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Energies, Volume 10, Issue 3 (March 2017) – 151 articles

Cover Story (view full-size image): Still the ultimate achievable power conversion efficiency (PCE) of organic bulk-heterojunction solar cells is under debate. In this work, we investigated drift-diffusion based simulation analysis to discuss the theoretical PCE limits of the cell. We emphasize more on fundamentally different material properties and physical processes in organic semiconductors that originate from using a combination of two complementary donor and acceptor material. The simulated results expected to serve as a guideline for future material research and improvement of the power conversion efficiency of the cell. View this paper.

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17 pages, 3640 KiB

Open AccessArticle

Circulating Current Reduction Strategy for Parallel-Connected Inverters Based IPT Systems

by Ruikun Mai, Liwen Lu, Yong Li, Tianren Lin and Zhengyou He

Energies 2017, 10(3), 261; https://doi.org/10.3390/en10030261 - 23 Feb 2017

Cited by 12 | Viewed by 5864

Multiple inverters connected in parallel is a promising method to upgrade the power capacity of inductive power transfer (IPT) systems. Due to a slight unbalance of the control signals, the inner resistances of the inverters and other uncertainties, circulating currents exist among the [...] Read more.

Multiple inverters connected in parallel is a promising method to upgrade the power capacity of inductive power transfer (IPT) systems. Due to a slight unbalance of the control signals, the inner resistances of the inverters and other uncertainties, circulating currents exist among the parallel units which reduce the reliability of IPT systems. Firstly, the series-parallel resonant tank is employed in the multiple inverters based IPT system to eliminate the DC and harmonic circulating currents. The fundamental circulating currents in the paralleled inverter units are analyzed in detail. Then, for eliminating the fundamental circulating currents, a current decomposition method and a control diagram are proposed to avoid acquiring the phase of the current by detecting zero cross current point which increases the accuracy of the control algorithm. Finally, a 1-kW parallel-connected inverter IPT system is provided to verify the proposed approach. The experimental results show that the proposed method is effective for eliminating the fundamental circulating currents. The maximum efficiency of the system is up to 92.18% which is 0.53% higher compared to that without the current phasor control (91.65%). Full article

(This article belongs to the Special Issue Advanced Power Electronics and Control for Wireless Power Transfer Systems)

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30 pages, 3738 KiB

Open AccessArticle

The Business Model Evaluation Tool for Smart Cities: Application to SmartSantander Use Cases

by Raimundo Díaz-Díaz, Luis Muñoz and Daniel Pérez-González

Energies 2017, 10(3), 262; https://doi.org/10.3390/en10030262 - 23 Feb 2017

Cited by 60 | Viewed by 12865

New technologies open up the door to multiple business models applied to public services in smart cities. However, there is not a commonly adopted methodology for evaluating business models in smart cities that can help both practitioners and researchers to choose the best [...] Read more.

New technologies open up the door to multiple business models applied to public services in smart cities. However, there is not a commonly adopted methodology for evaluating business models in smart cities that can help both practitioners and researchers to choose the best option. This paper addresses this gap introducing the Business Model Evaluation Tool for Smart Cities. This methodology is a simple, organized, flexible and the transparent system that facilitates the work of the evaluators of potential business models. It is useful to compare two or more business models and take strategic decisions promptly. The method is part of a previous process of content analysis and it is based on the widely utilized Business Model Canvas. The evaluation method has been assessed by 11 experts and, subsequently it has been validated applying it to the case studies of Santander’s waste management and street lighting systems, which take advantage of innovative technologies commonly used in smart cities. Full article

(This article belongs to the Special Issue Innovations in Cyber-Physical Infrastructures and Systems for Energy Sustainability in Smart Cities)

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15 pages, 1553 KiB

Open AccessArticle

High-Titer Methane from Organosolv-Pretreated Spruce and Birch

by Leonidas Matsakas, Christos Nitsos, Dimitrij Vörös, Ulrika Rova and Paul Christakopoulos

Energies 2017, 10(3), 263; https://doi.org/10.3390/en10030263 - 23 Feb 2017

Cited by 21 | Viewed by 5549

The negative impact of fossil fuels and the increased demand for renewable energy sources has led to the use of novel raw material sources. Lignocellulosic biomass could serve as a possible raw material for anaerobic digestion and production of biogas. This work is [...] Read more.

The negative impact of fossil fuels and the increased demand for renewable energy sources has led to the use of novel raw material sources. Lignocellulosic biomass could serve as a possible raw material for anaerobic digestion and production of biogas. This work is aimed at using forest biomass, both softwood (spruce) and hardwood (birch), as a raw material for anaerobic digestion. We examined the effect of different operational conditions for the organosolv pretreatment (ethanol content, duration of treatment, and addition of acid catalyst) on the methane yield. In addition, we investigated the effect of addition of cellulolytic enzymes during the digestion. We found that inclusion of an acid catalyst during organosolv pretreatment improved the yields from spruce, but it did not affect the yields from birch. Shorter duration of treatment was advantageous with both materials. Methane yields from spruce were higher with lower ethanol content whereas higher ethanol content was more beneficial for birch. The highest yields obtained were 185 mL CH₄/g VS from spruce and 259.9 mL CH₄/g VS from birch. Addition of cellulolytic enzymes improved these yields to 266.6 mL CH₄/g VS and 284.2 mL CH₄/g VS, respectively. Full article

(This article belongs to the Special Issue Thermo-Chemical Conversion of Waste Biomass)

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14 pages, 7730 KiB

Open AccessArticle

Design and Implementation of Novel Smart Battery Management System for FPGA Based Portable Electronic Devices

by Fangrong Xue, Zhi Ling, Yubing Yang and Xingpo Miao

Energies 2017, 10(3), 264; https://doi.org/10.3390/en10030264 - 23 Feb 2017

Cited by 11 | Viewed by 7590

This paper presents the analysis and design of a smart battery management system for Field Programmable Gate Array (FPGA) based portable electronic devices. It is a novel concept of incorporating the functionality of a smart battery management system into the FPGA used by [...] Read more.

This paper presents the analysis and design of a smart battery management system for Field Programmable Gate Array (FPGA) based portable electronic devices. It is a novel concept of incorporating the functionality of a smart battery management system into the FPGA used by portable electronic devices, which provides the following advantages. (1) It lowers cost since the conventional commercial independent battery management circuit can be eliminated; (2) It offers more flexibility because FPGA based battery management algorithms can be specifically designed for different battery chemistries of different devices and can provide the flexibility of algorithms and functionalities updating as well. Smart battery management system concepts include four aspects: (1) smart charging; (2) battery balancing; (3) smart discharging; and (4) safety operating. One novel charging algorithm, which combines the merits of multistage charging and pulse charging, is proposed to charge a Li-ion battery pack smartly. A Proportional Integral (PI) control method is introduced to achieve the current control of charging circuit with considerable close loop stability. Simulation results from the PSIM 9.0.4 software package and experimental results from the prototype built in the lab are demonstrated to verify the effectiveness of smart charging. The realizations of battery balancing, smart discharging, and safety operating are also briefly described by taking advantage of the proposed FPGA based smart battery management system topology, which verify the feasibility of the proposed FPGA based smart battery management system for portable electronic devices. Full article

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13 pages, 1564 KiB

Open AccessArticle

Qualitative Analysis of Transesterification of Waste Pig Fat in Supercritical Alcohols

by Jeeban Poudel, Malesh Shah, Sujeeta Karki and Sea Cheon Oh

Energies 2017, 10(3), 265; https://doi.org/10.3390/en10030265 - 23 Feb 2017

Cited by 11 | Viewed by 4270

In this work, the characteristics of waste pig fat degradation using supercritical alcohols have been studied. Comparative analysis of the influence of supercritical methanol and supercritical ethanol as solvents on the transesterification was the primary focus of this research. The experiments were carried [...] Read more.

In this work, the characteristics of waste pig fat degradation using supercritical alcohols have been studied. Comparative analysis of the influence of supercritical methanol and supercritical ethanol as solvents on the transesterification was the primary focus of this research. The experiments were carried out with waste pig fat to alcohol weight ratios of 1:1.5 (molar ratio: 1:40.5 for methanol and 1:28 for ethanol), 1:2.0 (molar ratio: 1:54 for methanol and 1:37.5 for ethanol) and 1:2.5 (molar ratio: 1:67.5 for methanol and 1:47 for ethanol) at transesterification temperatures 250, 270 and 290 °C for holding time 0, 15, 30, 45 and 60 min. Increase in the transesterification and holding time increased the conversion while increase in alcohol amount from 1:1.5 to 1:2.0 and 1:2.5 had minimal effect on the conversion. Further, majority of the ester composition in using SCM as solvent falls in the carbon range of C17:0, C19:1 and C19:2 while that for SCE falls in the carbon range of C18:0, C20:1 and C20:2. Glycerol was only present while using SCM as solvent. Full article

(This article belongs to the Special Issue Thermo-Chemical Conversion of Waste Biomass)

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17 pages, 12810 KiB

Open AccessArticle

A Numerical Study on Natural Convection Heat Transfer of Handheld Projectors with a Fin Array

by Jin-Cherng Shyu, Tsuni Chang and Shun-Ching Lee

Energies 2017, 10(3), 266; https://doi.org/10.3390/en10030266 - 23 Feb 2017

Cited by 2 | Viewed by 4650

This study numerically investigates the effects of the number of bottom openings and the fin spacing on both the natural convection heat transfer and airflow field of the handheld projector with various orientations. The horizontally-oriented 120 mm × 53 mm × 19 mm [...] Read more.

This study numerically investigates the effects of the number of bottom openings and the fin spacing on both the natural convection heat transfer and airflow field of the handheld projector with various orientations. The horizontally-oriented 120 mm × 53 mm × 19 mm handheld projector, which had 11 bottom openings and was installed with either 7 plate fins or 13 rows of square pin, was considered as the primary case. The fin number varied from 6 plates to 13 plates or from 7 pin rows to 16 pin rows, while the bottom openings varied from 11 to 15 in this study with handheld projector held at a specified inclination ranging from −90° to 90°. The results showed that the heat transfer coefficient of a specific surface of the plate-fin array installed in the primary handheld projector increased from 6 to 7 W/m²·K as the heating power increased from 2 W to 7 W. The optimal fin spacing in the handheld projector possessing 11 bottom openings was 2.875 mm and 3.375 mm for the plate-fin and pin-fin, respectively, at a heating power of 7 W. Although the velocity magnitude of the airflow between fins increased as the bottom opening increased, it was not able to offset the reduction of the airflow velocity resulting from the fin spacing reduction. Full article

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20 pages, 7011 KiB

Open AccessArticle

A Cyber Physical Model Based on a Hybrid System for Flexible Load Control in an Active Distribution Network

by Yun Wang, Dong Liu and Chen Sun

Energies 2017, 10(3), 267; https://doi.org/10.3390/en10030267 - 24 Feb 2017

Cited by 20 | Viewed by 5599

To strengthen the integration of the primary and secondary systems, a concept of Cyber Physical Systems (CPS) is introduced to construct a CPS in Power Systems (Power CPS). The most basic work of the Power CPS is to build an integration model which [...] Read more.

To strengthen the integration of the primary and secondary systems, a concept of Cyber Physical Systems (CPS) is introduced to construct a CPS in Power Systems (Power CPS). The most basic work of the Power CPS is to build an integration model which combines both a continuous process and a discrete process. The advanced form of smart grid, the Active Distribution Network (ADN) is a typical example of Power CPS. After designing the Power CPS model architecture and its application in ADN, a Hybrid System based model and control method of Power CPS is proposed in this paper. As an application example, ADN flexible load is modeled and controlled with ADN feeder power control by a control strategy which includes the normal condition and the underpowered condition. In this model and strategy, some factors like load power consumption and load functional demand are considered and optimized. In order to make up some of the deficiencies of centralized control, a distributed control method is presented to reduce model complexity and improve calculation speed. The effectiveness of all the models and methods are demonstrated in the case study. Full article

(This article belongs to the Special Issue Innovations in Cyber-Physical Infrastructures and Systems for Energy Sustainability in Smart Cities)

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18 pages, 2170 KiB

Open AccessArticle

Equivalent Circulation Density Analysis of Geothermal Well by Coupling Temperature

by Xiuhua Zheng, Chenyang Duan, Zheng Yan, Hongyu Ye, Zhiqing Wang and Bairu Xia

Energies 2017, 10(3), 268; https://doi.org/10.3390/en10030268 - 23 Feb 2017

Cited by 14 | Viewed by 4721

The accurate control of the wellbore pressure not only prevents lost circulation/blowout and fracturing formation by managing the density of the drilling fluid, but also improves productivity by mitigating reservoir damage. Calculating the geothermal pressure of a geothermal well by constant parameters would [...] Read more.

The accurate control of the wellbore pressure not only prevents lost circulation/blowout and fracturing formation by managing the density of the drilling fluid, but also improves productivity by mitigating reservoir damage. Calculating the geothermal pressure of a geothermal well by constant parameters would easily bring big errors, as the changes of physical, rheological and thermal properties of drilling fluids with temperature are neglected. This paper researched the wellbore pressure coupling by calculating the temperature distribution with the existing model, fitting the rule of density of the drilling fluid with the temperature and establishing mathematical models to simulate the wellbore pressures, which are expressed as the variation of Equivalent Circulating Density (ECD) under different conditions. With this method, the temperature and ECDs in the wellbore of the first medium-deep geothermal well, ZK212 Yangyi Geothermal Field in Tibet, were determined, and the sensitivity analysis was simulated by assumed parameters, i.e., the circulating time, flow rate, geothermal gradient, diameters of the wellbore, rheological models and regimes. The results indicated that the geothermal gradient and flow rate were the most influential parameters on the temperature and ECD distribution, and additives added in the drilling fluid should be added carefully as they change the properties of the drilling fluid and induce the redistribution of temperature. To ensure the safe drilling and velocity of pipes tripping into the hole, the depth and diameter of the wellbore are considered to control the surge pressure. Full article

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23 pages, 5552 KiB

Open AccessArticle

Thermoeconomic Evaluation of Modular Organic Rankine Cycles for Waste Heat Recovery over a Broad Range of Heat Source Temperatures and Capacities

by Markus Preißinger and Dieter Brüggemann

Energies 2017, 10(3), 269; https://doi.org/10.3390/en10030269 - 24 Feb 2017

Cited by 28 | Viewed by 7587

Industrial waste heat recovery by means of an Organic Rankine Cycle (ORC) can contribute to the reduction of CO₂ emissions from industries. Before market penetration, high efficiency modular concepts have to be developed to achieve appropriate economic value for industrial decision makers. [...] Read more.

Industrial waste heat recovery by means of an Organic Rankine Cycle (ORC) can contribute to the reduction of CO₂ emissions from industries. Before market penetration, high efficiency modular concepts have to be developed to achieve appropriate economic value for industrial decision makers. This paper aims to investigate modularly designed ORC systems from a thermoeconomic point of view. The main goal is a recommendation for a suitable chemical class of working fluids, preferable ORC design and a range of heat source temperatures and thermal capacities in which modular ORCs can be economically feasible. For this purpose, a thermoeconomic model has been developed which is based on size and complexity parameters of the ORC components. Special emphasis has been laid on the turbine model. The paper reveals that alkylbenzenes lead to higher exergetic efficiencies compared to alkanes and siloxanes. However, based on the thermoeconomic model, the payback periods of the chemical classes are almost identical. With the ORC design, the developed model and the boundary conditions of this study, hexamethyldisiloxane is a suitable working fluid and leads to a payback period of less than 5 years for a heat source temperature of 400 to 600 °C and a mass flow rate of the gaseous waste heat stream of more than 4 kg/s. Full article

(This article belongs to the Special Issue Recent Advances in Organic Rankine Cycle Technology for Stationary Applications)

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19 pages, 9813 KiB

Open AccessArticle

Optimization of External Envelope Insulation Thickness: A Parametric Study

by Eleftheria Touloupaki and Theodoros Theodosiou

Energies 2017, 10(3), 270; https://doi.org/10.3390/en10030270 - 24 Feb 2017

Cited by 18 | Viewed by 4896

Almost four years after the implementation deadline of the energy performance of buildings Directive recast (2010/31/EU) and after being referred to the Court of Justice of the EU by the European Commission, Greece has not yet proceeded with the necessary calculations and legislative [...] Read more.

