3,4-ethylenedioxythiophene)/graphene oxide/manganese oxide (PEDOT/GO/MnO₂) ternary composite as an electrode material for a supercapacitor was evaluated. The ternary composite was sandwiched together and separated by filter paper soaked in 1 M KCl in order to investigate the supercapacitive properties. The ternary composite exhibits a higher specific capacitance (239.4 F/g) compared to PEDOT/GO (73.3 F/g) at 25 mV/s. The incorporation of MnO₂ which act as a spacer in the PEDOT/GO helps to improve the supercapacitive performance by maximizing the utilization of electrode materials by the electrolyte ions. The PEDOT/GO/MnO₂ ternary composite displays a specific energy and specific power of 7.9 Wh/kg and 489.0 W/kg, respectively. The cycling stability test revealed that the ternary composite is able to achieve 95% capacitance retention even after 1000 cycles due to the synergistic effect between the PEDOT, GO, and MnO₂ that helps to enhance the performance of the ternary composite for supercapacitor application. Full article

(This article belongs to the Section D: Energy Storage and Application)

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15 pages, 5010 KiB

Open AccessArticle

Influence of Water Immersion on Pore System and Methane Desorption of Shales: A Case Study of Batu Gajah and Kroh Shale Formations in Malaysia

by Ahmed Al-Mutarreb

, Shiferaw Regassa Jufar^*, Hesham Abdulelah

and Eswaran Padmanabhan

Shale Gas Research Group (SGRG), Institute of Hydrocarbon Recovery, Faculty of Petroleum & Geoscience, Universiti Teknologi PETRONAS, Seri Iskandar 32610, Malaysia

Energies 2018, 11(6), 1511; https://doi.org/10.3390/en11061511 - 11 Jun 2018

Cited by 7 | Viewed by 3354

Abstract

The influence of water on the pore system and gas desorption in shale remains an open question that is not yet fully understood. In this study, we present the effect of water on the shale pore system and recovered desorbed gas through a [...] Read more.

The influence of water on the pore system and gas desorption in shale remains an open question that is not yet fully understood. In this study, we present the effect of water on the shale pore system and recovered desorbed gas through a series of measurements on shale samples. We utilized the Brunauer-Emmett-Teller (BET) low pressure N₂ adsorption and Field Emission Scanning Electron Microscopy (FE-SEM) to observe and analyze the effects of water immersion and moisture on the pore system of shale samples from Batu Gajah (BG) and Kroh shale formations in Malaysia. The impact of water on desorption was then measured using the United States former Bureau of Mines (USBM) modified method. The results showed that the micropore and mesopore volumes of the Batu Gajah (BG) and Kroh (KH) shale samples were reduced by 64.84% and 44.12%, respectively, after the samples were immersed in water. The BET-specific surface area declined by 88.34% and 59.63% for the BG and KH sample, respectively. Desorption results showed that the methane desorbed volume was (KH: 1.22 cc/g, BG: 0.94 cc/g) for the water immersed sample, and (KH: 0.72 cc/g, BG: 0.60) for the equilibrated sample. The difference can be attributed to the proportion of the organic (total organic carbon) and inorganic (clay) content found in the two shale samples. The total organic carbon (TOC) existing in the KH sample was 12.1 wt %, which was greater than the organic carbon content of the BG sample (2.1 wt %). The clay content was found to be more dominant in the BG shale when compared to the KH shale. Full article

(This article belongs to the Section L: Energy Sources)

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12 pages, 1970 KiB

Open AccessArticle

Experimental Investigation of the Use of Waste Mineral Oils as a Fuel with Organic-Based Mn Additive

by Bülent Özdalyan¹

and Recep Ç. Orman^2,*

¹ Department of Mechanical Engineering, Karabük University, Karabük 78050, Turkey

² Department of Automotive Technology, Gazi University, Ankara 06980, Turkey

Energies 2018, 11(6), 1512; https://doi.org/10.3390/en11061512 - 11 Jun 2018

Cited by 3 | Viewed by 3700

Abstract

The heat values of waste mineral oils are equal to the heat value of the fuel oil. However, heat value alone is not sufficient for the use of waste minerals oils as fuel. However, the critical physical properties of fuels such as density [...] Read more.

The heat values of waste mineral oils are equal to the heat value of the fuel oil. However, heat value alone is not sufficient for the use of waste minerals oils as fuel. However, the critical physical properties of fuels such as density and viscosity need to be adapted to the system in order to be used. In this study, the engine oils used in the first 10,000 km of the vehicles were used as waste mineral oil. An organic-based Mn additive was synthesized to improve the properties of the waste mineral oil. It was observed that mixing the Mn additive with the waste mineral oil at different doses (4, 8, 12, and 16 ppm) improves the viscosity of the waste oil and the flash point. The resulting fuel was evaluated for emission using different loads in a 5 kW capacity generator to compare the fuel with standard diesel fuel and to determine the effect of Mn addition. In the experimental study, it was observed that the emission characteristics of the fuel obtained from waste mineral oil were worse than diesel fuel, but some improvement was observed with Mn addition. As a result, we found that the use of waste mineral oils in engines in fuel standards was not appropriate, but may be improved with additives. Full article

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29 pages, 533 KiB

Open AccessArticle

Jaya based Optimization Method with High Dispatchable Distributed Generation for Residential Microgrid

by Omaji Samuel¹

, Nadeem Javaid^1,*

, Mahmood Ashraf²

, Farruh Ishmanov³, Muhammad Khalil Afzal⁴

and Zahoor Ali Khan⁵

¹ Department of Computer Science, COMSATS University Islamabad, Islamabad 44000, Pakistan

² Department of Computer Science, Federal Urdu University of Arts, Science and Technology, Islamabad 44000, Pakistan

³ Department of Electronics and Communication Engineering, Kwangwoon University, Seoul 01897, Korea

⁴ Department of Computer Science, COMSATS University Islamabad, Wah Campus, Wah Cantonment 47040, Pakistan

⁵ CIS, Higher Colleges of Technology, Fujairah 4114, United Arab Emirates

Energies 2018, 11(6), 1513; https://doi.org/10.3390/en11061513 - 11 Jun 2018

Cited by 16 | Viewed by 3685

Abstract

This paper presents a model for optimal energy management under the time-of-use (ToU) and critical peak price (CPP) market in a microgrid. The microgrid consists of intermittent dispatchable distributed generators, energy storage systems, and multi-home load demands. The optimal energy management problem is [...] Read more.

This paper presents a model for optimal energy management under the time-of-use (ToU) and critical peak price (CPP) market in a microgrid. The microgrid consists of intermittent dispatchable distributed generators, energy storage systems, and multi-home load demands. The optimal energy management problem is a challenging task due to the inherent stochastic behavior of the renewable energy resources. In the past, medium-sized distributed energy resource generation was injected into the main grid with no feasible control mechanism to prevent the waste of power generated by a distributed energy resource which has no control mechanism, especially when the grid power limit is altered. Thus, a Jaya-based optimization method is proposed to shift dispatchable distributed generators within the ToU and CPP scheduling horizon. The proposed model coordinates the power supply of the microgrid components, and trades with the main grid to reduce its fuel costs, production costs, and also maximize the monetary profit from sales revenue. The proposed method is implemented on two microgrid operations: the standalone and grid-connected modes. The simulation results are compared with other optimization methods: enhanced differential evolution (EDE) and strawberry algorithm (SBA). Finally, simulation results show that the Jaya-based optimization method minimizes the fuel cost by up to 38.13%, production cost by up to 93.89%, and yields a monetary benefit of up to 72.78% from sales revenue. Full article

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15 pages, 10712 KiB

Open AccessArticle

Effect of Blade Pitch Angle on the Aerodynamic Characteristics of a Straight-bladed Vertical Axis Wind Turbine Based on Experiments and Simulations

by Yanzhao Yang^1,2, Zhiping Guo¹, Qing Song³, Yanfeng Zhang^1,2 and Qing’an Li^4,5,*

¹ College of Mechanical Engineering, Inner Mongolia University of Technology, Hohhot 010051, China

² Graduate School of Bioresources, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan

³ School of Electrical Engineering, University of Jinan, Jinan 250022, China

⁴ CAS Laboratory of Wind Energy Utilization, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China

⁵ Division of Mechanical Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan

Energies 2018, 11(6), 1514; https://doi.org/10.3390/en11061514 - 11 Jun 2018

Cited by 31 | Viewed by 5994

Abstract

The blade pitch angle has a significant influence on the aerodynamic characteristics of horizontal axis wind turbines. However, few research results have revealed its impact on the straight-bladed vertical axis wind turbine (Sb-VAWT). In this paper, wind tunnel experiments and CFD simulations were [...] Read more.

The blade pitch angle has a significant influence on the aerodynamic characteristics of horizontal axis wind turbines. However, few research results have revealed its impact on the straight-bladed vertical axis wind turbine (Sb-VAWT). In this paper, wind tunnel experiments and CFD simulations were performed at the Sb-VAWT to investigate the effect of different blade pitch angles on the pressure distribution on the blade surface, the torque coefficient, and the power coefficient. In this study, the airfoil type was NACA0021 with two blades. The Sb-VAWT had a rotor radius of 1.0 m with a spanwise length of 1.2 m. The simulations were based on the k-ω Shear Stress Transport (SST) turbulence model and the wind tunnel experiments were carried out using a high-speed multiport pressure device. As a result, it was found that the maximum pressure difference on the blade surface was obtained at the blade pitch angle of β = 6° in the upstream region. However, the maximum pressure coefficient was shown at the blade pitch angle of β = 8° in the downstream region. The torque coefficient acting on a single blade reached its maximum value at the blade pitch angle of β = 6°. As the tip speed ratio increased, the power coefficient became higher and reached the optimum level. Subsequently, further increase of the tip speed ratio only led to a quick reversion of the power coefficient. In addition, the results from CFD simulations had also a good agreement with the results from the wind tunnel experiments. As a result, the blade pitch angle did not have a significant influence on the aerodynamic characteristics of the Sb-VAWT. Full article

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20 pages, 5581 KiB

Open AccessArticle

An Improved Heating System with Waste Pressure Utilization in a Combined Heat and Power Unit

by Heng Chen

, Jidong Xu, Yao Xiao, Zhen Qi, Gang Xu^* and Yongping Yang

National Thermal Power Engineering and Technology Research Center, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(6), 1515; https://doi.org/10.3390/en11061515 - 11 Jun 2018

Cited by 15 | Viewed by 3039

Abstract

An improved heating system integrated with waste pressure utilization (WPU) for combined heat and power (CHP) cogeneration was proposed. The new heating system efficiently utilized the excess pressure of the extraction heating steam to drive the WPU turbine and generator for producing electricity, [...] Read more.

An improved heating system integrated with waste pressure utilization (WPU) for combined heat and power (CHP) cogeneration was proposed. The new heating system efficiently utilized the excess pressure of the extraction heating steam to drive the WPU turbine and generator for producing electricity, achieving higher energy efficiency and lower fuel consumption of the CHP unit. The results of the detailed thermodynamic analysis showed that applying the proposed concept in a typical 300 MW coal-fired CHP unit could reduce the standard coal consumption rate by 9.84 g/(kW·h), with a thermal efficiency improvement of 1.97% (absolute value). Compared to that of the original heating process, the energy efficiency of the proposed process decreased by 0.55% (absolute value), but its exergy efficiency increased dramatically by 17.97% (absolute value), which meant that the proposed configuration could make better use of the steam energy and contribute to the better performance of the CHP unit. As the unit generation load and supply and return-water temperatures declined and the unit heating load rose, the WPU system would generate more electricity and its energy-saving benefit would be enhanced. This work provides a promising approach to further advance the CHP technology and district heating systems. Full article

(This article belongs to the Section F: Electrical Engineering)

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12 pages, 265 KiB

Open AccessArticle

Emission Factors and Energy Properties of Agro and Forest Biomass in Aspect of Sustainability of Energy Sector

by Grzegorz Maj

Department of Power Engineering and Transportation, University of Life Sciences in Lublin, Gleboka 28, 20-612 Lublin, Poland

Energies 2018, 11(6), 1516; https://doi.org/10.3390/en11061516 - 11 Jun 2018

Cited by 29 | Viewed by 3833

Abstract

The paper presents the possibility of managing forest and agricultural biomass for energy purposes in the aspect of environmental protection and sustainable development. The results of experimental studies of physicochemical properties of four types of plant biomass, i.e., a wheat straw, oat grains, [...] Read more.

The paper presents the possibility of managing forest and agricultural biomass for energy purposes in the aspect of environmental protection and sustainable development. The results of experimental studies of physicochemical properties of four types of plant biomass, i.e., a wheat straw, oat grains, larch needles and rapeseed pods are shown. The study consisted of determining the energy parameters in the form of gross and net calorific values of the test material. In addition, the ash and moisture content of the material was tested. Moreover, an elementary analysis for the tested materials by determining the content of carbon, hydrogen and nitrogen was performed. The studies have shown energy potential for the examined materials, in particular oat grains, where the gross calorific value amounted to 17.16 MJ·kg⁻¹, net calorific value to 15.37 MJ·kg⁻¹ and ash content to 2.71%. Larch needles are characterised by the highest carbon content of 45.73%, oat grains by hydrogen at 6.53%, 1.53% nitrogen and sulphur 0.11%. Determined emission rates indicate a reduction of 31–41% CO, 30–39% CO₂, 22–55% NO_x, 95–97% SO₂, 47–97% dust depending on the type of used biomass in relation to hard coal. Full article

(This article belongs to the Section A: Sustainable Energy)

17 pages, 3825 KiB

Open AccessArticle

Design, Fabrication, and Performance Test of a 100-W Helical-Blade Vertical-Axis Wind Turbine at Low Tip-Speed Ratio

by Dowon Han¹, Young Gun Heo^1,2, Nak Joon Choi³, Sang Hyun Nam¹, Kyoung Ho Choi² and Kyung Chun Kim^1,*

¹ School of Mechanical Engineering, Pusan National University, Busan 46241, Korea

² DNDE Co., Busan 48059, Korea

³ ICT Co., Busan 48059, Korea

Energies 2018, 11(6), 1517; https://doi.org/10.3390/en11061517 - 11 Jun 2018

Cited by 26 | Viewed by 17804

Abstract

A 100-W helical-blade vertical-axis wind turbine was designed, manufactured, and tested in a wind tunnel. A relatively low tip-speed ratio of 1.1 was targeted for usage in an urban environment at a rated wind speed of 9 m/s and a rotational speed of [...] Read more.

A 100-W helical-blade vertical-axis wind turbine was designed, manufactured, and tested in a wind tunnel. A relatively low tip-speed ratio of 1.1 was targeted for usage in an urban environment at a rated wind speed of 9 m/s and a rotational speed of 170 rpm. The basic dimensions were determined through a momentum-based design method according to the IEC 61400-2 protocol. The power output was estimated by a mathematical model that takes into account the aerodynamic performance of the NACA0018 blade shape. The lift and drag of the blade with respect to the angle of attack during rotation were calculated using 2D computational fluid dynamics (CFD) simulation to take into account stall region. The average power output calculated by the model was 108.34 W, which satisfies the target output of 100 W. The manufactured wind turbine was tested in a large closed-circuit wind tunnel, and the power outputs were measured for given wind speeds. At the design condition, the measured power output was 114.7 W, which is 5.9% higher than that of the mathematical model. This result validates the proposed design method and power estimation by the mathematical model. Full article

(This article belongs to the Special Issue 10 Years Energies - Horizon 2028)

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13 pages, 3726 KiB

Open AccessArticle

Optimizing Waste Heat Utilization in Vehicle Bio-Methane Plants

by Feng Zhen^1,2,3,4

, Jia Zhang⁵, Wenzhe Li⁴, Yongming Sun^1,2,3,* and Xiaoying Kong^1,2,3

¹ Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, NO. 2 Nengyuan Road, Tianhe District, Guangzhou 510640, China

² CAS Key Laboratory of Renewable Energy, Guangzhou 510640, China

³ Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, Guangzhou 510640, China

⁴ College of Engineering, Northeast Agricultural University, Harbin 150030, China

⁵ Guangzhou Special Pressure Equipment Inspection and Research Institute, Guangzhou 510000, China

Energies 2018, 11(6), 1518; https://doi.org/10.3390/en11061518 - 11 Jun 2018

Cited by 2 | Viewed by 3692

Abstract

Current vehicle bio-methane plants have drawbacks associated with high energy consumption and low recovery levels of waste heat produced during the gasification process. In this paper, we have optimized the performance of heat exchange networks using pinch analysis and through the introduction of [...] Read more.

Current vehicle bio-methane plants have drawbacks associated with high energy consumption and low recovery levels of waste heat produced during the gasification process. In this paper, we have optimized the performance of heat exchange networks using pinch analysis and through the introduction of heat pump integration technology. Optimal results for the heat exchange network of a bio-gas system producing 10,000 cubic meters have been calculated using a pinch point temperature of 50 °C, a minimum heating utility load of 234.02 kW and a minimum cooling utility load of 201.25 kW. These optimal parameters are predicted to result in energy savings of 116.08 kW (19.75%), whilst the introduction of new heat pump integration technology would afford further energy savings of 95.55 kW (16.25%). The combined energy saving value of 211.63 kW corresponds to a total energy saving of 36%, with economic analysis revealing that these reforms would give annual savings of 103,300 USD. The installation costs required to introduce these process modifications are predicted to require an initial investment of 423,200 USD, which would take 4.1 years to reach payout time based on predicted annual energy savings. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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24 pages, 3383 KiB

Open AccessArticle

Reliability and Maintenance Prioritization Analysis of Combined Cooling, Heating and Power Systems

by Jinming Jiang¹, Xindong Wei², Weijun Gao^1,*, Soichiro Kuroki¹ and Zhonghui Liu¹

¹ Faculty of Environmental Engineering, the University of Kitakyushu, Kitakyushu 808-0135, Japan

² School of Environmental and Municipal Engineering, Jilin Jianzhu University, Changchun 130118, China

Energies 2018, 11(6), 1519; https://doi.org/10.3390/en11061519 - 11 Jun 2018

Cited by 19 | Viewed by 3052

Abstract

A combined cooling, heating, and power (CCHP) system is a complex and repairable system containing a large number of components and series of subsystems. When a failure occurs in one component, it might cause a failure of a subsystem or whole system. Traditional [...] Read more.

A combined cooling, heating, and power (CCHP) system is a complex and repairable system containing a large number of components and series of subsystems. When a failure occurs in one component, it might cause a failure of a subsystem or whole system. Traditional maintenance methods might lead to the waste of maintenance resources and a high cost of maintenance. The reliability and maintenance prioritization analyses can help managers optimize maintenance strategies and reduce the total cost. A reliability importance index is one of the factors in maintenance prioritization analysis. This paper aims at selecting the component reliability importance indices to identify the priority of component maintenance of a CCHP system from the perspective of maintenance cost. Failure cost importance index (FCI) and Potential failure cost importance index (PI) are developed for the maintenance prioritization analysis of a CCHP system. A Markov model based on the state–space method (SSM) is used to analyze the reliability and availability of a CCHP system. A set of actual survey reliability data of CCHP systems is used to support the validity of the reliability importance indices. The results indicate that the FCI and PI might lead to different rankings of maintenance prioritization. The FCI and PI will help managers make a reasonable decision for maintenance on a cost basis. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 3433 KiB

Open AccessArticle

Boundary Conditions Accuracy Effect on the Numerical Simulations of the Thermal Performance of Building Elements

by Paris A. Fokaides^1,2,*

, Angeliki Kylili¹

and Ioannis Kyriakides³

¹ School of Engineering, Frederick University, Nicosia 1036, Cyprus

² Faculty of Civil Engineering and Architecture, Kaunas University of Technology, Kaunas 51367, Lithuania

³ Department of Electrical and Computer Engineering, University of Nicosia, Nicosia 2147, Cyprus

Energies 2018, 11(6), 1520; https://doi.org/10.3390/en11061520 - 11 Jun 2018

Cited by 5 | Viewed by 3045

Abstract

Numerical simulation is widely used in the field of computational building physics for the definition of the thermal performance of building elements. An integral component of numerical simulation using finite elements is the boundary conditions, which, in the case of simulating the thermal [...] Read more.

Numerical simulation is widely used in the field of computational building physics for the definition of the thermal performance of building elements. An integral component of numerical simulation using finite elements is the boundary conditions, which, in the case of simulating the thermal performance of a building element, are usually expressed in terms of the external surface temperature as a function of time. The purpose of this study is to examine the effect of the accuracy of the boundary conditions on the thermal performance simulation of building elements. The assumption that the temperature versus time is a sinusoidal function, applied in standard methods, is comparatively assessed with the actual function for diverse climatic conditions using finite elements simulation. The findings of the analysis indicate that the sinusoidal function fails to accurately simulate real boundary conditions. The originality of this study lies within the adoption of a signal reconstruction algorithm, which follows a novel approach by reconstructing the actual temperature versus time signal for the simulation of the actual boundary conditions. Full article

(This article belongs to the Special Issue Building Energy Use: Modeling and Analysis)

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14 pages, 5267 KiB

Open AccessArticle

Calculation of Hybrid Ionized Field of AC/DC Transmission Lines by the Meshless Local Petorv–Galerkin Method

by Qiang Li^1,*, Hao Yang¹, Fan Yang¹, Degui Yao², Guangzhou Zhang³, Jia Ran¹ and Bing Gao¹

¹ State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University, Chongqing 400044, China

² State Grid Henan Electric Power Corporation Research Institute, Zhengzhou 450052, China

³ State Grid Electric Power Research Institute, Wuhan Nanrui Co., Ltd., Wuhan 430060, China

Energies 2018, 11(6), 1521; https://doi.org/10.3390/en11061521 - 12 Jun 2018

Cited by 2 | Viewed by 2777

Abstract

To save land resources, the construction of the high-voltage direct current (HVDC) and high-voltage alternating current (HVAC) hybrid transmission lines in the same corridor is inevitable. To provide suggestions for the construction of the AC/DC parallel lines, the hybrid ionized field of AC/DC [...] Read more.

To save land resources, the construction of the high-voltage direct current (HVDC) and high-voltage alternating current (HVAC) hybrid transmission lines in the same corridor is inevitable. To provide suggestions for the construction of the AC/DC parallel lines, the hybrid ionized field of AC/DC transmission lines was calculated by the meshless local Petorv–Galerkin (MLPG) method for the first time. In this method, the radius of local sub-domain is adjusted to the nodes close to the global boundary, but not exactly on the boundary. It can avoid the boundary integral, as well as having simplified calculation. The method was validated by comparing with measured results and calculation results. The MLPG method is beneficial to obtaining high-precision results by constructing the more complex shape function. Finally, a field distribution of the parallel line of about ±800 kV DC/500 kV AC was calculated. Moreover, the influence of different parallel spacing and AC voltage level on the hybrid ionized field was analyzed, which provides theoretical basis for real parallel lines design. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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20 pages, 5953 KiB

Open AccessArticle

Performance and Emission Analysis of Rubber Seed, Palm, and Their Combined Blend in a Multi-Cylinder Diesel Engine

by Ibrahim Khalil Adam^1,2, Abdul Rashid Abdul Aziz¹, Morgan R. Heikal^1,3, Suzana Yusup⁴, Firmansyah^1,*, Ahmad Shahrul Ahmad¹ and Ezrann Zharif Zainal Abidin¹

¹ Centre for Automotive Research and Electric Mobility, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak Darul Ridzuan, Malaysia

² Mechanical Engineering Department, Blue Nile University, 143 Er Roseires, Ad Damazin, Sudan

³ Advance Engineering Centre, University of Brighton; Brighton BN2 4GJ, UK

⁴ Center of Biofuel and Biochemical Research, Biomass Processing Laboratory; Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak Darul Ridzuan, Malaysia

Energies 2018, 11(6), 1522; https://doi.org/10.3390/en11061522 - 12 Jun 2018

Cited by 14 | Viewed by 3284

Abstract

In consideration of its vast resources in Malaysia, the potential use of a nonedible biodiesel source from rubber seed oil (RSO) is explored. However, a mixture with a high saturation content feedstock is required to increase its oxidation stability, which is caused by [...] Read more.

In consideration of its vast resources in Malaysia, the potential use of a nonedible biodiesel source from rubber seed oil (RSO) is explored. However, a mixture with a high saturation content feedstock is required to increase its oxidation stability, which is caused by its 78.93% unsaturation content. Two blends of 20% and 50% v/v rubber seed biodiesel (RB) or palm biodiesel (PB) and varying percentage mixtures of these two feedstock oils biodiesel (RPB) were evaluated on combustion performance in a 55 kW multi-cylinder diesel engine at full load conditions. The results showed that feedstock blending offered benefits in terms of fuel properties enhancement, improved engine performance, and reduced emissions. In comparison to RB, RPB showed higher brake power (BP) of 1.18–2.97% and lower brake specific fuel consumption (BSFC) of 0.85–3.69%, smoke opacity (11.89–14.19%), carbon monoxide (CO) of 2.48–6.93%, hydrocarbon (HC) of 2.36–9.34%, and Nitrogen oxide (NO) emissions of 2.34–5.93%. The cylinder pressures and heat release rates (HRR) of RPB blends were 8.47–11.43% and 36.02–46.61% higher than diesel, respectively. The start of combustion angles (SOC) of RB and RPB blends were from −13 to −15 °C and from −13.2 to −15.6 crank angle degree (°CA) before top dead center (BTDC), but the combustion delays were 6–8 °C and 5.4–7.8 °C shorter when compared to diesel fuel which were −10 °C BTDC and 11 °C, respectively. It can be concluded that RPB blends showed better performance and emissions over the individual rubber seed and palm biodiesel blends and can replace diesel fuel in unmodified engines. Full article

(This article belongs to the Section A: Sustainable Energy)

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15 pages, 1287 KiB

Open AccessArticle

A Thermal Rating Calculation Approach for Wind Power Grid-Integrated Overhead Lines

by Mengxia Wang¹, Mingqiang Wang^1,*, Jinxin Huang², Zhe Jiang³

and Jinyan Huang⁴

¹ Key Laboratory of Power System Intelligent Dispatch and Control, Shandong University, Jinan 250061, China

² State Grid of Technology College, Jinan 250002, China

³ Electric Power Research Institute, State Grid Shandong Electric Power Company, Jinan 250003, China

⁴ ZaoZhuang Power Supply Company of State Grid Shandong Electric Power Company, ZaoZhuang 264000, China

Energies 2018, 11(6), 1523; https://doi.org/10.3390/en11061523 - 12 Jun 2018

Cited by 3 | Viewed by 2790

Abstract

Currently, the rapid increase in wind power integration in power systems is resulting in an increasing power flow in the grid-integrated power transmission lines of wind farms. The wind power curtailment caused by the current limits (thermal ratings) of the wind power integration [...] Read more.

Currently, the rapid increase in wind power integration in power systems is resulting in an increasing power flow in the grid-integrated power transmission lines of wind farms. The wind power curtailment caused by the current limits (thermal ratings) of the wind power integration overhead lines (WPIOLs) is becoming increasingly common. Aiming at this issue, the influence of conductor heating on the loss of tensile strength (LOTS) and sag of a WPIOL was analyzed in this paper. Then a decision model is proposed for the thermal ratings of WPIOLs, which regards the minimized wind power curtailment as objective and introduces permissible cumulative LOTS and sag of the conductor as constraints. Based on this model, the thermal rating for a WPIOL can be decided to ensure the expected service life of the conductor and safe clearance. In addition, case studies are used to demonstrate that the proposed approach is capable of improving the conservatism of conventional thermal rating calculation and reducing the wind power curtailment by improving the utilization efficiency of WPIOLs. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 2464 KiB

Open AccessArticle

Waterflooding Huff-n-puff in Tight Oil Cores Using Online Nuclear Magnetic Resonance

by Ting Chen^1,2,3,*

, Zhengming Yang^2,3, Yunhong Ding^2,3, Yutian Luo^1,2,3, Dan Qi^1,2,3, Wei Lin^1,2,3

and Xinli Zhao^1,2,3

¹ School of Engineering Sciences, University of Chinese Academy of Sciences, Beijing 100049, China

² Institute of Porous Flow and Fluid Mechanics, Chinese Academy of Sciences, Langfang 065007, China

³ PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China

Energies 2018, 11(6), 1524; https://doi.org/10.3390/en11061524 - 12 Jun 2018

Cited by 38 | Viewed by 3784

Abstract

Given the difficulty in developing waterflooding in tight oil reservoirs, using waterflooding huff-n-puff is an effective method to improve oil recovery. Online nuclear magnetic resonance (NMR) can detect the change in internal oil and water during the core displacement process, and magnetic resonance [...] Read more.