Almost four years after the implementation deadline of the energy performance of buildings Directive recast (2010/31/EU) and after being referred to the Court of Justice of the EU by the European Commission, Greece has not yet proceeded with the necessary calculations and legislative measures on the minimum, cost-optimal energy performance requirements for buildings. This paper aims to identify the optimal thickness of insulation that is cost-effective to apply in urban multi-family domestic buildings in the four climate zones of Greece. A reference building is selected in order to perform calculations over ten scenarios of external insulation thickness for each climate zone on a basic and three sensitivity analysis calculations according to the EU comparative methodology framework. The resulting energy savings for each insulation scenario are calculated, and then the cost-effectiveness of the measure is examined in financial and macroeconomic perspective for an economic lifecycle of 30 years. The results demonstrate the inadequacy of the national regulation’s current insulation limits and the externalities (funding gaps) that need to be addressed in order to achieve the effective improvement of energy efficiency in Greek homes. Full article

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19 pages, 4834 KiB

Open AccessArticle

Fuzzy Logic-Based Operation of Battery Energy Storage Systems (BESSs) for Enhancing the Resiliency of Hybrid Microgrids

by Akhtar Hussain, Van-Hai Bui and Hak-Man Kim

Energies 2017, 10(3), 271; https://doi.org/10.3390/en10030271 - 24 Feb 2017

Cited by 36 | Viewed by 6627

The resiliency of power systems can be enhanced during emergency situations by using microgrids, due to their capability to supply local loads. However, precise prediction of disturbance events is very difficult rather the occurrence probability can be expressed as, high, medium, or low, [...] Read more.

The resiliency of power systems can be enhanced during emergency situations by using microgrids, due to their capability to supply local loads. However, precise prediction of disturbance events is very difficult rather the occurrence probability can be expressed as, high, medium, or low, etc. Therefore, a fuzzy logic-based battery energy storage system (BESS) operation controller is proposed in this study. In addition to BESS state-of-charge and market price signals, event occurrence probability is taken as crisp input for the BESS operation controller. After assessing the membership levels of all the three inputs, BESS operation controller decides the operation mode (subservient or resilient) of BESS units. In subservient mode, BESS is fully controlled by an energy management system (EMS) while in the case of resilient mode, the EMS follows the commands of the BESS operation controller for scheduling BESS units. Therefore, the proposed hybrid microgrid model can operate in normal, resilient, and emergency modes with the respective objective functions and scheduling horizons. Due to the consideration of resilient mode, load curtailment can be reduced during emergency operation periods. Numerical simulations have demonstrated the effectiveness of the proposed strategy for enhancing the resiliency of hybrid microgrids. Full article

(This article belongs to the Special Issue Resilience of Energy Systems 2017)

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35 pages, 24357 KiB

Open AccessFeature PaperArticle

An Enhanced VOF Method Coupled with Heat Transfer and Phase Change to Characterise Bubble Detachment in Saturated Pool Boiling

by Anastasios Georgoulas, Manolia Andredaki and Marco Marengo

Energies 2017, 10(3), 272; https://doi.org/10.3390/en10030272 - 24 Feb 2017

Cited by 60 | Viewed by 11915

The present numerical investigation identifies quantitative effects of fundamental controlling parameters on the detachment characteristics of isolated bubbles in cases of pool boiling in the nucleate boiling regime. For this purpose, an improved Volume of Fluid (VOF) approach, developed previously in the general [...] Read more.

The present numerical investigation identifies quantitative effects of fundamental controlling parameters on the detachment characteristics of isolated bubbles in cases of pool boiling in the nucleate boiling regime. For this purpose, an improved Volume of Fluid (VOF) approach, developed previously in the general framework of OpenFOAM Computational Fluid Dynamics (CFD) Toolbox, is further coupled with heat transfer and phase change. The predictions of the model are quantitatively verified against an existing analytical solution and experimental data in the literature. Following the model validation, four different series of parametric numerical experiments are performed, exploring the effect of the initial thermal boundary layer (ITBL) thickness for the case of saturated pool boiling of R113 as well as the effects of the surface wettability, wall superheat and gravity level for the cases of R113, R22 and R134a refrigerants. It is confirmed that the ITBL is a very important parameter in the bubble growth and detachment process. Furthermore, for all of the examined working fluids the bubble detachment characteristics seem to be significantly affected by the triple-line contact angle (i.e., the wettability of the heated plate) for equilibrium contact angles higher than 45°. As expected, the simulations revealed that the heated wall superheat is very influential on the bubble growth and detachment process. Finally, besides the novelty of the numerical approach, a last finding is the fact that the effect of the gravity level variation in the bubble detachment time and the volume diminishes with the increase of the ambient pressure. Full article

(This article belongs to the Special Issue Advanced Thermal Simulation of Energy Systems)

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13 pages, 6070 KiB

Open AccessArticle

The Influence of BMSs on the Characterization and Modeling of Series and Parallel Li-Ion Packs

by Sandra Castano-Solis, Daniel Serrano-Jimenez, Lucia Gauchia and Javier Sanz

Energies 2017, 10(3), 273; https://doi.org/10.3390/en10030273 - 25 Feb 2017

Cited by 20 | Viewed by 5062

This work analyzes the effects of a BMS (battery management system) on the characterization and modeling of series and parallel connections of Li-ion cell packs. The Li-ion pack studied consists of four series modules connected in parallel. This pack has been characterized by [...] Read more.

This work analyzes the effects of a BMS (battery management system) on the characterization and modeling of series and parallel connections of Li-ion cell packs. The Li-ion pack studied consists of four series modules connected in parallel. This pack has been characterized by means of charge, discharge and frequency tests. As a result of these tests, series and parallel influence on battery parameters have been determined. A model considering the effects of a BMS is established and compared with a model based on a single-cell approach. Experimental validations show that the single cell based approach gives poor results in comparison with a model that considers BMS effects. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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14 pages, 2656 KiB

Open AccessArticle

Numerical Analysis of Shell-and-Tube Type Latent Thermal Energy Storage Performance with Different Arrangements of Circular Fins

by Sebastian Kuboth, Andreas König-Haagen and Dieter Brüggemann

Energies 2017, 10(3), 274; https://doi.org/10.3390/en10030274 - 25 Feb 2017

Cited by 43 | Viewed by 7242

Latent thermal energy storage (LTS) systems are versatile due to their high-energy storage density within a small temperature range. In shell-and-tube type storage systems fins can be used in order to achieve enhanced charging and discharging power. Typically, circular fins are evenly distributed [...] Read more.

Latent thermal energy storage (LTS) systems are versatile due to their high-energy storage density within a small temperature range. In shell-and-tube type storage systems fins can be used in order to achieve enhanced charging and discharging power. Typically, circular fins are evenly distributed over the length of the heat exchanger pipe. However, it is yet to be proven that this allocation is the most suitable for every kind of system and application. Consequently, within this paper, a simulation model was developed in order to examine the effect of different fin distributions on the performance of shell-and-tube type latent thermal storage units at discharge. The model was set up in MATLAB Simulink R2015b (The MathWorks, Inc., Natick, MA, USA) based on the enthalpy method and validated by a reference model designed in ANSYS Fluent 15.0 (ANSYS, Inc., Canonsburg, PA, USA). The fin density of the heat exchanger pipe was increased towards the pipe outlet. This concentration of fins was implemented linearly, exponentially or suddenly with the total number of fins remaining constant during the variation of fin allocations. Results show that there is an influence of fin allocation on storage performance. However, the average storage performance at total discharge only increased by three percent with the best allocation compared to an equidistant arrangement. Full article

(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))

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22 pages, 4792 KiB

Open AccessArticle

Thermodynamic Performance Analysis of a Biogas-Fuelled Micro-Gas Turbine with a Bottoming Organic Rankine Cycle for Sewage Sludge and Food Waste Treatment Plants

by Sunhee Kim, Taehong Sung and Kyung Chun Kim

Energies 2017, 10(3), 275; https://doi.org/10.3390/en10030275 - 26 Feb 2017

Cited by 13 | Viewed by 9876

In the Republic of Korea, efficient biogas-fuelled power systems are needed to use the excess biogas that is currently burned due to a lack of suitable power technology. We examined the performance of a biogas-fuelled micro-gas turbine (MGT) system and a bottoming organic [...] Read more.

In the Republic of Korea, efficient biogas-fuelled power systems are needed to use the excess biogas that is currently burned due to a lack of suitable power technology. We examined the performance of a biogas-fuelled micro-gas turbine (MGT) system and a bottoming organic Rankine cycle (ORC). The MGT provides robust operation with low-grade biogas, and the exhaust can be used for heating the biodigester. Similarly, the bottoming ORC generates additional power output with the exhaust gas. We selected a 1000-kW MGT for four co-digestion plants with 28,000-m³ capacity. A 150-kW ORC system was selected for the MGT exhaust gas. We analysed the effects of the system size, methane concentration, and ORC operating conditions. Based on the system performance, we analysed the annual performance of the MGT with a combined heat and power (CHP) system, bottoming ORC, or both a bottoming ORC and CHP system. The annual net power outputs for each system were 7.4, 8.5, and 9.0 MWh per year, respectively. Full article

(This article belongs to the Special Issue Recent Advances in Organic Rankine Cycle Technology for Stationary Applications)

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20 pages, 3721 KiB

Open AccessArticle

Using a Hybrid Cost-FMEA Analysis for Wind Turbine Reliability Analysis

by Nacef Tazi, Eric Châtelet and Youcef Bouzidi

Energies 2017, 10(3), 276; https://doi.org/10.3390/en10030276 - 27 Feb 2017

Cited by 79 | Viewed by 10815

Failure mode and effects analysis (FMEA) has been proven to be an effective methodology to improve system design reliability. However, the standard approach reveals some weaknesses when applied to wind turbine systems. The conventional criticality assessment method has been criticized as having many [...] Read more.

Failure mode and effects analysis (FMEA) has been proven to be an effective methodology to improve system design reliability. However, the standard approach reveals some weaknesses when applied to wind turbine systems. The conventional criticality assessment method has been criticized as having many limitations such as the weighting of severity and detection factors. In this paper, we aim to overcome these drawbacks and develop a hybrid cost-FMEA by integrating cost factors to assess the criticality, these costs vary from replacement costs to expected failure costs. Then, a quantitative comparative study is carried out to point out average failure rate, main cause of failure, expected failure costs and failure detection techniques. A special reliability analysis of gearbox and rotor-blades are presented. Full article

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21 pages, 4299 KiB

Open AccessArticle

A Refined Self-Tuning Filter-Based Instantaneous Power Theory Algorithm for Indirect Current Controlled Three-Level Inverter-Based Shunt Active Power Filters under Non-sinusoidal Source Voltage Conditions

by Yap Hoon, Mohd Amran Mohd Radzi, Mohd Khair Hassan and Nashiren Farzilah Mailah

Energies 2017, 10(3), 277; https://doi.org/10.3390/en10030277 - 27 Feb 2017

Cited by 26 | Viewed by 4783

In this paper, a refined reference current generation algorithm based on instantaneous power (pq) theory is proposed, for operation of an indirect current controlled (ICC) three-level neutral-point diode clamped (NPC) inverter-based shunt active power filter (SAPF) under non-sinusoidal source voltage conditions. SAPF is [...] Read more.

In this paper, a refined reference current generation algorithm based on instantaneous power (pq) theory is proposed, for operation of an indirect current controlled (ICC) three-level neutral-point diode clamped (NPC) inverter-based shunt active power filter (SAPF) under non-sinusoidal source voltage conditions. SAPF is recognized as one of the most effective solutions to current harmonics due to its flexibility in dealing with various power system conditions. As for its controller, pq theory has widely been applied to generate the desired reference current due to its simple implementation features. However, the conventional dependency on self-tuning filter (STF) in generating reference current has significantly limited mitigation performance of SAPF. Besides, the conventional STF-based pq theory algorithm is still considered to possess needless features which increase computational complexity. Furthermore, the conventional algorithm is mostly designed to suit operation of direct current controlled (DCC) SAPF which is incapable of handling switching ripples problems, thereby leading to inefficient mitigation performance. Therefore, three main improvements are performed which include replacement of STF with mathematical-based fundamental real power identifier, removal of redundant features, and generation of sinusoidal reference current. To validate effectiveness and feasibility of the proposed algorithm, simulation work in MATLAB-Simulink and laboratory test utilizing a TMS320F28335 digital signal processor (DSP) are performed. Both simulation and experimental findings demonstrate superiority of the proposed algorithm over the conventional algorithm. Full article

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17 pages, 351 KiB

Open AccessArticle

Tuning the Complexity of Photovoltaic Array Models to Meet Real-time Constraints of Embedded Energy Emulators

by Emanuele Lattanzi, Matteo Dromedari, Valerio Freschi and Alessandro Bogliolo

Energies 2017, 10(3), 278; https://doi.org/10.3390/en10030278 - 27 Feb 2017

Cited by 5 | Viewed by 3588

Reproducibility of experimental conditions is a fundamental requirement for designing energy efficient, self-sustainable wireless sensor networks (WSNs). At the same time, it represents a significant challenge because of the variability and the unpredictability of many energy harvesting sources, and because of the dynamic [...] Read more.

Reproducibility of experimental conditions is a fundamental requirement for designing energy efficient, self-sustainable wireless sensor networks (WSNs). At the same time, it represents a significant challenge because of the variability and the unpredictability of many energy harvesting sources, and because of the dynamic operating conditions of the devices to which energy is supplied. Energy source emulation is considered a suitable solution to enable the exploration of the design space of networked embedded systems. However, in order to guarantee the compatibility with real-time performance of resource-constrained embedded platforms, particular attention has to be paid to the complexity of the models. In this paper, we propose an approach aimed at tuning the complexity of models of photovoltaic (PV) arrays implemented on a target embedded emulator, featuring low cost and small form factor. Experimental results performed on different models of PV array, show that the proposed solution is flexible and accurate enough to meet the real-time constraints of typical sensor networks applications without impairing the precision in the emulation of the energy sources. Full article

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20 pages, 5729 KiB

Open AccessArticle

Comparison Study of Two Semi-Active Hybrid Energy Storage Systems for Hybrid Electric Vehicle Applications and Their Experimental Validation

by Haitao Min, Changlu Lai, Yuanbin Yu, Tao Zhu and Cong Zhang

Energies 2017, 10(3), 279; https://doi.org/10.3390/en10030279 - 28 Feb 2017

Cited by 28 | Viewed by 8998

Both the battery/supercapacitor (SC) and SC/battery are two common semi-active configurations of hybrid energy storage systems (HESSs) in hybrid electric vehicles, which can take advantage of the battery’s and supercapacitor’s respective characteristics, including the energy ability, power ability and the long lifetime. To [...] Read more.

Both the battery/supercapacitor (SC) and SC/battery are two common semi-active configurations of hybrid energy storage systems (HESSs) in hybrid electric vehicles, which can take advantage of the battery’s and supercapacitor’s respective characteristics, including the energy ability, power ability and the long lifetime. To explore in depth the characteristics and applicability of the two kinds of HESS, an analysis and comparison study is proposed in this paper. Based on the data collected from public transit hybrid electric bus (PTHEB) with battery-only on-board energy storage, the range and distribution probability of electric power/energy demand is comprehensively statistically analyzed with the decomposing and normalizing methods. Accordingly, the performance of each topology under different parameter matching conditions but same mass, volume and cost values with battery-only energy storage, are presented and compared quantitatively. The results show that both HESS configurations can meet the electric power demand of the hybrid electric vehicle (HEV) through reasonable design. In particular, the SC/battery can make better use of the SC features resulting in high efficiency and long life cycles compared with the battery/SC. Equally, it proves that the SC/battery topology is a better choice for the HEV. Finally, an experimental validation of a real HEV is carried out, which indicated that a 7% fuel economy improvement can be achieved by a SC/battery system compared with battery-only topology. Full article

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

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16 pages, 6868 KiB

Open AccessArticle

An Efficient Phase-Locked Loop for Distorted Three-Phase Systems

by Yijia Cao, Jiaqi Yu, Yong Xu, Yong Li and Jingrong Yu

Energies 2017, 10(3), 280; https://doi.org/10.3390/en10030280 - 27 Feb 2017

Cited by 15 | Viewed by 5678

This paper proposed an efficient phase-locked loop (PLL) that features zero steady-state error of phase and frequency under voltage sag, phase jump, harmonics, DC offsets and step-and ramp-changed frequency. The PLL includes the sliding Goertzel discrete Fourier transform (SGDFT) filter-based fundamental positive sequence [...] Read more.