Given the difficulty in developing waterflooding in tight oil reservoirs, using waterflooding huff-n-puff is an effective method to improve oil recovery. Online nuclear magnetic resonance (NMR) can detect the change in internal oil and water during the core displacement process, and magnetic resonance imaging (MRI) in real time. To improve the tight oil reservoir development effectiveness, cores with different permeability were selected for a waterflooding huff-n-puff experiment. Combined with online NMR equipment, the fluid saturation, recovery rate, and residual oil distribution were studied. The experiments showed that, for tight oil cores, more than 80% of the pores were sub-micro- and micro-nanopores. More than 77.8% of crude oil existed in the sub-micro- and micropores, and movable fluids mainly existed in the micropores with a radius larger than 1 μm. The NMR data and the MRI images both demonstrated that the recovery ratio of waterflooding after waterflooding huff-n-puff was higher than that of conventional waterflooding, and, therefore, residual oil was lower. Choosing two cycles’ of waterflooding, huff-n-puff was more suitable for tight oil reservoir development. The production of crude oil increased by 22.2% in the field pilot test, which preliminarily proved that waterflooding huff-n-puff was suitable for tight oil reservoirs. Full article

(This article belongs to the Section L: Energy Sources)

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18 pages, 8177 KiB

Open AccessArticle

Application of Synchrosqueezed Wavelet Transforms for Extraction of the Oscillatory Parameters of Subsynchronous Oscillation in Power Systems

by Yan Zhao^1,*, Haohan Cui², Hong Huo² and Yonghui Nie³

¹ School of Power Transmission and Distribution Technology, Northeast Electric Power University, Jilin 132012, China

² School of Electrical Engineering, Northeast Electric Power University, Jilin 132012, China

³ Academic Administration Office, Northeast Electric Power University, Jilin 132012, China

Energies 2018, 11(6), 1525; https://doi.org/10.3390/en11061525 - 12 Jun 2018

Cited by 12 | Viewed by 3495

Abstract

The most classical subsynchronous oscillation (SSO) mode extraction methods have some shortcomings, such as lower mode identification and poor anti-noise properties. Thus, this paper proposes a new time-frequency analysis method, namely, synchrosqueezed wavelet transforms (SWT). SWT combines the advantages of empirical mode decomposition [...] Read more.

The most classical subsynchronous oscillation (SSO) mode extraction methods have some shortcomings, such as lower mode identification and poor anti-noise properties. Thus, this paper proposes a new time-frequency analysis method, namely, synchrosqueezed wavelet transforms (SWT). SWT combines the advantages of empirical mode decomposition (EMD) and wavelet, which has the adaptability of EMD, and improve the ability of anti-mode mixing on EMD and wavelet. Thus, better anti-noise property and higher mode identification can be achieved. Firstly, the SSO signal is transformed by SWT and its time-frequency spectrum is obtained. Secondly, the attenuation characteristic of each intrinsic mode type (IMT) component in its time-frequency spectrum is analyzed by an automatic identification algorithm, and determine which IMT component needs reconstruction. After that, the selected IMT components with divergent characteristic are reconstructed. Thirdly, high-accuracy detection for mode parameter identification is achieved by the Hilbert transform (HT). Simulation and application examples prove the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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12 pages, 1392 KiB

Open AccessArticle

Comparative Performance of Semi-Transparent PV Modules and Electrochromic Windows for Improving Energy Efficiency in Buildings

by Nuria Martín-Chivelet^1,*, Cecilia Guillén²

, Juan Francisco Trigo², José Herrero², Juan José Pérez¹ and Faustino Chenlo¹

¹ CIEMAT—Building Integrated Photovoltaics Group, Avda. Complutense, 40, 28040 Madrid, Spain

² CIEMAT—Polycrystalline Materials Group, Avda. Complutense, 40, 28040 Madrid, Spain

Energies 2018, 11(6), 1526; https://doi.org/10.3390/en11061526 - 12 Jun 2018

Cited by 27 | Viewed by 3334

Abstract

Advanced constructive materials, such as electrochromic smart windows (ECSWs) and building integrated photovoltaics modules (BIPV), can improve the energy efficiency in buildings. A good optical and thermal characterization of these elements is necessary to assess and compare their performance. The existing testing procedures [...] Read more.

Advanced constructive materials, such as electrochromic smart windows (ECSWs) and building integrated photovoltaics modules (BIPV), can improve the energy efficiency in buildings. A good optical and thermal characterization of these elements is necessary to assess and compare their performance. The existing testing procedures for glass in buildings are applied to both types of elements, and it is considered that while the optical procedures are suitable and allow good comparison of the two technologies, the indoor thermal testing procedures are not valid for BIPV nor ECSWs, because temperature of these absorbing elements strongly depend on the irradiance, something not considered in the current standards. To show and characterize this dependence, simultaneously monitoring of different photovoltaics (PV) modules and electrochromic windows has been performed outdoors under solar irradiance. A relationship between the surface temperature, the irradiance, and the ambient temperature has been obtained for each sample to compare both technologies. Full article

(This article belongs to the Special Issue Energy Efficient and Smart Cities)

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32 pages, 2940 KiB

Open AccessArticle

China’s Contributions to Global Green Energy and Low-Carbon Development: Empirical Evidence under the Belt and Road Framework

by Hongze Li^1,2, FengYun Li^1,* and Xinhua Yu¹

¹ School of Economics and Management, North China Electric Power University, Beijing 102206, China

² Beijing Key Laboratory of New Energy and Low-Carbon Development, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(6), 1527; https://doi.org/10.3390/en11061527 - 12 Jun 2018

Cited by 30 | Viewed by 3305

Abstract

This paper aims to explore China’s contributions to global green energy and low-carbon (GELC) development based on the Belt and Road (B&R) Initiative. Basic situations of B&R countries reveal an urgent requirement for developing green energy. Carbon intensity is an efficient indicator reflecting [...] Read more.

This paper aims to explore China’s contributions to global green energy and low-carbon (GELC) development based on the Belt and Road (B&R) Initiative. Basic situations of B&R countries reveal an urgent requirement for developing green energy. Carbon intensity is an efficient indicator reflecting the degree of GELC development, which is affected by many factors. By analyzing the spatial distribution of carbon intensities in 29 B&R countries excluding China, the spatial agglomeration and positive radiation effects are discovered, while the negative radiation effects are disappearing, indicating that the studied B&R countries lack an effective driving mechanism to promote GELC development. Besides, the spatial convergence results support significant absolute and conditional convergences in the 29 B&R countries, and a faster convergence speed when considering control variables. Therefore, B&R countries trend to converge to a steady stable carbon intensity to achieve the GELC development. Furthermore, the investment rate and openness play a driving role in pushing the decrease of carbon intensity growth rate, revealing that the B&R Initiative can promote reducing the global carbon emissions and developing global green energy. Moreover, the carbon intensity of the country will be positively affected by those of the surrounding areas, indicating that reducing carbon emission is a global governance issue requiring the participation of all countries. Finally, several policy suggestions are proposed to promote the global GELC development under B&R framework, according to the empirical findings. Full article

(This article belongs to the Section A: Sustainable Energy)

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22 pages, 5952 KiB

Open AccessArticle

Potential of Russian Regions to Implement CO₂-Enhanced Oil Recovery

by Alexey Cherepovitsyn¹

, Sergey Fedoseev², Pavel Tcvetkov^3,*

, Ksenia Sidorova¹ and Andrzej Kraslawski^4,5

¹ Organization and Management Department, Saint-Petersburg Mining University, 21 Line, 2, St. Petersburg 199106, Russia

² Kola Science Centre of the RAS, Fersman st., 24a, Apatite 184209, Russia

³ Department of Informatics and Computer Technologies, Saint-Petersburg Mining University, 21 Line, 2, St. Petersburg 199106, Russia

⁴ School of Business and Management, Lappeenranta University of Technology, P.O. Box 20, FI-53851 Lappeenranta, Finland

⁵ Faculty of Process and Environmental Engineering, Lodz University of Technology, ul. Wolczanska 213, 90-924 Lodz, Poland

Energies 2018, 11(6), 1528; https://doi.org/10.3390/en11061528 - 12 Jun 2018

Cited by 19 | Viewed by 6929

Abstract

The paper assesses the techno-economic potential of Russia to implement carbon capture and storage technologies that imply the capture of anthropogenic CO₂ and its injection into geologic reservoirs for long-term storage. The focus is on CO₂ enhanced oil recovery projects that [...] Read more.

The paper assesses the techno-economic potential of Russia to implement carbon capture and storage technologies that imply the capture of anthropogenic CO₂ and its injection into geologic reservoirs for long-term storage. The focus is on CO₂ enhanced oil recovery projects that seem to be the most economically promising option of carbon capture and storage. The novelty of the work lies in the formulation of a potential assessment method of CO₂ enhanced oil recovery, which allows for establishing a connection between energy production and oil extraction from the viewpoint of CO₂ supply and demand. Using linear optimization, the most promising combinations of CO₂ sources and sinks are identified and an economic evaluation of these projects is carried out. Based on this information, regions of Russia are ranked according to their prospects in regards to CO₂ capture and enhanced oil recovery storage. The results indicate that Russia has a significant potential to utilize its power plants as CO₂ sources for enhanced oil recovery projects. It has been estimated that 71 coal-fired power plants, and 185 of the gas-fired power plants of Russia annually produce 297.1 and 309.6 Mt of CO₂ that can cover 553.4 Mt of the demand of 322 Russian oil fields. At the same time, the total CO₂ storage capacity of the Russian fields is estimated at 7382.6 Mt, however, due to geological and technical factors, only 22.6% can be used for CO₂-EOR projects. Of the 183 potential projects identified in the regional analysis phase, 99 were found to be cost-effective, with an average unit cost of € 19.07 per ton of CO₂ and a payback period of 8.71 years. The most promising of the estimated regions is characterized by a well-developed energy industry, relatively low transportation costs, numerous large and medium-sized oil fields at the final stages of development, and favorable geological conditions that minimize the cost of injection. Geographically, they are located in the North-Western, Volga, and Ural Federal districts. Full article

(This article belongs to the Special Issue Enhanced Oil Recovery)

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19 pages, 7467 KiB

Open AccessArticle

Novel Method for Identifying Fault Location of Mixed Lines

by Lei Wang^1,*

, Hui Liu¹, Le Van Dai^2,3

and Yuwei Liu¹

¹ School of Electrical and Electronic Engineering, Hubei University of Technology, Wuhan 430068, China

² Institute of Research and Development, Duy Tan University, Danang 550000, Vietnam

³ Office of Science Research and Development, Lac Hong University, Bien Hoa 810000, Vietnam

Energies 2018, 11(6), 1529; https://doi.org/10.3390/en11061529 - 12 Jun 2018

Cited by 91 | Viewed by 3968

Abstract

The identification and localization of a fault are a basic requirement for optimal operation of a modern power system. An effective fault identification method significantly reduces outage time, improves the electrical supply reliability, and enhances the speed of protection control. This paper proposes [...] Read more.

The identification and localization of a fault are a basic requirement for optimal operation of a modern power system. An effective fault identification method significantly reduces outage time, improves the electrical supply reliability, and enhances the speed of protection control. This paper proposes a novel method based on the theory of the two-terminal traveling wave range to identify the fault location in a voltage source converter based high voltage direct current (VSC-HVDC) system containing mixed cable and overhead line segments. It uses variational mode decomposition (VMD) and the Teager energy operator (TEO) as a new method to detect the traveling wave fault through a fault signal. The effectiveness of the proposed method is verified via time domain simulation of the hybrid VSC-HVDC transmission system using PSCAD/EMTDC and MATLAB software. Simulation results show that the proposed method demonstrates high fault location accuracy and excellent robustness with a slight effect on transient resistance and fault types, and that it performs better than the existing transient detection techniques, such as wavelet transform and ensemble empirical mode decomposition. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 30637 KiB

Open AccessArticle

LES Investigation of Terrain-Induced Turbulence in Complex Terrain and Economic Effects of Wind Turbine Control

by Takanori Uchida

Research Institute for Applied Mechanics (RIAM), Kyushu University, 6-1 Kasuga-kouen, Kasuga, Fukuoka 816-8580, Japan

Energies 2018, 11(6), 1530; https://doi.org/10.3390/en11061530 - 12 Jun 2018

Cited by 14 | Viewed by 3850

Abstract

In the present study, numerical wind simulation was conducted by reproducing the realistic topography near wind turbine sites with high spatial resolutions and using the Large-Eddy Simulation (LES) technique. The topography near wind turbine sites serves as the origin of the terrain-induced turbulence. [...] Read more.

In the present study, numerical wind simulation was conducted by reproducing the realistic topography near wind turbine sites with high spatial resolutions and using the Large-Eddy Simulation (LES) technique. The topography near wind turbine sites serves as the origin of the terrain-induced turbulence. The obtained numerical simulation results showed that the terrain-induced turbulence is generated at a small terrain feature located upstream of the wind turbine. The generated terrain-induced turbulence affects the wind turbine directly. The wind speed and wind direction at the wind turbine site are significantly changed with time. In the present study, a combination of the series of wind simulation results and on-site operation experience led to a decision to adopt an “automatic shutdown program”. Here, an “automatic shutdown program” means the automatic suspension of wind turbine operation based on the wind speed and wind direction meeting the conditions associated with significant effects of terrain-induced turbulence at a wind turbine site. The adoption of the “automatic shutdown program” has successfully led to a large reduction in the number of occurrences of wind turbine damage, thus, creating major positive economic effects. Full article

(This article belongs to the Collection Wind Turbines)

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16 pages, 7314 KiB

Open AccessArticle

Energy Management Strategy for Hybrid Electric Vehicle Based on Driving Condition Identification Using KGA-Means

by Shuxian Li¹, Minghui Hu^1,*, Changchao Gong¹, Sen Zhan² and Datong Qin¹

¹ State Key Laboratory of Mechanical Transmissions, School of Automotive Engineering, Chongqing University, Chongqing 400044, China

² Chongqing Changan Automobile Co., Ltd., Chongqing 400023, China

Energies 2018, 11(6), 1531; https://doi.org/10.3390/en11061531 - 12 Jun 2018

Cited by 19 | Viewed by 4846

Abstract

In order to solve the problem related to adaptive energy management strategies based on driving condition identification being difficult to be applied to a real hybrid electric vehicle (HEV) controller, this paper proposes an energy management strategy by combining the driving condition identification [...] Read more.

In order to solve the problem related to adaptive energy management strategies based on driving condition identification being difficult to be applied to a real hybrid electric vehicle (HEV) controller, this paper proposes an energy management strategy by combining the driving condition identification algorithm based on genetic optimized K-means clustering algorithm (KGA-means), and the equivalent consumption minimization strategy (ECMS). The simulation results show that compared with ECMS, the energy management strategy proposed in this article drives the engine working point closer to the best efficiency curve, and smooths out the state of charge (SOC) change and better maintains the SOC in a highly efficient area. As a result, the vehicle fuel consumption reduces by 6.84%. Full article

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18 pages, 3705 KiB

Open AccessArticle

Static and Dynamic Networking of Smart Meters Based on the Characteristics of the Electricity Usage Information

by Yaxin Huang¹

, Yunlian Sun^1,* and Shimin Yi²

¹ School of Electrical Engineering, Wuhan University, Wuhan 430072, China

² Guangdong Power Grid Co., Ltd., Guangzhou 510620, China

Energies 2018, 11(6), 1532; https://doi.org/10.3390/en11061532 - 12 Jun 2018

Cited by 4 | Viewed by 3051

Abstract

The normal communication between smart meter and concentrator is a key factor influencing the normal function of users’ power consumption systems. To solve the communication failure of the smart meter caused by the signal conflict as well as the collected consecutive information abnormality [...] Read more.

The normal communication between smart meter and concentrator is a key factor influencing the normal function of users’ power consumption systems. To solve the communication failure of the smart meter caused by the signal conflict as well as the collected consecutive information abnormality from the same smart meter, according to the chain optimization index, the networking method of static and dynamic combination proposed in this paper is first used to picked out the optimal relay for a smart meter belonging to multiple relay communication ranges. Meanwhile, the communication with other secondary relays is closed to avoid signal conflict. Then the paper forms different combinations of collected data and these combinations are trained in the extreme learning machine (ELM) to find the characteristics value of power consumption information. Finally, in MATLAB simulation, if ELM detects the abnormal information, new communication path could be promptly found through dynamic adjustment of chain optimization weighted coefficient and the weighted coefficient of the number of the relayed smart meters. It solves the problem of consecutive information abnormality from the same smart meter and raises the reliability of smart meter’s communication, having a significantly meaning to guarantee the normal function of users’ power consumption system. Full article

(This article belongs to the Collection Smart Grid)

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16 pages, 3797 KiB

Open AccessArticle

The Effect of Control Strategy on Tidal Stream Turbine Performance in Laboratory and Field Experiments

by Carwyn Frost^1,*

, Ian Benson¹, Penny Jeffcoate², Björn Elsäßer³

and Trevor Whittaker¹

¹ School of Natural and Built Environment, Queens University Belfast, David Keir Building, Queen’s University, Belfast BT7 1NN, UK

² Sustainable Marine Energy, Edinburgh EH6 6QW, UK

³ Danish Hydraulics Institute (DHI), Ports and Offshore Technology, Agern Allé 5, 2970 Hørsholm, Danmark

Energies 2018, 11(6), 1533; https://doi.org/10.3390/en11061533 - 12 Jun 2018

Cited by 14 | Viewed by 3674

Abstract

The first aim of the research presented here is to examine the effect of turbine control by comparing a passive open-loop control strategy with a constant rotational speed proportional–integral–derivative (PID) feedback loop control applied to the same experimental turbine. The second aim is [...] Read more.

The first aim of the research presented here is to examine the effect of turbine control by comparing a passive open-loop control strategy with a constant rotational speed proportional–integral–derivative (PID) feedback loop control applied to the same experimental turbine. The second aim is to evaluate the effect of unsteady inflow on turbine performance by comparing results from a towing-tank, in the absence of turbulence, with results from the identical machine in a tidal test site. The results will also inform the reader of: (i) the challenges of testing tidal turbines in unsteady tidal flow conditions in comparison to the controlled laboratory environment; (ii) calibration of acoustic Doppler flow measurement instruments; (iii) characterising the inflow to a turbine and identifying the uncertainties from unsteady inflow conditions by adaptation of the International Electrotechnical Commission technical specification (IEC TS): 62600-200. The research shows that maintaining a constant rotational speed with a control strategy yields a 13.7% higher peak power performance curve in the unsteady flow environment, in comparison to an open-loop control strategy. The research also shows an 8.0% higher peak power performance in the lab compared to the field, demonstrating the effect of unsteady flow conditions on power performance. The research highlights the importance of a tidal turbines control strategy when designing experiments. Full article

(This article belongs to the Special Issue Wave and Tidal Energy)

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30 pages, 11758 KiB

Open AccessArticle

Rapid Fault Diagnosis of a Back-to-Back MMC-HVDC Transmission System under AC Line Fault

by Qing Huai^1,*

, Kaipei Liu¹, Liang Qin¹

, Jian Le¹, Kun Wang¹, Shu Zhu¹, Yuye Li¹, Xiaobing Liao¹ and Hua Ding²

¹ School of Electrical Engineering, Wuhan University, Wuhan 430072, China

² State Grid Energy Conservation Service Co., Ltd., Beijing 100052, China

Energies 2018, 11(6), 1534; https://doi.org/10.3390/en11061534 - 12 Jun 2018

Cited by 5 | Viewed by 2690

Abstract

The integration of a modular multilevel converter-based high-voltage direct current (MMC-HVDC) transmission system in power networks has led to a high requirement for the rapidity of fault recognition. This study focused on the rapid fault diagnosis of an alternating current (AC) line fault [...] Read more.

The integration of a modular multilevel converter-based high-voltage direct current (MMC-HVDC) transmission system in power networks has led to a high requirement for the rapidity of fault recognition. This study focused on the rapid fault diagnosis of an alternating current (AC) line fault in a back-to-back (BTB) MMC-HVDC system via fault detection and classification. Discrete wavelet transform and modulus maxima were applied to extract the fault features. Phase-mode transformation and normalization were adopted to widen the application range. Simulation and calculation results indicated that the proposed method can detect all fault types in an AC transmission line on the basis of single-side fault information within 1 ms under different values of transition resistance, fault inception angle, and fault distance. The BTB MMC-HVDC model was built using real-time laboratory (RT-LAB) based on the matrix laboratory (MATLAB) software platform, and the fault diagnosis algorithm was performed in MATLAB. Full article

(This article belongs to the Section F: Electrical Engineering)

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11 pages, 4270 KiB

Open AccessArticle

Preparation of Hierarchical Porous Carbon from Waterweed and Its Application in Lithium/Sulfur Batteries

by Chunyong Liang¹, Xiaomin Zhang¹, Yan Zhao^1,*, Taizhe Tan², Yongguang Zhang^1,* and Zhihong Chen^3,*

¹ School of Materials Science & Engineering, Research Institute for Energy Equipment Materials, Hebei University of Technology, Tianjin 300130, China

² Synergy Innovation Institute of GDUT, Heyuan 517000, China

³ Shenyang Institute of Automation, Guangzhou, Chinese Academy of Sciences, Guangzhou 511458, China

Energies 2018, 11(6), 1535; https://doi.org/10.3390/en11061535 - 13 Jun 2018

Cited by 10 | Viewed by 2297

Abstract

A nanostructured carbon (NSC) material with a hierarchical porous structure is synthesized through the carbonization of a waterweed, namely Echinodorus amazonicus Rataj. The fabricated NSC is used as an electrode material for sulfur of lithium/sulfur (Li/S) batteries. The NSC provides for a high [...] Read more.

A nanostructured carbon (NSC) material with a hierarchical porous structure is synthesized through the carbonization of a waterweed, namely Echinodorus amazonicus Rataj. The fabricated NSC is used as an electrode material for sulfur of lithium/sulfur (Li/S) batteries. The NSC provides for a high pore volume (0.19 cm³ g⁻¹) and large specific surface area (111.25 m² g⁻¹). Because of the highly hierarchical porous structure of the NSC material, allowing polysulfides to remain in the carbon framework after cycling, the sulfur/NSC composite exhibits an excellent electrochemical performance. Full article

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14 pages, 734 KiB

Open AccessArticle

The Impact of Financial Development on Energy Consumption: Evidence from an Oil-Rich Economy

by Shahriyar Mukhtarov^1,2, Jeyhun I. Mikayilov^3,4,5,*, Jeyhun Mammadov¹ and Elvin Mammadov^1,6

¹ Department of Economics and Management, Khazar University, 41 Mehseti Str., Baku AZ1096, Azerbaijan

² Department of Economics and Management, Azerbaijan State University of Economics (UNEC), Istiqlaliyyat Str. 6, Baku AZ1141, Azerbaijan

³ King Abdullah Petroleum Studies and Research Center, P.O. Box 88550, Riyadh 11672, Saudi Arabia

⁴ Department of Statistics and Econometrics, Azerbaijan State University of Economics, Istiqlaliyyat Str., 6, Baku AZ1001, Azerbaijan

⁵ Institute for Scientific Research on Economic Reforms, 88a, Hasan Bey Zardabi Avenue, Baku AZ1011, Azerbaijan

⁶ School of Business, Azerbaijan State University of Economics (UNEC), Istiqlaliyyat Str. 6, Baku AZ1141, Azerbaijan

Energies 2018, 11(6), 1536; https://doi.org/10.3390/en11061536 - 13 Jun 2018

Cited by 58 | Viewed by 5152

Abstract

This paper examines the relationship between energy consumption, financial development, and economic growth in an oil-rich economy—Azerbaijan—employing cointegration techniques to the data ranging from 1992 to 2015. The results confirm the existence of a long-run relationship among the variables. Also, we find that [...] Read more.

This paper examines the relationship between energy consumption, financial development, and economic growth in an oil-rich economy—Azerbaijan—employing cointegration techniques to the data ranging from 1992 to 2015. The results confirm the existence of a long-run relationship among the variables. Also, we find that there is a positive and statistically significant impact of financial development and economic growth on energy consumption in the long-run. The positive and statistically significant coefficient of financial development and decreasing volatility in the proxy for financial development over time can be considered as improvements in the financial system. Estimation results show that a 1% increase in financial development, proxied by the private credit indicator, and economic development increases energy consumption by 0.19% and 0.12%, respectively. The positive and significant impact of financial development on energy consumption on the backdrop of relatively cheaper energy prices due to rich oil and gas resources, should be considered by policymakers in their energy use, financial development, and economic growth related decisions. Full article

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20 pages, 2780 KiB

Open AccessArticle

Jerk Analysis of a Power-Split Hybrid Electric Vehicle Based on a Data-Driven Vehicle Dynamics Model

by Xiaohua Zeng¹, Haoyong Cui¹, Dafeng Song^1,*, Nannan Yang¹, Tong Liu¹, Huiyong Chen², Yinshu Wang² and Yulong Lei¹

¹ State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun 130025, China

² Zhengzhou Yutong Bus Co., Ltd., Zhengzhou 450016, China

Energies 2018, 11(6), 1537; https://doi.org/10.3390/en11061537 - 13 Jun 2018

Cited by 22 | Viewed by 5388

Abstract

Given its highly coupled multi-power sources with diverse dynamic response characteristics, the mode transition process of a power-split Hybrid Electric Vehicle (HEV) can easily lead to unanticipated passenger-felt jerks. Moreover, difficulties in parameter estimation, especially power-source dynamic torque estimation, result in new challenges [...] Read more.

Given its highly coupled multi-power sources with diverse dynamic response characteristics, the mode transition process of a power-split Hybrid Electric Vehicle (HEV) can easily lead to unanticipated passenger-felt jerks. Moreover, difficulties in parameter estimation, especially power-source dynamic torque estimation, result in new challenges for jerk reduction. These two aspects entangle with each other and constitute a complicated coupling problem which obstructs the realization of a valid anti-jerk method. In this study, a vehicle dynamics model with reference to a data-driven modeling method is first established, integrating a full-time artificial neural network engine dynamic model that can accurately predict engine dynamic torque. Then the essential reason for the occurrence of vehicle jerks in real driving conditions is analyzed. Finally, to smooth the mode transition process, a more practical anti-jerk strategy based on power-source torque changing rate limitation (TCRL) is proposed. Verification studies indicate that the data-driven vehicle dynamics model has enough accuracy to reflect the vehicle dynamic characteristics, and the proposed TCRL strategy could reduce the vehicle jerk by up to 85.8%, without any sacrifice of vehicle performance. This research provides a feasible method for precise modeling of vehicle dynamics and a reference for improving the riding comfort of hybrid electric vehicles. Full article

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17 pages, 2887 KiB

Open AccessArticle

A Power Coupling System for Electric Tracked Vehicles during High-Speed Steering with Optimization-Based Torque Distribution Control

by Hong Huang^1,2, Li Zhai^1,2,*

and Zeda Wang^1,2

¹ National Engineering Laboratory for Electric Vehicles, Beijing Institute of Technology, Beijing 100081, China

² Co-Innovation Center of Electric Vehicles in Beijing, Beijing Institute of Technology, Beijing 100081, China

Energies 2018, 11(6), 1538; https://doi.org/10.3390/en11061538 - 13 Jun 2018

Cited by 11 | Viewed by 5199

Abstract

It is significant to improve the steering maneuverability of dual-motor drive tracked vehicles (2MDTVs), which have wide applications in the tracked vehicle industry. In this paper, we focus on the problem of insufficient propulsion motor power during high-speed steering. Some correction formulas are [...] Read more.