This paper proposed an efficient phase-locked loop (PLL) that features zero steady-state error of phase and frequency under voltage sag, phase jump, harmonics, DC offsets and step-and ramp-changed frequency. The PLL includes the sliding Goertzel discrete Fourier transform (SGDFT) filter-based fundamental positive sequence component separator (FPSCS), the synchronousreference-frame PLL (SRF-PLL) and the secondary control path (SCP). In order to obtain an accurate fundamental positive sequence component, SGDFT filter is introduced as it features better filtering ability at the frequencies that are integer times of fundamental frequency. Meanwhile, the second order Lagrange-interpolation method is employed to approximate the actual sampling number including both integer and fractional parts as grid frequency may deviate from the rated value. Moreover, an improved SCP with single-step comparison filtering algorithm is employed as it updates reference angular frequency according to the FPSC, which promises a zero steady-state error of phase and improves the frequency tracking speed. In this paper, the mathematical model of the proposed PLL is constructed, its stability is analyzed. Also, design procedure of the control parameters is presented. The effectiveness of the proposed PLL is confirmed by experimental results and comparison with advanced pre-filtering PLLs. Full article

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

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13 pages, 2503 KiB

Open AccessArticle

Relative Voltage Control of the Wind Farms Based on the Local Reactive Power Regulation

by Yangyang Zhao, Jianyun Chai and Xudong Sun

Energies 2017, 10(3), 281; https://doi.org/10.3390/en10030281 - 27 Feb 2017

Cited by 10 | Viewed by 4041

The fast and coordinated voltage control of distributed nodes inside a large scale wind farm is a stringent issue. To achieve the reactive power compensation without a dedicated upper communication system, this paper proposes a relative control strategy based on the local reactive [...] Read more.

The fast and coordinated voltage control of distributed nodes inside a large scale wind farm is a stringent issue. To achieve the reactive power compensation without a dedicated upper communication system, this paper proposes a relative control strategy based on the local reactive power regulation. This method can realize the voltage coordination of the key equipment and feeder line nodes, on the basis of the relative voltage observations. Firstly, the stability analysis of a certain wind farm with pre-known parameters and structure is studied under the wind power fluctuations. Secondly, the optimal capacity configurations of the reactive power compensators are discussed, with multiple nodes inside the wind farms. Simulation results of a specific wind farm in North Hebei, China, validate the effectiveness of the proposed control, which is equipped with fast and stable voltage dynamic responses, as well as local reactive power compensations without remote communication. Full article

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15 pages, 4351 KiB

Open AccessArticle

Performance Analyses of Counter-Flow Closed Wet Cooling Towers Based on a Simplified Calculation Method

by Xiaoqing Wei, Nianping Li, Jinqing Peng, Jianlin Cheng, Jinhua Hu and Meng Wang

Energies 2017, 10(3), 282; https://doi.org/10.3390/en10030282 - 27 Feb 2017

Cited by 22 | Viewed by 7183

As one of the most widely used units in water cooling systems, the closed wet cooling towers (CWCTs) have two typical counter-flow constructions, in which the spray water flows from the top to the bottom, and the moist air and cooling water flow [...] Read more.

As one of the most widely used units in water cooling systems, the closed wet cooling towers (CWCTs) have two typical counter-flow constructions, in which the spray water flows from the top to the bottom, and the moist air and cooling water flow in the opposite direction vertically (parallel) or horizontally (cross), respectively. This study aims to present a simplified calculation method for conveniently and accurately analyzing the thermal performance of the two types of counter-flow CWCTs, viz. the parallel counter-flow CWCT (PCFCWCT) and the cross counter-flow CWCT (CCFCWCT). A simplified cooling capacity model that just includes two characteristic parameters is developed. The Levenberg–Marquardt method is employed to determine the model parameters by curve fitting of experimental data. Based on the proposed model, the predicted outlet temperatures of the process water are compared with the measurements of a PCFCWCT and a CCFCWCT, respectively, reported in the literature. The results indicate that the predicted values agree well with the experimental data in previous studies. The maximum absolute errors in predicting the process water outlet temperatures are 0.20 and 0.24 °C for the PCFCWCT and CCFCWCT, respectively. These results indicate that the simplified method is reliable for performance prediction of counter-flow CWCTs. Although the flow patterns of the two towers are different, the variation trends of thermal performance are similar to each other under various operating conditions. The inlet air wet-bulb temperature, inlet cooling water temperature, air flow rate, and cooling water flow rate are crucial for determining the cooling capacity of a counter-flow CWCT, while the cooling tower effectiveness is mainly determined by the flow rates of air and cooling water. Compared with the CCFCWCT, the PCFCWCT is much more applicable in a large-scale cooling water system, and the superiority would be amplified when the scale of water distribution system increases. Without multiple iterative calculations and extensive experimental data, the simplified method could be used to effectively analyze the thermal performance of counter-flow CWCTs in operation. It is useful for optimization operation of counter-flow CWCTs such that to improve the energy efficiency of the overall cooling water system. Full article

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19 pages, 5972 KiB

Open AccessCommunication

Sustainability of the Renewable Energy Extraction Close to the Mediterranean Islands

by Vincenzo Franzitta and Domenico Curto

Energies 2017, 10(3), 283; https://doi.org/10.3390/en10030283 - 27 Feb 2017

Cited by 44 | Viewed by 4774

The aim of this work is to explore the possibility of transitioning a fuel powered island to a renewable powered one. This transition is analyzed for the real MV/LV distribution system of the island of Pantelleria, in the Mediterranean Sea. Particularly, this work [...] Read more.

The aim of this work is to explore the possibility of transitioning a fuel powered island to a renewable powered one. This transition is analyzed for the real MV/LV distribution system of the island of Pantelleria, in the Mediterranean Sea. Particularly, this work is focused on a renewable source nowadays totally unused: wave energy. Thanks to the innovative generator prototype designed by Department of Energy of University of Palermo (Italy), wave energy is able to represent a primary source for the production of electric energy in the Mediterranean islands. The procedures applied in the present article, as well as the main equations used, are the result of previous applications made in different technical fields that show a good replicability. Full article

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21 pages, 2734 KiB

Open AccessArticle

Development of a Real-Time Virtual Nitric Oxide Sensor for Light-Duty Diesel Engines

by Seungha Lee, Youngbok Lee, Gyujin Kim and Kyoungdoug Min

Energies 2017, 10(3), 284; https://doi.org/10.3390/en10030284 - 1 Mar 2017

Cited by 16 | Viewed by 4801

This study describes the development of a semi-physical, real-time nitric oxide (NO) prediction model that is capable of cycle-by-cycle prediction in a light-duty diesel engine. The model utilizes the measured in-cylinder pressure and information obtained from the engine control unit (ECU). From the [...] Read more.

This study describes the development of a semi-physical, real-time nitric oxide (NO) prediction model that is capable of cycle-by-cycle prediction in a light-duty diesel engine. The model utilizes the measured in-cylinder pressure and information obtained from the engine control unit (ECU). From the inputs, the model takes into account the pilot injection burning and mixing, which affects the in-cylinder mixture formation. The representative in-cylinder temperature for NO formation was determined from the mixture composition calculation. The selected temperature and mixture composition was substituted using a simplified form of the NO formation rate equation for the cycle-by-cycle estimation. The reactive area and the duration of NO formation were assumed to be limited by the fuel quantity. The model predictability was verified not only using various steady-state conditions, including the variation of the EGR rate, the boost pressure, the rail pressure, and the injection timing, but also using transient conditions, which represent the worldwide harmonized light vehicles test procedure (WLTC). The WLTC NO prediction results produced less than 3% error with the measured value. In addition, the proposed model maintained its reliability in terms of hardware aging, the changing and artificial perturbations during steady-state and transient engine operations. The model has been shown to require low computational effort because of the cycle-by-cycle, engine-out NO emission prediction and control were performed simultaneously in an embedded system for the automotive application. We expect that the developed NO prediction model can be helpful in emission calibration during the engine design stage or in the real-time controlling of the exhaust NO emission for improving fuel consumption while satisfying NO emission legislation. Full article

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15 pages, 3105 KiB

Open AccessArticle

Sensitivity of the Drift-Diffusion Approach in Estimating the Power Conversion Efficiency of Bulk Heterojunction Polymer Solar Cells

by Amir Hossein Fallahpour, Aldo Di Carlo and Paolo Lugli

Energies 2017, 10(3), 285; https://doi.org/10.3390/en10030285 - 28 Feb 2017

Cited by 2 | Viewed by 7967

There are numerous theoretical approaches to estimating the power conversion efficiency (PCE) of organic solar cells (OSCs), ranging from the empirical approach to calculations based on general considerations of thermodynamics. Depending on the level of abstraction and model assumptions, the accuracy of PCE [...] Read more.

There are numerous theoretical approaches to estimating the power conversion efficiency (PCE) of organic solar cells (OSCs), ranging from the empirical approach to calculations based on general considerations of thermodynamics. Depending on the level of abstraction and model assumptions, the accuracy of PCE estimation and complexity of the calculation can change dramatically. In particular, PCE estimation with a drift-diffusion approach (widely investigated in the literature), strongly depends on the assumptions made for the physical models and optoelectrical properties of semiconducting materials. This has led to a huge deviation as well as complications in the analysis of simulated results aiming to understand the factors limiting the performance of OSCs. In this work, we intend to highlight the complex relation between mobility, exciton dynamics, nanoscale dimension, and loss mechanisms in one framework. Our systematic analysis represents key information on the sensitivity of the drift-diffusion approach, to estimate how physical parameters and physical processes bind the PCE of the device under the influence of structure, contact, and material layer properties. The obtained results ultimately led to recommendations for putting effort into certain properties to get the most out of avoidable losses, presented the impact and importance of modification of material properties, and in particular, recommended to what degree the design of new material could improve OSC performance. Full article

(This article belongs to the Special Issue Solar Photovoltaics Trilemma: Efficiency, Stability and Cost Reduction 2017)

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10 pages, 3093 KiB

Open AccessArticle

Reduction of Furfural to Furfuryl Alcohol in Liquid Phase over a Biochar-Supported Platinum Catalyst

by Ariadna Fuente-Hernández, Roland Lee, Nicolas Béland, Ingrid Zamboni and Jean-Michel Lavoie

Energies 2017, 10(3), 286; https://doi.org/10.3390/en10030286 - 28 Feb 2017

Cited by 32 | Viewed by 9192

In this work, the liquid phase hydrogenation of furfural has been studied using a biochar-supported platinum catalyst in a batch reactor. Reactions were performed between 170 °C and 320 °C, using 3 wt % and 5 wt % of Pt supported on a [...] Read more.

In this work, the liquid phase hydrogenation of furfural has been studied using a biochar-supported platinum catalyst in a batch reactor. Reactions were performed between 170 °C and 320 °C, using 3 wt % and 5 wt % of Pt supported on a maple-based biochar under hydrogen pressure varying from 500 psi to 1500 psi for reaction times between 1 h and 6 h in various solvents. Under all reactive conditions, furfural conversion was significant, whilst under specific conditions furfuryl alcohol (FA) was obtained in most cases as the main product showing a selectivity around 80%. Other products as methylfuran (MF), furan, and trace of tetrahydrofuran (THF) were detected. Results showed that the most efficient reaction conditions involved a 3% Pt load on biochar and operations for 2 h at 210 °C and 1500 psi using toluene as solvent. When used repetitively, the catalyst showed deactivation although only a slight variation in selectivity toward FA at the optimal experimental conditions was observed. Full article

(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)

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23 pages, 712 KiB

Open AccessArticle

Improving the Reliability of Optimised Link State Routing in a Smart Grid Neighbour Area Network based Wireless Mesh Network Using Multiple Metrics

by Yakubu Tsado, Kelum A. A. Gamage, Bamidele Adebisi, David Lund, Khaled M. Rabie and Augustine Ikpehai

Energies 2017, 10(3), 287; https://doi.org/10.3390/en10030287 - 28 Feb 2017

Cited by 27 | Viewed by 5135

Reliable communication is the backbone of advanced metering infrastructure (AMI). Within the AMI, the neighbourhood area network (NAN) transports a multitude of trafﬁc, each with unique requirements. In order to deliver an acceptable level of reliability and latency, the underlying network, such as [...] Read more.

Reliable communication is the backbone of advanced metering infrastructure (AMI). Within the AMI, the neighbourhood area network (NAN) transports a multitude of trafﬁc, each with unique requirements. In order to deliver an acceptable level of reliability and latency, the underlying network, such as the wireless mesh network(WMN), must provide or guarantee the quality-of-service (QoS) level required by the respective application trafﬁc. Existing WMN routing protocols, such as optimised link state routing (OLSR), typically utilise a single metric and do not consider the requirements of individual trafﬁc; hence, packets are delivered on a best-effort basis. This paper presents a QoS-aware WMN routing technique that employs multiple metrics in OLSR optimal path selection for AMI applications. The problems arising from this approach are non deterministic polynomial time (NP)-complete in nature, which were solved through the combined use of the analytical hierarchy process (AHP) algorithm and pruning techniques. For smart meters transmitting Internet Protocol (IP) packets of varying sizes at different intervals, the proposed technique considers the constraints of NAN and the applications’ trafﬁc characteristics. The technique was developed by combining multiple OLSR path selection metrics with the AHP algorithminns-2. Compared with the conventional link metric in OLSR, the results show improvements of about 23% and 45% in latency and Packet Delivery Ratio (PDR), respectively, in a 25-node grid NAN. Full article

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15 pages, 789 KiB

Open AccessArticle

The Production of Engineered Biochars in a Vertical Auger Pyrolysis Reactor for Carbon Sequestration

by Patrick Brassard, Stéphane Godbout, Vijaya Raghavan, Joahnn H. Palacios, Michèle Grenier and Dan Zegan

Energies 2017, 10(3), 288; https://doi.org/10.3390/en10030288 - 28 Feb 2017

Cited by 60 | Viewed by 8251

Biomass pyrolysis and the valorization of co-products (biochar, bio-oil, syngas) could be a sustainable management solution for agricultural and forest residues. Depending on its properties, biochar amended to soil could improve fertility. Moreover, biochar is expected to mitigate climate change by reducing soil [...] Read more.

Biomass pyrolysis and the valorization of co-products (biochar, bio-oil, syngas) could be a sustainable management solution for agricultural and forest residues. Depending on its properties, biochar amended to soil could improve fertility. Moreover, biochar is expected to mitigate climate change by reducing soil greenhouse gas emissions, if its C/N ratio is lower than 30, and sequestrating carbon if its O/Corg and H/Corg ratios are lower than 0.2 and 0.7, respectively. However, the yield and properties of biochar are influenced by biomass feedstock and pyrolysis operating parameters. The objective of this research study was to validate an approach based on the response surface methodology, to identify the optimal pyrolysis operating parameters (temperature, solid residence time, and carrier gas flowrate), in order to produce engineered biochars for carbon sequestration. The pyrolysis of forest residues, switchgrass, and the solid fraction of pig manure, was carried out in a vertical auger reactor following a Box-Behnken design, in order to develop response surface models. The optimal pyrolysis operating parameters were estimated to obtain biochar with the lowest H/Corg and O/Corg ratios. Validation pyrolysis experiments confirmed that the selected approach can be used to accurately predict the optimal operating parameters for producing biochar with the desired properties to sequester carbon. Full article

(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)

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19 pages, 5155 KiB

Open AccessArticle

Optimizing the Performance of Solo Duck Wave Energy Converter in Tide

by Jinming Wu, Yingxue Yao, Wei Li, Liang Zhou and Malin Göteman

Energies 2017, 10(3), 289; https://doi.org/10.3390/en10030289 - 28 Feb 2017

Cited by 27 | Viewed by 6968

The high efficiency performance of the Edinburgh Duck wave energy converter (WEC) in 2D regular wave tests makes it a promising wave energy conversion scheme. A solo Duck WEC will be able to apply the point absorber effect to further enhance its performance. [...] Read more.

The high efficiency performance of the Edinburgh Duck wave energy converter (WEC) in 2D regular wave tests makes it a promising wave energy conversion scheme. A solo Duck WEC will be able to apply the point absorber effect to further enhance its performance. Since released degree of freedom will decrease the efficiency, a Duck WEC with fixed pitching axis will be a better option. However, for fixed supported WECs, tide is a non-ignorable consideration. In this paper, a movable mass method is utilized in the whole tidal range to not only balance the Duck to appropriate beak angles, but also follow the variation of hydrodynamic coefficients to keep cancelling the reactance of the system impedance so that complex conjugate control can be realized to optimize the power capture performance of the Duck WEC in tide. Results show that the beak angle should be adjusted to as large a value as possible so that the response amplitude of the Duck at maximum relative capture width will be reasonable small, and the lowest weight of the movable mass is found when its designed position locates at the center of the Duck profile. Full article

(This article belongs to the Special Issue Numerical Modelling of Wave and Tidal Energy)

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19 pages, 3676 KiB

Open AccessFeature PaperArticle

In Situ Surface-Enhanced Raman Spectroscopy Study of the Electrocatalytic Effect of PtFe/C Nanocatalyst on Ethanol Electro-Oxidation in Alkaline Medium

by A. C. Gómez-Monsiváis, I. Velázquez-Hernández, L. Álvarez-Contreras, M. Guerra-Balcázar, L. G. Arriaga, N. Arjona and J. Ledesma-García

Energies 2017, 10(3), 290; https://doi.org/10.3390/en10030290 - 1 Mar 2017

Cited by 14 | Viewed by 7538

Currently, the ethanol electro-oxidation reaction has attracted considerable attention in fuel cells because of new green ethanol synthetic methods based on biomass processes that have emerged. In this study, PtFe/C and Pt/C nanoparticles were synthesized by a chemical reduction method and tested in [...] Read more.

Currently, the ethanol electro-oxidation reaction has attracted considerable attention in fuel cells because of new green ethanol synthetic methods based on biomass processes that have emerged. In this study, PtFe/C and Pt/C nanoparticles were synthesized by a chemical reduction method and tested in the ethanol electro-oxidation reaction. Furthermore, the electrocatalytic effect of the PtFe bimetallic catalyst was analyzed by in situ surface-enhanced Raman spectroscopy (SERS) coupled to an electrochemical cell. X-ray diffractograms showed typical face-centered cubic structures with crystallite sizes of 3.31 and 3.94 for Pt/C and PtFe/C, respectively. TEM micrographs revealed nanoparticle sizes of 2 ± 0.4 nm and 3 ± 0.6 nm for Pt/C and PtFe/C respectively. PtFe/C exhibited a Pt₉₀Fe₁₀ composition by both X-ray fluorescence and energy-dispersive X-ray spectroscopy. A better electrocatalytic activity as function of concentration was obtained through the incorporation of a small amount of Fe into the Pt lattice and the presence of Fe²⁺/Fe³⁺ (observed by X-ray photoelectron spectroscopy). According to SERS experiments, the presence of these iron species promotes the chemisorption of ethanol, the formation of formic acid as main product and renewal of the catalytic sites, resulting in current densities that were at least three fold higher than the values obtained for the Pt/C nanocatalyst. Full article

(This article belongs to the Special Issue Direct Alcohol Fuel Cells)

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16 pages, 3267 KiB

Open AccessArticle

Decentralized Framework for Optimal Price-Based Power System Operation Using Feedback Control Mechanism

by Young Gyu Jin, Seung Wan Kim, Si Young Lee and Yong Tae Yoon

Energies 2017, 10(3), 291; https://doi.org/10.3390/en10030291 - 1 Mar 2017

Cited by 2 | Viewed by 4052

Future power systems are expected to have distributed energy resources (DERs). A price-based operation (PBO), where dynamic prices are used as the control signal, can be an alternative scheme to address challenging operational issues in the future power systems. In this paper, a [...] Read more.

Future power systems are expected to have distributed energy resources (DERs). A price-based operation (PBO), where dynamic prices are used as the control signal, can be an alternative scheme to address challenging operational issues in the future power systems. In this paper, a decentralized framework for optimal PBO using a feedback control mechanism is proposed to determine the nodal prices for power balance and congestion management. The substructures and feedback controllers of the proposed framework are derived based on the optimal power flow (OPF) method. Thus, the framework guarantees optimality for all situations in real-time and enables the use of various types of controllers. The effectiveness of the proposed framework is verified with the IEEE 39 bus network under some scenarios, such as the failure of a generator and a transmission line. The results clearly demonstrate that the proposed framework successfully resolves the balance and congestion problems by generating appropriate nodal prices in the PBO and provides a solution similar to the optimal solution determined by the conventional OPF method. Full article

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19 pages, 5573 KiB

Open AccessArticle

Mechanical Behavior and Permeability Evolution of Reconstituted Coal Samples under Various Unloading Confining Pressures—Implications for Wellbore Stability Analysis

by Qiangui Zhang, Xiangyu Fan, Yongchang Liang, Minghui Li, Guangzhi Li, Tianshou Ma and Wen Nie

Energies 2017, 10(3), 292; https://doi.org/10.3390/en10030292 - 2 Mar 2017

Cited by 32 | Viewed by 4528

Low pressure, low permeability, and low saturation of Chinese coal-bed methane (CBM) reservoirs make underbalanced drilling (UBD) widely used for mining CBM in China. In this study, mechanical behavior and permeability of coal rock were investigated under different degrees of unloading confining pressure [...] Read more.

Low pressure, low permeability, and low saturation of Chinese coal-bed methane (CBM) reservoirs make underbalanced drilling (UBD) widely used for mining CBM in China. In this study, mechanical behavior and permeability of coal rock were investigated under different degrees of unloading confining pressure (UCP)-reloading axial stress (RAS) by a triaxial experimental apparatus. These tests revealed that: (1) peak deviatoric stress of coal rock in UCP-RAS is lower than that in a conventional triaxial compression (CTC) test, and the peak deviatoric stress linearly relates the degree of unloading confining pressure. The deformation modulus of coal in UCP-RAS is lower than that in CTC, while the lateral expansion ratio is larger than that in CTC; (2) higher UCP leads to a faster increase of permeability during RAS until the failure of coal; (3) the cohesion and internal friction angle tested by UCP-RAS are lower by 4.57% and 15.18% than those tested by CTC. In addition, a field case (Zhaozhuang well, Qinshui Basin, China) of a well collapse problem validates the higher probability of wellbore collapse due to the increase of equivalent collapse fluid density, which is calculated by using coal rock parameters tested by UCP-RAS rather than by CTC. Full article

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17 pages, 5868 KiB

Open AccessArticle

Optimal Cooperative Management of Energy Storage Systems to Deal with Over- and Under-Voltages

by Ghassem Mokhtari, Ghavameddin Nourbakhsh, Amjad Anvari-Moghadam, Negareh Ghasemi and Aminmohammad Saberian

Energies 2017, 10(3), 293; https://doi.org/10.3390/en10030293 - 2 Mar 2017

Cited by 8 | Viewed by 4250

This paper presents an optimal cooperative voltage control approach, which coordinates storage units in a distribution network. This technique is developed for storage systems’ active power management with a local strategy to provide robust voltage control and a distributed strategy to deliver optimal [...] Read more.

This paper presents an optimal cooperative voltage control approach, which coordinates storage units in a distribution network. This technique is developed for storage systems’ active power management with a local strategy to provide robust voltage control and a distributed strategy to deliver optimal storage utilization. Accordingly, three control criteria based on predefined node voltage limits are used for network operation including normal, over-voltage, and under-voltage control modes. The contribution of storage units for voltage support is determined using the control modes and the coordination strategies proposed in this paper. This technique is evaluated in two case studies to assess its capability. Full article

(This article belongs to the Collection Smart Grid)

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17 pages, 6009 KiB

Open AccessArticle

Analysis of Pressure Rise in a Closed Container Due to Internal Arcing

by Peng Li, Jiangjun Ruan, Daochun Huang, Ziqing OuYang, Li Zhang, Mingyang Long and Mengting Wei

Energies 2017, 10(3), 294; https://doi.org/10.3390/en10030294 - 2 Mar 2017

Cited by 13 | Viewed by 7959

When an arc fault occurs in a medium-voltage (MV) metal enclosed switchgear, the arc heats the filling gas, resulting in a pressure rise, which may seriously damage the switchgear, the building it is contained in, or even endanger maintenance personnel. A pressure rise [...] Read more.

When an arc fault occurs in a medium-voltage (MV) metal enclosed switchgear, the arc heats the filling gas, resulting in a pressure rise, which may seriously damage the switchgear, the building it is contained in, or even endanger maintenance personnel. A pressure rise calculation method based on computational fluid dynamics (CFD) has been put forward in this paper. The pressure rise was calculated and the arc tests between the copper electrodes were performed in the container under different gap lengths by the current source. The results show that the calculated pressure rise agrees well with the measurement, and the relative error of the average pressure rise is about 2%. Arc volume has less effect on the pressure distribution in the container. Arc voltage Root-Mean-Square (RMS) has significant randomness with the change of arc current, and increases with the increase of gap length. The average arc voltage gradients measure at about 26, 20 and 16 V/cm when the gap lengths are 5, 10 and 15 cm, respectively. The proportion (thermal transfer coefficient k_p) of the arc energy leading to the pressure rise in the container is about 44.9%. The pressure is symmetrically distributed in the container before the pressure wave reaches the walls and the process of the energy release is similar to an explosion. The maximum overpressure in the corner is increased under the reflection and superimposition effects of the pressure wave, but the pressure waves will be of no importance any longer than a few milliseconds in the closed container. Full article

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19 pages, 338 KiB

Open AccessArticle

On Long-Term Transmission Rights in the Nordic Electricity Markets

by Petr Spodniak, Mikael Collan and Mari Makkonen

Energies 2017, 10(3), 295; https://doi.org/10.3390/en10030295 - 2 Mar 2017

Cited by 7 | Viewed by 5758

In vein with the new energy market rules drafted in the EU this paper presents and discusses two contract types for hedging the risks connected to long-term transmission rights, the financial transmission right (FTR) and the electricity price area differentials (EPAD) that are [...] Read more.

In vein with the new energy market rules drafted in the EU this paper presents and discusses two contract types for hedging the risks connected to long-term transmission rights, the financial transmission right (FTR) and the electricity price area differentials (EPAD) that are used in the Nordic electricity markets. The possibility to replicate the FTR contracts with a combination of EPAD contracts is presented and discussed. Based on historical evidence and empirical analysis of ten Nordic interconnectors and twenty bidding areas, we investigate the pricing accuracy of the replicated FTR contracts by quantifying ex-post forward risk premia. The results show that the majority of the studied FTR contain a negative risk premium, especially the monthly and the quarterly contracts. Reverse flow (unnatural) pricing was identified for two interconnectors. From a theoretical policy point of view the results imply that it may be possible to continue with the EPAD-based system by using EPAD Combos in the Nordic countries, even if FTR contracts would prevail elsewhere in the EU. In practice the pricing of bi-directional EPAD contracts is more complex and may not always be very efficient. The efficiency of the EPAD market structure should be discussed from various points of view before accepting their status quo as a replacement for FTRs in the Nordic electricity markets. Full article

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23 pages, 7865 KiB

Open AccessArticle

Isolated DC-DC Converter for Bidirectional Power Flow Controlling with Soft-Switching Feature and High Step-Up/Down Voltage Conversion

by Chih-Lung Shen, You-Sheng Shen and Cheng-Tao Tsai

Energies 2017, 10(3), 296; https://doi.org/10.3390/en10030296 - 2 Mar 2017

Cited by 10 | Viewed by 8688

In this paper, a novel isolated bidirectional DC-DC converter is proposed, which is able to accomplish high step-up/down voltage conversion. Therefore, it is suitable for hybrid electric vehicle, fuel cell vehicle, energy backup system, and grid-system applications. The proposed converter incorporates a coupled [...] Read more.

In this paper, a novel isolated bidirectional DC-DC converter is proposed, which is able to accomplish high step-up/down voltage conversion. Therefore, it is suitable for hybrid electric vehicle, fuel cell vehicle, energy backup system, and grid-system applications. The proposed converter incorporates a coupled inductor to behave forward-and-flyback energy conversion for high voltage ratio and provide galvanic isolation. The energy stored in the leakage inductor of the coupled inductor can be recycled without the use of additional snubber mechanism or clamped circuit. No matter in step-up or step-down mode, all power switches can operate with soft switching. Moreover, there is a inherit feature that metal–oxide–semiconductor field-effect transistors (MOSFETs) with smaller on-state resistance can be adopted because of lower voltage endurance at primary side. Operation principle, voltage ratio derivation, and inductor design are thoroughly described in this paper. In addition, a 1-kW prototype is implemented to validate the feasibility and correctness of the converter. Experimental results indicate that the peak efficiencies in step-up and step-down modes can be up to 95.4% and 93.6%, respectively. Full article

(This article belongs to the Special Issue Grid-Connected Photovoltaic Systems)

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23 pages, 19081 KiB

Open AccessFeature PaperArticle

An Active Power Filter Based on a Three-Level Inverter and 3D-SVPWM for Selective Harmonic and Reactive Compensation

by José Luis Monroy-Morales, David Campos-Gaona, Máximo Hernández-Ángeles, Rafael Peña-Alzola and José Leonardo Guardado-Zavala

Energies 2017, 10(3), 297; https://doi.org/10.3390/en10030297 - 3 Mar 2017

Cited by 19 | Viewed by 8349

Active Power Filters (APFs) have been used for reducing waveform distortion and improving power quality. However, this function can be improved by means of a selective harmonic compensation. Since an APF has rating restrictions, it is convenient to have the option of selecting [...] Read more.

Active Power Filters (APFs) have been used for reducing waveform distortion and improving power quality. However, this function can be improved by means of a selective harmonic compensation. Since an APF has rating restrictions, it is convenient to have the option of selecting an individual or a set of particular harmonics in order to compensate and apply the total APF capabilities to eliminate these harmonics, in particular those with a greater impact on the Total Harmonic Distortion (THD). This paper presents the development of a new APF prototype based on a three-phase three-level Neutral Point Clamped (NPC) inverter with selective harmonic compensation capabilities and reactive power compensation. The selective harmonic compensation approach uses several Synchronous Rotating Frames (SRF), to detect and control individual or a set of harmonics using d and q variables. The APF includes a Three-Dimensional Space Vector Modulator (3D-SVPWM) in order to generate the compensation currents. Because of its multilevel topology, the proposed active power filter can be used in diverse power quality applications at sub-transmission and distribution voltage levels. Simulation and experimental results are shown to validate the proposed solution and assess the prototype performance in different scenarios. Full article

(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)

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14 pages, 695 KiB

Open AccessArticle

Heavy Metals and Polycyclic Aromatic Hydrocarbons in Urban Leaf Litter Designated for Combustion

by Meike Nitsche, Nodirjon Nurmatov, Frank Hensgen and Michael Wachendorf

Energies 2017, 10(3), 298; https://doi.org/10.3390/en10030298 - 3 Mar 2017

Cited by 8 | Viewed by 4408

Vast amounts of leaf litter have to be disposed of by city administrations. This biomass has the potential for energy conversion, but contamination with pollutants can adversely affect this usage. We investigated leaf litter samples from the city of Kassel by analyzing their [...] Read more.

Vast amounts of leaf litter have to be disposed of by city administrations. This biomass has the potential for energy conversion, but contamination with pollutants can adversely affect this usage. We investigated leaf litter samples from the city of Kassel by analyzing their heavy metal and polycyclic aromatic hydrocarbon (PAH) concentrations. Leaf samples were indeed contaminated with heavy metals and PAHs and contamination was influenced by provenience and collection technique. A simple cleaning system of washing and subsequent mechanical dewatering significantly reduced heavy metal concentration. Regression models were developed for contamination with heavy metals which showed that contamination could be successfully estimated using the total ash content of the sample as a predictor, with an R² of up to 0.77. It can be concluded that leaf litter from cities is a possible feedstock for energetic conversion, provided a cleaning step is applied. Full article

(This article belongs to the Special Issue Biomass Combustion for Heat and Power Generation)

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27 pages, 5048 KiB

Open AccessArticle

Optimum Design and Operation of an HVAC Cooling Tower for Energy and Water Conservation

by Clemente García Cutillas, Javier Ruiz Ramírez and Manuel Lucas Miralles

Energies 2017, 10(3), 299; https://doi.org/10.3390/en10030299 - 3 Mar 2017

Cited by 33 | Viewed by 8982

The energy consumption increase in the last few years has contributed to developing energy efficiency policies in many countries, the main goal of which is decreasing CO

_{2}

emissions. One of the reasons for this increment has been caused by the use of [...] Read more.