It is significant to improve the steering maneuverability of dual-motor drive tracked vehicles (2MDTVs), which have wide applications in the tracked vehicle industry. In this paper, we focus on the problem of insufficient propulsion motor power during high-speed steering. Some correction formulas are introduced to improve the accuracy of the mathematical model. A steering coupling system and an optimization-based torque distribution control strategy is adopted to improve the lateral stability of the vehicle. The 2MDTV model and the proposed control strategy are built in the multi-body software RecurDyn and the control software Matlab/Simulink, respectively. According to the real-time steering simulation by the hardware-in-the-loop (HIL) method, the 2MDTV with the coupling device outputs more power during high-speed steering. The results show the speed during steering is quite high though, the stability of the vehicle can be achieved due to using the torque distribution strategy, and the steering maneuverability of the vehicle is also improved. Full article

(This article belongs to the Special Issue The International Symposium on Electric Vehicles (ISEV2017))

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19 pages, 5386 KiB

Open AccessArticle

Study of Power Quality at the Point of Common Coupling of a Low Voltage Grid and a Distributed Generation System of 7.8 kWp in a Tropical Region

by Agustín Valverde Granja¹

, Teófilo Miguel De Souza², Pedro Magalhães Sobrinho² and Daniel Felipe Arévalo Santos^1,*

¹ Facultad de Ingeniería, Universidad de Ibagué, Ibagué 730001, Colombia

² School of Engineering, Universidade Estadual Paulista (UNESP) Câmpus Guaratinguetá, Guaratinguetá 01049-010, Brazil

Energies 2018, 11(6), 1539; https://doi.org/10.3390/en11061539 - 13 Jun 2018

Cited by 9 | Viewed by 2896

Abstract

In this paper we analyze an experimental 1000 kWh/month distributed generation system in a tropical region connected to a point of common coupling in a low voltage grid that was characterized according to NTC 5001. This photovoltaic system has 7.8 kWp and uses [...] Read more.

In this paper we analyze an experimental 1000 kWh/month distributed generation system in a tropical region connected to a point of common coupling in a low voltage grid that was characterized according to NTC 5001. This photovoltaic system has 7.8 kWp and uses 30 polycrystalline silicon-panels of 260 Wp each. Its maximum energy produced was 850 kWh/month, equivalent to 72.65% of the installed capacity. Finally, there was an increase of 2% with respect to the minimum voltage value that was recorded. The voltage unbalance decreases between 3.5 and 70% and voltage harmonics in each line increased by 7% on line U1, 0.8% on U2, 3% on U3 and current harmonics have a 22% increase. Likewise, the total active and reactive power were increased by 58% and 42% respectively, and the thermography study allowed to establish a temperature increase at the point of common coupling of 7.5%. Therefore, it is expected that this paper can serve as a reference for the application of Colombian law 1715 in solar energy. Full article

(This article belongs to the Special Issue Building renewable energy and thermal energy storage system 2018)

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14 pages, 4300 KiB

Open AccessArticle

Pressure Detrending in Harmonic Pulse Test Interpretation: When, Why and How

by Dario Viberti

, Eloisa Salina Borello^*

and Francesca Verga

Department of Environment, Land and Infrastructure Engineering (DIATI), Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Turin, Italy

Energies 2018, 11(6), 1540; https://doi.org/10.3390/en11061540 - 13 Jun 2018

Cited by 4 | Viewed by 3055

Abstract

In reservoir engineering, one of the main sources of information for the characterization of reservoir and well parameters is well testing. An alternative to the standard drawdown/buildup test is Harmonic Pulse Testing (HPT) because it can provide well performance and reservoir behavior monitoring [...] Read more.

In reservoir engineering, one of the main sources of information for the characterization of reservoir and well parameters is well testing. An alternative to the standard drawdown/buildup test is Harmonic Pulse Testing (HPT) because it can provide well performance and reservoir behavior monitoring without having to interrupt field production, which is appealing from an economic standpoint. Recorded pressure analysis is performed in the frequency domain by adopting a derivative approach similar to conventional well testing. To this end, pressure and rate data must be decomposed into harmonic components. Test interpretability can be significantly improved if pressure data are detrended prior to interpretation, filtering out non periodic events such as discontinuous production from neighboring wells and flow regime variations that did not respect the designed test periodicity. Therefore, detrending offers the possibility of overcoming the limitation of HPT applicability due to the difficulty of imposing a regularly pulsing rate for the whole test duration (typically lasting several days). This makes HPT attractive for well performance monitoring, especially in gas reservoirs converted to underground gas storage. In this paper, different detrending methodologies are discussed and applied to synthetic and real data. Results show that, if a proper detrending strategy is adopted, information provided by HPT interpretation can be maximized and/or improved. Full article

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17 pages, 18251 KiB

Open AccessArticle

Forecasting the Long-Term Wind Data via Measure-Correlate-Predict (MCP) Methods

by Sajid Ali^1,2, Sang-Moon Lee² and Choon-Man Jang^1,2,*

¹ Smart City Construction Engineering, University of Science & Technology (UST), 217, Gajeong-ro, Yuseong-gu, Daejeon 34113, Korea

² Environmental & Plant Engineering Research Division, Korea Institute of Civil Engineering and Building Technology (KICT), Daehwa-dong 283, Goyangdae-ro, Ilsanseo-Gu, Goyang-si 10223, Korea

Energies 2018, 11(6), 1541; https://doi.org/10.3390/en11061541 - 13 Jun 2018

Cited by 8 | Viewed by 3745

Abstract

The current study aims to forecast and analyze wind data such as wind speed at a test site called “Urumsill” on Deokjeok Island, South Korea. The measured wind data available at the aforementioned test site are only for two years (2015 and 2016), [...] Read more.

The current study aims to forecast and analyze wind data such as wind speed at a test site called “Urumsill” on Deokjeok Island, South Korea. The measured wind data available at the aforementioned test site are only for two years (2015 and 2016), making it impossible to analyze the long-term wind characteristics. In order to overcome this problem, two measure-correlate-predict (MCP) techniques were adopted using long-term wind data (2000–2016), measured by a meteorological mast (met-mast) installed at a distance of 3 km from the test site. The wind data measured at the test site in 2016 were selected as training data to build the MCP models, whereas wind data of 2015 were used to test the accuracy of MCP models (test data). The wind data at both sites were measured at a height of 10 m and showed a good agreement for the year 2016 (training period). Using the comparison results of the year 2016, wind speed predictions were made for the rest of the years (2000–2016) at the test site. The forecasted values of wind speed had maximum relative error in the range of ±0.8 m/s for the test year of 2105. The predicted wind data values were further analyzed by estimating the mean wind speed, the Weibull shape, and the scale parameters, on a seasonal and an annual basis, in order to understand the wind behavior in the region. The accuracy and presence of possible errors in the forecasted wind data are discussed and presented. Full article

(This article belongs to the Special Issue Solar and Wind Energy Forecasting)

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19 pages, 9274 KiB

Open AccessArticle

Heat and Mass Transfer Behavior Prediction and Thermal Performance Analysis of Earth-to-Air Heat Exchanger by Finite Volume Method

by Qinggong Liu¹, Zhenyu Du^1,* and Yi Fan²

¹ College of Environmental Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China

² School of Engineering, University of Hull, Hull HU6 7RX, UK

Energies 2018, 11(6), 1542; https://doi.org/10.3390/en11061542 - 13 Jun 2018

Cited by 15 | Viewed by 3390

Abstract

A comprehensive numerical study on coupled heat and mass transfer in an earth-to-air heat exchanger (EAHE) is conducted by self-complied program based on the finite volume method. The soil thermal and moisture coupled characteristics in the vicinity of the pipe and the thermal [...] Read more.

A comprehensive numerical study on coupled heat and mass transfer in an earth-to-air heat exchanger (EAHE) is conducted by self-complied program based on the finite volume method. The soil thermal and moisture coupled characteristics in the vicinity of the pipe and the thermal performance of the EAHE are evaluated by a two-dimensional simulation model. The model of the EAHE is verified by the experimental data, which achieved a good agreement with each other. The numerical results show that there is an obvious moisture peak in the radial direction, and the peak position radially moves away from the wall of the pipe over time. It is also found that the thermal performance of the heat and mass transfer model in soil is better than the pure heat conduction model. Full article

(This article belongs to the Special Issue Building renewable energy and thermal energy storage system 2018)

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16 pages, 2364 KiB

Open AccessArticle

Three-Stage Anaerobic Sequencing Batch Reactor (ASBR) for Maximum Methane Production: Effects of COD Loading Rate and Reactor Volumetric Ratio

by Achiraya Jiraprasertwong¹, Kornpong Vichaitanapat¹, Malinee Leethochawalit² and Sumaeth Chavadej^1,3,*

¹ The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok 10330, Thailand

² Innovative Learning Center, Srinakharinwirot University, Bangkok 10110, Thailand

³ Center of Excellence on Petrochemical and Materials Technology, Chulalongkorn University, Bangkok 10330, Thailand

Energies 2018, 11(6), 1543; https://doi.org/10.3390/en11061543 - 13 Jun 2018

Cited by 14 | Viewed by 4774

Abstract

A three-stage anaerobic sequencing batch reactor system was developed as a new anaerobic process with an emphasis on methane production from ethanol wastewater. The three-stage anaerobic sequencing batch reactor system consisted of three bioreactors connected in series. It was operated at 37 °C [...] Read more.

A three-stage anaerobic sequencing batch reactor system was developed as a new anaerobic process with an emphasis on methane production from ethanol wastewater. The three-stage anaerobic sequencing batch reactor system consisted of three bioreactors connected in series. It was operated at 37 °C with a fixed recycle ratio of 1:1 (final effluent flow rate to feed flow rate) and the washout sludge from the third bioreactor present in the final effluent was allowed to be recycled to the first bioreactor. The pH of the first bioreactor was controlled at 5.5, while the pH values of the other two bioreactors were not controlled. Under the optimum chemical oxygen demand loading rate of 18 kg/m³d (based on the feed chemical oxygen demand load and total volume of the three bioreactors) with a bioreactor volumetric ratio of 5:5:20, the system provided the highest gas production performance in terms of yields of both hydrogen and methane and the highest overall chemical oxygen demand removal. Interestingly, the three-stage anaerobic sequencing batch reactor system gave a much higher energy production rate and a higher optimum chemical oxygen demand loading rate than previously reported anaerobic systems since it was able to maintain very high microbial concentrations in all bioreactors with very high values of both alkalinity and solution pH, especially in the third bioreactor, resulting in sufficient levels of micronutrients for anaerobic digestion. Full article

(This article belongs to the Section A: Sustainable Energy)

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20 pages, 4992 KiB

Open AccessArticle

The Integrated Switching Control Strategy for Grid-Connected and Islanding Operation of Micro-Grid Inverters Based on a Virtual Synchronous Generator

by Kai Shi, Guanglei Zhou, Peifeng Xu^*, Haihan Ye and Fei Tan

School of Electrical and Information Engineering, Jiangsu University, Zhenjiang 212000, China

Energies 2018, 11(6), 1544; https://doi.org/10.3390/en11061544 - 13 Jun 2018

Cited by 18 | Viewed by 2634

Abstract

In allusion to the virtual synchronous generator (VSG)-based voltage source inverters in micro-grids, an integrated control method combining a quasi-synchronization algorithm and an islanding detection algorithm is proposed to improve the power supply reliability and quality, which can simultaneously meet the operational requirements [...] Read more.

In allusion to the virtual synchronous generator (VSG)-based voltage source inverters in micro-grids, an integrated control method combining a quasi-synchronization algorithm and an islanding detection algorithm is proposed to improve the power supply reliability and quality, which can simultaneously meet the operational requirements of both grid-connected mode (GCM) and off-grid mode (OGM), and the smooth switching between them. The quasi-synchronization algorithm of the micro-grid inverter is designed to realize a flexible grid connection. Moreover, for quickly detecting islanding phenomena, a novel islanding detection algorithm based on the VSG’s inherent characteristics is put forward. Finally, the validity and availability of the proposed models and control strategies are comprehensively verified by simulation results based on Matlab/Simulink. Full article

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16 pages, 15525 KiB

Open AccessArticle

Exhaust Tuning of an Internal Combustion Engine by the Combined Effects of Variable Exhaust Pipe Diameter and an Exhaust Valve Timing System

by Pauras Sawant¹, Michael Warstler² and Saiful Bari^3,*

¹ Department of Mechanical Engineering and Engineering Science, University of North Carolina at Charlotte, Charlotte, NC 28223, USA

² Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USA

³ School of Engineering, University of South Australia, Mawson Lakes, SA 5095, Australia

Energies 2018, 11(6), 1545; https://doi.org/10.3390/en11061545 - 13 Jun 2018

Cited by 11 | Viewed by 15345

Abstract

Changes to engine geometry and specifications can produce better torque, power, volumetric efficiency and more. The technique known as wave tuning can lead to better engine torque and power. This paper focuses on increasing the engine torque by improving the exhaust fluid flow [...] Read more.

Changes to engine geometry and specifications can produce better torque, power, volumetric efficiency and more. The technique known as wave tuning can lead to better engine torque and power. This paper focuses on increasing the engine torque by improving the exhaust fluid flow through the exhaust manifold. Phasing and intensity of the pressure waves in the exhaust manifold have significant effects on scavenging, valve overlapping and pumping losses. In this research, individual and combined effects of variable exhaust runner diameter and exhaust valve timing on the fluid flow from exhaust of the engine are studied using computer simulation. An engine simulation software, Ricardo Wave, is utilized in this research. The analysis is conducted on a 1-D model of a KTM 510 cc single cylinder, four-stroke Sl engine. The data gathered shows that varying only the exhaust pipe diameter continuously with speed yields an average of 4.23% improvement in torque from the original engine model. However, due to practical constraints, the diameter is limited to vary in three steps (36 mm, 45 mm and 60 mm). This has reduced the average improvement of torque to 3.78%. Varying the valve timing alone gains an average of 1.94% improvement in torque. Varying both the exhaust pipe diameter in three steps and the exhaust valve timing yields an average of 4.69% improvement in torque. This average is conducted over the engine speed ranges from 2000 to 11,000 rpm. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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14 pages, 3853 KiB

Open AccessArticle

A Four-Level T-Type Neutral Point Piloted Inverter for Solar Energy Applications

by Saddam Shueai Alnamer^1,*

, Saad Mekhilef¹

and Hazlie Bin Mokhlis²

¹ Power Electronics and Renewable Energy Research Laboratory (PEARL), Department of Electrical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

² Department of Electrical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

Energies 2018, 11(6), 1546; https://doi.org/10.3390/en11061546 - 13 Jun 2018

Cited by 5 | Viewed by 4426

Abstract

Multilevel inverters provide an output signal with low harmonic distortion and superior output voltages. This work proposes a new four-level T-type neutral point piloted (T-NPP) topology with higher efficiency and low total harmonic distortion (THD) and with the ability to withstand high voltage [...] Read more.

Multilevel inverters provide an output signal with low harmonic distortion and superior output voltages. This work proposes a new four-level T-type neutral point piloted (T-NPP) topology with higher efficiency and low total harmonic distortion (THD) and with the ability to withstand high voltage stresses, especially for high-power applications. The proposed topology is designed in such manner that the direct current (DC)-voltage stresses split over the components with strong possibilities to increase the load current and switching frequency. However, the operation of the proposed topology is based on two essential principles. The first principle is that each upper and lower switch of each leg consists of two insulated gate bipolar transistors (IGBTs) connected in series in order to withstand high voltage stresses and make it split over the two IGBTs in each switch. The second principle is using the DC-link circuit (T1 & T2) to generate 2Vdc and 1Vdc by connecting the bidirectional switches of each leg to the DC-link’s mid-point. Furthermore, the proposed four-level T-NPP inverter outperforms other converters by the high number of output voltage level, low number of components, simple structure and higher efficiency. Finally, the proposed T-NPP topology concept was validated via simulation, experiments and theoretical analysis. Full article

(This article belongs to the Special Issue Power Electronics 2018)

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16 pages, 4721 KiB

Open AccessArticle

Space Charge Modulated Electrical Breakdown of Oil Impregnated Paper Insulation Subjected to AC-DC Combined Voltages

by Yuanwei Zhu¹, Shengtao Li^1,*, Daomin Min¹, Shijun Li¹, Huize Cui¹ and George Chen^1,2

¹ State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi’an 710049, China

² School of Electronics and Computer Science University of Southampton, Southampton SO17 1BJ, UK

Energies 2018, 11(6), 1547; https://doi.org/10.3390/en11061547 - 13 Jun 2018

Cited by 8 | Viewed by 3177

Abstract

Based on the existing acknowledgment that space charge modulates AC and DC breakdown of insulating materials, this investigation promotes the related investigation into the situations of more complex electrical stress, i.e., AC-DC combined voltages. Experimentally, the AC-DC breakdown characteristics of oil impregnated paper [...] Read more.

Based on the existing acknowledgment that space charge modulates AC and DC breakdown of insulating materials, this investigation promotes the related investigation into the situations of more complex electrical stress, i.e., AC-DC combined voltages. Experimentally, the AC-DC breakdown characteristics of oil impregnated paper insulation were systematically investigated. The effects of pre-applied voltage waveform, AC component ratio, and sample thickness on AC-DC breakdown characteristics were analyzed. After that, based on an improved bipolar charge transport model, the space charge profiles and the space charge induced electric field distortion during AC-DC breakdown were numerically simulated to explain the differences in breakdown characteristics between the pre-applied AC and pre-applied DC methods under AC-DC combined voltages. It is concluded that large amounts of homo-charges are accumulated during AC-DC breakdown, which results in significantly distorted inner electric field, leading to variations of breakdown characteristics of oil impregnated paper insulation. Therefore, space charges under AC-DC combined voltages must be considered in the design of converter transformers. In addition, this investigation could provide supporting breakdown data for insulation design of converter transformers and could promote better understanding on the breakdown mechanism of insulating materials subjected to AC-DC combined voltages. Full article

(This article belongs to the Section F: Electrical Engineering)

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13 pages, 2576 KiB

Open AccessArticle

Design Criterion of Damper Component of Passive-Type Mount Module without Using Base Mass-Block

by Chan-Jung Kim

Department of mechanical design engineering, Pukyong National University, Busan 48547, Korea

Energies 2018, 11(6), 1548; https://doi.org/10.3390/en11061548 - 13 Jun 2018

Cited by 5 | Viewed by 2107

Abstract

Passive-type mount modules have been used frequently to isolate excitation from the target mechanical system, and electric power plants use the mount devices to control the harmonic excitation source from a combustion engine. The mount structure is composed of a spring component, a [...] Read more.

Passive-type mount modules have been used frequently to isolate excitation from the target mechanical system, and electric power plants use the mount devices to control the harmonic excitation source from a combustion engine. The mount structure is composed of a spring component, a stacked thin-panel, and a heavy base-mass block, and installation as well as maintenance of the structures are difficult. To tackle this problem associated with mount modules, I investigate in this work the feasibility of a simplified mount module with no base mass-block; the harmonic frequency of interest was selected from 30 (Hz) to 120 (Hz) owing to the constant rotating speed of the combustion engine at 1800 (rev/min). The design criterion of the damper components was formulated from the response index at the electric power plant, and the influence of the damper component at the proposed mount was calculated theoretically from the linearized system models. The theoretical result was compared with the measured response index at the electric power plant, and the comparison result revealed the superior capability of the proposed mount module in controlling the reaction motion at the electric power plant. Full article

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17 pages, 7657 KiB

Open AccessArticle

Permanent Magnet Synchronous Motor with Different Rotor Structures for Traction Motor in High Speed Trains

by Marcel Torrent^1,*, José Ignacio Perat¹ and José Antonio Jiménez²

¹ Department of Electrical Engineering (DEE), Universitat Politècnica de Catalunya UPC BARCELONATECH, EPSEVG, Víctor Balaguer 1, 08800 Vilanova i la Geltrú, Barcelona, Spain

² Faculty of Civil Engineering, Universitat Politècnica de Catalunya UPC EPSEVG, Víctor Balaguer 1, 08800 Vilanova i la Geltrú, Barcelona, Spain

Energies 2018, 11(6), 1549; https://doi.org/10.3390/en11061549 - 13 Jun 2018

Cited by 41 | Viewed by 8491

Abstract

In this work we proposed to study the use of permanent magnet synchronous motors (PMSM) for railway traction in the high-speed trains (HST) of Renfe Operadora (the Spanish national railway operator). Currently, induction motors (IM) are used in AVE classes 102–112 trains, so, [...] Read more.

In this work we proposed to study the use of permanent magnet synchronous motors (PMSM) for railway traction in the high-speed trains (HST) of Renfe Operadora (the Spanish national railway operator). Currently, induction motors (IM) are used in AVE classes 102–112 trains, so, the IM used as a traction motor in these trains has been studied and characterized by comparing the results with data provided by Renfe. A PMSM of equivalent power to the IM has been dimensioned, and different electromagnetic structures of the PMSM rotor have been evaluated. The simulation by the finite element method and analysis of the equivalent electrical circuit used in all the motors have been studied to evaluate the performance of the motors in this application. Efficiency is calculated at different operating points due to its impact on the energy consumption of railway traction. The implementation of the PMSM evaluated is recommended, mainly due to the improvements achieved in efficiency as compared with the IM currently used. Full article

(This article belongs to the Section F: Electrical Engineering)

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16 pages, 4273 KiB

Open AccessArticle

Flow Structure and Heat Transfer of Jet Impingement on a Rib-Roughened Flat Plate

by Abdulrahman H. Alenezi^1,*

, Abdulrahman Almutairi¹, Hamad M. Alhajeri¹, Abdulmajid Addali² and Abdelaziz A. A. Gamil³

¹ Mechanical Power and Refrigeration Technology Department, College of Technological Studies, Shuwaikh Educational, P. O. Box 23167, Safat, Al-Asamah 13092, Kuwait

² Advanced Centre for Technology, Tripoli, Libya

³ Department of Power and Propulsion, Cranfield University, Cranfield, Bedfordshire MK43 0AL, UK

Energies 2018, 11(6), 1550; https://doi.org/10.3390/en11061550 - 13 Jun 2018

Cited by 14 | Viewed by 4756

Abstract

The jet impingement technique is an effective method to achieve a high heat transfer rate and is widely used in industry. Enhancing the heat transfer rate even minimally will improve the performance of many engineering systems and applications. In this numerical study, the [...] Read more.

The jet impingement technique is an effective method to achieve a high heat transfer rate and is widely used in industry. Enhancing the heat transfer rate even minimally will improve the performance of many engineering systems and applications. In this numerical study, the convective heat transfer process between orthogonal air jet impingement on a smooth, horizontal surface and a roughened uniformly heated flat plate is studied. The roughness element takes the form of a circular rib of square cross-section positioned at different radii around the stagnation point. At each location, the effect of the roughness element on heat transfer rate was simulated for six different heights and the optimum rib location and rib dimension determined. The average Nusselt number has been evaluated within and beyond the stagnation region to better quantify the heat transfer advantages of ribbed surfaces over smooth surfaces. The results showed both flow and heat transfer features vary significantly with rib dimension and location on the heated surface. This variation in the streamwise direction included both augmentation and decrease in heat transfer rate when compared to the baseline no-rib case. The enhancement in normalized averaged Nusselt number obtained by placing the rib at the most optimum radial location R/D = 2 was 15.6% compared to the baseline case. It was also found that the maximum average Nusselt number for each location was achieved when the rib height was close to the corresponding boundary layer thickness of the smooth surface at the same rib position. Full article

(This article belongs to the Special Issue Fluid Flow and Heat Transfer)

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14 pages, 2331 KiB

Open AccessArticle

Increasing Profits in Food Waste Biorefinery—A Techno-Economic Analysis

by Juan-Rodrigo Bastidas-Oyanedel^*

and Jens Ejbye Schmidt

Chemistry Department, Khalifa University of Science and Technology, Masdar Campus, P.O. Box 54224 Abu Dhabi, United Arab Emirates

Energies 2018, 11(6), 1551; https://doi.org/10.3390/en11061551 - 13 Jun 2018

Cited by 84 | Viewed by 6981

Abstract

The present manuscript highlights the economic profit increase when combining organic waste anaerobic digestion with other mixed culture anaerobic fermentation technologies, e.g., lactic acid fermentation and dark fermentation. Here we consider the conversion of 50 tonnes/day of food waste into methane, power generation [...] Read more.

The present manuscript highlights the economic profit increase when combining organic waste anaerobic digestion with other mixed culture anaerobic fermentation technologies, e.g., lactic acid fermentation and dark fermentation. Here we consider the conversion of 50 tonnes/day of food waste into methane, power generation (from CHP of biomethane), lactic acid, polylactic acid, hydrogen, acetic acid and butyric acid. The economic assessment shows that the basic alternative, i.e., anaerobic digestion with methane selling to the grid, generates 19 USD/t_VS (3 USD/t_foodwaste) of profit. The highest profit is obtained by dark fermentation with separation and purification of acetic and butyric acids, i.e., 296 USD/t_VS (47 USD/t_foodwaste). The only alternative that presented losses is the power generation alternative, needing tipping fees and/or subsidy of 176 USD/t_VS (29 USD/t_foodwaste). The rest of the alternatives generate profit. From the return on investment (ROI) and payback time, the best scenario is the production of polylactic acid, with 98% ROI, and 7.8 years payback time. Production of butyric acid ROI and payback time was 74% and 9.1 years. Full article

(This article belongs to the Special Issue BioEnergy and BioChemicals Production from Biomass and Residual Resources)

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14 pages, 5062 KiB

Open AccessArticle

Thermal Conductance along Hexagonal Boron Nitride and Graphene Grain Boundaries

by Timon Rabczuk^1,2,*,†, Mohammad Reza Azadi Kakavand^3,†

, Raahul Palanivel Uma⁴, Ali Hossein Nezhad Shirazi⁵ and Meysam Makaremi⁶

¹ Division of Computational Mechanics, Ton Duc Thang University, Ho Chi Minh City, Vietnam

² Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam

³ Unit of Strength of Materials and Structural Analysis, Institute of Basic Sciences in Engineering Sciences, University of Innsbruck, 6020 Innsbruck, Austria

⁴ Institute of Mechanics, University of Duisburg-Essen, 45141 Essen, Germany

⁵ Institute of Structural Mechanics, Bauhaus-University of Weimar, 99423 Weimar, Germany

⁶ Faculty of Applied Science & Engineering, University of Toronto, Toronto, ON M5S 3E4, Canada

^† These authors contributed equally to this work.

Energies 2018, 11(6), 1553; https://doi.org/10.3390/en11061553 - 14 Jun 2018

Cited by 6 | Viewed by 4241

Abstract

We carried out molecular dynamics simulations at various temperatures to predict the thermal conductivity and the thermal conductance of graphene and hexagonal boron-nitride (h-BN) thin films. Therefore, several models with six different grain boundary configurations ranging from 33–140 nm in length were generated. [...] Read more.

We carried out molecular dynamics simulations at various temperatures to predict the thermal conductivity and the thermal conductance of graphene and hexagonal boron-nitride (h-BN) thin films. Therefore, several models with six different grain boundary configurations ranging from 33–140 nm in length were generated. We compared our predicted thermal conductivity of pristine graphene and h-BN with previously conducted experimental data and obtained good agreement. Finally, we computed the thermal conductance of graphene and h-BN sheets for six different grain boundary configurations, five sheet lengths ranging from 33 to 140 nm and three temperatures (i.e., 300 K, 500 K and 700 K). The results show that the thermal conductance remains nearly constant with varying length and temperature for each grain boundary. Full article

(This article belongs to the Special Issue Computational Methods of Multi-Physics Problems)

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15 pages, 3603 KiB

Open AccessArticle

Short-Term Load Forecasting Using a Novel Deep Learning Framework

by Xiaoyu Zhang, Rui Wang^*, Tao Zhang, Yajie Liu and Yabing Zha

College of System Engineering, National University of Defense Technology, Changsha 410073, China

Energies 2018, 11(6), 1554; https://doi.org/10.3390/en11061554 - 14 Jun 2018

Cited by 17 | Viewed by 2669

Abstract

Short-term load forecasting is the basis of power system operation and analysis. In recent years, the use of a deep belief network (DBN) for short-term load forecasting has become increasingly popular. In this study, a novel deep-learning framework based on a restricted Boltzmann [...] Read more.