The energy consumption increase in the last few years has contributed to developing energy efficiency policies in many countries, the main goal of which is decreasing CO

_{2}

emissions. One of the reasons for this increment has been caused by the use of air conditioning systems due to new comfort standards. In that regard, cooling towers and evaporative condensers are presented as efficient devices that operate with low-level water temperature. Moreover, the energy consumption and the cost of the equipment are lower than other systems like air condensers at the same operation conditions. This work models an air conditioning system in TRNSYS software, the main elements if which are a cooling tower, a water-water chiller and a reference building. The cooling tower model is validated using experimental data in a pilot plant. The main objective is to implement an optimizing control strategy in order to reduce both energy and water consumption. Furthermore a comparison between three typical methods of capacity control is carried out. Additionally, different cooling tower configurations are assessed, involving six drift eliminators and two water distribution systems. Results show the influence of optimizing the control strategy and cooling tower configuration, with a maximum energy savings of 10.8% per story and a reduction of 4.8% in water consumption. Full article

(This article belongs to the Special Issue The 1st “The Belt and Road Initiative” International Conference on Sustainable Refrigeration and Air Conditioning)

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16 pages, 1597 KiB

Open AccessArticle

A Dynamic Economic Dispatch Model for Uncertain Power Demands in an Interconnected Microgrid

by Young-Sik Jang and Mun-Kyeom Kim

Energies 2017, 10(3), 300; https://doi.org/10.3390/en10030300 - 3 Mar 2017

Cited by 13 | Viewed by 6003

In this paper, we propose a dynamic economic dispatch (DED) model with sharing of responsibility for supply–demand balance under uncertain demands in a microgrid (MG). For developing the proposed model, an energy band operation scheme, including a tie-line flow (TLF) contraction between the [...] Read more.

In this paper, we propose a dynamic economic dispatch (DED) model with sharing of responsibility for supply–demand balance under uncertain demands in a microgrid (MG). For developing the proposed model, an energy band operation scheme, including a tie-line flow (TLF) contraction between the main grid and the microgrid (MG), is constructed for preventing considerable changes in the TLFs caused by DED optimization. The proposed scheme generalizes the relationship between TLF contractions and MG operational costs. Moreover, a chance-constrained approach is applied to prevent short- and over-supply risks caused by unpredictable demands in the MG. Based on this approach, it is possible to determine the reasonable ramping capability versus operational cost under uncertain power demands in the MG. Full article

(This article belongs to the Collection Smart Grid)

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20 pages, 12622 KiB

Open AccessArticle

A Novel Parametric Modeling Method and Optimal Design for Savonius Wind Turbines

by Baoshou Zhang, Baowei Song, Zhaoyong Mao, Wenlong Tian, Boyang Li and Bo Li

Energies 2017, 10(3), 301; https://doi.org/10.3390/en10030301 - 3 Mar 2017

Cited by 62 | Viewed by 11654

Under the inspiration of polar coordinates, a novel parametric modeling and optimization method for Savonius wind turbines was proposed to obtain the highest power output, in which a quadratic polynomial curve was bent to describe a blade. Only two design parameters are needed [...] Read more.

Under the inspiration of polar coordinates, a novel parametric modeling and optimization method for Savonius wind turbines was proposed to obtain the highest power output, in which a quadratic polynomial curve was bent to describe a blade. Only two design parameters are needed for the shape-complicated blade. Therefore, this novel method reduces sampling scale. A series of transient simulations was run to get the optimal performance coefficient (power coefficient C p) for different modified turbines based on computational fluid dynamics (CFD) method. Then, a global response surface model and a more precise local response surface model were created according to Kriging Method. These models defined the relationship between optimization objective Cp and design parameters. Particle swarm optimization (PSO) algorithm was applied to find the optimal design based on these response surface models. Finally, the optimal Savonius blade shaped like a “hook” was obtained. Cm (torque coefficient), Cp and flow structure were compared for the optimal design and the classical design. The results demonstrate that the optimal Savonius turbine has excellent comprehensive performance. The power coefficient Cp is significantly increased from 0.247 to 0.262 (6% higher). The weight of the optimal blade is reduced by 17.9%. Full article

(This article belongs to the Special Issue Wind Turbine 2017)

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12 pages, 3963 KiB

Open AccessArticle

Experimental Investigation of the Transpired Solar Air Collectors and Metal Corrugated Packing Solar Air Collectors

by Wandong Zheng, Huan Zhang, Shijun You and Yindan Fu

Energies 2017, 10(3), 302; https://doi.org/10.3390/en10030302 - 3 Mar 2017

Cited by 17 | Viewed by 4699

The thermal performance of three novel solar air collectors with perforating corrugated plate, slit-perforated plate, and corrugated packing were experimentally studied in this paper. Experiments were conducted in Tianjin to study the thermal and dynamic performance of the collectors in cold and severe [...] Read more.

The thermal performance of three novel solar air collectors with perforating corrugated plate, slit-perforated plate, and corrugated packing were experimentally studied in this paper. Experiments were conducted in Tianjin to study the thermal and dynamic performance of the collectors in cold and severe cold regions. A chamber with a PID (Proportion Integration Differentiation) temperature controller was designed to control the inlet air temperature of the three collectors. Effects of radiation intensity, inlet air temperature, and flow rate on the thermal efficiency and outlet air temperature were experimentally studied. The results indicated that the thermal efficiency of the three collectors in severe cold regions could be much higher than 50% and the collector with perforating corrugated plate had the highest thermal efficiency. The inlet air flow rate had significant effects on the thermal comfort of buildings in cold and severe cold regions and it should be lower than 45 m³/h. The results indicated that the pressure drops of collectors with perforating corrugated plate were a little larger than the collectors with slit-perforated plate, but the thermal efficiency and outlet air temperature was higher. Therefore, the collector with perforating corrugated plate was more suitable to use in cold and severe cold regions. Full article

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

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13 pages, 17069 KiB

Open AccessArticle

Study on the Progressive Failure Characteristics of Longmaxi Shale under Uniaxial Compression Conditions by X-ray Micro-Computed Tomography

by Xiao Li, Yongting Duan, Shouding Li and Runqing Zhou

Energies 2017, 10(3), 303; https://doi.org/10.3390/en10030303 - 3 Mar 2017

Cited by 38 | Viewed by 5499

To investigate the deformation-failure process of Longmaxi shale under uniaxial compression conditions from the mesoscopic and macroscopic points of view, novel X-ray microComputed Tomography (micro-CT) equipment combined with unique loading apparatus was used. Cylindrical shale samples (4 mm in diameter and 8 mm [...] Read more.

To investigate the deformation-failure process of Longmaxi shale under uniaxial compression conditions from the mesoscopic and macroscopic points of view, novel X-ray microComputed Tomography (micro-CT) equipment combined with unique loading apparatus was used. Cylindrical shale samples (4 mm in diameter and 8 mm in height) were produced to perform a series of uniaxial compression tests. CT scanning images at different time points during the loading process were obtained to study the characteristics of the progressive failure. In addition, stereograms were reconstructed and vertical slices were selected to explain the failure mechanism. From the results of the testing the low-density area, local per-peak cracks, numerous post-peak cracks and secondary cracks consecutively appeared in the CT images. Vertical and inclined fissures in the samples could be observed from the stereograms’ surfaces and from internal slices. The cracking indicates that the failure process of shale is progressive and the failure mechanism of shale under uniaxial compression is mainly tension destruction or comprehensive tension-shear destruction. Full article

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

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14 pages, 5381 KiB

Open AccessArticle

A Study on the Optimization of Surfactants in the Main and Vice Slug in Weak Base ASP Flooding

by Bin Huang, Wei Zhang, Huan Liu, Cheng Fu, Pengxin Feng and Ying Wang

Energies 2017, 10(3), 304; https://doi.org/10.3390/en10030304 - 3 Mar 2017

Cited by 7 | Viewed by 4724

In ASP (Alkali-Surfactant-Polymer) flooding processes, surfactants help to enhance oil recovery by lowering the interfacial tension between the oil and water. However, due to the high cost of surfactants and the stability of the emulsion that varies with surfactant concentration, it is necessary [...] Read more.

In ASP (Alkali-Surfactant-Polymer) flooding processes, surfactants help to enhance oil recovery by lowering the interfacial tension between the oil and water. However, due to the high cost of surfactants and the stability of the emulsion that varies with surfactant concentration, it is necessary to optimize the surfactant concentration in ASP flooding. In this study, we combined numerical simulation and physical experimental research to solve this problem. In order to screen for the optimal surfactant concentration in the main and vice slugs, CMG (Computer Measurement Group) numerical simulation software was used to change the surfactant concentration in the injected compound system and the oil recovery factor and the recovery percent of reserves were compared. The physical experiments were also carried out with different surfactant concentrations and the results verified the simulation results. It shows that the recovery factor increases with the surfactant concentration. The optimal surfactant concentration in the main and vice slug are 0.3% and 0.15%, respectively. As for improving the recovery factor, it is more efficient to increase the mass fraction of the surfactant in the vice slug than in the main slug. It demonstrates that the amount of surfactant in the main slug plays a more important role in displacing oil from the formation. Full article

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21 pages, 2573 KiB

Open AccessArticle

Control Strategy Optimization for Parallel Hybrid Electric Vehicles Using a Memetic Algorithm

by Yu-Huei Cheng and Ching-Ming Lai

Energies 2017, 10(3), 305; https://doi.org/10.3390/en10030305 - 3 Mar 2017

Cited by 35 | Viewed by 11356

Hybrid electric vehicle (HEV) control strategy is a management approach for generating, using, and saving energy. Therefore, the optimal control strategy is the sticking point to effectively manage hybrid electric vehicles. In order to realize the optimal control strategy, we use a robust [...] Read more.

Hybrid electric vehicle (HEV) control strategy is a management approach for generating, using, and saving energy. Therefore, the optimal control strategy is the sticking point to effectively manage hybrid electric vehicles. In order to realize the optimal control strategy, we use a robust evolutionary computation method called a “memetic algorithm (MA)” to optimize the control parameters in parallel HEVs. The “local search” mechanism implemented in the MA greatly enhances its search capabilities. In the implementation of the method, the fitness function combines with the ADvanced VehIcle SimulatOR (ADVISOR) and is set up according to an electric assist control strategy (EACS) to minimize the fuel consumption (FC) and emissions (HC, CO, and NOx) of the vehicle engine. At the same time, driving performance requirements are also considered in the method. Four different driving cycles, the new European driving cycle (NEDC), Federal Test Procedure (FTP), Economic Commission for Europe + Extra-Urban driving cycle (ECE + EUDC), and urban dynamometer driving schedule (UDDS) are carried out using the proposed method to find their respectively optimal control parameters. The results show that the proposed method effectively helps to reduce fuel consumption and emissions, as well as guarantee vehicle performance. Full article

(This article belongs to the Special Issue Energy Management, Control, and System Architectures for Electric Vehicle Applications)

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16 pages, 2322 KiB

Open AccessArticle

Optimization of a Bubbling Fluidized Bed Plant for Low-Temperature Gasification of Biomass

by María Pilar González-Vázquez, Roberto García, Covadonga Pevida and Fernando Rubiera

Energies 2017, 10(3), 306; https://doi.org/10.3390/en10030306 - 4 Mar 2017

Cited by 33 | Viewed by 6385

Investigation into clean energies has been focused on finding an alternative to fossil fuels in order to reduce global warming while at the same time satisfying the world’s energy needs. Biomass gasification is seen as a promising thermochemical conversion technology as it allows [...] Read more.

Investigation into clean energies has been focused on finding an alternative to fossil fuels in order to reduce global warming while at the same time satisfying the world’s energy needs. Biomass gasification is seen as a promising thermochemical conversion technology as it allows useful gaseous products to be obtained from low-energy-density solid fuels. Air–steam mixtures are the most commonly used gasification agents. The gasification performances of several biomass samples and their mixtures were compared. One softwood (pine) and one hardwood (chestnut), their torrefied counterparts, and other Spanish-based biomass wastes such as almond shell, olive stone, grape and olive pomaces or cocoa shell were tested, and their behaviors at several different stoichiometric ratios (SR) and steam/air ratios (S/A) were compared. The optimum SR was found to be in the 0.2–0.3 range for S/A = 75/25. At these conditions a syngas stream with 35% of H₂ + CO and a gas yield of 2 L gas/g fuel were obtained, which represents a cold-gas efficiency of almost 50%. The torrefaction process does not significantly affect the quality of the product syngas. Some of the obtained chars were analyzed to assess their use as precursors for catalysts, combustion fuel or for agricultural purposes such as soil amendment. Full article

(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)

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21 pages, 6582 KiB

Open AccessArticle

Wind Energy Potential and Power Law Indexes Assessment for Selected Near-Coastal Sites in Malaysia

by Aliashim Albani and Mohd Zamri Ibrahim

Energies 2017, 10(3), 307; https://doi.org/10.3390/en10030307 - 5 Mar 2017

Cited by 60 | Viewed by 9218

This paper investigated the wind energy potential by analysing a certain amount of gathered 10-min measured data at four stations located at coastal sites in Malaysia, i.e., Kudat, Mersing, Kijal, and Langkawi. The wind data are collected from a total of four new [...] Read more.

This paper investigated the wind energy potential by analysing a certain amount of gathered 10-min measured data at four stations located at coastal sites in Malaysia, i.e., Kudat, Mersing, Kijal, and Langkawi. The wind data are collected from a total of four new wind measurement masts with sensors mounted at various heights on the tower. The measured data have enabled the establishment of wind resource maps and the power law indexes (PLIs) analysis. In addition, the dependence of PLI upon surface temperature and terrain types is studied, as they are associated to the form of exponential fits. Moreover, the accuracy of exponential fits is assessed by comparing the results with the 1/7 law via the capacity factor (CF) discrepancies. In order to do so, the wind turbine with a hub-height similar to the maximum height of the measured data at each site is selected to simulate energy production. Accordingly, the discrepancy of CF based on the extrapolated data by employing 1/7 laws and exponential fits, in spite of being computed using measured data, is determined as well. Furthermore, the large discrepancy of the wind data and the CF, which has been determined with the application of 1/7, is compared to the exponential fits. This is because; discrepancy in estimation of vertical wind speed could lead to inaccurate CF computation. Meanwhile, from the energy potential analysis based on the computed CF, only Kudat and Mersing display a promising potential to develop a medium capacity of wind turbine power, while the other sites may be suitable for wind turbines at a small scale. Full article

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16 pages, 2286 KiB

Open AccessArticle

Angle Control-Based Multi-Terminal Out-of-Step Protection System

by Antans Sauhats, Andrejs Utans, Dmitrijs Antonovs and Andrejs Svalovs

Energies 2017, 10(3), 308; https://doi.org/10.3390/en10030308 - 4 Mar 2017

Cited by 16 | Viewed by 3899

From time to time a sequence of unexpected and overlapping contingencies may lead to power system angular instability and even blackouts if not addressed adequately by means of an out-of-step (OOS) protection system. The motivation of the paper is an attempt to develop [...] Read more.

From time to time a sequence of unexpected and overlapping contingencies may lead to power system angular instability and even blackouts if not addressed adequately by means of an out-of-step (OOS) protection system. The motivation of the paper is an attempt to develop a workable prototype of the OOS protection system. The deficiencies of the protection currently used in the Latvian Power System network are highlighted and a new protection structure is proposed. The protection system comprises of several strategically located terminals, exchanging information in real time by means of a communication network. The OOS condition detection method is based on system-wide generation sources, electromotive forces, vectors, and angle control. The network splitting decision is based on generator coherence evaluation. Protection terminals determine online the groups of coherent generators and choose the splitting boundary from a predefined transmission lines (TLs) cut sets list. The protection system structure, algorithm of operation, and possible IEC 61850 communication standard-based implementation are described. Full article

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

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17 pages, 4000 KiB

Open AccessArticle

A Novel High-Frequency Voltage Standing-Wave Ratio-Based Grounding Electrode Line Fault Supervision in Ultra-High Voltage DC Transmission Systems

by Yufei Teng, Xiaopeng Li, Qi Huang, Yifei Wang, Shi Jing, Zhenchao Jiang and Wei Zhen

Energies 2017, 10(3), 309; https://doi.org/10.3390/en10030309 - 5 Mar 2017

Cited by 15 | Viewed by 5364

In order to improve the fault monitoring performance of grounding electrode lines in ultra-high voltage DC (UHVDC) transmission systems, a novel fault monitoring approach based on the high-frequency voltage standing-wave ratio (VSWR) is proposed in this paper. The VSWR is defined considering a [...] Read more.

In order to improve the fault monitoring performance of grounding electrode lines in ultra-high voltage DC (UHVDC) transmission systems, a novel fault monitoring approach based on the high-frequency voltage standing-wave ratio (VSWR) is proposed in this paper. The VSWR is defined considering a lossless transmission line, and the characteristics of the VSWR under different conditions are analyzed. It is shown that the VSWR equals 1 when the terminal resistance completely matches the characteristic impedance of the line, and when a short circuit fault occurs on the grounding electrode line, the VSWR will be greater than 1. The VSWR will approach positive infinity under metallic earth fault conditions, whereas the VSWR in non-metallic earth faults will be smaller. Based on these analytical results, a fault supervision criterion is formulated. The effectiveness of the proposed VSWR-based fault supervision technique is verified with a typical UHVDC project established in Power Systems Computer Aided Design/Electromagnetic Transients including DC(PSCAD/EMTDC). Simulation results indicate that the proposed strategy can reliably identify the grounding electrode line fault and has strong anti-fault resistance capability. Full article

(This article belongs to the Collection Smart Grid)

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21 pages, 8829 KiB

Open AccessArticle

Pressure Losses in Hydraulic Manifolds

by Barbara Zardin, Giovanni Cillo, Carlo Alberto Rinaldini, Enrico Mattarelli and Massimo Borghi

Energies 2017, 10(3), 310; https://doi.org/10.3390/en10030310 - 6 Mar 2017

Cited by 32 | Viewed by 8098

Hydraulic manifolds are used to realize compact circuit layout, but may introduce a high pressure drop in the system. Their design is in fact oriented more toward achieving minimum size and weight than to reducing pressure losses. This work studies the pressure losses [...] Read more.

Hydraulic manifolds are used to realize compact circuit layout, but may introduce a high pressure drop in the system. Their design is in fact oriented more toward achieving minimum size and weight than to reducing pressure losses. This work studies the pressure losses in hydraulic manifolds using different methods: Computational Fluid Dynamic (CFD) analysis; semi-empirical formulation derived from the scientific literature, when available; and experimental characterization. The purpose is to obtain the pressure losses when the channels’ connections within the manifold are not ascribable to the few classic cases studied in the literature, in particular for 90° bends (elbows) with expansion/contraction and offset intersection of channels. Moreover, since CFD analysis is used to predict pressure losses, general considerations of the manifold design may be outlined and this will help the design process in the optimization of flow passages. The main results obtained show how CFD analysis overestimates the experimental results; nevertheless, the numerical analysis represents the correct trends of the pressure losses. Full article

(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems)

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18 pages, 13700 KiB

Open AccessArticle

Analysis of Power Loss and Improved Simulation Method of a High Frequency Dual-Buck Full-Bridge Inverter

by Zhun Meng, Yi-Feng Wang, Liang Yang and Wei Li

Energies 2017, 10(3), 311; https://doi.org/10.3390/en10030311 - 6 Mar 2017

Cited by 10 | Viewed by 4864

A high frequency dual-buck full-bridge inverter for small power renewable energy application is proposed in this paper. A switching frequency of 400 kHz is achieved with the adoption of the SiC power device. A two-pole two-zero (2P2Z) compensator is employed in the outer [...] Read more.

A high frequency dual-buck full-bridge inverter for small power renewable energy application is proposed in this paper. A switching frequency of 400 kHz is achieved with the adoption of the SiC power device. A two-pole two-zero (2P2Z) compensator is employed in the outer voltage loop to generate the current reference for inner current loop. A 3P3Z compensator is adopted in the inner current loop to track the current reference. A systematic way for calculating the losses of high frequency inverter is presented, and the losses of the components are thoroughly analyzed. The turn-on and turn-off procedures of the inverter are discussed in detail. The losses caused by high frequency are calculated accurately, and the loss distribution is established as well. The procedure of the loss analysis gives a practical example for calculating the loss of similar type inverters. Moreover, deviation between pulse width modulation (PWM) control signal and switching response in high frequency switching is thoroughly analyzed. The influence of deviation is verified by designed experiment. Hence, a compensation method is proposed in order to minimize the influence. The compensation effect is validated by experiment and simulation. Finally, a 1-kW prototype is built to verify the feasibility of the theoretical analyses. The grid-connected maximum output power experiment is completed at 1 kW with the efficiency of 96.1% and the total harmonic distortion (THD) of 1.8%. The comparison experiments of power loss between Si and SiC power devices are carried out. The experiment results confirm the loss calculation method to be valid. Full article

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14 pages, 6411 KiB

Open AccessArticle

A Redundancy Mechanism Design for Hall-Based Electronic Current Transformers

by Kun-Long Chen, Ren-Shuo Wan, Yi Guo, Nanming Chen and Wei-Jen Lee

Energies 2017, 10(3), 312; https://doi.org/10.3390/en10030312 - 6 Mar 2017

Cited by 13 | Viewed by 4346

Traditional current transformers (CTs) suffer from DC and AC saturation and remanent magnetization in many industrial applications. Moreover, the drawbacks of traditional CTs, such as closed iron cores, bulky volume, and heavy weight, further limit the development of an intelligent power protection system. [...] Read more.

Traditional current transformers (CTs) suffer from DC and AC saturation and remanent magnetization in many industrial applications. Moreover, the drawbacks of traditional CTs, such as closed iron cores, bulky volume, and heavy weight, further limit the development of an intelligent power protection system. In order to compensate for these drawbacks, we proposed a novel current measurement method by using Hall sensors, which is called the Hall-effect current transformer (HCT). The existing commercial Hall sensors are electronic components, so the reliability of the HCT is normally worse than that of the traditional CT. Therefore, our study proposes a redundancy mechanism for the HCT to strengthen its reliability. With multiple sensor modules, the method has the ability to improve the accuracy of the HCT as well. Additionally, the proposed redundancy mechanism monitoring system provides a condition-based maintenance for the HCT. We verify our method with both simulations and an experimental test. The results demonstrate that the proposed HCT with a redundancy mechanism can almost achieve Class 0.2 for measuring CTs according to IEC Standard 60044-8. Full article

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

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20 pages, 1322 KiB

Open AccessArticle

Strategic Maintenance Scheduling of an Offshore Wind Farm in a Deregulated Power System

by Peyman Mazidi, Yaser Tohidi and Miguel A. Sanz-Bobi

Energies 2017, 10(3), 313; https://doi.org/10.3390/en10030313 - 6 Mar 2017

Cited by 19 | Viewed by 5036

This paper proposes a model for strategic maintenance scheduling of offshore wind farms (SMSOWF) in a deregulated power system. The objective of the model is to plan the maintenance schedules in a way to maximize the proﬁt of the offshore wind farm. In [...] Read more.

This paper proposes a model for strategic maintenance scheduling of offshore wind farms (SMSOWF) in a deregulated power system. The objective of the model is to plan the maintenance schedules in a way to maximize the proﬁt of the offshore wind farm. In addition, some network constraints, such as transmission lines capacity, and wind farm constraints, such as labor working shift, wave height limit and wake effect, as well as unexpected outages, are included in deterministic and stochastic studies. Moreover, the proposedmodel provides theability to incorporate information from condition monitoring systems. SMSOWF is formulated through a bi-level formulation and then transformed into a single-level through Karush–Kuhn–Tucker conditions. The model is validated through a test system, and the results demonstrate applicability, advantages and challenges of harnessing the full potential of the model. Full article

(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)

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15 pages, 3367 KiB

Open AccessArticle

Simulation of Steam Gasification in a Fluidized Bed Reactor with Energy Self-Sufficient Condition

by Ajaree Suwatthikul, Siripong Limprachaya, Paisan Kittisupakorn and Iqbal Mohammed Mujtaba

Energies 2017, 10(3), 314; https://doi.org/10.3390/en10030314 - 6 Mar 2017

Cited by 34 | Viewed by 9014

The biomass gasification process is widely accepted as a popular technology to produce fuel for the application in gas turbines and Organic Rankine Cycle (ORC). Chemical reactions of this process can be separated into three reaction zones: pyrolysis, combustion, and reduction. In this [...] Read more.

The biomass gasification process is widely accepted as a popular technology to produce fuel for the application in gas turbines and Organic Rankine Cycle (ORC). Chemical reactions of this process can be separated into three reaction zones: pyrolysis, combustion, and reduction. In this study, sensitivity analysis with respect to three input parameters (gasification temperature, equivalence ratio, and steam-to-biomass ratio) has been carried out to achieve energy self-sufficient conditions in a steam gasification process under the criteria that the carbon conversion efficiency must be more than 70%, and carbon dioxide gas is lower than 20%. Simulation models of the steam gasification process have been carried out by ASPEN Plus and validated with both experimental data and simulation results from Nikoo & Mahinpey (2008). Gasification temperature of 911 °C, equivalence ratio of 0.18, and a steam-to-biomass ratio of 1.78, are considered as an optimal operation point to achieve energy self-sufficient condition. This operating point gives the maximum of carbon conversion efficiency at 91.03%, and carbon dioxide gas at 15.18 volumetric percentages. In this study, life cycle assessment (LCA) is included to compare the environmental performance of conventional and energy self-sufficient gasification for steam biomass gasification. Full article

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20 pages, 13699 KiB

Open AccessEditor’s ChoiceArticle

An Autonomous Coil Alignment System for the Dynamic Wireless Charging of Electric Vehicles to Minimize Lateral Misalignment

by Karam Hwang, Jaeyong Cho, Dongwook Kim, Jaehyoung Park, Jong Hwa Kwon, Sang Il Kwak, Hyun Ho Park and Seungyoung Ahn

Energies 2017, 10(3), 315; https://doi.org/10.3390/en10030315 - 7 Mar 2017

Cited by 66 | Viewed by 11190

This paper proposes an autonomous coil alignment system (ACAS) for electric vehicles (EVs) with dynamic wireless charging (DWC) to mitigate the reduction in received power caused by lateral misalignment between the source and load coils. The key component of the ACAS is a [...] Read more.

This paper proposes an autonomous coil alignment system (ACAS) for electric vehicles (EVs) with dynamic wireless charging (DWC) to mitigate the reduction in received power caused by lateral misalignment between the source and load coils. The key component of the ACAS is a novel sensor coil design, which can detect the load coil’s left or right position relative to the source coil by observing the change in voltage phase. This allows the lateral misalignment to be estimated through the wireless power transfer (WPT) system alone, which is a novel tracking method for vehicular applications. Once misalignment is detected, the vehicle’s lateral position is self-adjusted by an autonomous steering function. The feasibility of the overall operation of the ACAS was verified through simulation and experiments. In addition, an analysis based on experimental results was conducted, demonstrating that 26% more energy can be transferred during DWC with the ACAS, just by keeping the vehicle’s load coil aligned with the source coil. Full article

(This article belongs to the Special Issue Advanced Power Electronics and Control for Wireless Power Transfer Systems)

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18 pages, 7983 KiB

Open AccessArticle

Reluctance Machine for a Hollow Cylinder Flywheel

by Magnus Hedlund, Tobias Kamf, Juan De Santiago, Johan Abrahamsson and Hans Bernhoff

Energies 2017, 10(3), 316; https://doi.org/10.3390/en10030316 - 7 Mar 2017

Cited by 4 | Viewed by 8315

A hollow cylinder flywheel rotor with a novel outer rotor switched reluctance machine (SRM) mounted on the interior rim is presented, with measurements, numerical analysis and analytical models. Practical experiences from the construction process are also discussed. The flywheel rotor does not have [...] Read more.

A hollow cylinder flywheel rotor with a novel outer rotor switched reluctance machine (SRM) mounted on the interior rim is presented, with measurements, numerical analysis and analytical models. Practical experiences from the construction process are also discussed. The flywheel rotor does not have a shaft and spokes and is predicted to store 181

Wh / kg

at ultimate tensile strength (UTS) according to simulations. The novel SRM is an axial flux machine, chosen due to its robustness and tolerance for high strain. The computed maximum tip speed of the motor at UTS is 1050

m / s

. A small-scale proof-of-concept electric machine prototype has been constructed, and the machine inductance has been estimated from measurements of voltage and current and compared against results from analytical models and finite element analysis (FEA). The prototype measurements were used to simulate operation during maximal speed for a comparison towards other high-speed electric machines, in terms of tip speed and power. The mechanical design of the flywheel was performed with an analytical formulation assuming planar stress in concentric shells of orthotropic (unidirectionally circumferentially wound) carbon composites. The analytical approach was verified with 3D FEA in terms of stress and strain. Full article

(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)

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24 pages, 8722 KiB

Open AccessArticle

Wind Farm Wake: The 2016 Horns Rev Photo Case

by Charlotte Bay Hasager, Nicolai Gayle Nygaard, Patrick J. H. Volker, Ioanna Karagali, Søren Juhl Andersen and Jake Badger

Energies 2017, 10(3), 317; https://doi.org/10.3390/en10030317 - 7 Mar 2017

Cited by 38 | Viewed by 27470

Offshore wind farm wakes were observed and photographed in foggy conditions at Horns Rev 2 on 25 January 2016 at 12:45 UTC. These new images show highly contrasting conditions regarding the wind speed, turbulence intensity, atmospheric stability, weather conditions and wind farm wake [...] Read more.

Offshore wind farm wakes were observed and photographed in foggy conditions at Horns Rev 2 on 25 January 2016 at 12:45 UTC. These new images show highly contrasting conditions regarding the wind speed, turbulence intensity, atmospheric stability, weather conditions and wind farm wake development as compared to the Horns Rev 1 photographs from 12 February 2008. The paper examines the atmospheric conditions from satellite images, radiosondes, lidar and wind turbine data and compares the observations to results from atmospheric meso-scale modelling and large eddy simulation. Key findings are that a humid and warm air mass was advected from the southwest over cold sea and the dew-point temperature was such that cold-water advection fog formed in a shallow layer. The flow was stably stratified and the freestream wind speed was 13 m/s at hub height, which means that most turbines produced at or near rated power. The wind direction was southwesterly and long, narrow wakes persisted several rotor diameters downwind of the wind turbines. Eventually mixing of warm air from aloft dispersed the fog in the far wake region of the wind farm. Full article

(This article belongs to the Collection Wind Turbines)

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14 pages, 3991 KiB

Open AccessArticle

Detent Force Reduction of a C-Core Linear Flux-Switching Permanent Magnet Machine with Multiple Additional Teeth

by Yi Du, Gang Yang, Li Quan, Xiaoyong Zhu, Feng Xiao and Haoyang Wu

Energies 2017, 10(3), 318; https://doi.org/10.3390/en10030318 - 7 Mar 2017

Cited by 17 | Viewed by 4759

C-core linear flux-switching permanent magnet (PM) machines (LFSPMs) are attracting more and more attention due to their advantages of simplicity and robustness of the secondary side, high power density and high torque density, in which both PMs and armature windings are housed in [...] Read more.

C-core linear flux-switching permanent magnet (PM) machines (LFSPMs) are attracting more and more attention due to their advantages of simplicity and robustness of the secondary side, high power density and high torque density, in which both PMs and armature windings are housed in the primary side. The primary salient tooth wound with a concentrated winding consists of C-shaped iron core segments between which PMs are sandwiched and the magnetization directions of these PMs are adjacent and alternant in the horizontal direction. On the other hand, the secondary side is composed of a simple iron core with salient teeth so that it is very suitable for long stroke applications. However, the detent force of the C-core LFSPM machine is relatively high and the magnetic circuit is unbalanced due to the end effect. Thus, a new multiple additional tooth which consists of an active and a traditional passive additional tooth, is employed at each end side of the primary in this paper, so that the asymmetry due to end effect can be depressed and the detent force can be reduced by adjusting the passive additional tooth position. By using the finite element method, the characteristics and performances of the proposed machine are analyzed and verified. Full article

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27 pages, 463 KiB

Open AccessEditor’s ChoiceArticle

A Hybrid Genetic Wind Driven Heuristic Optimization Algorithm for Demand Side Management in Smart Grid

by Nadeem Javaid, Sakeena Javaid, Wadood Abdul, Imran Ahmed, Ahmad Almogren, Atif Alamri and Iftikhar Azim Niaz

Energies 2017, 10(3), 319; https://doi.org/10.3390/en10030319 - 7 Mar 2017

Cited by 161 | Viewed by 10439

In recent years, demand side management (DSM) techniques have been designed for residential, industrial and commercial sectors. These techniques are very effective in flattening the load profile of customers in grid area networks. In this paper, a heuristic algorithms-based energy management controller is [...] Read more.