Short-term load forecasting is the basis of power system operation and analysis. In recent years, the use of a deep belief network (DBN) for short-term load forecasting has become increasingly popular. In this study, a novel deep-learning framework based on a restricted Boltzmann machine (RBM) and an Elman neural network is presented. This novel framework is used for short-term load forecasting based on the historical power load data of a town in the UK. The obtained results are compared with an individual use of a DBN and Elman neural network. The experimental results demonstrate that our proposed model can significantly ameliorate the prediction accuracy. Full article

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21 pages, 6053 KiB

Open AccessArticle

Petrographic Controls on Pore and Fissure Characteristics of Coals from the Southern Junggar Coalfield, Northwest China

by Sandong Zhou^1,2,3, Dameng Liu^1,2,*, Yidong Cai^1,2, Zuleima Karpyn³ and Yanbin Yao^1,2

¹ School of Energy Resource, China University of Geosciences (Beijing), Beijing 100083, China

² Coal Reservoir Laboratory of National Engineering Research Center of CBM Development & Utilization, China University of Geosciences, Beijing 100083, China

³ John and Willie Leone Family Department of Energy and Mineral Engineering, Pennsylvania State University, State College, PA 16802, USA

Energies 2018, 11(6), 1556; https://doi.org/10.3390/en11061556 - 14 Jun 2018

Cited by 8 | Viewed by 3006

Abstract

The productive potential of coalbed methane projects is controlled by pore and fissure characteristics, which are intrinsically related to coal petrology. This work attempts to identify the influence of petrographic factors on the development of pore and fissure systems in the southern Junggar [...] Read more.

The productive potential of coalbed methane projects is controlled by pore and fissure characteristics, which are intrinsically related to coal petrology. This work attempts to identify the influence of petrographic factors on the development of pore and fissure systems in the southern Junggar Coalfield, Northwest China. Here, Middle Jurassic coal (lignite and subbituminous) petrology in coal seam No. 45 of the southern Junggar Coalfield (SJC) is studied with respect to the characteristics of pore and fissure structure with the aid of optical microscopes, scanning electron microscopy, mercury intrusion porosimetry, and nuclear magnetic resonance analysis. Maceral analysis shows coals at the SJC are dominated by vitrinite (38–87 vol %), with moderate quantities of inertinite (1–28 vol %) and liptinite (0.5–30 vol %). Decomposition of plants occurs under slightly oxic–anoxic conditions, with good tissue retention. Four types of coal facies are classified using petrographic indices, comprising (1) lower delta plain marsh, (2) lower delta plain fen, (3) upper delta plain wet forest swamp; and (4) piedmont plain moor. Pores and fissures are generally observed in telinite, collotelinite, fusinite, and semifusinite in SJC coals, indicating that the generation of pores and fissures is strongly influenced by coal macerals. Pore and fissure structures of coals in coal facies (1) appear weakly connected, whereas those in coal facies (2) reveal good connectivity. Coals in coal facies (3) and (4) show moderate connectivity between pore and fissure structure. Therefore, pore and fissure structures are significantly controlled by coal facies. This work provides practical recommendations and implementation methods for petrological studies in future coalbed methane exploration/development in the SJC. This study also serves to predict the physical properties of pores and fissures and interpret the control mechanism of coalbed methane production using coal petrology. Full article

(This article belongs to the Section L: Energy Sources)

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14 pages, 1462 KiB

Open AccessArticle

Regional Determinants of Energy Efficiency: Residential Energy Demand in Japan

by Akihiro Otsuka

Association of International Arts and Science, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027, Japan

Energies 2018, 11(6), 1557; https://doi.org/10.3390/en11061557 - 14 Jun 2018

Cited by 12 | Viewed by 2752

Abstract

Controlling the rapid growth of residential energy demand and enhancing energy efficiency are key policy issues in Japan. Thus, this study aims to estimate a residential energy demand function by conducting a stochastic frontier analysis and analyze the regional determinants of energy efficiency. [...] Read more.

Controlling the rapid growth of residential energy demand and enhancing energy efficiency are key policy issues in Japan. Thus, this study aims to estimate a residential energy demand function by conducting a stochastic frontier analysis and analyze the regional determinants of energy efficiency. The results indicate that population density and electrification rate foster energy efficiency and exert the same degree of impact. The study also highlights that population concentration has a nonlinear effect on energy efficiency. In other words, when combined with population concentration, the promotion of electrification policies can significantly contribute toward improving energy efficiency in the residential sector and consequently, have a positive effect on Japan’s regional economy. Full article

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19 pages, 2348 KiB

Open AccessArticle

A Method for Load Classification and Energy Scheduling Optimization to Improve Load Reliability

by Yinze Ren¹, Hongbin Wu^1,*

, Hejun Yang¹

, Shihai Yang² and Zhixin Li²

¹ School of Electrical Engineering and Automation, Hefei University of Technology, Hefei 230009, China

² State Grid Jiangsu Electric Power Co. Ltd., Nanjing 210024, China

Energies 2018, 11(6), 1558; https://doi.org/10.3390/en11061558 - 14 Jun 2018

Cited by 4 | Viewed by 2220

Abstract

With the large amount of distributed generation in use, the structure of the distribution system is increasingly complex. Therefore, it is necessary to establish a method to improve load reliability. Based on the reliability model of distributed generation, this paper investigates the time [...] Read more.

With the large amount of distributed generation in use, the structure of the distribution system is increasingly complex. Therefore, it is necessary to establish a method to improve load reliability. Based on the reliability model of distributed generation, this paper investigates the time sequential simulation of a wind/solar/storage combined power supply system under off-grid operation. After classifying the load by power supply region, the load weight coefficient is established, which modifies the reliability index of the load point and system. The modified expected energy not supplied (EENS) is adopted as the objective function, and the particle swarm optimization algorithm is used to solving the optimal energy scheduling for improving the load reliability. Finally, the load reliability is calculated with a hybrid method. Using the IEEE-RBTS Bus 6 system as an example, the correctness and validity of the proposed method are verified as an effective way to improve load reliability. Full article

(This article belongs to the Section F: Electrical Engineering)

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16 pages, 6214 KiB

Open AccessArticle

A Simplified Physical Model Construction Method and Gas-Water Micro Scale Flow Simulation in Tight Sandstone Gas Reservoirs

by Fengjiao Wang¹

, Yikun Liu^1,*, Chaoyang Hu^1,*, Anqi Shen¹

, Shuang Liang¹ and Bo Cai²

¹ Department of Petroleum Engineering, Northeast Petroleum University, Daqing 163318, China

² Petrochina Exploration and Development Research Institute at Langfang, Langfang 065007, China

Energies 2018, 11(6), 1559; https://doi.org/10.3390/en11061559 - 14 Jun 2018

Cited by 7 | Viewed by 2610

Abstract

Accuracy defects exist when modeling fluid transport by the classical capillary bundle model for tight porous media. In this study, a three-dimensional simplified physical model construction method was developed for tight sandstone gas reservoirs based on the geological origin, sedimentary compaction and clay [...] Read more.

Accuracy defects exist when modeling fluid transport by the classical capillary bundle model for tight porous media. In this study, a three-dimensional simplified physical model construction method was developed for tight sandstone gas reservoirs based on the geological origin, sedimentary compaction and clay mineral-cementation. The idea was to reduce the porosity of the tangent spheres physical model considering the synergistic effect of the above two factors and achieve a simplified model with the same flow ability as the actual tight core. Regarding the wall surface of the simplified physical model as the boundary and using the Lattice Boltzmann (LB) method, the relative permeability curves of gas and water in the simplified model were fitted with experimental results and a synergistic coefficient could be obtained, which we propose for characterizing the synergistic effect of sedimentary compaction and clay mineral-cementation. The simplified physical model and the results simulated by the LB method are verified with the experimental results under indoor experimental conditions, and the two are consistent. Finally, we have carried out a simulation of gas flooding water under conditions of high temperature and high pressure which are consistent with the actual tight sandstone gas reservoir. The simulation results show that both gas and water have relatively stronger seepage ability compared with the results of laboratory experiments. Moreover, the interfacial tension between gas and water is lower, and the swept volume is larger during placement. In addition, the binding ability of the rock surface to the water film adhered to it becomes reduced. The method proposed in this study could indicate high frequency change of pores and throats and used to reflect the seepage resistance caused by frequent collisions with the wall in microscopic numerical simulations of tight sandstone gas reservoirs. Full article

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30 pages, 5251 KiB

Open AccessArticle

A Novel Hybrid Interval Prediction Approach Based on Modified Lower Upper Bound Estimation in Combination with Multi-Objective Salp Swarm Algorithm for Short-Term Load Forecasting

by Jiyang Wang¹, Yuyang Gao^2,*

and Xuejun Chen³

¹ Faculty of Information Technology, Macau University of Science and Technology, Macau 999078, China

² School of Statistics, Dongbei University of Finance and Economics, Dalian 116025, China

³ Gansu Meteorological Service Centre, Lanzhou 730020, China

Energies 2018, 11(6), 1561; https://doi.org/10.3390/en11061561 - 14 Jun 2018

Cited by 64 | Viewed by 3945

Abstract

Effective and reliable load forecasting is an important basis for power system planning and operation decisions. Its forecasting accuracy directly affects the safety and economy of the operation of the power system. However, attaining the desired point forecasting accuracy has been regarded as [...] Read more.

Effective and reliable load forecasting is an important basis for power system planning and operation decisions. Its forecasting accuracy directly affects the safety and economy of the operation of the power system. However, attaining the desired point forecasting accuracy has been regarded as a challenge because of the intrinsic complexity and instability of the power load. Considering the difficulties of accurate point forecasting, interval prediction is able to tolerate increased uncertainty and provide more information for practical operation decisions. In this study, a novel hybrid system for short-term load forecasting (STLF) is proposed by integrating a data preprocessing module, a multi-objective optimization module, and an interval prediction module. In this system, the training process is performed by maximizing the coverage probability and by minimizing the forecasting interval width at the same time. To verify the performance of the proposed hybrid system, half-hourly load data are set as illustrative cases and two experiments are carried out in four states with four quarters in Australia. The simulation results verified the superiority of the proposed technique and the effects of the submodules were analyzed by comparing the outcomes with those of benchmark models. Furthermore, it is proved that the proposed hybrid system is valuable in improving power grid management. Full article

(This article belongs to the Special Issue Short-Term Load Forecasting by Artificial Intelligent Technologies)

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14 pages, 5329 KiB

Open AccessArticle

Mechanical Performance of Methane Hydrate–Coal Mixture

by Xia Gao¹, Tongchuan Yang¹, Kai Yao^2,*

, Baoyong Zhang^3,*, Qiang Wu³ and Chuanhai Liu³

¹ School of Architectural & Civil Engineering, Heilongjiang University of Science & Technology, Harbin 150022, China

² Department of Civil & Environmental Engineering, National University of Singapore, Singapore 117576, Singapore

³ School of Safety Engineering, Heilongjiang University of Science & Technology, Harbin 150022, China

Energies 2018, 11(6), 1562; https://doi.org/10.3390/en11061562 - 14 Jun 2018

Cited by 7 | Viewed by 2587

Abstract

Understanding mechanical behaviors of a methane hydrate–coal mixture are important for its associated application in coal and gas outburst prevention. A triaxial compression apparatus for a specimen of the methane hydrate–coal mixture was developed to measure its strength and deformation properties. Triaxial compression [...] Read more.

Understanding mechanical behaviors of a methane hydrate–coal mixture are important for its associated application in coal and gas outburst prevention. A triaxial compression apparatus for a specimen of the methane hydrate–coal mixture was developed to measure its strength and deformation properties. Triaxial compression tests were performed on coal briquette samples under different confining pressures and methane hydrate saturation. Strain softening behavior of the methane hydrate–coal mixture can be identified for all the specimens under various conditions. The larger the methane hydrate saturation or confining pressure, the larger the peak strength, elastic modulus and peak strain. Mathematical relationships for correlating the peak strength with the methane hydrate saturation or confining pressure were also proposed. Full article

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11 pages, 2216 KiB

Open AccessArticle

AC Flashover Performance of 10 kV Rod-Plane Air-Gapped Arresters under Rain Conditions

by Jiazheng Lu, Pengkang Xie^*

, Jianping Hu, Zhenglong Jiang and Zhen Fang

State Key Laboratory of Disaster Prevention & Reduction for Power Grid Transmission & Distribution Equipment, State Grid Hunan Electric Power Corporation Disaster Prevention & Reduction Center, Changsha 410007, China

Energies 2018, 11(6), 1563; https://doi.org/10.3390/en11061563 - 14 Jun 2018

Cited by 6 | Viewed by 2367

Abstract

According to operational experience of power systems, the outdoor insulation strength can be reduced due to the effect of rain. Till now, little work has been done to investigate the flashover performance of air gapped arresters under rain conditions. Therefore, in this paper, [...] Read more.

According to operational experience of power systems, the outdoor insulation strength can be reduced due to the effect of rain. Till now, little work has been done to investigate the flashover performance of air gapped arresters under rain conditions. Therefore, in this paper, experiments were carried out and the AC flashover performance of 10 kV arresters with different air gap structures was studied. The experimental results show that, for the tested arresters, the flashover current mainly flows through the air gaps and zinc oxide varistors under rain conditions. It is also confirmed that the flashover voltages decrease with the increasing of rain intensity and conductivity. In the windward direction, the wind can distort the water streams between the air gaps and rise the flashover voltages. In the leeward direction, if the rod electrode is beyond the range of the plane electrode, the flashover voltage researches the smallest value when the wind speed is 4 m/s. Analysis and discussions have been done to explain the experimental results, and the research in this paper may provide reference to improve the flashover performance of air gapped arresters under rain conditions. Full article

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25 pages, 14177 KiB

Open AccessArticle

Investigations of Ventilation Airflow Characteristics on a Longwall Face—A Computational Approach

by Zhongwei Wang^1,*, Ting Ren², Liqiang Ma^3,4,*

and Jian Zhang⁵

¹ College of Safety Science and Engineering, Xi’an University of Science and Technology, Xi’an 710054, China

² School of Civil, Mining and Environmental Engineering, Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, NSW 2522, Australia

³ School of Energy, Xi’an University of Science and Technology, Xi’an 710054, China

⁴ Key Laboratory of Deep Coal Resource Mining, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China

⁵ College of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China

Energies 2018, 11(6), 1564; https://doi.org/10.3390/en11061564 - 14 Jun 2018

Cited by 25 | Viewed by 3350

Abstract

Mine ventilation has always been critical for underground mining operations to ensure operational efficiency and compliance with safety and health statutory requirements. To obtain a thorough understanding of the ventilation flow characteristics on a longwall face, innovative three dimensional (3D) models, incorporating key [...] Read more.

Mine ventilation has always been critical for underground mining operations to ensure operational efficiency and compliance with safety and health statutory requirements. To obtain a thorough understanding of the ventilation flow characteristics on a longwall face, innovative three dimensional (3D) models, incorporating key features of the longwall equipment and a zone of immediate goaf area, were developed. Mesh independent studies were conducted to determine the desirable mesh required for a mesh-independent solution. Then the model results were validated using field ventilation survey data. At both intersections of maingate/tailgate (MG/TG) and face where the flow boundary changes sharply, the occurrence of undesirable flow separation which causes additional energy loss was identified, as well as its extent of influence. The recirculation of airflow resulting from separation in the TG will lead to accumulation of high concentrations of mine gas, thus regular inspection or continuous monitoring of gas concentration in that area is highly recommended, especially when high gas emission is expected from the working seam. In addition, we also investigated the influence of shearer position and cutting sequence on longwall ventilation. Overall, the longwall models developed in this study together with the flow characteristics obtained will provide fundamental basis for the investigation of longwall gas and dust issues in the future. Full article

(This article belongs to the Section L: Energy Sources)

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15 pages, 3743 KiB

Open AccessArticle

Performance of LiCl Impregnated Mesoporous Material Coating over Corrugated Heat Exchangers in a Solid Sorption Chiller

by Hongzhi Liu¹, Katsunori Nagano^2,* and Junya Togawa²

¹ Department of Building Environment and Energy Engineering, University of Shanghai for Science and Technology, 516 Jungong Road, Shanghai 200093, China

² Environmental System Research Laboratory, Hokkaido University, N13-W8 Sapporo 060-8628, Japan

Energies 2018, 11(6), 1565; https://doi.org/10.3390/en11061565 - 14 Jun 2018

Cited by 9 | Viewed by 3167

Abstract

The composite material made by impregnating 40 wt. % lithium chloride (LiCl) into the mesopores of a kind of natural porous rock (Wakkanai Siliceous Shale: WSS) micropowders (short for “WSS + 40 wt. % LiCl”) had been developed previously, and can be regenerated [...] Read more.

The composite material made by impregnating 40 wt. % lithium chloride (LiCl) into the mesopores of a kind of natural porous rock (Wakkanai Siliceous Shale: WSS) micropowders (short for “WSS + 40 wt. % LiCl”) had been developed previously, and can be regenerated below 100 °C with a cooling coefficient of performance (COP) of approximately 0.3 when adopted as a sorbent in a sorption cooler. In this study, experiments have been carried out on an intermittent solid sorption chiller with the WSS + 40 wt. % LiCl coating over two aluminum corrugated heat exchangers. Based on the experimental condition (regeneration temperature of 80 °C, condensation temperature of 30 °C in the desorption process; sorption temperature of 30 °C and evaporation temperature of 12 °C in the sorption process), the water sorption amount changes from 20 wt. % to 70 wt. % in one sorption cooling cycle. Moreover, a specific cooling power (SCP) of 86 W/kg, a volumetric specific cooling power (VSCP) of 42 W/dm³, and a specific sorption power of 170 W/kg can be achieved with a total sorption and desorption time of 20 min. The obtained cooling COP is approximately 0.16. Full article

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8 pages, 2488 KiB

Open AccessArticle

Design and Implementation of the Battery Energy Storage System in DC Micro-Grid Systems

by Yuan-Chih Chang^*, Hao-Chin Chang and Chien-Yu Huang

Department of Electrical Engineering and Advanced Institute of Manufacturing with High-Tech Innovations, National Chung Cheng University, Chiayi 62102, Taiwan

Energies 2018, 11(6), 1566; https://doi.org/10.3390/en11061566 - 14 Jun 2018

Cited by 12 | Viewed by 4566

Abstract

The design and implementation of the battery energy storage system in DC micro-grid systems is demonstrated in this paper. The battery energy storage system (BESS) is an important part of a DC micro-grid because renewable energy generation sources are fluctuating. The BESS can [...] Read more.

The design and implementation of the battery energy storage system in DC micro-grid systems is demonstrated in this paper. The battery energy storage system (BESS) is an important part of a DC micro-grid because renewable energy generation sources are fluctuating. The BESS can provide energy while the renewable energy is absent in the DC micro-grid. The circuit topology of the proposed BESS will be introduced. The design of the voltage controller and the current controller for the battery charger/discharger are also illustrated. Finally, experimental results are provided to validate the performance of the BESS. Full article

(This article belongs to the Special Issue Selected Papers from the IEEE ICASI 2018)

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19 pages, 2563 KiB

Open AccessArticle

Evaluation of the Reactive Power Support Capability and Associated Technical Costs of Photovoltaic Farms’ Operation

by Luís F. N. Lourenço^1,*,†

, Renato M. Monaro¹

, Maurício B. C. Salles¹

, José R. Cardoso¹

and Loïc Quéval²

¹ Laboratory of Advanced Electric Grids (LGRID), Escola Politécnica, University of São Paulo, São Paulo 05508-010, Brazil

² Group of Electrical Engineering—Paris (GeePs), UMR CNRS 8507, Centrale Supélec, Univ. Paris-Sud, Université Paris-Saclay, Sorbonne Université, 3 & 11 rue Joliot-Curie, 91192 Plateau de Moulon Gif-sur-Yvette CEDEX, France

^† Current address: Av. Prof. Luciano Gualberto, 158-Butantã, São Paulo 05508-900, Brazil.

Energies 2018, 11(6), 1567; https://doi.org/10.3390/en11061567 - 14 Jun 2018

Cited by 11 | Viewed by 3633

Abstract

The share of photovoltaic (PV) farms is increasing in the energy mix as power systems move away from conventional carbon-emitting sources. PV farms are equipped with an expensive power converter, which is, most of the time, used well bellow its rated capacity. This [...] Read more.

The share of photovoltaic (PV) farms is increasing in the energy mix as power systems move away from conventional carbon-emitting sources. PV farms are equipped with an expensive power converter, which is, most of the time, used well bellow its rated capacity. This has led to proposals to use it to provide reactive power support to the grid. In this framework, this work presents a step-by-step methodology to obtain the reactive power support capability map and the associated technical costs of single- and two-stage PV farms during daytime operation. Results show that the use of two-stage PV farms can expand the reactive power support capability for low irradiance values in comparison to single-stage ones. Besides, despite losses being higher for two-stage PV farms, the technical cost in providing reactive power support is similar for both systems. Based on the obtained maps, it is demonstrated how the profits of a PV farm can be evaluated for the current ancillary services policy in Brazil. The proposed method is of interest to PV farm owners and grid operators to estimate the cost of providing reactive power support and to evaluate the economic feasibility in offering this ancillary service. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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32 pages, 21549 KiB

Open AccessArticle

A Scramjet Compression System for Hypersonic Air Transportation Vehicle Combined Cycle Engines

by Devendra Sen¹, Apostolos Pesyridis^1,2,*

and Andrew Lenton¹

¹ Centre for Advanced Powertrain and Fuels Research (CAPF), Department of Mechanical, Aerospace and Civil Engineering, Brunel University, London UB8 3PH, UK

² Metapulsion Engineering Limited, Northwood, Middlesex HA63LG, UK

Energies 2018, 11(6), 1568; https://doi.org/10.3390/en11061568 - 14 Jun 2018

Cited by 11 | Viewed by 9469

Abstract

This paper proposes a compression system for a scramjet, to be used as part of a combined cycle engine on a hypersonic transport vehicle that can achieve sustained flight at 8 Mach 8. Initially research into scramjet compression system and shock wave interaction [...] Read more.

This paper proposes a compression system for a scramjet, to be used as part of a combined cycle engine on a hypersonic transport vehicle that can achieve sustained flight at 8 Mach 8. Initially research into scramjet compression system and shock wave interaction was conducted to establish the foundation of the scramjet inlet and isolator sections. A Computational Fluid Dynamics (CFD) campaign was conducted, where the shock structure and flow characteristics was analysed between Mach 4.5–8. The compression system of a scramjet is of crucial importance in providing air at suitable Mach number, pressure and temperature to the combustion chamber. The use of turbojet engines in over-under configuration with the scramjet was investigated as well as the study of a combined cycle scramjet-ramjet configuration. It was identified that locating the scramjet in the centre with a rotated ramjet on either side, where its ramps make up the scramjet wall was the most optimal configuration, as it mitigated the effect of the oblique shocks propagating from the scramjet walls into the adjacent ramjet. Furthermore, this meant that the forebody of the vehicle could solely be used as the compression surface by the scramjet. In this paper, the sizing of the scramjet combustion chamber and nozzle were modified to match the flow properties of the oncoming flow with the purpose of producing the most optimum scramjet configuration for the cruise speed of Mach 8. CFD simulations showed that the scramjet inlet did not provide the levels of compression and stagnation pressure recovery initially required. However, it was found that the scramjet provided significantly more thrust than the drag of the aircraft at sustained Mach 8 flight, due to its utilisation of a very aerodynamic vehicle design. Full article

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22 pages, 3883 KiB

Open AccessArticle

Fast Transient Modulation for a Step Load Change in a Dual-Active-Bridge Converter with Extended-Phase-Shift Control

by Chuan Sun

and Xiaodong Li^*

Faculty of Information Technology, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macau SAR 999078, China

Energies 2018, 11(6), 1569; https://doi.org/10.3390/en11061569 - 14 Jun 2018

Cited by 14 | Viewed by 4379

Abstract

The manipulation of the bidirectional power in a dual-active-bridge converter relies on the adjustment of several phase-shift angles. Improper implementation of those adjustments during the transient process of a step load change may induce transient DC bias current in the transformer and accompanied [...] Read more.

The manipulation of the bidirectional power in a dual-active-bridge converter relies on the adjustment of several phase-shift angles. Improper implementation of those adjustments during the transient process of a step load change may induce transient DC bias current in the transformer and accompanied high peak current, which may result in excess loss and safety issues potentially. The paper proposes a load transient modulation to execute the adjustments of the two phase-shift angles for extended-phase-shift (EPS) control in a predictive manner. An unknown phase-shift is introduced to the gating signals of one bridge arm, and the gating signals of other bridge arms would be modified accordingly to realize the required adjustment of the two phase-shift angles together. With the proper selection of the introduced phase-shift, the power adjustment can be done in less than one high-frequency cycle without resulting in DC bias and overshoot current. Although there are four different operation modes existing in EPS, a universal solution of the unknown phase-shift can be obtained for all possible power transition cases between different modes. Validation of the proposed method is performed by means of both simulation and experimental tests. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 2482 KiB

Open AccessArticle

Development of Building Thermal Load and Discomfort Degree Hour Prediction Models Using Data Mining Approaches

by Yaolin Lin¹

, Shiquan Zhou¹, Wei Yang^2,*, Long Shi³ and Chun-Qing Li³

¹ School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan 430070, China

² College of Engineering and Science, Victoria University, Melbourne 8001, Australia

³ School of Engineering, RMIT University, Melbourne 3000, Australia

Energies 2018, 11(6), 1570; https://doi.org/10.3390/en11061570 - 14 Jun 2018

Cited by 15 | Viewed by 4307

Abstract

Thermal load and indoor comfort level are two important building performance indicators, rapid predictions of which can help significantly reduce the computation time during design optimization. In this paper, a three-step approach is used to develop and evaluate prediction models. Firstly, the Latin [...] Read more.

Thermal load and indoor comfort level are two important building performance indicators, rapid predictions of which can help significantly reduce the computation time during design optimization. In this paper, a three-step approach is used to develop and evaluate prediction models. Firstly, the Latin Hypercube Sampling Method (LHSM) is used to generate a representative 19-dimensional design database and DesignBuilder is then used to obtain the thermal load and discomfort degree hours through simulation. Secondly, samples from the database are used to develop and validate seven prediction models, using data mining approaches including multilinear regression (MLR), chi-square automatic interaction detector (CHAID), exhaustive CHAID (ECHAID), back-propagation neural network (BPNN), radial basis function network (RBFN), classification and regression trees (CART), and support vector machines (SVM). It is found that the MLR and BPNN models outperform the others in the prediction of thermal load with average absolute error of less than 1.19%, and the BPNN model is the best at predicting discomfort degree hour with 0.62% average absolute error. Finally, two hybrid models—MLR (MLR + BPNN) and MLR-BPNN—are developed. The MLR-BPNN models are found to be the best prediction models, with average absolute error of 0.82% in thermal load and 0.59% in discomfort degree hour. Full article

(This article belongs to the Special Issue Energy Efficiency in Plants and Buildings 2019)

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16 pages, 1905 KiB

Open AccessArticle

Impact of Plug-in Electric Vehicles Integrated into Power Distribution System Based on Voltage-Dependent Power Flow Analysis

by Yuttana Kongjeen and Krischonme Bhumkittipich^*

Department of Electrical Engineering, Rajamangala University of Technology Thanyaburi, Pathum Thani 12110, Thailand

Energies 2018, 11(6), 1571; https://doi.org/10.3390/en11061571 - 14 Jun 2018

Cited by 53 | Viewed by 5711

Abstract

This paper proposes the impact of plug-in electric vehicles (PEVs) integrated into a power distribution system based on voltage-dependent control. The gasolinegate situation has many people turning to electric vehicles as a more environmentally friendly option, especially in smart community areas. The advantage [...] Read more.

This paper proposes the impact of plug-in electric vehicles (PEVs) integrated into a power distribution system based on voltage-dependent control. The gasolinegate situation has many people turning to electric vehicles as a more environmentally friendly option, especially in smart community areas. The advantage of PEVs is modern vehicles that can use several types of fuel cells and batteries as energy sources. The proposed PEVs model was developed as a static load model in power distribution systems under balanced load conditions. The power flow analysis was determined by using certain parameters of the proposed electrical network. The main research objective was to determine the voltage magnitude profiles, the load voltage deviation, and total power losses of the electrical power system by using the new proposed methodology. Furthermore, it investigated the effects of the constant power load, the constant current load, the constant impedance load, and the plug-in electric vehicles load model. The IEEE 33 bus system was selected as the test system. The proposed methodology assigned the balanced load types in a steady state condition and used the new methodology to solve the power flow problem. The simulation results showed that increasing the plug-in electric vehicles load had an impact on the grids when compared with the other four load types. The lowest increased value for the plug-in electric vehicles load had an effect on the load voltage deviation (0.062), the total active power loss (120 kW) and the total reactive power loss (80 kVar), respectively. Therefore, this study verified that the load of PEVs can affect the electrical power system according to the time charging and charger position. Therefore, future work could examine the difference caused when PEVs are attached to the electrical power system by means of the conventional or complex load type. Full article

(This article belongs to the Special Issue Toward Sustainable Energy Systems for Smart Grids and Smart Societies)

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26 pages, 6182 KiB

Open AccessArticle

Techno-Economic Feasibility of Hybrid Solar Photovoltaic and Battery Energy Storage Power System for a Mobile Cellular Base Station in Soshanguve, South Africa

by Banjo A. Aderemi^1,*

, S. P. Daniel Chowdhury¹, Thomas O. Olwal¹

and Adnan M. Abu-Mahfouz^1,2

¹ Department of Electrical Engineering, Tshwane University of Technology Pretoria, Pretoria 0183, South Africa

² CSIR Meraka Institute Pretoria, Pretoria 0001, South Africa

Energies 2018, 11(6), 1572; https://doi.org/10.3390/en11061572 - 15 Jun 2018

Cited by 38 | Viewed by 5846

Abstract

Over the years, sustainability and impact on the environment, as well as operation expenditure, have been major concerns in the deployment of mobile cellular base stations (BSs) worldwide. This is because mobile cellular BSs are known to consume a high percentage of power [...] Read more.

Over the years, sustainability and impact on the environment, as well as operation expenditure, have been major concerns in the deployment of mobile cellular base stations (BSs) worldwide. This is because mobile cellular BSs are known to consume a high percentage of power within the mobile cellular network. Such energy consumption contributes to the emission of greenhouse gases (GHGs) through the use of conventional diesel generating set (gen-set). As a result, mobile cellular operators are faced with the dilemma of minimizing the power consumption, GHG emissions, and operation cost, while improving the quality of service (QoS) of the networks. In attempting to find a solution, this study presents the feasibility and simulation of a solar photovoltaic (PV)/battery hybrid power system (HPS), as a predominant source of power for a specific mobile cellular BS site situated in the Soshanguve area of the city of Pretoria, South Africa. It also presents the technical development and shows the environmental advantage and cost benefits of using a solar PV/battery HPS to power a BS site with a 24 h daily load of 241.10 kWh/d and peak load of 20.31 kW as compared to using the HPS with a solar PV/diesel gen-set/battery. The solar resource pattern for the city of Pretoria was collected from the National Aeronautics and Space Administration and was modeled statistically. The statistical modeling done using solar radiation resource exposure characteristic patterns of Pretoria, South Africa revealed an average annual daily solar radiation of 5.4645 Wh/m²/d and a 0.605 clearness index. The simulation and the design were done using Hybrid Optimization Model for Electric Renewables (HOMER) and Matlab/Simulink software. The simulation finding showed that the HPS of the solar PV/battery combination has about a 59.62% saving in the net present cost (NPC) and levelized cost of energy (LCOE) and an 80.87% saving in operating cost as against conventional BSs powered with a gen-set/battery. Full article

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10 pages, 2886 KiB

Open AccessArticle

Boron Monochalcogenides; Stable and Strong Two-Dimensional Wide Band-Gap Semiconductors

by Bohayra Mortazavi^1,2,*

and Timon Rabczuk³

¹ Institute of Structural Mechanics, Bauhaus-Universität Weimar, Marienstr. 15, D-99423 Weimar, Germany

² Institute for Materials Science and Max Bergman Center of Biomaterials, TU Dresden, 01062 Dresden, Germany

³ College of Civil Engineering, Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China

Energies 2018, 11(6), 1573; https://doi.org/10.3390/en11061573 - 15 Jun 2018

Cited by 37 | Viewed by 4048

Abstract

In this short communication, we conducted first-principles calculations to explore the stability of boron monochalcogenides (BX, X = S, Se or Te), as a new class of two-dimensional (2D) materials. We predicted BX monolayers with two different atomic stacking sequences of ABBA and [...] Read more.

In this short communication, we conducted first-principles calculations to explore the stability of boron monochalcogenides (BX, X = S, Se or Te), as a new class of two-dimensional (2D) materials. We predicted BX monolayers with two different atomic stacking sequences of ABBA and ABBC, referred in this work to 2H and 1T, respectively. Analysis of phonon dispersions confirm the dynamical stability of BX nanosheets with both 2H and 1T atomic lattices. Ab initio molecular dynamics simulations reveal the outstanding thermal stability of all predicted monolayers at high temperatures over 1500 K. BX structures were found to exhibit high elastic modulus and tensile strengths. It was found that BS and BTe nanosheets can show high stretchability, comparable to that of graphene. It was found that all predicted monolayers exhibit semiconducting electronic character, in which 2H structures present lower band gaps as compared with 1T lattices. The band-gap values were found to decrease from BS to BTe. According to the HSE06 results, 1T-BS and 2H-BTe show, respectively, the maximum (4.0 eV) and minimum (2.06 eV) electronic band gaps. This investigation introduces boron monochalcogenides as a class of 2D semiconductors with remarkable thermal, dynamical, and mechanical stability. Full article

(This article belongs to the Special Issue Computational Methods of Multi-Physics Problems)

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16 pages, 3888 KiB

Open AccessArticle

Advanced Thermodynamic Analysis Applied to an Integrated Solar Combined Cycle System

by Shucheng Wang^1,2,*

, Zhongguang Fu^1,2, Gaoqiang Zhang² and Tianqing Zhang²

¹ Key Laboratory of Condition Monitoring and Control for Power Plant Equipment, Ministry of Education, North China Electric Power University, Beijing 102206, China

² School of Energy Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(6), 1574; https://doi.org/10.3390/en11061574 - 15 Jun 2018

Cited by 6 | Viewed by 2721

Abstract

The variation performance of integrated solar combined cycle (ISCC) is presented using energy, conventional exergy and advanced exergy analysis methods to provide information about exergy destruction of components and efficiencies of overall plant. Moreover, the theory of dividing the exergy destruction of main [...] Read more.

The variation performance of integrated solar combined cycle (ISCC) is presented using energy, conventional exergy and advanced exergy analysis methods to provide information about exergy destruction of components and efficiencies of overall plant. Moreover, the theory of dividing the exergy destruction of main components into unavoidable/avoidable and exogenous/endogenous parts allows for further understanding the real potentials for improving. Besides, the exergy destruction rate and exergy efficiency of components as well as overall plant were hourly analyzed within a typical day. Results indicate the exergy destruction rate of overall system drops from 49.79% to 44.65% in summer and decreases from 49.79% to 47.59% in winter. As the solar irradiation intensity rises, the solar field efficiency reaches to 42.16% in winter and 47.5% in summer. The solar-to-electric energy efficiency gets to 13.69% in winter and 15.46% in summer. In addition, with the increase of solar energy input to the ISCC system, the exergy destruction of Brayton cycle components decreases; however, the exergy destruction of Rankine cycle components increases. Furthermore, the exergy destruction of solar field has a large extended from 14.55 MW to 58.03 MW. Moreover, the heat recovery steam generator (HRSG) and the steam turbines have the largest exergy destruction rate of 11.26% and 13.63% at 15:00 p.m. Full article

(This article belongs to the Section F: Electrical Engineering)

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24 pages, 3282 KiB

Open AccessArticle

Catalytic Oxidation of Synthesis Gas on Platinum at Low Temperatures for Power Generation Applications

by Junjie Chen^*

, Longfei Yan

, Wenya Song

and Deguang Xu

Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, Jiaozuo 454000, Henan, China

Energies 2018, 11(6), 1575; https://doi.org/10.3390/en11061575 - 15 Jun 2018

Cited by 2 | Viewed by 2835

Abstract

This paper addresses the issues related to the low-temperature catalytic oxidation of synthesis gas at high pressures under lean-burn conditions. The purpose of this study is to explore the mechanism responsible for the interplay between carbon monoxide and hydrogen during their combined oxidation [...] Read more.

This paper addresses the issues related to the low-temperature catalytic oxidation of synthesis gas at high pressures under lean-burn conditions. The purpose of this study is to explore the mechanism responsible for the interplay between carbon monoxide and hydrogen during their combined oxidation process. Particular attention is given to the temperature range from 500 to 770 K, which is relevant to the catalyst inlet temperature encountered in catalytic combustion gas turbine systems. Computational fluid dynamics simulations were performed by using a numerical model with detailed chemistry and transport. Reaction path analysis was conducted, and the rate-determining step in the reaction mechanism was finally identified. It was shown that there is a strong interplay between carbon monoxide and hydrogen during the combined oxidation process. The addition of hydrogen causes a great change in the adsorbed species on the surface of the catalyst. At temperatures as low as 600 K, the presence of hydrogen makes the active surface sites more available for adsorption, thus promoting the catalytic oxidation of carbon monoxide. The coupling steps between the two components make a small contribution to the promoting effect. At temperatures below 520 K, the presence of hydrogen inhibits the catalytic oxidation of carbon monoxide due to the competitive effect of hydrogen on oxygen adsorption. Full article

(This article belongs to the Special Issue Clean Fuels in Low Temperature Combustion)

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14 pages, 2701 KiB

Open AccessArticle

Experimental Investigation on Effect of Wall Roughness and Lubricant Film on the Adhered Fuel Film of N-Butanol-Diesel Blends after Spray Impingement

by Xingyu Liang^1,*, Hongsheng Zhang¹, Gequn Shu¹, Yuesen Wang¹

, Xiuxiu Sun¹, Hanzhengnan Yu² and Ming Ge¹

¹ State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China

² China Automotive Technology & Research Center, Tianjin 300300, China

Energies 2018, 11(6), 1576; https://doi.org/10.3390/en11061576 - 15 Jun 2018

Cited by 2 | Viewed by 2376

Abstract

The effect of wall roughness with different lubricant film thicknesses on the characteristics of adhered fuel films of diesel-n-butanol blending fuels after spray impingement has been investigated. Four steel plates with different types of roughness (root mean square height-Sq) that were coated with [...] Read more.

The effect of wall roughness with different lubricant film thicknesses on the characteristics of adhered fuel films of diesel-n-butanol blending fuels after spray impingement has been investigated. Four steel plates with different types of roughness (root mean square height-Sq) that were coated with different lubricant film thicknesses (h_l) were used as impinged walls. The experimental conditions included dry walls (h_l = 0), semi-wetted walls (SWW) with different thin oil films (0 < h_l/Sq < 1), and fully wetted walls (FWW) with a thick lubricant film (h_l > Sq). The results indicate that the adhered fuel mass ratio (ε) of blended fuel with 25% n-butanol (B25) was higher than that of blended fuel with 15% n-butanol (B15) under the same conditions. ε increased with an increase in Sq on the dry walls, but, under SWW conditions, it decreased with an increase in oil film thickness. The fuel film morphology was almost unaffected by the change in Sq, but the results implied that the roughness parameter-Skewness (Ssk) exerted a greater impact. The mean thickness h_a and accumulated diameter D_l of the adhered fuel film increased with an increase in h_l, but, under FWW conditions, the effect of the roughness on the adhered film’s features was insignificant. Full article

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15 pages, 5986 KiB

Open AccessArticle

Analysis and Elimination of Dead-Time Effect in Wireless Power Transfer System

by Xin Liu¹

, Tianfeng Wang¹, Nan Jin^2,*, Salman Habib¹, Muhammad Ali¹, Xijun Yang^1,* and Houjun Tang¹

¹ Key Laboratory of Control of Power Transmission and Transformation Ministry of Education, Shanghai Jiao Tong University, 800 Dongchuan RD., Shanghai 200240, China

² College of Electric and Information Engineering, Zhengzhou University of Light Industry, Zhengzhou 450002, China

Energies 2018, 11(6), 1577; https://doi.org/10.3390/en11061577 - 15 Jun 2018

Cited by 9 | Viewed by 2803

Abstract

Dead time between the complementary driving signals is needed to avoid short circuit in voltage source inverters (VSIs), however, this raises issues such as voltage distortion and harmonic generation. In wireless power transfer (WPT) systems, the ratio of dead time versus operating period [...] Read more.

Dead time between the complementary driving signals is needed to avoid short circuit in voltage source inverters (VSIs), however, this raises issues such as voltage distortion and harmonic generation. In wireless power transfer (WPT) systems, the ratio of dead time versus operating period becomes more problematic due to the high frequency, where the dead time can cause serious concerns regarding the phase errors and control performance deterioration. Therefore, this paper presents a comprehensive analysis of the dead-time effect for WPT systems based on a series–series (SS) topology. Firstly, it is found that voltage distortion appears in two regions in comparison with the three in one active bridge WPT system, and seven regions, as compared to the eight in dual active bridge (DAB) WPT system. Afterwards, a novel pulse width modulation (PWM) method is proposed, where the driving signals of the same phase leg are no longer complementary to each other. By employing the proposed method, the dead-time effect can be addressed up to a certain extent, and the desired voltage can be obtained in all the regions. In addition, the proposed method is not influenced by the system parameters, and can be easily applied to other high-frequency resonant converters. Simulated and experimental results are added to verify the feasibility and efficacy of the proposed control scheme. Full article

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13 pages, 8555 KiB

Open AccessArticle

Industrial-Scale Experimental Study on the Thermal Oxidation of Ventilation Air Methane and the Heat Recovery in a Multibed Thermal Flow-Reversal Reactor

by Bo Lan^1,2, You-Rong Li^1,*, Xu-Sheng Zhao² and Jian-Dong Kang²

¹ Key Laboratory of Low-grade Energy Utilization Technologies and Systems of Ministry of Education, College of Power Engineering, Chongqing University, Chongqing 400044, China

² China Coal Technology and Engineering Group Chongqing Research Institute, Chongqing 400037, China

Energies 2018, 11(6), 1578; https://doi.org/10.3390/en11061578 - 15 Jun 2018

Cited by 18 | Viewed by 2522

Abstract

In the present work, an industrial-scale experiment on ventilation air methane (VAM) utilization by a multibed thermal flow-reversal reactor (TFRR) is conducted in China. The influence of the inlet flow rate, feed methane concentration, and cycle time on the temperature distribution of the [...] Read more.

In the present work, an industrial-scale experiment on ventilation air methane (VAM) utilization by a multibed thermal flow-reversal reactor (TFRR) is conducted in China. The influence of the inlet flow rate, feed methane concentration, and cycle time on the temperature distribution of the bed and heat recovery efficiency are investigated. The methane conversion in the studied cases exceeds 97%. The results show that the methane concentration during self-maintained operation of the TFRR without heat recovery should not be less than 0.22 vol % when the inlet flow rate is 103,000 Nm³/h and the cycle time is 300 s. As the inlet flow rate decreases, the lower concentration limit of automatic thermal maintenance increases. The peak temperature of the bed approaches the inlet side as the feed methane concentration increases and the cycle time decreases. The heat recovery efficiency increases linearly with increasing inlet flow rate, rises parabolically with an increasing feed methane concentration, and decreases weakly with increasing cycle time. Full article

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16 pages, 4214 KiB

Open AccessArticle

Impact of Component Reliability on Large Scale Photovoltaic Systems’ Performance

by Stefan Baschel¹, Elena Koubli^2,*, Jyotirmoy Roy³ and Ralph Gottschalg⁴

¹ Vattenfall Innovation GmbH, Chausseestrasse 23, 10115 Berlin, Germany

² Centre for Renewable Energy Systems Technology, School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough, LE11 3TU, UK

³ juwi Renewable Energies Limited, Energie-Allee 1, 55286 Wörrstadt, Germany

⁴ Fraunhofer-Centre for Silicon-Photovoltaic CSP, Walter-Hülse-Strasse 1, 06120 Halle, Germany

Energies 2018, 11(6), 1579; https://doi.org/10.3390/en11061579 - 15 Jun 2018

Cited by 42 | Viewed by 6533

Abstract

In this work, the impact of component reliability on large scale photovoltaic (PV) systems’ performance is demonstrated. The analysis is largely based on an extensive field-derived dataset of failure rates of operation ranging from three to five years, derived from different large-scale PV [...] Read more.

In this work, the impact of component reliability on large scale photovoltaic (PV) systems’ performance is demonstrated. The analysis is largely based on an extensive field-derived dataset of failure rates of operation ranging from three to five years, derived from different large-scale PV systems. Major system components, such as transformers, are also included, which are shown to have a significant impact on the overall energy lost due to failures. A Fault Tree Analysis (FTA) is used to estimate the impact on reliability and availability for two inverter configurations. A Failure Mode and Effects Analysis (FMEA) is employed to rank failures in different subsystems with regards to occurrence and severity. Estimation of energy losses (EL) is realised based on actual failure probabilities. It is found that the key contributions to reduced energy yield are the extended repair periods of the transformer and the inverter. The very small number of transformer issues (less than 1%) causes disproportionate EL due to the long lead times for a replacement device. Transformer and inverter issues account for about 2/3 of total EL in large scale PV systems (LSPVSs). An optimised monitoring strategy is proposed in order to reduce repair times for the transformer and its contribution to EL. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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17 pages, 3100 KiB

Open AccessArticle

Combustion of Poplar and Pine Pellet Blends in a 50 kW Domestic Boiler: Emissions and Combustion Efficiency

by Esperanza Monedero^1,*

, Henar Portero¹ and Magín Lapuerta²

¹ Instituto de Investigación en Energías Renovables, Universidad de Castilla-La Mancha, Albacete 02006, Spain

² Escuela Técnica Superior de Ingenieros Industriales, Universidad de Castilla-La Mancha, Ciudad Real 13071, Spain

Energies 2018, 11(6), 1580; https://doi.org/10.3390/en11061580 - 15 Jun 2018

Cited by 19 | Viewed by 2957

Abstract

Poplar pellets with and without Ca, Mg-lignosulphonate and three poplar and pine pellet blends (with three different percentages of pine—5, 45 and 95 wt.%) were burned in a 50 kW domestic boiler in order to evaluate their suitability as fuels. The boiler efficiency [...] Read more.

Poplar pellets with and without Ca, Mg-lignosulphonate and three poplar and pine pellet blends (with three different percentages of pine—5, 45 and 95 wt.%) were burned in a 50 kW domestic boiler in order to evaluate their suitability as fuels. The boiler efficiency and emissions were analyzed and compared with those from tests with poplar pellet. It was found that the adequate adjustment of excess air and of flowrate of secondary air according to the fuel properties improve the combustion efficiency. The results show an improvement in CO and NO_x emissions and combustion efficiency when either Ca, Mg-lignosulphonate or pine were blended with poplar. However, the use of Ca, Mg-lignosulphonate is discouraged due to the observed increase in SO_x emissions. No operational problems related with unburned matter or ash were observed for any of the pellet blends tested. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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38 pages, 4905 KiB

Open AccessArticle

Fly Ash Formation and Characteristics from (co-)Combustion of an Herbaceous Biomass and a Greek Lignite (Low-Rank Coal) in a Pulverized Fuel Pilot-Scale Test Facility

by Aaron Fuller^1,*

, Jörg Maier¹, Emmanouil Karampinis^2,3, Jana Kalivodova^4,5, Panagiotis Grammelis^2,3, Emmanuel Kakaras^2,3 and Günter Scheffknecht¹

¹ Institute of Combustion and Power Plant Technology, University of Stuttgart, Pfaffenwaldring 23, 70569 Stuttgart, Germany

² Centre for Research & Technology Hellas/Chemical Process and Energy Resources Institute (CERTH/CPERI), Egialias 52, 15125 Marousi, Athens, Greece

³ National Technical University of Athens/Department of Mechanical Engineering/Laboratory of Steam Boilers and Thermal Plants (NTUA/LSBTP), Heroon Polytechniou 9, 15780 Zografou, Athens, Greece

⁴ The Energy Research Center of The Netherlands (ECN), Biomass, Coal and Environmental Research, Heat and Power Generation, P.O. Box 1, 1755 ZG Petten, The Netherlands

⁵ Research Centre Rez, Husinec-_Re_z _c.p. 130, 250 68 Husinec e_Re_z, Czech Republic

Energies 2018, 11(6), 1581; https://doi.org/10.3390/en11061581 - 15 Jun 2018

Cited by 38 | Viewed by 5206

Abstract

The lignite boilers are designed for lower quality fuels, and often the ash is not utilized. This work assessed the impact of combustion of an herbaceous biomass with a low-quality Greek lignite on the quality of the resulting fly ash. Test results were [...] Read more.

The lignite boilers are designed for lower quality fuels, and often the ash is not utilized. This work assessed the impact of combustion of an herbaceous biomass with a low-quality Greek lignite on the quality of the resulting fly ash. Test results were compared with those of fly ash samples from an industrial facility using the same fuel qualities. Inductively coupled plasma-optical (ICP) emission spectroscopy, X-ray powder diffraction (XRD), and scanning electron microscope (SEM) analyses were performed on the collected samples. Despite the significantly higher contents of K, Na and S in the biomass, at a 50% co-firing thermal share, the major and minor oxides in the fly ash were comparable to the lignite fly ash quality. This is attributed to the high ash content of the lignite, the low ash content of the biomass, and the much higher heating value of the biomass. There were improvements in fly ash performance characteristics with the herbaceous biomass in the fuel blend. The initial setting time and volume stability evaluations were improved with the biomass in the fuel blend. The work supports efforts of good practices in ash management, social responsibility, a circular economy, power plant renewable energy operations, and co-firing herbaceous biomass fuels in lignite power plants. Full article

(This article belongs to the Special Issue BioEnergy and BioChemicals Production from Biomass and Residual Resources)

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13 pages, 1528 KiB

Open AccessArticle

Influence of Hydrothermal Carbonization on Composition, Formation and Elimination of Biphenyls, Dioxins and Furans in Sewage Sludge

by Heiner Brookman^1,*, Fabian Gievers¹

, Volker Zelinski¹, Jan Ohlert² and Achim Loewen¹

¹ Faculty of Resource Management, University of Applied Sciences and Arts (HAWK), 37075 Göttingen, Germany

² Institute of Chemistry, University of Oldenburg, 26129 Oldenburg, Germany

Energies 2018, 11(6), 1582; https://doi.org/10.3390/en11061582 - 15 Jun 2018

Cited by 16 | Viewed by 4173

Abstract

In many areas of application, the influence of hydrothermal carbonization (HTC) on the composition of organic pollutants is still unexplored. In this study, sewage sludge (SS) was carbonized and the input as well as the hydrochar were examined for the organic pollutants: polychlorinated [...] Read more.

In many areas of application, the influence of hydrothermal carbonization (HTC) on the composition of organic pollutants is still unexplored. In this study, sewage sludge (SS) was carbonized and the input as well as the hydrochar were examined for the organic pollutants: polychlorinated biphenyls (PCB), polychlorinated dibenzo-dioxins (PCDDs), and polychlorinated dibenzo-furans (PCDFs). The process temperatures of carbonization were 200 °C, 220 °C, and 240 °C and the holding time was 5 h for all tests. The total concentration of PCBs was relatively stable for all temperatures, whereas the toxicity equivalent (WHO-TEQ) at 200 °C and 220 °C increases compared to the input material. The strongest impact on toxicity was observed for PCDDs where concentrations were reduced for higher temperatures, whereas the toxicity increases by more than 16 times for temperatures of 240 °C. The concentrations and toxicity of PCDFs were reduced for all carbonization temperatures. In hydrochar from HTC at 240 °C, the limit values for the application of SS in German agriculture have been exceeded. The results indicate that the process conditions for HTC should be controlled also for SS with average contamination if the hydrochar is to be used as material, especially in agriculture. Full article

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13 pages, 6316 KiB

Open AccessArticle

Physiochemical and Electrical Properties of Refined, Bleached and Deodorized Palm Oil under High Temperature Ageing for Application in Transformers

by Nur Aqilah Mohamad¹

, Norhafiz Azis^1,2,*, Jasronita Jasni¹, Mohd Zainal Abidin Ab Kadir^1,3

, Robiah Yunus⁴ and Zaini Yaakub⁵

¹ Centre for Electromagnetic and Lightning Protection Research (CELP), Department of Electrical and Electronic Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

² Institute of Advanced Technology (ITMA), Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

³ Institute of Power Engineering (IPE), Universiti Tenaga Nasional, 43000 Kajang, Selangor, Malaysia

⁴ Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

⁵ Hyrax Oil Sdn. Bhd, Lot 4937 Batu 5 1/2, Jalan Meru, Mukim Kapar, 41050 Klang, Selangor, Malaysia

Energies 2018, 11(6), 1583; https://doi.org/10.3390/en11061583 - 16 Jun 2018

Cited by 9 | Viewed by 2936

Abstract

This paper presents a high temperature ageing study of refined, bleached, and deodorized palm oil (RBDPO) olein at 170 °C in the presence of air. In total, two types of RBDPO were examined. The physiochemical and dielectric properties of RBDPO were measured and [...] Read more.

This paper presents a high temperature ageing study of refined, bleached, and deodorized palm oil (RBDPO) olein at 170 °C in the presence of air. In total, two types of RBDPO were examined. The physiochemical and dielectric properties of RBDPO were measured and analysed. We found that the moisture and viscosities for both RBDPO increased as the ageing progressed, whereas the acidities fluctuated at very low levels at less than 0.005 mg KOH/g. The ageing on the AC breakdown voltages of both RBDPO were not affected throughout the ageing processes. The dielectric dissipation factors and relative permittivities for both RBDPO increased as the resistivities decreased with the ageing time. Full article

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15 pages, 4113 KiB

Open AccessArticle

Heat Transfer Enhancement of TiO₂/Water Nanofluid at Laminar and Turbulent Flows: A Numerical Approach for Evaluating the Effect of Nanoparticle Loadings

by Budi Kristiawan^1,*

, Budi Santoso¹, Agung Tri Wijayanta^1,*, Muhammad Aziz²

and Takahiko Miyazaki^3,4

¹ Department of Mechanical Engineering, Universitas Sebelas Maret, Kampus UNS Kentingan, Jl. Ir. Sutami 36A Kentingan, Surakarta 57126, Indonesia

² Institute of Innovative Research, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan

³ Department of Energy and Environmental Engineering, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasuga-koen, Kasuga-shi, Fukuoka 816-8580, Japan

⁴ International Institute for Carbon-Neutral Energy Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

Energies 2018, 11(6), 1584; https://doi.org/10.3390/en11061584 - 16 Jun 2018

Cited by 45 | Viewed by 4287

Abstract

Titania-based nanofluid flowing inside a circular tube under the boundary condition of a horizontal uniformly heated wall was investigated numerically for both laminar and turbulent flows. In this work, an innovative numerical method using an Eulerian approach for the two-phase mixture model was [...] Read more.