In recent years, demand side management (DSM) techniques have been designed for residential, industrial and commercial sectors. These techniques are very effective in flattening the load profile of customers in grid area networks. In this paper, a heuristic algorithms-based energy management controller is designed for a residential area in a smart grid. In essence, five heuristic algorithms (the genetic algorithm (GA), the binary particle swarm optimization (BPSO) algorithm, the bacterial foraging optimization algorithm (BFOA), the wind-driven optimization (WDO) algorithm and our proposed hybrid genetic wind-driven (GWD) algorithm) are evaluated. These algorithms are used for scheduling residential loads between peak hours (PHs) and off-peak hours (OPHs) in a real-time pricing (RTP) environment while maximizing user comfort (UC) and minimizing both electricity cost and the peak to average ratio (PAR). Moreover, these algorithms are tested in two scenarios: (i) scheduling the load of a single home and (ii) scheduling the load of multiple homes. Simulation results show that our proposed hybrid GWD algorithm performs better than the other heuristic algorithms in terms of the selected performance metrics. Full article

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12 pages, 4051 KiB

Open AccessArticle

Analytical Calculation of Magnetic Field Distribution and Stator Iron Losses for Surface-Mounted Permanent Magnet Synchronous Machines

by Zhen Tian, Chengning Zhang and Shuo Zhang

Energies 2017, 10(3), 320; https://doi.org/10.3390/en10030320 - 7 Mar 2017

Cited by 27 | Viewed by 7508

Permanent-magnet synchronous machines (PMSMs) are widely used in electric vehicles owing to many advantages, such as high power density, high efficiency, etc. Iron losses can account for a significant component of the total loss in permanent-magnet (PM) machines. Consequently, these losses should be [...] Read more.

Permanent-magnet synchronous machines (PMSMs) are widely used in electric vehicles owing to many advantages, such as high power density, high efficiency, etc. Iron losses can account for a significant component of the total loss in permanent-magnet (PM) machines. Consequently, these losses should be carefully considered during the PMSM design. In this paper, an analytical calculation method has been proposed to predict the magnetic field distribution and stator iron losses in the surface-mounted permanent magnet (SPM) synchronous machines. The method introduces the notion of complex relative air-gap permeance to take into account the effect of slotting. The imaginary part of the relative air-gap permeance is neglected to simplify the calculation of the magnetic field distribution in the slotted air gap for the surface-mounted permanent-magnet (SPM) machine. Based on the armature reaction magnetic field analysis, the stator iron losses can be estimated by the modified Steinmetz equation. The stator iron losses under load conditions are calculated according to the varying d-q-axis currents of different control methods. In order to verify the analysis method, finite element simulation results are compared with analytical calculations. The comparisons show good performance of the proposed analytical method. Full article

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

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18 pages, 1410 KiB

Open AccessFeature PaperArticle

An Economic Model-Based Predictive Control to Manage the Users’ Thermal Comfort in a Building

by Yaser Imad Alamin, María Del Mar Castilla, José Domingo Álvarez and Antonio Ruano

Energies 2017, 10(3), 321; https://doi.org/10.3390/en10030321 - 7 Mar 2017

Cited by 35 | Viewed by 4761

The goal of maintaining users’ thermal comfort conditions in indoor environments may require complex regulation procedures and a proper energy management. This problem is being widely analyzed, since it has a direct effect on users’ productivity. This paper presents an economic model-based predictive [...] Read more.

The goal of maintaining users’ thermal comfort conditions in indoor environments may require complex regulation procedures and a proper energy management. This problem is being widely analyzed, since it has a direct effect on users’ productivity. This paper presents an economic model-based predictive control (MPC) whose main strength is the use of the day-ahead price (DAP) in order to predict the energy consumption associated with the heating, ventilation and air conditioning (HVAC). In this way, the control system is able to maintain a high thermal comfort level by optimizing the use of the HVAC system and to reduce, at the same time, the energy consumption associated with it, as much as possible. Later, the performance of the proposed control system is tested through simulations with a non-linear model of a bioclimatic building room. Several simulation scenarios are considered as a test-bed. From the obtained results, it is possible to conclude that the control system has a good behavior in several situations, i.e., it can reach the users’ thermal comfort for the analyzed situations, whereas the HVAC use is adjusted through the DAP; therefore, the energy savings associated with the HVAC is increased. Full article

(This article belongs to the Special Issue Smart Home Energy Management)

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12 pages, 2282 KiB

Open AccessArticle

Study of the Effect of Clay Particles on Low Salinity Water Injection in Sandstone Reservoirs

by Sina Rezaei Gomari and Nikhil Joseph

Energies 2017, 10(3), 322; https://doi.org/10.3390/en10030322 - 7 Mar 2017

Cited by 16 | Viewed by 5036

The need for optimal recovery of crude oil from sandstone and carbonate reservoirs around the world has never been greater for the petroleum industry. Water-flooding has been applied to the supplement primary depletion process or as a separate secondary recovery method. Low salinity [...] Read more.

The need for optimal recovery of crude oil from sandstone and carbonate reservoirs around the world has never been greater for the petroleum industry. Water-flooding has been applied to the supplement primary depletion process or as a separate secondary recovery method. Low salinity water injection is a relatively new method that involves injecting low salinity brines at high pressure similar to conventional water-flooding techniques, in order to recover crude oil. The effectiveness of low salinity water injection in sandstone reservoirs depends on a number of parameters such as reservoir temperature, pressure, type of clay particle and salinity of injected brine. Clay particles present on reservoir rock surfaces adsorb polar components of oil and modify wettability of sandstone rocks to the oil-wet state, which is accountable for the reduced recovery rates by conventional water-flooding. The extent of wettability alteration caused by three low salinity brines on oil-wet sandstone samples containing varying clay content (15% or 30%) and type of clay (kaolinite/montmorillonite) were analyzed in the laboratory experiment. Contact angles of mica powder and clay mixture (kaolinite/montmorillonite) modified with crude oil were measured before and after injection with three low salinity sodium chloride brines. The effect of temperature was also analyzed for each sample. The results of the experiment indicate that samples with kaolinite clay tend to produce higher contact angles than samples with montmorillonite clay when modified with crude oil. The highest degree or extent of wettability alteration from oil-wet to intermediate-wet state upon injection with low salinity brines was observed for samples injected with brine having salinity concentration of 2000 ppm. The increase in temperature tends to produce contact angles values lying in the higher end of the intermediate-wet range (75°–115°) for samples treated at 50 °C, while their corresponding samples treated at 25 °C produced contact angle values lying in the lower end of intermediate-wet range. Full article

(This article belongs to the Special Issue Oil and Gas Engineering)

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14 pages, 6946 KiB

Open AccessArticle

A Witricity-Based High-Power Device for Wireless Charging of Electric Vehicles

by Zhongyu Dai, Junhua Wang, Mengjiao Long and Hong Huang

Energies 2017, 10(3), 323; https://doi.org/10.3390/en10030323 - 7 Mar 2017

Cited by 29 | Viewed by 7686

In this paper, a Witricity-based high-power device is proposed for wireless charging of electric vehicles. According to the specific requirements of three-stage charging for electric vehicles, four compensation modes of the Witricity system are analyzed by the Loosely Coupled Theory among transformer coils [...] Read more.

In this paper, a Witricity-based high-power device is proposed for wireless charging of electric vehicles. According to the specific requirements of three-stage charging for electric vehicles, four compensation modes of the Witricity system are analyzed by the Loosely Coupled Theory among transformer coils and the Substitution Theorem in circuit theory. In addition, when combining voltage withstand levels, the current withstand capability, the switching frequency of electronic switching tubes, and the features of the resonant circuit, the series-parallel (SP) compensation mode is selected as the best compensation mode for matching the capacitor of the system. The performances of coils with different ferrite core arrangements are compared by simulations and models. The feasibility of the system is verified theoretically and the system functions are evaluated by the joint simulation of Simplorer and Maxwell. Finally, a Witricity-based high-power device is proposed as designed, and the correctness of theoretical analyses and simulation results are verified. Full article

(This article belongs to the Special Issue Advanced Power Electronics and Control for Wireless Power Transfer Systems)

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22 pages, 7616 KiB

Open AccessArticle

Development of Decision Support Process for Building Energy Conservation Measures and Economic Analysis

by Bo-Eun Choi, Ji-Hyun Shin, Jin-Hyun Lee, Sun-Sook Kim and Young-Hum Cho

Energies 2017, 10(3), 324; https://doi.org/10.3390/en10030324 - 7 Mar 2017

Cited by 8 | Viewed by 4360

As policies for energy efficiency of buildings are being actively implemented, building energy performance improvement is urgently required. However, in Korea, information on measures and technologies for building energy efficiency is dispersed and concrete methods are not established, making it difficult to apply [...] Read more.

As policies for energy efficiency of buildings are being actively implemented, building energy performance improvement is urgently required. However, in Korea, information on measures and technologies for building energy efficiency is dispersed and concrete methods are not established, making it difficult to apply effective measures. Therefore, it is required to apply and evaluate energy efficiency measures through database construction integrating diverse information. In this study, the energy efficiency measures in the architectural sector that satisfy domestic legal standards are built. Because of the economic evaluation is necessary for the constructed alternatives, an economic efficiency database was established. The target building was set up, and energy efficiency measures were derived. In addition, a methodology that can induce energy efficient decision making of buildings was proposed, and the energy use evaluation and the economic analysis for each of the alternatives derived from applying the methodology to the target building were carried out. Furthermore, the optimal energy efficiency measures for the target building were suggested through the application of the decision-making process. Full article

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11 pages, 2256 KiB

Open AccessArticle

Effects of Biogas Substrate Recirculation on Methane Yield and Efficiency of a Liquid-Manure-Based Biogas Plant

by Frauke P. C. Müller, Gerd-Christian Maack and Wolfgang Buescher

Energies 2017, 10(3), 325; https://doi.org/10.3390/en10030325 - 8 Mar 2017

Cited by 11 | Viewed by 4355

Biogas plants are the most complex systems and are heavily studied in the field of renewable energy. A biogas system is mainly influenced by biological and technical parameters that strongly interact with each other. One recommended practice when operating a biogas plant is [...] Read more.

Biogas plants are the most complex systems and are heavily studied in the field of renewable energy. A biogas system is mainly influenced by biological and technical parameters that strongly interact with each other. One recommended practice when operating a biogas plant is the recirculation of the substrate from the second fermenter into the first fermenter, which extends the recirculation amount (RA) and, in turn, the recirculation rate (RR). This technique should be applied to support and secure the biogas process. In this investigation, the RA was varied, starting with the recommended “best practice” of 10.0 m³/d (RR 40%). Every ten days, the RA was reduced in steps of 1.5 m³/d, with 5.5 m³/d (RR 27%) being the final value. The basic question to be addressed concerns to what extent the RR influences the methane yield and thereby influence the efficiency of a manure-based biogas plant in practice. Diverting the “best practice” to a RR of 27% stabilised the fermentation process and lead to significantly higher methane yields with smaller standard deviations. In addition, with a reduced RR, the standard optimal acid concentration within the biogas substrate was approximately reached. Full article

(This article belongs to the Special Issue Energy and Waste Management)

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21 pages, 1740 KiB

Open AccessArticle

A Chance-Constrained Economic Dispatch Model in Wind-Thermal-Energy Storage System

by Yanzhe Hu, Yang Li, Mengjie Xu, Li Zhou and Mingjian Cui

Energies 2017, 10(3), 326; https://doi.org/10.3390/en10030326 - 8 Mar 2017

Cited by 21 | Viewed by 4854

As a type of renewable energy, wind energy is integrated into the power system with more and more penetration levels. It is challenging for the power system operators (PSOs) to cope with the uncertainty and variation of the wind power and its forecasts. [...] Read more.

As a type of renewable energy, wind energy is integrated into the power system with more and more penetration levels. It is challenging for the power system operators (PSOs) to cope with the uncertainty and variation of the wind power and its forecasts. A chance-constrained economic dispatch (ED) model for the wind-thermal-energy storage system (WTESS) is developed in this paper. An optimization model with the wind power and the energy storage system (ESS) is first established with the consideration of both the economic benefits of the system and less wind curtailments. The original wind power generation is processed by the ESS to obtain the final wind power output generation (FWPG). A Gaussian mixture model (GMM) distribution is adopted to characterize the probabilistic and cumulative distribution functions with an analytical expression. Then, a chance-constrained ED model integrated by the wind-energy storage system (W-ESS) is developed by considering both the overestimation costs and the underestimation costs of the system and solved by the sequential linear programming method. Numerical simulation results using the wind power data in four wind farms are performed on the developed ED model with the IEEE 30-bus system. It is verified that the developed ED model is effective to integrate the uncertain and variable wind power. The GMM distribution could accurately fit the actual distribution of the final wind power output, and the ESS could help effectively decrease the operation costs. Full article

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

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18 pages, 3261 KiB

Open AccessArticle

Biogas Engine Waste Heat Recovery Using Organic Rankine Cycle

by Alberto Benato and Alarico Macor

Energies 2017, 10(3), 327; https://doi.org/10.3390/en10030327 - 8 Mar 2017

Cited by 58 | Viewed by 14020

Italy is a leading country in the biogas sector. Energy crops and manure are converted into biogas using anaerobic digestion and, then, into electricity using internal combustion engines (ICEs). Therefore, there is an urgent need for improving the efficiency of these engines taking [...] Read more.

Italy is a leading country in the biogas sector. Energy crops and manure are converted into biogas using anaerobic digestion and, then, into electricity using internal combustion engines (ICEs). Therefore, there is an urgent need for improving the efficiency of these engines taking the real operation into account. To this purpose, in the present work, the organic Rankine cycle (ORC) technology is used to recover the waste heat contained in the exhaust gases of a 1 MW_el biogas engine. The ICE behavior being affected by the biogas characteristics, the ORC unit is designed, firstly, using the ICE nameplate data and, then, with data measured during a one-year monitoring activity. The optimum fluid and the plant configuration are selected in both cases using an “in-house” optimization tool. The optimization goal is the maximization of the net electric power while the working fluid is selected among 115 pure fluids and their mixtures. Results show that a recuperative ORC designed using real data guarantees a 30% higher net electric power than the one designed with ICE nameplate conditions. Full article

(This article belongs to the Special Issue Recent Advances in Organic Rankine Cycle Technology for Stationary Applications)

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14 pages, 3455 KiB

Open AccessArticle

Optimized Design and Feasibility of a Heating System with Energy Storage by Pebble Bed in a Solar Attic

by Hao Cheng, Xinke Wang and Min Zhou

Energies 2017, 10(3), 328; https://doi.org/10.3390/en10030328 - 8 Mar 2017

Cited by 5 | Viewed by 4209

For efficient application of solar energy, a pebble bed energy storage heating system in a solar attic is optimally designed and operated. To study the characteristics of the heating system, a numerical model for the system is presented and is validated with the [...] Read more.

For efficient application of solar energy, a pebble bed energy storage heating system in a solar attic is optimally designed and operated. To study the characteristics of the heating system, a numerical model for the system is presented and is validated with the experiment data in the literature. Based on the model, the influence of the envelopes of the solar house and the meteorological condition on the system performance is investigated. The results show that the envelopes, except those on the north face, with more glazed exterior surfaces can be beneficial to raise the temperature of the solar house. It is also found that outdoor temperature may have less impact on the energy storage in the system compared with solar radiation. Furthermore, through optimizing the system design and operation, solar energy can account for 56% of the energy requirement in the heating season in Xi’an (about 34° N, 108° E), which has an average altitude of 397.5 m and moderate solar irradiation. Also, the suitability of the system in northwest China is investigated, and the outcome demonstrates that the external comprehensive temperature should be more than 269 K if a 50% energy saving rate is expected. Full article

(This article belongs to the Special Issue The 1st “The Belt and Road Initiative” International Conference on Sustainable Refrigeration and Air Conditioning)

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12 pages, 1490 KiB

Open AccessArticle

Fundamental Analysis of Thermal Overload in Diesel Engines: Hypothesis and Validation

by Sangram Kishore Nanda, Boru Jia, Andrew Smallbone and Anthony Paul Roskilly

Energies 2017, 10(3), 329; https://doi.org/10.3390/en10030329 - 8 Mar 2017

Cited by 7 | Viewed by 4880

‘Thermal Overload’ can be defined as a condition under which design threshold values such as the surface temperature of combustion chamber components is exceeded [...] Full article

(This article belongs to the Special Issue Internal Combustion Engines 2017)

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6 pages, 1752 KiB

Open AccessLetter

Effect of Load Change on the Thevenin Equivalent Impedance of Power System

by Tiankui Sun, Zhimin Li, Shuang Rong, Jian Lu and Weixing Li

Energies 2017, 10(3), 330; https://doi.org/10.3390/en10030330 - 8 Mar 2017

Cited by 7 | Viewed by 3353

This paper discusses the effect of load change on the Thevenin equivalent impedance of power systems. In this paper, the Thevenin equivalent impedance influenced by the derivative of active load with respect to reactive load (dP dQ) is analyzed. The Thevenin equivalent impedance [...] Read more.