Titania-based nanofluid flowing inside a circular tube under the boundary condition of a horizontal uniformly heated wall was investigated numerically for both laminar and turbulent flows. In this work, an innovative numerical method using an Eulerian approach for the two-phase mixture model was used to simulate the flow and convective heat transfer characteristics. The effect of nanoparticle loading and Reynolds number on the flow and heat transfer characteristics was observed. The Reynolds number was 500 and 1200 for laminar flow, while for turbulent flow, the Reynolds number was varied in the range from 4000 to 14,000. A comparison with the established empirical correlations was made. The results clearly showed at the laminar and turbulent flows that the existing nanoparticles provided a considerable enhancement in the convective heat transfer. For laminar flow, the numerical results found that the enhancement in the convective heat transfer coefficient of nanofluids were 4.63, 11.47, and 20.20% for nanoparticle loadings of 0.24, 0.60, and 1.18 vol.%, respectively. On the other hand, for turbulent flow, the corresponding heat transfer increases were 4.04, 10.33, and 21.87%. Full article

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17 pages, 5312 KiB

Open AccessArticle

Impact of Ambient Temperature on Shunt Capacitor Placement in a Distorted Radial Distribution System

by Essam A. Al-Ammar^*

, Ghazi A. Ghazi

and Wonsuk Ko

Department of Electrical Engineering, Faculty of Engineering, King Saud University, Riyadh 11461, Saudi Arabia

Energies 2018, 11(6), 1585; https://doi.org/10.3390/en11061585 - 16 Jun 2018

Cited by 11 | Viewed by 2698

Abstract

In electrical distribution systems, shunt capacitors are installed in order to reduce system losses, to enhance the voltage profile, and to free up system capacity. Nevertheless, the installation of shunt capacitors in distribution systems with distorted waveforms will magnify the distortion level of [...] Read more.

In electrical distribution systems, shunt capacitors are installed in order to reduce system losses, to enhance the voltage profile, and to free up system capacity. Nevertheless, the installation of shunt capacitors in distribution systems with distorted waveforms will magnify the distortion level of harmonics if they are not set at appropriate locations relative to the harmonics. This paper proposes a hybrid method to determine the placement and sizing of shunt capacitors in distorted radial distribution systems, taking into account the presence of harmonic distortion with consideration of ambient temperature effects, (this technique consists of the fuzzy expert system approach and the Genetic Algorithm method). This hybrid technique is applied to an IEEE 34-bus radial standard distribution system as well as a real distribution system in the Saudi Electricity Company. The simulation results show that harmonic distortion considerably reduces and the efficiency of distribution systems increases with a reduction in power loss and enhancement of voltage regulation. Full article

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21 pages, 5864 KiB

Open AccessArticle

Selection of Energy Efficiency Projects for Dwelling Stock to Achieve Optimal Project Portfolio at the Regional Level by Applying LCC. An Analysis Based on Three Scenarios in the South-Muntenia Region of Romania

by Cezar-Petre Simion^*, Ciprian Nicolescu and Mihai Cioc

Department of Management, The Bucharest University of Economic Studies, București 010374, Romania

Energies 2018, 11(6), 1586; https://doi.org/10.3390/en11061586 - 17 Jun 2018

Cited by 8 | Viewed by 2658

Abstract

The joint action of the European directives and the national strategies make the issue of energy efficiency of the dwelling stock one of the main research directions in the field. The purpose of this study is to create and apply a methodology for [...] Read more.

The joint action of the European directives and the national strategies make the issue of energy efficiency of the dwelling stock one of the main research directions in the field. The purpose of this study is to create and apply a methodology for developing the portfolio of projects to increase the energy efficiency of the dwelling stock at a regional level through the use of life cycle cost. For this, eight types of energy efficiency improvement projects and three implementation scenarios were selected for the dwelling stock. For each project life cycle cost was determined in each county of the South-Muntenia region based on the estimation of the energy requirements, the costs of implementation and exploitation. In all three scenarios, the P3 Energy Efficiency Project (the reference building without shutters under the Romanian normative) had minimal life cycle cost in most counties in the region. For each scenario the life cycle cost was determined for the optimal portfolio of projects at regional level. The maximum scenario was chosen as the optimal scenario for regional implementation. Full article

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18 pages, 2428 KiB

Open AccessArticle

Life Cycle Analysis of Integrated Gasification Combined Cycle Power Generation in the Context of Southeast Asia

by Yabo Wang^1,*, Victor Nian^1,2,*

, Hailong Li³ and Jun Yuan⁴

¹ Tianjin Key Laboratory of Refrigeration Technology, Tianjin University of Commerce, Tianjin 300134, China

² Energy Studies Institute, National University of Singapore, Singapore 119620, Singapore

³ Future Energy Centre, School of Business, Society and Engineering, Mälardalen University, 721 23 Västerås, Sweden

⁴ China Institute of FTZ Supply Chain, Shanghai Maritime University, Shanghai 201306, China

Energies 2018, 11(6), 1587; https://doi.org/10.3390/en11061587 - 17 Jun 2018

Cited by 7 | Viewed by 4103

Abstract

Coal remains a major source of electricity production even under the current state of developments in climate policies due to national energy priorities. Coal remains the most attractive option, especially to the developing economies in Southeast Asia, due to its abundance and affordability [...] Read more.

Coal remains a major source of electricity production even under the current state of developments in climate policies due to national energy priorities. Coal remains the most attractive option, especially to the developing economies in Southeast Asia, due to its abundance and affordability in the region, despite the heavily polluting nature of this energy source. Gasification of coal running on an integration gasification combined cycle (IGCC) power generation with carbon capture and storage (CCS) represents an option to reduce the environmental impacts of power generation from coal, but the decarbonization potential and suitability of IGCC in the context of Southeast Asia remain unclear. Using Singapore as an example, this paper presents a study on the life cycle analysis (LCA) of IGCC power generation with and without CCS based on a generic process-driven analysis method. We further evaluate the suitability of IGCC with and without CCS as an option to address the energy and climate objectives for the developing economies in Southeast Asia. Findings suggest that the current IGCC technology is a much less attractive option in the context of Southeast Asia when compared to other available power generation technologies, such as solar photovoltaic systems, coal with CCS, and potentially nuclear power technologies. Full article

(This article belongs to the Section F: Electrical Engineering)

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21 pages, 5568 KiB

Open AccessArticle

Electricity Price Forecasting with Dynamic Trees: A Benchmark Against the Random Forest Approach

by Javier Pórtoles¹

, Camino González^2,*

and Javier M. Moguerza³

¹ Doctorate Programme in Information Technologies and Communications, University Rey Juan Carlos, c/ Tulipán s/n, 28933 Móstoles, Spain

² Statistical Laboratory, Escuela Técnica Superior de Ingenieros Industriales, Universidad Politécnica de Madrid, c/ José Gutiérrez Abascal, 2, 28006 Madrid, Spain

³ Data Science Laboratory, University Rey Juan Carlos, c/ Tulipán s/n, 28933 Móstoles, Spain

Energies 2018, 11(6), 1588; https://doi.org/10.3390/en11061588 - 17 Jun 2018

Cited by 27 | Viewed by 4729

Abstract

Dynamic Trees are a tree-based machine learning technique specially designed for online environments where data are to be analyzed sequentially as they arrive. Our purpose is to test this methodology for the very first time for Electricity Price Forecasting (EPF) by using data [...] Read more.

Dynamic Trees are a tree-based machine learning technique specially designed for online environments where data are to be analyzed sequentially as they arrive. Our purpose is to test this methodology for the very first time for Electricity Price Forecasting (EPF) by using data from the Iberian market. For benchmarking the results, we will compare them against another tree-based technique, Random Forest, a widely used method that has proven its good results in many fields. The benchmark includes several versions of the Dynamic Trees approach for a very short term EPF (one-hour ahead) and also a short term (one-day ahead) approach but only with the best versions. The numerical results show that Dynamic Trees are an adequate method, both for very short and short term EPF—even improving upon the performance of the Random Forest method. The comparison with other studies for the Iberian market suggests that Dynamic Trees is a proper and promising method for EPF. Full article

(This article belongs to the Special Issue Forecasting Models of Electricity Prices 2018)

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13 pages, 3227 KiB

Open AccessArticle

Approaches for Safety Analysis of Gas-Pipeline Functionality in Terms of Failure Occurrence: A Case Study

by Barbara Tchórzewska-Cieślak, Katarzyna Pietrucha-Urbanik^*, Marek Urbanik and Janusz R. Rak

Faculty of Civil and Environmental Engineering, Rzeszow University of Technology, 35-959 Rzeszow, Poland

Energies 2018, 11(6), 1589; https://doi.org/10.3390/en11061589 - 17 Jun 2018

Cited by 22 | Viewed by 3552

Abstract

The development of appropriate assessment methods of gas-pipeline functionality contributes to the reduction of failure consequences and helps engineers to make the right decisions as to the optimal solution choice for technical facilities, as well as provides procedures to protect their users and [...] Read more.

The development of appropriate assessment methods of gas-pipeline functionality contributes to the reduction of failure consequences and helps engineers to make the right decisions as to the optimal solution choice for technical facilities, as well as provides procedures to protect their users and the surrounding environment. This paper presents methods for the assessment of gas network operation. Pipe failure data were collected from a gas distribution network. A statistical analysis of the failure of gas networks was made. An attempt was made to isolate seasonal and accidental fluctuations in the tested failure stream. The Poisson distribution was proposed as a model of failure distribution of gas networks. The conducted analysis allowed us to propose the forecasting method of acceptable failure consequences using the homogeneous Markov chain. The obtained results are valuable for supporting the management of urban gas networks, mainly in terms of the strategic modernization plans and the rehabilitation techniques. Full article

(This article belongs to the Section D: Energy Storage and Application)

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14 pages, 4032 KiB

Open AccessArticle

One-Pot Hydrothermal Synthesis of Novel Cu-MnS with PVP Cabbage-Like Nanostructures for High-Performance Supercapacitors

by S. Srinivasa Rao¹, Ikkurthi Kanaka Durga², Bandari Naresh², Bak Jin-Soo², T.N.V. Krishna², Cho In-Ho², Jin-Woo Ahn¹ and Hee-Je Kim^2,*

¹ Department of Mechatronics Engineering, Kyungsung University, 309 Suyeong-ro, Nam-gu, Busan 48434, Korea

² School of Electrical Engineering, Pusan National University, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 46241, Korea

Energies 2018, 11(6), 1590; https://doi.org/10.3390/en11061590 - 17 Jun 2018

Cited by 40 | Viewed by 8092

Abstract

This paper reports the facile synthesis of a novel architecture of Cu-MnS with PVP, where the high theoretical capacitance of MnS, low-cost, and high electrical conductivity of Cu, as well as appreciable surface area with high thermal and mechanical conductivity of PVP, as [...] Read more.

This paper reports the facile synthesis of a novel architecture of Cu-MnS with PVP, where the high theoretical capacitance of MnS, low-cost, and high electrical conductivity of Cu, as well as appreciable surface area with high thermal and mechanical conductivity of PVP, as a single entity to fabricate a high-performance electrode for supercapacitor. Benefiting from their unique structures, the Cu-MnS with 2PVP electrode materials show a high specific capacitance of 833.58 F g⁻¹ at 1 A g⁻¹, reversibility for the charge/discharge process, which are much higher than that of the MnS-7 h, Cu-MnS, and Cu-MnS with 1 and 3PVP. The presence of an appropriate amount of PVP in Cu-MnS is favorable for improving the electrochemical performance of the electrode and the existence of Cu was inclined to enhance the electrical conductivity. The Cu-MnS with 2PVP electrode is a good reference for researchers to design and fabricate new electrode materials with enhanced capacitive performance. Full article

(This article belongs to the Special Issue Advances in Supercapacitor Technology and Applications)

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20 pages, 7594 KiB

Open AccessArticle

The Integration of 3D Modeling and Simulation to Determine the Energy Potential of Low-Temperature Geothermal Systems in the Pisa (Italy) Sedimentary Plain

by Alessandro Sbrana^1,*, Paola Marianelli^1,*

, Giuseppe Pasquini¹, Paolo Costantini¹, Francesco Palmieri²

, Valentina Ciani³ and Michele Sbrana³

¹ Dipartimento di Scienze della Terra, University of Pisa, Via S. Maria 53, 56126 Pisa, Italy

² Istituto Nazionale di Oceanografia e di Geofisica Sperimentale—OGS, Borgo Grotta Gigante 42/C, 34010 Sgonico (TS), Italy

³ Terra Energy, Via Lenin 132-56017 San Giuliano Terme (PI), Italy

Energies 2018, 11(6), 1591; https://doi.org/10.3390/en11061591 - 18 Jun 2018

Cited by 11 | Viewed by 5488

Abstract

Shallow, low-temperature geothermal resources can significantly reduce the environmental impact of heating and cooling. Based on a replicable standard workflow for three-dimensional (3D) geothermal modeling, an approach to the assessment of geothermal energy potential is proposed and applied to the young sedimentary basin [...] Read more.

Shallow, low-temperature geothermal resources can significantly reduce the environmental impact of heating and cooling. Based on a replicable standard workflow for three-dimensional (3D) geothermal modeling, an approach to the assessment of geothermal energy potential is proposed and applied to the young sedimentary basin of Pisa (north Tuscany, Italy), starting from the development of a geothermal geodatabase, with collated geological, stratigraphic, hydrogeological, geophysical and thermal data. The contents of the spatial database are integrated and processed using software for geological and geothermal modeling. The models are calibrated using borehole data. Model outputs are visualized as three-dimensional reconstructions of the subsoil units, their volumes and depths, the hydrogeological framework, and the distribution of subsoil temperatures and geothermal properties. The resulting deep knowledge of subsoil geology would facilitate the deployment of geothermal heat pump technology, site selection for well doublets (for open-loop systems), or vertical heat exchangers (for closed-loop systems). The reconstructed geological–hydrogeological models and the geothermal numerical simulations performed help to define the limits of sustainable utilization of an area’s geothermal potential. Full article

(This article belongs to the Special Issue Geothermal Energy: Utilization and Technology 2018)

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17 pages, 5300 KiB

Open AccessArticle

A Dual-Function Instantaneous Power Theory for Operation of Three-Level Neutral-Point-Clamped Inverter-Based Shunt Active Power Filter

by Yap Hoon^1,2,*

, Mohd Amran Mohd Radzi^1,2

, Mohd Khair Hassan¹

and Nashiren Farzilah Mailah^1,2

¹ Department of Electrical and Electronic Engineering, Faculty of Engineering, Universiti Putra Malaysia, Serdang 43400, Malaysia

² Centre for Advanced Power and Energy Research (CAPER), Faculty of Engineering, Universiti Putra Malaysia, Serdang 43400, Malaysia

Energies 2018, 11(6), 1592; https://doi.org/10.3390/en11061592 - 18 Jun 2018

Cited by 14 | Viewed by 3153

Abstract

This paper proposes a simple yet effective reference current generation algorithm based on instantaneous power

p q

theory to enhance mitigation performance of a three-phase three-level neutral-point-clamped (NPC) inverter-based shunt active power filter (SAPF). The proposed algorithm is developed for dual functionality: generate [...] Read more.

This paper proposes a simple yet effective reference current generation algorithm based on instantaneous power

p q

theory to enhance mitigation performance of a three-phase three-level neutral-point-clamped (NPC) inverter-based shunt active power filter (SAPF). The proposed algorithm is developed for dual functionality: generate reference current and synchronization phase to effectively govern operation of SAPF in mitigating harmonic current and compensating reactive power. Three key modifications are implemented: (1) replacement of numerical low-pass filter (LPF) with an average power detector to improve mitigation performance; (2) removal of needless reactive element to reduce algorithm complexity; and (3) integration of phase tracking feature to eliminate the needs of phase-locked loop (PLL). Simulation work of SAPF with the proposed algorithm was conducted and assessed in MATLAB–Simulink. In addition, to verify feasibility of the proposed algorithm, a laboratory prototype as constructed with TMS320F28335 digital signal processor (DSP) programmed as the controller. Performance of SAPF achieved by utilizing the proposed algorithm was thoroughly investigated and benchmarked with that demonstrated using the existing

p q

theory algorithm to evaluate the inherent advantages. Simulation and experimental results are obtained for different nonlinear loads and test conditions. Responses demonstrated by SAPF in both simulation and experimental works reveal superiority of the proposed algorithm over the existing algorithm. Full article

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20 pages, 5159 KiB

Open AccessEditor’s ChoiceArticle

A Class of Control Strategies for Energy Internet Considering System Robustness and Operation Cost Optimization

by Haochen Hua

, Chuantong Hao, Yuchao Qin and Junwei Cao^*

Research Institute of Information Technology, Tsinghua University, Beijing 100084, China

Energies 2018, 11(6), 1593; https://doi.org/10.3390/en11061593 - 18 Jun 2018

Cited by 29 | Viewed by 3524

Abstract

Aiming at restructuring the conventional energy delivery infrastructure, the concept of energy Internet (EI) has become popular in recent years. Outstanding benefits from an EI include openness, robustness and reliability. Most of the existing literatures focus on the conceptual design of EI and [...] Read more.

Aiming at restructuring the conventional energy delivery infrastructure, the concept of energy Internet (EI) has become popular in recent years. Outstanding benefits from an EI include openness, robustness and reliability. Most of the existing literatures focus on the conceptual design of EI and are lack of theoretical investigation on developing specific control strategies for the operation of EI. In this paper, a class of control strategies for EI considering system robustness and operation cost optimization is investigated. Focusing on the EI system robustness issue, system parameter uncertainty, external disturbance and tracking error are taken into consideration, and we formulate such robust control issue as a structure specified mixed

H_{2} / H_{\infty}

control problem. When formulating the operation cost optimization problem, three aspects are considered: realizing the bottom-up energy management principle, reducing the cost involved by power delivery from power grid (PG) to microgrid (MG), and avoiding the situation of over-control. We highlight that this is the very first time that the above targets are considered simultaneously in the field of EI. The integrated control issue is considered in frequency domain and is solved by a particle swarm optimization (PSO) algorithm. Simulation results show that our proposed method achieves the targets. Full article

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23 pages, 8569 KiB

Open AccessArticle

Low-Frequency Oscillation Suppression of the Vehicle–Grid System in High-Speed Railways Based on H∞ Control

by Zhaozhao Geng, Zhigang Liu^*

, Xinxuan Hu and Jing Liu

School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, China

Energies 2018, 11(6), 1594; https://doi.org/10.3390/en11061594 - 18 Jun 2018

Cited by 16 | Viewed by 4591

Abstract

Recently, a traction blockade in the depots of numerous electric multiple units (EMUs) of high-speed railways has occured and resulted in some accidents in train operation. The traction blockade is caused by the low-frequency oscillation (LFO) of the vehicle–grid (EMUs–traction network) system. To [...] Read more.

Recently, a traction blockade in the depots of numerous electric multiple units (EMUs) of high-speed railways has occured and resulted in some accidents in train operation. The traction blockade is caused by the low-frequency oscillation (LFO) of the vehicle–grid (EMUs–traction network) system. To suppress the LFO, a scheme of EMUs line-side converter based on the H∞ control is proposed in this paper. First, the mathematical model of the four-quadrant converter in EMUs is presented. Second, the state variables are determined and the weighting functions are selected. Then, an H∞ controller based on the dq coordinate is designed. Moreover, compared with the simulation results of traditional proportional integral (PI) control, auto-disturbance rejection control (ADRC) and multivariable control (MC) based on Matlab/Simulink and the RT-LAB platform, the simulation results of the proposed H∞ control confirm that the H∞ controller applied in EMUs of China Railway High-Speed 3 has better dynamic and static performances. Finally, a whole cascade system model of EMUs and a traction network is built, in which a reduced-order model of a traction network is adopted. The experimental results of multi-EMUs accessed in the traction network indicate that the H∞ controller has good suppression performance for the LFO of the vehicle–grid system. In addition, through the analysis of sensitivity of the H∞ controller and the traditional PI controller, it is indicated that the H∞ controller has better robustness. Full article

(This article belongs to the Special Issue Advanced Control Techniques for Power Converters)

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19 pages, 285 KiB

Open AccessArticle

Volatility Spillovers between Energy and Agricultural Markets: A Critical Appraisal of Theory and Practice

by Chia-Lin Chang¹

, Yiying Li² and Michael McAleer^3,4,5,6,7,*

¹ Department of Applied Economics, Department of Finance, National Chung Hsing University, 40227 Taichung, Taiwan

² Department of Quantitative Finance, National Tsing Hua University, 30013 Hsinchu, Taiwan

³ Department of Finance, Asia University, 41354 Taichung, Taiwan

⁴ Discipline of Business Analytics, University of Sydney Business School, Sydney, NSW 2006, Australia

⁵ Econometric Institute, Erasmus School of Economics, Erasmus University Rotterdam, 3062 PA Rotterdam, The Netherlands

⁶ Department of Economic Analysis and ICAE, Complutense University of Madrid, 28040 Madrid, Spain

⁷ Institute of Advanced Sciences, Yokohama National University, 240-8501 Yokohama, Japan

Energies 2018, 11(6), 1595; https://doi.org/10.3390/en11061595 - 19 Jun 2018

Cited by 25 | Viewed by 4006

Abstract

Energy and agricultural commodities and markets have been examined extensively, albeit separately, for a number of years. In the energy literature, the returns, volatility and volatility spillovers (namely, the delayed effect of a returns shock in one asset on the subsequent volatility or [...] Read more.

Energy and agricultural commodities and markets have been examined extensively, albeit separately, for a number of years. In the energy literature, the returns, volatility and volatility spillovers (namely, the delayed effect of a returns shock in one asset on the subsequent volatility or covolatility in another asset), among alternative energy commodities, such as oil, gasoline and ethanol across different markets, have been analysed using a variety of univariate and multivariate models, estimation techniques, data sets, and time frequencies. A similar comment applies to the separate theoretical and empirical analysis of a wide range of agricultural commodities and markets. Given the recent interest and emphasis in bio-fuels and green energy, especially bio-ethanol, which is derived from a range of agricultural products, it is not surprising that there is a topical and developing literature on the spillovers between energy and agricultural markets. Modelling and testing spillovers between the energy and agricultural markets has typically been based on estimating multivariate conditional volatility models, specifically the Baba, Engle, Kraft, and Kroner (BEKK) and dynamic conditional correlation (DCC) models. A serious technical deficiency is that the Quasi-Maximum Likelihood Estimates (QMLE) of a Full BEKK matrix, which is typically estimated in examining volatility spillover effects, has no asymptotic properties, except by assumption, so that no valid statistical test of volatility spillovers is possible. Some papers in the literature have used the DCC model to test for volatility spillovers. However, it is well known in the financial econometrics literature that the DCC model has no regularity conditions, and that the QMLE of the parameters of DCC has no asymptotic properties, so that there is no valid statistical testing of volatility spillovers. The purpose of the paper is to evaluate the theory and practice in testing for volatility spillovers between energy and agricultural markets using the multivariate Full BEKK and DCC models, and to make recommendations as to how such spillovers might be tested using valid statistical techniques. Three new definitions of volatility and covolatility spillovers are given, and the different models used in empirical applications are evaluated in terms of the new definitions and statistical criteria. Full article

(This article belongs to the Special Issue Multivariate Modelling of Fossil Fuel and Carbon Emission Prices)

18 pages, 2731 KiB

Open AccessArticle

Analysis of Carbon Storage and Its Contributing Factors—A Case Study in the Loess Plateau (China)

by Gaohuan Liu¹ and Zhonghe Zhao^1,2,*

¹ State Key Laboratory of Resources and Environmental Information System, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China

² University of Chinese Academy of Sciences, Beijing 100049, China

Energies 2018, 11(6), 1596; https://doi.org/10.3390/en11061596 - 19 Jun 2018

Cited by 15 | Viewed by 4229

Abstract

The Chinese Loess Plateau is an ecologically fragile and sensitive area. The carbon storage dynamics in this region and the contributions from land use/land cover change (LUCC) and carbon density from 2000 to 2010 were analyzed in this paper. Normalized difference vegetation index [...] Read more.

The Chinese Loess Plateau is an ecologically fragile and sensitive area. The carbon storage dynamics in this region and the contributions from land use/land cover change (LUCC) and carbon density from 2000 to 2010 were analyzed in this paper. Normalized difference vegetation index (NDVI), biomass and soil carbon data in 2000 were used for regression analysis of biomass and soil carbon, and an inversion analysis was used to estimate biomass and soil carbon in 2005 and 2010. Quadrat data, including aboveground biomass and soil organic carbon, were used to calibrate the model output. Carbon storage and sequestration were calculated by the InVEST toolset with four carbon pools, including aboveground biomass, belowground biomass, dead wood and soil carbon. The results showed that carbon storage increased steadily from 2000 to 2010, increasing by 0.260 billion tons, and that woodland area increased and arable land decreased; the overall trend in land cover improved, but the improvement was not pronounced. Carbon storage in the Loess Plateau was correlated with geographical factors. We found that when assuming a constant carbon density, carbon storage decreased, accounting for −1% of the carbon storage dynamics. When assuming no land conversion, carbon storage increased, accounting for 101% of the carbon storage dynamics. Full article

(This article belongs to the Special Issue Carbon Capture and Storage)

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16 pages, 2559 KiB

Open AccessArticle

The Influence of Operating Parameters on Adsorption/Desorption Characteristics and Performance of the Fluidised Desiccant Cooler

by Zbigniew Rogala^*, Piotr Kolasiński

and Przemysław Błasiak

Department of Thermodynamics, Theory of Machines and Thermal Systems, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wroclaw, Poland

Energies 2018, 11(6), 1597; https://doi.org/10.3390/en11061597 - 19 Jun 2018

Cited by 8 | Viewed by 3394

Abstract

This paper concerns the issue of the proper selection of the operating parameters of the fluidised desiccant cooler. Despite the fact that fluidised desiccant cooling technology is being reported in the literature as an efficient way to provide cooling for the purposes of [...] Read more.

This paper concerns the issue of the proper selection of the operating parameters of the fluidised desiccant cooler. Despite the fact that fluidised desiccant cooling technology is being reported in the literature as an efficient way to provide cooling for the purposes of air-conditioning, the improper control of its operation can lead to a significantly worse performance than expected. The objective of the presented theoretical study is to provide guidelines on the proper selection of such operating parameters of a fluidized desiccant cooler, such as superficial air velocity, desiccant particle diameter, bed switching time, and desiccant filling height. The influence of the chosen operating parameters on the performance of fluidised desiccant cooling technology is investigated based on their impact on electric and thermal coefficients of performance (COP) and specific cooling power (SCP). Moreover, the influence of the outlet air temperature, humidity, and desiccant water uptake on the adsorption/desorption characteristics was investigated, contributing to better understanding of sorption processes. Full article

(This article belongs to the Special Issue Energy Systems Engineering)

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23 pages, 10769 KiB

Open AccessArticle

Analysis and Optimization of the Electromagnetic Performance of a Novel Stator Modular Ring Drive Thruster Motor

by Yukai Li^1,2,*

, Baowei Song^1,2, Zhaoyong Mao¹ and Wenlong Tian¹

¹ School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China

² Key Laboratory for Unmanned Underwater Vehicle, Northwestern Polytechnical University, Xi’an 710072, China

Energies 2018, 11(6), 1598; https://doi.org/10.3390/en11061598 - 19 Jun 2018

Cited by 14 | Viewed by 7350

Abstract

A rim driven thruster (RDT) is an integrated deep-sea motor thruster that has been widely studied. In order to improve the performance of RDT, a novel RDT motor with a modular stator is proposed in this paper. The electromagnetic performance of the new [...] Read more.

A rim driven thruster (RDT) is an integrated deep-sea motor thruster that has been widely studied. In order to improve the performance of RDT, a novel RDT motor with a modular stator is proposed in this paper. The electromagnetic performance of the new RDT motor is analyzed by the finite element method (FEM). The influence of structure parameters on the electromagnetic performance of the new RDT motor are analyzed in detail. It is shown that the effect of additional tooth width and pole arc coefficient on the electromagnetic performance of the stator modular RDT motor is significant. To obtain the optimal design with a maximum average electromagnetic torque and minimum torque fluctuation ratio, a multi-objective optimization design method combining the non-dominated sorting genetic algorithm II (NSGA-II), Kriging method and FEM is presented in this paper. A set of Pareto optimal solutions is obtained, and the optimal design point is selected from the Pareto fronts. Compared with the initial design, the average electromagnetic torque of the optimized model is improved by 16.591% and the fluctuation ratio is reduced to 3.18%. Full article

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15 pages, 5570 KiB

Open AccessArticle

A New Plugging Technology and Its Application for the Extensively Collapsed Ore Pass in the Non-Empty Condition

by He Chen^1,2,3,4, Shibo Yu^1,2,3,4,*

, Zhixiu Wang^2,4 and Ye Yuan^2,4

¹ School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China

² BGRIMM Technology Group, Beijing 100160, China

³ Beijing General Research Institute of Mining & Metallurgy, Beijing 100160, China

⁴ National Center for International Research on Green Mining of Metallic Mines, Beijing 102628, China

Energies 2018, 11(6), 1599; https://doi.org/10.3390/en11061599 - 19 Jun 2018

Cited by 5 | Viewed by 3126

Abstract

Aiming at some long ore passes with severe damages and extensive collapses, we describe an optimal measure to plug a local area of ore pass in order to maintain the capacity of continued use. This paper, taking a new plug for the extensively [...] Read more.

Aiming at some long ore passes with severe damages and extensive collapses, we describe an optimal measure to plug a local area of ore pass in order to maintain the capacity of continued use. This paper, taking a new plug for the extensively collapsed long ore pass in the non-empty condition as a breakthrough, builds a structure-plugging system for ore pass based on plug effect, suspension effect, arch effect, and span-reducing effect. Meanwhile, a key plugging technology has been integrated which includes a stability evaluation method of plugging structure, controlled technology of drilling with casing in the composite rock mass, and controllable grouting for inhomogeneous loose rock mass. According to this structure-plugging system and technology, a case has been successful for the main ore pass in the Xingshan Iron Mine in China, which has created a precedent in the world. The practice results show that using this technology to plug the extensively collapsed long ore pass has a series of advantages including of scientific design, strong safety, high efficiency, and low cost. Full article

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19 pages, 2087 KiB

Open AccessArticle

A Frequency Control Strategy Considering Large Scale Wind Power Cluster Integration Based on Distributed Model Predictive Control

by Bohao Sun^1,*

, Yong Tang¹, Lin Ye²

, Chaoyu Chen², Cihang Zhang² and Wuzhi Zhong¹

¹ China Electric Power Research Institute, Haidian District, Beijing 100192, China

² College of Information and Electrical Engineering, China Agricultural University, Beijing 100083, China

Energies 2018, 11(6), 1600; https://doi.org/10.3390/en11061600 - 19 Jun 2018

Cited by 9 | Viewed by 3431

Abstract

With large scale wind integration and increasing wind penetration in power systems, relying solely on conventional generators for frequency control is not enough to satisfy system frequency stability requirements. It is imperative that wind power have certain capabilities to participate in frequency control [...] Read more.

With large scale wind integration and increasing wind penetration in power systems, relying solely on conventional generators for frequency control is not enough to satisfy system frequency stability requirements. It is imperative that wind power have certain capabilities to participate in frequency control by cooperating with conventional power sources. Firstly, a multi-area interconnected power system frequency response model containing wind power clusters and conventional generators is established with consideration of several nonlinear constraints. Moreover, a distributed model predictive control (DMPC) strategy considering Laguerre functions is proposed, which implements online rolling optimization by using ultra-short-term wind power forecasting data in order to realize advanced frequency control. Finally, a decomposition-coordination control algorithm considering Nash equilibrium is presented, which realizes online fast optimization of multivariable systems with constraints. Simulation results demonstrate the feasibility and effectiveness of the proposed control strategy and algorithm. Full article

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20 pages, 5587 KiB

Open AccessArticle

Influence of High-Speed Train Power Consumption and Arc Fault Resistances on a Novel Ground Fault Location Method for 2 × 25 kV Railway Power Supply Systems

by Carlos A. Platero^1,*

, Jesús Serrano¹, Máximo López-Toledo¹ and Ricardo Granizo²

¹ Department of Electrical Engineering, ETS Ingenieros Industriales, Universidad Politécnica de Madrid, C/José Gutierrez Abascal, 2, 28006 Madrid, Spain

² Department of Electrical Engineering, ETS Ingeniería y Diseño Industrial, Universidad Politécnica de Madrid, C/Ronda de Valencia, 3, 28012 Madrid, Spain

Energies 2018, 11(6), 1601; https://doi.org/10.3390/en11061601 - 19 Jun 2018

Cited by 5 | Viewed by 4145

Abstract

The 2 × 25 kV power supply system is the most frequently used traction rail system to provide the huge power needed by high-speed trains. However, locating the ground fault in this power supply system is more complicated than in other configurations of [...] Read more.

The 2 × 25 kV power supply system is the most frequently used traction rail system to provide the huge power needed by high-speed trains. However, locating the ground fault in this power supply system is more complicated than in other configurations of electrical railway power supply due to the installation of autotransformers throughout the line section. In previous papers, the authors have described a ground fault location method with an insignificant installation cost. The method and, moreover, the location discriminate between whether the ground fault is located between a positive conductor and ground or a negative conductor and ground. The current of the high-speed train influences the accuracy of the location of the ground fault. An additional factor which influences the location method is the existence of an arc resistance between the positive or negative conductor and ground. In this paper, the influence of high-speed train currents and arc resistances are analysed to evaluate the error in the location method. The major conclusion of the paper is that the location method has an acceptable precision even taking into consideration the high-speed train current and arc resistance. The validation of the method has been performed by laboratory tests and computer simulations with satisfactory results. Full article

(This article belongs to the Section F: Electrical Engineering)

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24 pages, 6715 KiB

Open AccessArticle

Strategic Behavior of Retailers for Risk Reduction and Profit Increment via Distributed Generators and Demand Response Programs

by Mahmood Hosseini Imani¹

, Shaghayegh Zalzar²

, Amir Mosavi^3,4

and Shahaboddin Shamshirband^5,6,*

¹ Department of Electrical Engineering, Faculty of Engineering, University of Guilan, Rasht 4199613776, Iran

² Department of Energy, Politecnico di Torino, 10129 Turin, Italy

³ Institute of Structural Mechanics, Bauhaus University Weimar, 99423 Weimar, Germany

⁴ Institute of Automation, Kando Kalman Faculty of Electrical Engineering, Obuda University, 1431 Budapest, Hungary

⁵ Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam

⁶ Faculty of Information Technology, Ton Duc Thang University, Ho Chi Minh City, Vietnam

Energies 2018, 11(6), 1602; https://doi.org/10.3390/en11061602 - 19 Jun 2018

Cited by 26 | Viewed by 4314

Abstract

Following restructuring of power industry, electricity supply to end-use customers has undergone fundamental changes. In the restructured power system, some of the responsibilities of the vertically integrated distribution companies have been assigned to network managers and retailers. Under the new situation, retailers are [...] Read more.

Following restructuring of power industry, electricity supply to end-use customers has undergone fundamental changes. In the restructured power system, some of the responsibilities of the vertically integrated distribution companies have been assigned to network managers and retailers. Under the new situation, retailers are in charge of providing electrical energy to electricity consumers who have already signed contract with them. Retailers usually provide the required energy at a variable price, from wholesale electricity markets, forward contracts with energy producers, or distributed energy generators, and sell it at a fixed retail price to its clients. Different strategies are implemented by retailers to reduce the potential financial losses and risks associated with the uncertain nature of wholesale spot electricity market prices and electrical load of the consumers. In this paper, the strategic behavior of retailers in implementing forward contracts, distributed energy sources, and demand-response programs with the aim of increasing their profit and reducing their risk, while keeping their retail prices as low as possible, is investigated. For this purpose, risk management problem of the retailer companies collaborating with wholesale electricity markets, is modeled through bi-level programming approach and a comprehensive framework for retail electricity pricing, considering customers’ constraints, is provided in this paper. In the first level of the proposed bi-level optimization problem, the retailer maximizes its expected profit for a given risk level of profit variability, while in the second level, the customers minimize their consumption costs. The proposed programming problem is modeled as Mixed Integer programming (MIP) problem and can be efficiently solved using available commercial solvers. The simulation results on a test case approve the effectiveness of the proposed demand-response program based on dynamic pricing approach on reducing the retailer’s risk and increasing its profit. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 2618 KiB

Open AccessArticle

Investigation of Discharge Coefficients for Single Element Lean Direct Injection Modules

by Han Yu, Pengfei Zhu, Jianqin Suo^* and Longxi Zheng

School of Power and Energy, Northwestern Polytechnical University, Xi’an 710072, China

Energies 2018, 11(6), 1603; https://doi.org/10.3390/en11061603 - 19 Jun 2018

Cited by 4 | Viewed by 3859

Abstract

Lean direct injection (LDI) combustion has a high potential as a low pollution combustion method for gas turbines. The present research aims to further investigate the discharge coefficient of an LDI module, axial swirler and convergent outlet under non-reaction and reaction conditions by [...] Read more.

Lean direct injection (LDI) combustion has a high potential as a low pollution combustion method for gas turbines. The present research aims to further investigate the discharge coefficient of an LDI module, axial swirler and convergent outlet under non-reaction and reaction conditions by theoretical, numerical and experimental methods. The functional relationship between the discharge coefficient of the LDI module, axial swirler and convergent outlet was established, and the effect of swirl angle (30°, 32°, 34°, 36°, 38°, 40°) and vane number (11, 12, 13, 14, 15, 16) on discharge coefficient was studied, and finally the differences in effective flow area of LDI combustor under different inlet conditions were analyzed. The results indicate that the flow separation on the suction side increases as the swirl angle increases, which leads to a decrease of the discharge coefficient of the axial swirler, however the discharge coefficient of the convergent outlet remains unchanged first and then decreases. As the vane number increases, the flow separation on the suction side decreases and the flow friction loss increases, so that the discharge coefficient of the axial swirler and convergent outlet will first increase with the increase of vane number and then decrease with further increases. The effective flow area of combustor changes as the conditions change, but it is approximately equal under high power conditions and normal temperature and pressure conditions. Full article

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14 pages, 5076 KiB

Open AccessArticle

Improvement in Harmonic Compensation of a Smart Charger with a Constant DC-Capacitor Voltage-Control-Based Strategy for Electric Vehicles in Single-Phase Three-Wire Distribution Feeders

by Kei Nishikawa^1,†, Fuka Ikeda^2,†, Yuki Okamoto^1,†, Hiroaki Yamada^1,†, Toshihiko Tanaka^1,*,† and Masayuki Okamoto^2,†

¹ Department of Electrical and Electronic Engineering, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi 755-8611, Japan

² Department of Electrical Engineering, National Institute of Technology, Ube College, 2-14-1 Tokiwadai, Ube, Yamaguchi 755-8555, Japan

^† These authors contributed equally to this work.

Energies 2018, 11(6), 1604; https://doi.org/10.3390/en11061604 - 19 Jun 2018

Cited by 3 | Viewed by 3362

Abstract

This paper presents an improvement in harmonic compensation performance of a previously proposed smart charger (SC) with a constant dc-capacitor voltage-control (CDCVC) strategy for electric vehicles (EVs) in single-phase three-wire distribution feeders (SPTWDFs). A controller for 3rd harmonic currents in d-q [...] Read more.

This paper presents an improvement in harmonic compensation performance of a previously proposed smart charger (SC) with a constant dc-capacitor voltage-control (CDCVC) strategy for electric vehicles (EVs) in single-phase three-wire distribution feeders (SPTWDFs). A controller for 3rd harmonic currents in d-q coordinates is added to the previously proposed SC. This addition improves harmonic compensation performance of the source currents. We briefly introduce harmonic current compensation using the previously proposed CDCVC-based algorithm for the SC. Then, the basic principles of the proposed controller for the 3rd harmonic currents in d-q coordinates are discussed in detail. It is shown that synchronization of the current controllers for both the fundamental and 3rd harmonic components is required. The switching frequency of a three-leg pulse-width modulated rectifier with a bidirectional dc–dc converter, which performs the SC, is determined considering the synchronization of the current controllers. Simulation and experimental results demonstrate that balanced and sinusoidal source currents with a unity power factor are achieved during both battery charging and discharging operations in EVs, improving the harmonic compensation performance of the previously proposed SC. Experimental results also demonstrate that the total harmonic distortion values of source currents are improved by 8.4% and 3.6% with the proposed controller for 3rd harmonic currents, when the SC is discharging, for example. Full article

(This article belongs to the Special Issue Power Electronics for Energy Storage)

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21 pages, 3269 KiB

Open AccessArticle

Short-Term Forecasting for Energy Consumption through Stacking Heterogeneous Ensemble Learning Model

by Mergani A. Khairalla^1,2,*

, Xu Ning¹, Nashat T. AL-Jallad¹ and Musaab O. El-Faroug³

¹ School of Computer Science and Technology, Wuhan University of Technology, Wuhan 430070, China

² School of Science and Technology, Nile Valley University, Atbara 346, Sudan

³ Faculty of Engineering, Elimam Elmahdi University, Kosti 11588, Sudan

Energies 2018, 11(6), 1605; https://doi.org/10.3390/en11061605 - 19 Jun 2018

Cited by 64 | Viewed by 6565

Abstract

In the real-life, time-series data comprise a complicated pattern, hence it may be challenging to increase prediction accuracy rates by using machine learning and conventional statistical methods as single learners. This research outlines and investigates the Stacking Multi-Learning Ensemble (SMLE) model for time [...] Read more.

In the real-life, time-series data comprise a complicated pattern, hence it may be challenging to increase prediction accuracy rates by using machine learning and conventional statistical methods as single learners. This research outlines and investigates the Stacking Multi-Learning Ensemble (SMLE) model for time series prediction problem over various horizons with a focus on the forecasts accuracy, directions hit-rate, and the average growth rate of total oil demand. This investigation presents a flexible ensemble framework in light of blend heterogeneous models for demonstrating and forecasting nonlinear time series. The proposed SMLE model combines support vector regression (SVR), backpropagation neural network (BPNN), and linear regression (LR) learners, the ensemble architecture consists of four phases: generation, pruning, integration, and ensemble prediction task. We have conducted an empirical study to evaluate and compare the performance of SMLE using Global Oil Consumption (GOC). Thus, the assessment of the proposed model was conducted at single and multistep horizon prediction using unique benchmark techniques. The final results reveal that the proposed SMLE model outperforms all the other benchmark methods listed in this study at various levels such as error rate, similarity, and directional accuracy by 0.74%, 0.020%, and 91.24%, respectively. Therefore, this study demonstrates that the ensemble model is an extremely encouraging methodology for complex time series forecasting. Full article

(This article belongs to the Special Issue Short-Term Load Forecasting by Artificial Intelligent Technologies)

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17 pages, 1414 KiB

Open AccessArticle

Reactive Power Planning for Regional Power Grids Based on Active and Reactive Power Adjustments of DGs

by Yangwu Shen¹, Feifan Shen^2,*, Yaling Chen³, Liqing Liang¹, Bin Zhang¹ and Deping Ke⁴

¹ Sate Grid Hunan Electric Power Corporation Research Institute, Changsha 410007, China

² Department of Electrical Engineering, Technical University of Denmark, kgs. Lyngby, 2008 Copenhagen, Denmark

³ School of Humanities and Management, Hunan University of Chinese Medicine, Changsha 410208, China

⁴ Department of Electrical Engineering, Wuhan University, Wuhan 430000, China

Energies 2018, 11(6), 1606; https://doi.org/10.3390/en11061606 - 20 Jun 2018

Cited by 1 | Viewed by 3129

Abstract

To deal with extreme overvoltage scenarios with small probabilities in regional power grids, the traditional reactive power planning model requires a huge VAR compensator investment. Obviously, such a decision that makes a large investment to cope with a small probability event is not [...] Read more.

To deal with extreme overvoltage scenarios with small probabilities in regional power grids, the traditional reactive power planning model requires a huge VAR compensator investment. Obviously, such a decision that makes a large investment to cope with a small probability event is not economic. Therefore, based on the scenario analysis of power outputs of distributed generations and load consumption, a novel reactive power planning model considering the active and reactive power adjustments of distributed generations is proposed to derive the optimal allocation of VAR compensators and ensure bus voltages within an acceptable range under extreme overvoltage scenarios. The objective of the proposed reactive power planning model is to minimize the VAR compensator investment cost and active power adjustment cost of distributed generations. Moreover, since the proposed reactive power planning model is formulated as a mixed-integer nonlinear programming problem, a primal-dual interior point method-based particle swarm optimization algorithm is developed to effectively solve the proposed model. Simulation results were conducted with the modified IEEE 30-bus system to verify the effectiveness of the proposed reactive power planning model. Full article

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14 pages, 2385 KiB

Open AccessArticle

The Effect of a Vertical Electric Field on the Surface Flashover Characteristics of a Bushing Model

by Mingxi Zhu¹

, Liming Wang¹, Fanghui Yin^1,*

, Masoud Farzaneh², Hongwei Mei¹

and Lu Wen¹

¹ Laboratory of Advanced Technology of Electrical Engineering and Energy, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, Guangdong, China

² Applied Science, Université du Québec à Chicoutimi (UQAC), 555 Boulevard de l’Université, Chicoutimi, QC G7H 2B1, Canada

Energies 2018, 11(6), 1607; https://doi.org/10.3390/en11061607 - 20 Jun 2018

Cited by 8 | Viewed by 3925

Abstract

High-voltage bushings play a crucial role in energy conveyance. Their specialized electric structure makes the bushing more vulnerable to surface discharge. However, the influence of a vertical electric field on the surface flashover of bushing structures remains unclear. To investigate this mechanism, four [...] Read more.

High-voltage bushings play a crucial role in energy conveyance. Their specialized electric structure makes the bushing more vulnerable to surface discharge. However, the influence of a vertical electric field on the surface flashover of bushing structures remains unclear. To investigate this mechanism, four simplified bushing samples were built and the influence of pollution, leakage length, and the electric field component vertical to the dielectric surface on flashover properties of the bushing samples were tested. It was found that the surface pollution level was the decisive factor that influenced flashover voltage. When the leakage length and form factor were the same, the pollution flashover of the bushing structure was lower than that of the post structure. It was also found that increasing the leakage length was not very effective in improving the flashover voltage of bushings when the equivalent salt deposit density (ESDD) was high. No obvious correlation was found between pollution flashover voltage and electric field stress. Furthermore, the uneven wetting flashover performance of the bushings was tested. Under this condition, the flashover voltage decreased with an increase of the electric field component vertical to the dielectric surface. In addition, the electric field distribution of the samples was calculated and the results were in accordance with the experimental results. Full article

(This article belongs to the Section F: Electrical Engineering)

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28 pages, 8081 KiB

Open AccessArticle

A Fully Coupled Numerical Model for Microwave Heating Enhanced Shale Gas Recovery

by Jia Liu^1,2, Jianguo Wang^1,3,*

, Chunfai Leung² and Feng Gao^1,3

¹ State Key Laboratory for Geomechanics & Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, China

² Center for Offshore Research and Engineering, National University of Singapore, E1A-07-03, 1 Engineering Drive 2, Singapore 117576, Singapore

³ School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, China

Energies 2018, 11(6), 1608; https://doi.org/10.3390/en11061608 - 20 Jun 2018

Cited by 39 | Viewed by 5142

Abstract

Formation heat treatment (FHT) can be achieved by converting electromagnetic energy into heat energy (that is microwave heating or MWH). Experimental evidence shows that such FHT can significantly enhance oil and gas recovery. As relatively few research studies have been reported on microwave [...] Read more.

Formation heat treatment (FHT) can be achieved by converting electromagnetic energy into heat energy (that is microwave heating or MWH). Experimental evidence shows that such FHT can significantly enhance oil and gas recovery. As relatively few research studies have been reported on microwave heating enhanced shale gas recovery (MWH-EGR), a fully coupled electromagnetic-thermo-hydro-mechanical (ETHM) model is developed for the MWH-EGR in the present study. In the ETHM model, a thermal-induced gas adsorption model is firstly proposed for shale gas adsorption and fitted by experimental data. This thermal-induced adsorption model considers the increase of matrix pore space due to the desorption of the adsorbed phase. Further, a thermal-induced fracture model in shale matrix is established and fitted by experimental data. Finally, this ETHM model is applied to a fractured shale gas reservoir to simulate gas production. Numerical results indicated that the thermal-induced fracturing and gas desorption make predominant contributions to the evolution of matrix porosity. The MWH can increase cumulative gas production by 44.9% after 31.7 years through promoting gas desorption and matrix diffusion. These outcomes can provide effective insights into shale gas recovery enhancement by microwave assistance. Full article

(This article belongs to the Section L: Energy Sources)

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20 pages, 3452 KiB

Open AccessArticle

Wind Farm Blockage and the Consequences of Neglecting Its Impact on Energy Production

by James Bleeg^1,*

, Mark Purcell², Renzo Ruisi^1,3 and Elizabeth Traiger¹

¹ DNV GL, Group Technology & Research, Power & Renewables, Bristol BS2 0PS, UK

² DNV GL, Energy, Project Development, Melbourne 3008, Australia

³ DNV GL, Energy, Project Development, Glasgow G1 2PR, UK

Energies 2018, 11(6), 1609; https://doi.org/10.3390/en11061609 - 20 Jun 2018

Cited by 101 | Viewed by 21113

Abstract

Measurements taken before and after the commissioning of three wind farms reveal that the wind speeds just upstream of each wind farm decrease relative to locations farther away after the turbines are turned on. At a distance of two rotor diameters upstream, the [...] Read more.

Measurements taken before and after the commissioning of three wind farms reveal that the wind speeds just upstream of each wind farm decrease relative to locations farther away after the turbines are turned on. At a distance of two rotor diameters upstream, the average derived relative slowdown is 3.4%; at seven to ten rotor diameters upstream, the average slowdown is 1.9%. Reynolds-Averaged Navier-Stokes (RANS) simulations point to wind-farm-scale blockage as the primary cause of these slowdowns. Blockage effects also cause front row turbines to produce less energy than they each would operating in isolation. Wind energy prediction procedures in use today ignore this effect, resulting in an overprediction bias that pervades the entire wind farm. Full article

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13 pages, 2495 KiB

Open AccessArticle

Electro-Thermal Modeling of Metal-Oxide Arrester under Power Frequency Applied Voltages

by Jiazheng Lu, Pengkang Xie^*

, Zhen Fang and Jianping Hu

State Key Laboratory of Disaster Prevention & Reduction for Power Grid Transmission & Distribution Equipment, State Grid Hunan Electric Power Corporation Disaster Prevention & Reduction Center, Changsha 410007, China

Energies 2018, 11(6), 1610; https://doi.org/10.3390/en11061610 - 20 Jun 2018

Cited by 14 | Viewed by 3937

Abstract

Metal-oxide arresters (MOAs) are used to absorb the electrical energy resulting from overvoltages in power systems. However, temperature rises caused by the absorbed energy can lead to the electrothermal failure of MOAs. Therefore, it is necessary to analyze the electric and thermal characteristics [...] Read more.

Metal-oxide arresters (MOAs) are used to absorb the electrical energy resulting from overvoltages in power systems. However, temperature rises caused by the absorbed energy can lead to the electrothermal failure of MOAs. Therefore, it is necessary to analyze the electric and thermal characteristics of MOAs. In this paper, in order to study the electric and thermal characteristics of MOAs under power frequency voltage, an improved electrothermal model of an MOA is presented. The proposed electrothermal model can be divided into an electric model and a thermal model. In the electric model, based on the conventional MOA electric circuit, the effect of temperature on the voltage–current (V–I) characteristics of an MOA has been obtained. Using temperature and applied voltage as input data, the current flows through the MOA can be calculated using the artificial neural network (ANN) method. In the thermal model, the thermal circuit of a MOA has been built. The varistor power loss obtained from the electric model is used as input data, and the temperature of the zinc oxide varistors can be calculated. Therefore, compared with the existing MOA models, the interaction of leakage current and temperature can be considered in the proposed model. Finally, experimental validations have been done, and the electrothermal characteristics of an MOA have been studied by simulation and experimental methods. The electrothermal model proposed in this paper can assist with the prediction of the electric and thermal characteristics of MOAs. Full article

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11 pages, 6566 KiB

Open AccessArticle

3-Leg Inverter Control for 2-Phase Outer Rotor Coreless Torque Actuator in Hybrid Multi-D.O.F System

by Kyoung Jin Joo¹

, Gang Seok Lee¹, Hyun Seok Hong¹, Sung Hong Won² and Ju Lee^1,*

¹ Department of Electrical Engineering, Hanyang University, Seoul 04763, Korea

² Department of Electric System, Dongyang Mirae University 62-160, GoChuk-Dong, GuRo-Gu, Seoul 08221, Korea

Energies 2018, 11(6), 1611; https://doi.org/10.3390/en11061611 - 20 Jun 2018

Cited by 1 | Viewed by 4431

Abstract

Since an existing 3-phase inner rotor torque actuator (TA) has severe torque ripples, it is not appropriate for a gimbal system that requires precise position control. Therefore, a coreless TA is considered to eliminate the core causing torque ripples. In order to compensate [...] Read more.

Since an existing 3-phase inner rotor torque actuator (TA) has severe torque ripples, it is not appropriate for a gimbal system that requires precise position control. Therefore, a coreless TA is considered to eliminate the core causing torque ripples. In order to compensate for several problems (e.g., problems of production structures and output degradation) when a coreless type is used, the final 2-phase outer rotor is proposed for the low vibration and high power TA in the gimbal system. To control the 2-phase TA applied to such the gimbal system, special inverter control methods, such as bi-directional drive for tilting control and control for output torque improvement, are required. The 2-phase 3-leg inverter is free of DC capacitor voltage unbalance compared to the 2-leg inverter, and is economical because it uses less power switches than the 4-leg inverter. Therefore, the 2-phase 3-leg inverter is applied to drive the 2-phase outer rotor coreless TA of a hybrid gimbal system, and it is verified through simulation. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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11 pages, 4373 KiB

Open AccessArticle

Research on the Pressure Ratio Characteristics of a Swash Plate-Rotating Hydraulic Transformer

by Chongbo Jing, Junjie Zhou^*, Shihua Yuan and Siyuan Zhao

School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China

Energies 2018, 11(6), 1612; https://doi.org/10.3390/en11061612 - 20 Jun 2018

Cited by 9 | Viewed by 4171

Abstract

This paper presents a theoretical model and its experimental validation for the pressure ratio of a swash plate-rotating hydraulic transformer. The structure and principle of the new type of transformer are described. The swash plate-rotating type can reduce the throttling loss caused by [...] Read more.

This paper presents a theoretical model and its experimental validation for the pressure ratio of a swash plate-rotating hydraulic transformer. The structure and principle of the new type of transformer are described. The swash plate-rotating type can reduce the throttling loss caused by the valve plate in traditional hydraulic transformers. The theoretical model of the pressure ratio was derived based on the displacements functioning as the pump and motor in the transformer, accounting for the friction losses. A specific experimental setup including the prototype was established to validate the principle and pressure ratio of the machine. The results show that the transformer has a wider pressure range. The increase in pressure at port A and the rotating speed of the cylinder can reduce the pressure ratio slightly due to the torque loss. The present work indicates the useful potential of the swash plate-rotating hydraulic transformer. Full article

(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems 2018)

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18 pages, 2463 KiB

Open AccessArticle

Fully-distributed Load Frequency Control Strategy in an Islanded Microgrid Considering Plug-In Electric Vehicles

by Xiao Qi^1,2,*

, Yan Bai¹, Huanhuan Luo³, Yiqing Zhang², Guiping Zhou³ and Zhonghua Wei³

¹ School of Control and Computer Engineering, North China Electric Power University, Beijing 102206, China

² Synergy Innovation Center for Energy Economics of Shandong, Shandong Institute of Business and Technology, Yantai 264005, China

³ State Grid Liaoning Electric Power Supply Co., Ltd., Shenyang 110004, China

Energies 2018, 11(6), 1613; https://doi.org/10.3390/en11061613 - 20 Jun 2018

Cited by 23 | Viewed by 3945

Abstract

With large-scale integration of electric vehicles, this paper investigates the load frequency control problem in an islanded microgrid with plug-in electric vehicles (PEVs), which can be regarded as mobile battery energy storages to provide a valuable contribution to frequency regulation. A novel fully-distributed [...] Read more.

With large-scale integration of electric vehicles, this paper investigates the load frequency control problem in an islanded microgrid with plug-in electric vehicles (PEVs), which can be regarded as mobile battery energy storages to provide a valuable contribution to frequency regulation. A novel fully-distributed control strategy is proposed to achieve fast frequency regulation of islanded microgrids and effective coordination control of distributed energy sources. Firstly, distributed control based on an improved linear active disturbance rejection algorithm is realized through a multi-agent system, and it greatly enhances the anti-disturbance capability of the microgrid. Then, in order to guarantee the effectiveness of PEVs in frequency regulation, PEVs are controlled following the controllable power rate (CPR) calculated from the consensus-based multi-agent system. Furthermore, the system control construction in this paper is well designed to avoid the negative effects caused by system communication time delay. Finally, numerical simulations under different disturbances are carried out to demonstrate the effectiveness of the proposed control strategy in comparison with other previous control strategies. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2018)

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10 pages, 2225 KiB

Open AccessArticle

SnSb Alloy Blended with Hard Carbon as Anode for Na-Ion Batteries

by Ying Ching Lu¹, Nikolay Dimov², Shigeto Okada³ and Thi Hang Bui^4,*

¹ Department of Chemical Engineering, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Fukuoka 816-8580, Japan

² International Institute for Carbon-Neutral Energy Research, Kyushu University, Fukuoka 819-0395, Japan

³ Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 816-8580, Japan

⁴ International Training Institute for Materials Science, Hanoi University of Science and Technology, No. 1 Dai Co Viet, Hanoi 100000, Vietnam

Energies 2018, 11(6), 1614; https://doi.org/10.3390/en11061614 - 20 Jun 2018

Cited by 13 | Viewed by 5477

Abstract

SnSb binary alloys blended with reduced graphene oxide (SnSb/RGO) or mixtures of SnSb/RGO with hard carbon (SnSb/RGO+HC) were tested as anode materials for sodium-ion batteries. The presence of hard carbon in the SnSb/RGO+HC blend improves its cycle efficiency and rate performance substantially. The [...] Read more.

SnSb binary alloys blended with reduced graphene oxide (SnSb/RGO) or mixtures of SnSb/RGO with hard carbon (SnSb/RGO+HC) were tested as anode materials for sodium-ion batteries. The presence of hard carbon in the SnSb/RGO+HC blend improves its cycle efficiency and rate performance substantially. The synergy between the SnSb/RGO and the hard carbon phase is explained by the buffer action of the hard carbon, preventing SnSb interparticle agglomeration during the repeated recharge cycles. The feasibility of SnSb alloy anode for sodium-ion batteries was confirmed in full cell configuration vs. Na₃V₂(PO₄)₂F₃ cathode. Full article

(This article belongs to the Special Issue Electrochemical Energy Conversion and Storage Technologies 2018)

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20 pages, 3653 KiB

Open AccessArticle

The Future of Fossil Fired Power Plants in Germany—A Lifetime Analysis

by Peter Markewitz^1,*, Martin Robinius¹

and Detlef Stolten^1,2

¹ Institute of Electrochemical Process Engineering (IEK-3), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

² RWTH Aachen University, c/o Institute of Electrochemical Process Engineering (IEK-3), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

Energies 2018, 11(6), 1616; https://doi.org/10.3390/en11061616 - 20 Jun 2018

Cited by 15 | Viewed by 5843

Abstract

In many German energy projections, the assumption of power plant lifetimes plays a central role, since it is often used in projections for the existing fleet of power plants or as a criterion for decommissioning in model-based investigations. The result of these analyses [...] Read more.

In many German energy projections, the assumption of power plant lifetimes plays a central role, since it is often used in projections for the existing fleet of power plants or as a criterion for decommissioning in model-based investigations. The result of these analyses is a power plant capacity retirement graph, which is then used to determine the replacement demand. Especially in the context of the German Energy transition (“Energiewende”) the amount and dynamics of replacement play an important role. Against this background, a large number of studies have been evaluated and fleet developments compared. Many studies refer to empirical values for the assumption of lifetimes without specifying them in greater detail. This approach was used to conduct an ex post lifetime analysis—accurate to each number of units—of German power plants that have been decommissioned since 1990. The analysis is conducted with the aid of a power plant database, which has been continuously updated for each individual unit since 1985. In addition to the power plants currently in operation, the database includes also includes power plant units that have been successively decommissioned over the past decades. The ex post analysis presents the first lifetime analysis for decommissioned German plants, which can serve as a basis for future power plant fleet projections. The analyses show that the lifetime of fossil-fired power plants has extended considerably. For example, whereas the real lifetimes of coal-fired power plants were in a range of 30 to 35 years in the 1990s, today they amount to 40 to 45 years on average. Full article

(This article belongs to the Section F: Electrical Engineering)

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Review

Jump to: Research, Other

33 pages, 2874 KiB

Open AccessReview

Overview of Electric Field Applications in Energy and Process Engineering

by Lars Zigan

Lehrstuhl für Technische Thermodynamik (LTT) and Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), D-91058 Erlangen, Germany

Energies 2018, 11(6), 1361; https://doi.org/10.3390/en11061361 - 27 May 2018

Cited by 27 | Viewed by 11877

Abstract

Heat and mass transfer as well as chemical reactions in technical processes can be enhanced by using electric fields. This paper provides an overview of current fundamental and applied research as well as potential technical applications of electric fields in energy and process [...] Read more.

Heat and mass transfer as well as chemical reactions in technical processes can be enhanced by using electric fields. This paper provides an overview of current fundamental and applied research as well as potential technical applications of electric fields in energy and process engineering. This includes electrosprays, technical combustors as well as electrochemical reforming and plasma gasification of waste or biomass. Other emerging fields are plasma technologies for treatment of water, surfaces and gases including flue gases. In particle or aerosol-laden flows, plasmas are used to promote particle nucleation and surface growth for controlled nanomaterial synthesis. Furthermore, non-invasive diagnostics based on electromagnetic fields and electric fluid properties are relevant techniques for online control and optimization of technical processes. Finally, an overview of laser-based techniques is provided for studying electro-hydrodynamic effects, temperature, and species concentrations in plasma and electric-field enhanced processes. Full article

(This article belongs to the Special Issue Electric Fields in Energy & Process Engineering)

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26 pages, 7562 KiB

Open AccessEditor’s ChoiceReview

A Review of Particulate Number (PN) Emissions from Gasoline Direct Injection (GDI) Engines and Their Control Techniques

by Mohsin Raza¹

, Longfei Chen^1,*, Felix Leach^2,*

and Shiting Ding¹

¹ School of Energy and Power Engineering, Energy and Environment International Center, Beihang University, Beijing 100191, China

² Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, UK

Energies 2018, 11(6), 1417; https://doi.org/10.3390/en11061417 - 1 Jun 2018

Cited by 186 | Viewed by 13102

Abstract

Particulate Matter (PM) emissions from gasoline direct injection (GDI) engines, particularly Particle Number (PN) emissions, have been studied intensively in both academia and industry because of the adverse effects of ultrafine PM emissions on human health and other environmental concerns. GDI engines are [...] Read more.

Particulate Matter (PM) emissions from gasoline direct injection (GDI) engines, particularly Particle Number (PN) emissions, have been studied intensively in both academia and industry because of the adverse effects of ultrafine PM emissions on human health and other environmental concerns. GDI engines are known to emit a higher number of PN emissions (on an engine-out basis) than Port Fuel Injection (PFI) engines, due to the reduced mixture homogeneity in GDI engines. Euro 6 emission standards have been introduced in Europe (and similarly in China) to limit PN emissions from GDI engines. This article summarises the current state of research in GDI PN emissions (engine-out) including a discussion of PN formation, and the characteristics of PN emissions from GDI engines. The effect of key GDI engine operating parameters is analysed, including air-fuel ratio, ignition and injection timing, injection pressure, and EGR; in addition the effect of fuel composition on particulate emissions is explored, including the effect of oxygenate components such as ethanol. Full article

(This article belongs to the Special Issue Recent Advances in Internal Combustion Engines Operation and Emissions)

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20 pages, 2133 KiB

Open AccessReview

AC Ship Microgrids: Control and Power Management Optimization

by Monaaf D. A. Al-Falahi¹

, Tomasz Tarasiuk²

, Shantha Gamini Jayasinghe^1,*

, Zheming Jin³, Hossein Enshaei¹

and Josep M. Guerrero³

¹ National Centre for Ports and Shipping, Australian Maritime College, University of Tasmania, Tasmania 7248, Australia

² Department of Marine Electrical Power Engineering, Gdynia Maritime University, Gdynia 81225, Poland

³ Institute of Energy Technology, Aalborg University, Aalborg 9100, Denmark

Energies 2018, 11(6), 1458; https://doi.org/10.3390/en11061458 - 5 Jun 2018

Cited by 62 | Viewed by 8992

Abstract

At sea, the electrical power system of a ship can be considered as an islanded microgrid. When connected to shore power at berth, the same power system acts as a grid connected microgrid or an extension of the grid. Therefore, ship microgrids show [...] Read more.

At sea, the electrical power system of a ship can be considered as an islanded microgrid. When connected to shore power at berth, the same power system acts as a grid connected microgrid or an extension of the grid. Therefore, ship microgrids show some resemblance to terrestrial microgrids. Nevertheless, due to the presence of large dynamic loads, such as electric propulsion loads, keeping the voltage and frequency within a permissible range and ensuring the continuity of supply are more challenging in ship microgrids. Moreover, with the growing demand for emission reductions and fuel efficiency improvements, alternative energy sources and energy storage technologies are becoming popular in ship microgrids. In this context, the integration of multiple energy sources and storage systems in ship microgrids requires an efficient power management system (PMS). These challenging environments and trends demand advanced control and power management solutions that are customized for ship microgrids. This paper presents a review on recent developments of control technologies and power management strategies proposed for AC ship microgrids. Full article

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14 pages, 1096 KiB

Open AccessReview

A Survey on Equivalence Modeling for Large-Scale Photovoltaic Power Plants

by Pingping Han¹, Zihao Lin^1,*

, Lei Wang¹, Guijun Fan¹ and Xiaoan Zhang²

¹ Anhui Provincial Laboratory of New Energy Utilization and Energy Conservation, Hefei University of Technology, Hefei 230009, China

² Intelligent Manufacturing Institute, Hefei University of Technology, Hefei 230009, China

Energies 2018, 11(6), 1463; https://doi.org/10.3390/en11061463 - 6 Jun 2018

Cited by 19 | Viewed by 2883

Abstract

Due to the huge data of large-scale photovoltaic (PV) power plants, the establishment of its equivalent model is more practical than a detailed model. In connection with the current research status, this paper reviews the steady-state equivalent model and transient equivalent model of [...] Read more.

Due to the huge data of large-scale photovoltaic (PV) power plants, the establishment of its equivalent model is more practical than a detailed model. In connection with the current research status, this paper reviews the steady-state equivalent model and transient equivalent model of PV power plants. The steady-state equivalent model is used for power flow calculation and static stability analysis. Transient equivalent models contain the single-machine equivalent model and the multi-machine equivalent models, which are used for the simulation analysis of large disturbances. The calculation of equivalent parameters and the equivalence of power collection system are briefly introduced. The conclusion and problems to be solved are put forward at the end. The establishment of the equivalent model simplifies the detailed model, which is convenient for the planning and simulation analysis of the PV power plant, and can also accurately characterize the operating characteristics of the PV power plant, which is of great significance. Full article

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32 pages, 7901 KiB

Open AccessReview

Cost-Optimal Analysis for Nearly Zero Energy Buildings Design and Optimization: A Critical Review

by Maria Ferrara¹

, Valentina Monetti¹ and Enrico Fabrizio^1,2,*

¹ Dipartimento Energia (DENERG), Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy

² FULL—Future Urban Legacy Lab., Via Agostino da Montefeltro 2, 10134 Torino, Italy

Energies 2018, 11(6), 1478; https://doi.org/10.3390/en11061478 - 6 Jun 2018

Cited by 71 | Viewed by 8132

Abstract

Since the introduction of the recast of the EPBD European Directive 2010/31/EU, many studies on the cost-effective feasibility of nearly zero-energy buildings (NZEBs) were carried out either by academic research bodies and by national bodies. In particular, the introduction of the cost-optimal methodology [...] Read more.

Since the introduction of the recast of the EPBD European Directive 2010/31/EU, many studies on the cost-effective feasibility of nearly zero-energy buildings (NZEBs) were carried out either by academic research bodies and by national bodies. In particular, the introduction of the cost-optimal methodology has given a strong impulse to research in this field. This paper presents a comprehensive and significant review on scientific works based on the application of cost-optimal analysis applications in Europe since the EPBD recast entered into force, pointing out the differences in the analyzed studies and comparing their outcomes before the new recast of EPBD enters into force in 2018. The analysis is conducted with special regard to the methods used for the energy performance assessment, the global cost calculation, and for the selection of the energy efficiency measures leading to design optimization. A critical discussion about the assumptions on which the studies are based and the resulting gaps between the resulting cost-optimal performance and the zero energy target is provided together with a summary of the resulting cost-optimal set of technologies to be used for cost-optimal NZEB design in different contexts. It is shown that the cost-optimal approach results as an effective method for delineating the future of NZEB design throughout Europe while emerging criticalities and open research issues are presented. Full article

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20 pages, 9323 KiB

Open AccessReview

Upstream Flow Control for the Savonius Rotor under Various Operation Conditions

by Can Kang^1,*

, Wisdom Opare^1,2, Chen Pan¹ and Ziwen Zou¹

¹ School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China

² Faculty of Engineering, Takoradi Technical University, Takoradi P.O. Box 256, Ghana

Energies 2018, 11(6), 1482; https://doi.org/10.3390/en11061482 - 6 Jun 2018

Cited by 11 | Viewed by 3717

Abstract

Applications of the Savonius rotor have been extended in recent years, necessitating an in-depth investigation on flow characteristics of such a fluid energy converting device. For the wake flow downstream of the Savonius rotor, studies have been reported extensively. Nevertheless, literature specifically devoted [...] Read more.

Applications of the Savonius rotor have been extended in recent years, necessitating an in-depth investigation on flow characteristics of such a fluid energy converting device. For the wake flow downstream of the Savonius rotor, studies have been reported extensively. Nevertheless, literature specifically devoted to the upstream flow of the Savonius rotor can rarely be found. This review collects and compiles findings from relevant studies to prove the significance of upstream flow patterns to the operation of the Savonius rotor. Then attempts from experimental and numerical aspects to substantiate the important effect of the upstream flow are implemented. Based on practical cases and laboratory works, upstream flow patterns for the Savonius rotor are divided into four types, namely uniform flow, guided flow, rotor wake flow and oscillating flow. Accordingly, conditions under which these upstream flow patterns arise are analyzed respectively. Experimental and numerical results are presented to clarify the influential factors underlying diverse upstream flow patterns. Furthermore, the relationship between the performance of the Savonius and the upstream flow is elucidated, facilitating the development of techniques of controlling the upstream flow. This review provides a systematic reference for the control of the upstream flow for the Savonius rotor, which has the tendency of developing into an independent technical branch. Full article

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41 pages, 3041 KiB

Open AccessReview

Mitigation of Power Quality Issues Due to High Penetration of Renewable Energy Sources in Electric Grid Systems Using Three-Phase APF/STATCOM Technologies: A Review

by Wajahat Ullah Khan Tareen^1,2,*, Muhammad Aamir³, Saad Mekhilef¹

, Mutsuo Nakaoka¹, Mehdi Seyedmahmoudian⁴

, Ben Horan⁵

, Mudasir Ahmed Memon¹

and Nauman Anwar Baig²

¹ Power Electronics and Renewable Energy Research Laboratory (PEARL), Department of Electrical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

² Department of Electrical Engineering, International Islamic University, Islamabad 44000, Pakistan

³ Department of Electrical Engineering, Bahria University, Islamabad 44000, Pakistan

⁴ School of Software and Electrical Engineering, Swinburne University of Technology, VIC 3122, Australia

⁵ School of Engineering, Deakin University, Waurn Ponds, VIC 3216, Australia

Energies 2018, 11(6), 1491; https://doi.org/10.3390/en11061491 - 7 Jun 2018

Cited by 54 | Viewed by 7362

Abstract

This study summarizes an analytical review on the comparison of three-phase static compensator (STATCOM) and active power filter (APF) inverter topologies and their control schemes using industrial standards and advanced high-power configurations. Transformerless and reduced switch count topologies are the leading technologies in [...] Read more.

This study summarizes an analytical review on the comparison of three-phase static compensator (STATCOM) and active power filter (APF) inverter topologies and their control schemes using industrial standards and advanced high-power configurations. Transformerless and reduced switch count topologies are the leading technologies in power electronics that aim to reduce system cost and offer the additional benefits of small volumetric size, lightweight and compact structure, and high reliability. A detailed comparison of the topologies, control strategies and implementation structures of grid-connected high-power converters is presented. However, reducing the number of power semiconductor devices, sensors, and control circuits requires complex control strategies. This study focuses on different topological devices, namely, passive filters, shunt and hybrid filters, and STATCOMs, which are typically used for power quality improvement. Additionally, appropriate control schemes, such as sinusoidal pulse width modulation (SPWM) and space vector PWM techniques, are selected. According to recent developments in shunt APF/STATCOM inverters, simulation and experimental results prove the effectiveness of APF/STATCOM systems for harmonic mitigation based on the defined limit in IEEE-519. Full article

(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems)

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20 pages, 2448 KiB

Open AccessReview

Dimethyl Carbonate as a Promising Oxygenated Fuel for Combustion: A Review

by Ayoub O. G. Abdalla^1,2 and Dong Liu^1,2,*

¹ MIIT Key Laboratory of Thermal Control of Electronic Equipment, School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, China

² Advanced Combustion Laboratory, School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, China

Energies 2018, 11(6), 1552; https://doi.org/10.3390/en11061552 - 14 Jun 2018

Cited by 70 | Viewed by 7687

Abstract

Energy shortage and environmental problems are two dominant subjects. Dimethyl carbonate (DMC) is one of the oxygenated fuels with increasing interest as the alternative to diesel fuel or additive for conventional hydrocarbon fuels. In the last decade, comprehensive studies on DMC have been [...] Read more.

Energy shortage and environmental problems are two dominant subjects. Dimethyl carbonate (DMC) is one of the oxygenated fuels with increasing interest as the alternative to diesel fuel or additive for conventional hydrocarbon fuels. In the last decade, comprehensive studies on DMC have been carried out in terms of synthesis, use, and oxidation and combustion mechanism. DMC synthesis from greenhouse gas such as carbon dioxide can achieve the carbon circulation between air and fuel. Ethylene carbonate route is one of the most promising ways to utilize carbon dioxide and synthesize DMC in terms of particle efficiency, energy consumption per one unit of product, and net carbon dioxide emission. In addition, the results show that pure DMC in compression ignition (CI) engines or DMC addition in diesel/gasoline could decrease emissions significantly. Moreover, DMC pyrolysis form carbon dioxide before carbon monoxide which is different from other oxygenated fuels. However, DMC can produce formaldehyde during oxidation process in high concentration, which is harmful to the environment and human health as well. The present DMC kinetic model needs to update the major reactions constant through recognizing the initial decomposition routes and low-temperature oxidation. In addition, further studies on the DMC/hydrocarbon fuels mixtures for the interaction chemistry are needed. Full article

(This article belongs to the Section L: Energy Sources)

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22 pages, 1241 KiB

Open AccessEditor’s ChoiceReview

Peer to Peer Distributed Energy Trading in Smart Grids: A Survey

by Juhar Abdella^*

and Khaled Shuaib

College of Information Technology, The United Arab Emirates University, Al Ain 15551, UAE

Energies 2018, 11(6), 1560; https://doi.org/10.3390/en11061560 - 14 Jun 2018

Cited by 169 | Viewed by 13340

Abstract

Due to the expansion of distributed renewable energy resources, peer to peer energy trading (P2P DET) is expected to be one of the key elements of next generation power systems. P2P DET can provide various benefits such as creating a competitive energy market, [...] Read more.

Due to the expansion of distributed renewable energy resources, peer to peer energy trading (P2P DET) is expected to be one of the key elements of next generation power systems. P2P DET can provide various benefits such as creating a competitive energy market, reducing power outages, increasing overall efficiency of power systems and supplementing alternative sources of energy according to user preferences. Because of these promising advantages, P2P DET has attracted the attention of several researchers. Current research related to P2P DET include demand response optimization, power routing, network communication, security and privacy. This paper presents a review of the main research topics revolving around P2P DET. Particularly, we present a comprehensive survey of existing demand response optimization models, power routing devices and power routing algorithms. We also identify some key challenges faced in realizing P2P DET. Furthermore, we discuss state of the art enabling technologies such as Energy Internet, Blockchain and Software Defined Networking (SDN) and we provide insights into future research directions. Full article

(This article belongs to the Collection Smart Grid)

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26 pages, 3787 KiB

Open AccessReview

Thermal Performance through Heat Retention in Integrated Collector-Storage Solar Water Heaters: A Review

by Ruth M. Saint^1,*

, Céline Garnier¹, Francesco Pomponi²

and John Currie³

¹ School of Engineering & the Built Environment, Edinburgh Napier University, Edinburgh EH10 5DT, UK

² Resource Efficient Built Environment Lab (REBEL), Edinburgh Napier University, Edinburgh EH10 5DT, UK

³ Scottish Energy Centre, Edinburgh Napier University, Edinburgh EH10 5DT, UK

Energies 2018, 11(6), 1615; https://doi.org/10.3390/en11061615 - 20 Jun 2018

Cited by 11 | Viewed by 5998

Abstract

Solar thermal systems are a long-standing technology that is receiving increased attention, in terms of research and development, due to ambitious climate change targets and the need for renewable energy solutions. Integrated collector-storage solar water heaters (ICSSWHs) are a potential contributing solution and [...] Read more.

Solar thermal systems are a long-standing technology that is receiving increased attention, in terms of research and development, due to ambitious climate change targets and the need for renewable energy solutions. Integrated collector-storage solar water heaters (ICSSWHs) are a potential contributing solution and numerous studies have focussed on the optimisation of their thermal performance and efficiency. A major drawback of these systems is the heavy heat losses experienced during non-collection periods. To combat this, various heat retention strategies have been proposed and evaluated, including baffles plates, additional insulation, multiple glazing layers, selective coatings, and phase change materials. This paper aims to bring together these studies through a systematic review of the existing literature surrounding the performance of ICSSWH systems, focusing on heat retention. This review provides a comprehensive and up-to-date point of reference on relevant research and developments for researchers in this field. Full article

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Other

Jump to: Research, Review

11 pages, 3115 KiB

Open AccessCase Report

Sealing Failure Analysis on V-Shaped Sealing Rings of an Inserted Sealing Tool Used for Multistage Fracturing Processes

by Gang Hu^1,2,*, Guorong Wang^1,*, Liming Dai^2,*, Peng Zhang¹, Ming Li³ and Yukun Fu⁴

¹ School of Mechatronic Engineering, Southwest Petroleum University, Chengdu 610500, China

² Industrial Systems Engineering, University of Regina, Regina, SK S4S 0A2, Canada

³ Sanden Chongqing Automative Air Conditionting CO. Ltd., Chongqing 401120, China

⁴ Engeering Technology Reasearch Insititute, PetroChina Southwest Oil & Gas Field Company, Chengdu 610017, China

Energies 2018, 11(6), 1432; https://doi.org/10.3390/en11061432 - 3 Jun 2018

Cited by 16 | Viewed by 3202

Abstract

The inserted sealing tool is a critical downhole implement that is used to balance the downhole pressure in multistage fracturing operations and prevent fracturing fluid from overflow and/or backward flow. The sealing ring of an inserted sealing tool plays an important role in [...] Read more.

The inserted sealing tool is a critical downhole implement that is used to balance the downhole pressure in multistage fracturing operations and prevent fracturing fluid from overflow and/or backward flow. The sealing ring of an inserted sealing tool plays an important role in downhole sealing since a sealing failure would ail the fracturing operation. In order to improve the sealing performance and reduce the potential fracturing failures, this research aims to investigate the influence of V-shaped sealing ring geometries on sealing performance. Constitutive experiments of rubber materials were carried out and the parameters of the constitutive relationship of rubber materials were obtained. A two-dimensional axisymmetric model considering the sealing ring has been established and influences are investigated with considerations of various system parameters and operating conditions. It is found that the stresses concentrated at the shoulder and inner vertex of the sealing ring have direct impact on the damage of the sealing rings under operational conditions. Moreover, the sealing interference, among several other factors, greatly affects the life of the sealing ring. A new design of the sealing ring is suggested with optimized geometric parameters. Its geometric parameters are the edge height of 5 mm, the vertex angle of 90°–100°, and the interference of 0.1 mm, which show a better performance and prolonged operation life of the sealing ring. Full article

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2 pages, 159 KiB

Open AccessComment

Comments to Paper Entitled: Development of a Data-Driven Predictive Model of Supply Air Temperature in an Air-Handling Unit for Conserving Energy. Energies 2018, 11, 407

by Yaolin Lin^1,*

and Wei Yang²

¹ School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan 430070, China

² College of Engineering and Science, Victoria University, Melbourne 8001, Australia

Energies 2018, 11(6), 1453; https://doi.org/10.3390/en11061453 - 4 Jun 2018

Cited by 1 | Viewed by 2693

Abstract

I have read, with interest, the article authorized by Hong and Kim, which was published in Energies 2018, 11, 407; doi:10.3390/en11020407: entitled “Development of a Data-Driven Predictive Model of Supply Air Temperature in an Air-Handling Unit for Conserving Energy”[...] Full article

2 pages, 151 KiB

Open AccessReply

Response to Comments by Yaolin Lin and Wei Yang “Development of a Data-Driven Predictive Model of Supply Air Temperature in an Air-Handling Unit for Conserving Energy”. Energies 2018, 11, 407

by Goopyo Hong¹ and Byungseon Sean Kim^2,*

¹ SH Urban Research Center, Seoul Housing & Communities Corporation, 621, Gaepo-ro, Gangnam-gu, Seoul 06336, Korea

² Department of Architectural Engineering, Yonsei University, 50 Yonsei Street, Seodaemun-gu, Seoul 03722, Korea

Energies 2018, 11(6), 1494; https://doi.org/10.3390/en11061494 - 7 Jun 2018

Viewed by 1718

Abstract

We would like to thank Yaolin Lin and Wei Yang for their comments [...] Full article

(This article belongs to the Section A: Sustainable Energy)

13 pages, 3302 KiB

Open AccessCase Report

Characterization of a Thermoelectric Generator (TEG) System for Waste Heat Recovery

by Oswaldo Hideo Ando Junior^*

, Nelson H. Calderon and Samara Silva De Souza

Department of Renewable Energies, UNILA, Federal University of Latin American Integration, Av. Sílvio Américo Sasdelli, 1842 Foz do Iguaçu-PR, Brazil

Energies 2018, 11(6), 1555; https://doi.org/10.3390/en11061555 - 14 Jun 2018

Cited by 36 | Viewed by 6805

Abstract

This paper presents the development and characterization of a thermoelectric generator (TEG) system for waste heat recovery to low temperature in industrial processes. The relevance of this mode of electric energy harvest is that it is clean energy and it depends only on [...] Read more.

This paper presents the development and characterization of a thermoelectric generator (TEG) system for waste heat recovery to low temperature in industrial processes. The relevance of this mode of electric energy harvest is that it is clean energy and it depends only on the capture of losses. These residual energies from industrial processes are, in principle, released into the environment without being exploited. With the proposed device, the waste energy will not be released into the environment and will be used for electrical generation, which is useful for heat production. The characterization of TEGs that are used a data-acquisition system have measured data for the voltage, current, and temperature, in real-time, for temperatures down to 200 °C without signal degradation. As a result, the measured data has revealed an open circuit voltage of V_OC = 0.4306 × ΔT, internal resistance of R₀ = 9.41 Ω, with tolerance ΔR_int = ±0.77 Ω, where R_int = 9.41 ± 0.77 Ω. The measurements were made on the condition that the maximum output was obtained at a temperature gradient of ΔT = 80 °C, resulting in a maximum power gain of P_out ≈ 29 W. Full article

(This article belongs to the Special Issue Energy Economy, Sustainable Energy and Energy Saving)

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