This paper discusses the effect of load change on the Thevenin equivalent impedance of power systems. In this paper, the Thevenin equivalent impedance influenced by the derivative of active load with respect to reactive load (dP dQ) is analyzed. The Thevenin equivalent impedance forms a closed curve in a complex plane and shrinks to one point when voltage collapses. The magnitude of the Thevenin equivalent impedance at the collapse point is equal to the magnitude of the load impedance. Therefore, the impedance match theory still holds under the effect of the load change. These features are verified on a New England 39-bus system. Full article

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18 pages, 2005 KiB

Open AccessArticle

Signal-Based Gas Leakage Detection for Fluid Power Accumulators in Wind Turbines

by Jesper Liniger, Nariman Sepehri, Mohsen Soltani and Henrik C. Pedersen

Energies 2017, 10(3), 331; https://doi.org/10.3390/en10030331 - 8 Mar 2017

Cited by 12 | Viewed by 4910

This paper describes the development and application of a signal-based fault detection method for identifying gas leakage in hydraulic accumulators used in wind turbines [...] Full article

(This article belongs to the Special Issue Wind Turbine 2017)

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13 pages, 4750 KiB

Open AccessArticle

Study the Flow behind a Semi-Circular Step Cylinder (Laser Doppler Velocimetry (LDV) and Computational Fluid Dynamics (CFD))

by S. M. Sayeed-Bin-Asad, Tord Staffan Lundström and Anders Gustav Andersson

Energies 2017, 10(3), 332; https://doi.org/10.3390/en10030332 - 9 Mar 2017

Cited by 11 | Viewed by 6840

Laser Doppler Velocimetry (LDV) measurements, flow visualizations and unsteady Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) simulations have been carried out to study the turbulent wake that is formed behind a semi-circular step cylinder at a constant flow rate. The semi-circular cylinder has [...] Read more.

Laser Doppler Velocimetry (LDV) measurements, flow visualizations and unsteady Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) simulations have been carried out to study the turbulent wake that is formed behind a semi-circular step cylinder at a constant flow rate. The semi-circular cylinder has two diameters, a so-called step cylinder. The results from the LDV measurements indicate that wake length and vortex shedding frequency varies with the cylinder diameter. This implies that a step cylinder can be used to attract fish of different size. By visualizations of the formation of a recirculation region and the well-known von Kármán vortex street behind the cylinder are disclosed. The simulation results predict the wake length and shedding frequency well for the flow behind the large cylinder but fail to capture the dynamics of the flow near the step in diameter to some extent and the flow behind the small cylinder to a larger extent when compared with measurements. Full article

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

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14 pages, 3314 KiB

Open AccessArticle

Improved Electrogeometric Model Suitable for EHV and UHV Transmission Lines Developed through Breakdown Testing for Long Air Gaps

by Yeqiang Deng, Yu Wang, Zhijun Li, Min Dai, Xishan Wen, Lei Lan, Yunzhu An and Shenglong E

Energies 2017, 10(3), 333; https://doi.org/10.3390/en10030333 - 9 Mar 2017

Cited by 5 | Viewed by 6299

As a type of engineering model used for solving lightning-shielding problems, the electrogeometric model has been widely used for assessing lightning-shielding failure in high-voltage and extra-high-voltage transmission lines. However, with the increase of voltage levels in ultra-high-voltage lines and the growth of the [...] Read more.

As a type of engineering model used for solving lightning-shielding problems, the electrogeometric model has been widely used for assessing lightning-shielding failure in high-voltage and extra-high-voltage transmission lines. However, with the increase of voltage levels in ultra-high-voltage lines and the growth of the air gap, the results previously yielded by the electrogeometric model are no longer consistent with those observed. Therefore, this study corrected the equation for the relationship between lightning current and striking distance, by using data on a negative polarity 50% discharge voltage from the rod-rod gap −20/2500 μs switching impulse test wherein an air gap of up to 10 m was first tested. Subsequently, the return stroke velocity distribution observed by Idone was newly applied. In addition, the correction factor for the ground was corrected in this study. Thus, an improved electrogeometric model for application in EHV and UHV transmission lines is proposed in this paper. By employing the improved electrogeometric model to calculate the frequency of lightning strikes of 500 and 1000 kV transmission lines in Japan and a 1000 kV transmission line in China, we found that the results calculated using the improved electrogeometric model were closer to the actual observations in Japan than was the original electrogeometric model. The improved electrogeometric model provides a more reliable foundation for lightning-shielding design of extra-high-voltage and ultra-high-voltage transmission lines. Full article

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15 pages, 7939 KiB

Open AccessArticle

Flame Structure and Chemiluminescence Emissions of Inverse Diffusion Flames under Sinusoidally Driven Plasma Discharges

by Maria Grazia De Giorgi, Aldebara Sciolti, Stefano Campilongo and Antonio Ficarella

Energies 2017, 10(3), 334; https://doi.org/10.3390/en10030334 - 9 Mar 2017

Cited by 20 | Viewed by 7057

Reduction of nitric oxides (NOx) in aircraft engines and in gas turbines by lean combustion is of great interest in the design of novel combustion systems. However, the stabilization of the flame under lean conditions is a main issue. In this context, the [...] Read more.

Reduction of nitric oxides (NOx) in aircraft engines and in gas turbines by lean combustion is of great interest in the design of novel combustion systems. However, the stabilization of the flame under lean conditions is a main issue. In this context, the present work investigates the effects of sinusoidal dielectric barrier discharge (DBD) on a lean inverse diffusive methane/air flame in a Bunsen-type burner under different actuation conditions. The flame appearance was investigated with fixed methane loading (mass flux), but with varying inner airflow rate. High-speed flame imaging was done by using an intensified (charge-coupled device) CCD camera equipped with different optical filters in order to selectively record signals from the chemiluminescent species OH*, CH*, or CO2* to evaluate the flame behavior in presence of plasma actuation. The electrical power consumption was less than 33 W. It was evident that the plasma flame enhancement was significantly influenced by the plasma discharges, particularly at high inner airflow rates. The flame structure changes drastically when the dissipated plasma power increases. The flame area decreases due to the enhancement of mixing and chemical reactions that lead to a more anchored flame on the quartz exit with a reduction of the flame length. Full article

(This article belongs to the Special Issue Combustion and Propulsion)

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25 pages, 1248 KiB

Open AccessArticle

Orchestrating an Effective Formulation to Investigate the Impact of EMSs (Energy Management Systems) for Residential Units Prior to Installation

by Danish Mahmood, Nadeem Javaid, Sheraz Ahmed, Imran Ahmed, Iftikhar Azim Niaz, Wadood Abdul and Sanaa Ghouzali

Energies 2017, 10(3), 335; https://doi.org/10.3390/en10030335 - 9 Mar 2017

Cited by 6 | Viewed by 4164

Demand Response (DR) programs under the umbrella of Demand Side Management (DSM) tend to involve end users in optimizing their Power Consumption (PC) patterns and offer ﬁnancial incentives to shift the load at “low-priced” hours. However, users have their own preferences of anticipating [...] Read more.

Demand Response (DR) programs under the umbrella of Demand Side Management (DSM) tend to involve end users in optimizing their Power Consumption (PC) patterns and offer ﬁnancial incentives to shift the load at “low-priced” hours. However, users have their own preferences of anticipating the amount of consumed electricity. While installing an Energy Management System (EMS), the user must be assured that this investment gives optimum comfort of bill savings, as well as appliance utility considering Time of Use (ToU). Moreover, there is a difference between desired load distribution and optimally-scheduled load across a 24-h time frame for lowering electricity bills. This difference in load usage timings, if it is beyond the tolerance level of a user, increases frustration. The comfort level is a highly variable phenomenon. An EMS giving optimum comfort to one user may not be able to provide the same level of satisfaction to another who has different preferences regarding electricity bill savings or appliance utility. Under such a diversity of human behaviors, it is difﬁcult to select an EMS for an individual user. In this work, a numeric performance metric,“User Comfort Level (UCL)”isformulatedonthebasisofuserpreferencesoncostsaving,toleranceindelayregardinguse of an appliance and return of investment. The proposed framework (UCL) allows the user to select an EMS optimally that suits his.her preferences well by anticipating electricity bill reduction, tolerable delay in ToU of the appliance and return on investment. Furthermore, an extended literature analysis is conducted demonstrating generic strategies of EMSs. Five major building blocks are discussed and a comparative analysis is presented on the basis of the proposed performance metric. Full article

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19 pages, 4553 KiB

Open AccessArticle

An Improved LCL Filter Design in Order to Ensure Stability without Damping and Despite Large Grid Impedance Variations

by Marwa Ben Said-Romdhane, Mohamed Wissem Naouar, Ilhem Slama Belkhodja and Eric Monmasson

Energies 2017, 10(3), 336; https://doi.org/10.3390/en10030336 - 9 Mar 2017

Cited by 81 | Viewed by 10803

With the smart grid revolution, there is a growing interest in the use of power converters associated to LCL filters to interface between the main utility grid and loads or renewable energy sources. LCL filters are commonly used mainly due to their low [...] Read more.

With the smart grid revolution, there is a growing interest in the use of power converters associated to LCL filters to interface between the main utility grid and loads or renewable energy sources. LCL filters are commonly used mainly due to their low cost and high filtering performances. To achieve these performances, it is necessary to meticulously pick out the LCL filter parameters, taking into account grid code requirements and grid configuration and/or conditions. Several methodologies for LCL filter design have been presented and discussed in the literature. The main goal of this paper is to propose a simple, robust and systematic design methodology for LCL filter parameter tuning. The considered design methodology is aimed to overcome the shortcomings of classical design methodologies, namely, stable operation under different grid configurations and conditions. Compared to previous works, the proposed design methodology allows the achievement of robust LCL filter design with regard to large grid impedance variations without the use of any damping method. Also, it takes into account accuracy of capacitor standard values and proposes a simple design method for the converter side inductor that avoids saturation problems. An example of LCL filter design is presented and discussed. The obtained filter parameters were firstly tested using a Matlab-Simulink software tool. After that, they were tested through the development of an experimental set-up. The obtained simulation and experimental results show the reliability and efficiency of the proposed design methodology. Full article

(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)

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8 pages, 37005 KiB

Open AccessArticle

Development of a Vibration-Based Electromagnetic Energy Harvester by a Conductive Direct-Write Process

by Yao-Yun Feng, Shih-Jui Chen and You-Lin Tu

Energies 2017, 10(3), 337; https://doi.org/10.3390/en10030337 - 9 Mar 2017

Cited by 7 | Viewed by 4438

A conductive direct-write process of multilayered coils for micro electromagnetic generators is proposed. This novel approach of using silver ink to form the conductive structures largely reduces the fabrication complexity, and it provides a faster alternative to the conventional semiconductor methods. Multi-layered coils [...] Read more.

A conductive direct-write process of multilayered coils for micro electromagnetic generators is proposed. This novel approach of using silver ink to form the conductive structures largely reduces the fabrication complexity, and it provides a faster alternative to the conventional semiconductor methods. Multi-layered coils with insulation were accurately layered on a micromachined cantilevered diaphragm by a dispenser. Coils several layers thick could be used to increase the power output and double coils were separated by a layer of insulation. Six prototypes, all capable of efficient conversion of vibrational energy into electrical energy, were fabricated. The experimental results, which include measurements of the electromotive force and power output, are presented. Prototypes with two coils and thicker conducting layers had less resistance and the power output was much more than that of a single-coil unit. This generator can produce 82 nW of power at a resonance frequency of 275 Hz under 5 g excitation. Full article

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

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16 pages, 6644 KiB

Open AccessArticle

Numerical Study on the Effect of Lambda Value (Oxygen/Fuel Ratio) on Temperature Distribution and Efficiency of a Flameless Oxyfuel Combustion System

by Mersedeh Ghadamgahi, Patrik Ölund, Nils Å. I. Andersson and Pär Jönsson

Energies 2017, 10(3), 338; https://doi.org/10.3390/en10030338 - 9 Mar 2017

Cited by 3 | Viewed by 4155

The flameless oxyfuel combustion technology has been proven to be a promising new method to reduce the fuel consumption and pollutants in industrial applications [...] Full article

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23 pages, 1735 KiB

Open AccessArticle

Optimal Scheduling of Microgrid with Multiple Distributed Resources Using Interval Optimization

by Chongxin Huang, Dong Yue, Song Deng and Jun Xie

Energies 2017, 10(3), 339; https://doi.org/10.3390/en10030339 - 9 Mar 2017

Cited by 31 | Viewed by 5699

In this paper, an optimal day-ahead scheduling problem is studied for a microgrid with multiple distributed resources. For the sake of coping with the prediction uncertainties of renewable energies and loads and taking advantage of the time-of-use price for buying/selling electricity, an interval-based [...] Read more.

In this paper, an optimal day-ahead scheduling problem is studied for a microgrid with multiple distributed resources. For the sake of coping with the prediction uncertainties of renewable energies and loads and taking advantage of the time-of-use price for buying/selling electricity, an interval-based optimization model for maximum proﬁts is developed. To reduce the computational complexity in solving the model, the possibility degree comparison between an interval and a real number is used to convert the interval constraints into the general ones; meanwhile, some slack variables and complementary conditions are introduced to eliminate the absolute-value operation. Unlike the stochastic optimization, the interval optimization only needs the upper-lower bounds of the uncertain variables instead of their probability distribution functions, which is beneﬁcial to the practical application. Furthermore, the possible proﬁt interval and the expected optimal proﬁt can be determined by solving the optimization model. Numerical simulations are performed on a microgrid system modiﬁed from the benchmark low voltage network in the European Union project “Microgrid”, and the results demonstrate the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Smart Microgrids: Developing the Intelligent Power Grid of Tomorrow)

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14 pages, 4346 KiB

Open AccessArticle

A New Method of Ground Fault Location in 2 × 25 kV Railway Power Supply Systems

by Jesús Serrano, Carlos A. Platero, Máximo López-Toledo and Ricardo Granizo

Energies 2017, 10(3), 340; https://doi.org/10.3390/en10030340 - 10 Mar 2017

Cited by 11 | Viewed by 5528

Owing to the installation of autotransformers at regular intervals along the line, distance protection relays cannot be used with the aim of locating ground faults in 2 × 25 kV railway power supply systems. The reason is that the ratio between impedance and [...] Read more.

Owing to the installation of autotransformers at regular intervals along the line, distance protection relays cannot be used with the aim of locating ground faults in 2 × 25 kV railway power supply systems. The reason is that the ratio between impedance and distance to the fault point is not linear in these electrification systems, unlike in 1 × 25 kV power systems. Therefore, the location of ground faults represents a complicated task in 2 × 25 kV railway power supply systems. Various methods have been used to localize the ground fault position in 2 × 25 kV systems. The method described here allows the location of a ground fault to be economically found in an accurate way in real time, using the modules of the circulating currents in different autotransformers when the ground fault occurs. This method first needs to know the subsection and the conductor (catenary or feeder) with the defect, then localizes the ground fault’s position. Full article

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30 pages, 7760 KiB

Open AccessFeature PaperReview

High Performance Silicon Carbide Power Packaging—Past Trends, Present Practices, and Future Directions

by Sayan Seal and Homer Alan Mantooth

Energies 2017, 10(3), 341; https://doi.org/10.3390/en10030341 - 10 Mar 2017

Cited by 83 | Viewed by 15867

This paper presents a vision for the future of 3D packaging and integration of silicon carbide (SiC) power modules. Several major achievements and novel architectures in SiC modules from the past and present have been highlighted. Having considered these advancements, the major technology [...] Read more.

This paper presents a vision for the future of 3D packaging and integration of silicon carbide (SiC) power modules. Several major achievements and novel architectures in SiC modules from the past and present have been highlighted. Having considered these advancements, the major technology barriers preventing SiC power devices from performing to their fullest ability were identified. 3D wire bondless approaches adopted for enhancing the performance of silicon power modules were surveyed, and their merits were assessed to serve as a vision for the future of SiC power packaging. Current efforts pursuing 3D wire bondless SiC power modules were described, and the concept for a novel SiC power module was discussed. Full article

(This article belongs to the Special Issue Semiconductor Power Devices)

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16 pages, 22663 KiB

Open AccessArticle

Numerical Investigation of Periodic Fluctuations in Energy Efficiency in Centrifugal Pumps at Different Working Points

by Hehui Zhang, Shengxiang Deng and Yingjie Qu

Energies 2017, 10(3), 342; https://doi.org/10.3390/en10030342 - 10 Mar 2017

Cited by 10 | Viewed by 5523

In order to simulate the energy efficiency fluctuation behavior of an industrial centrifugal pump with a six-blade impeller, a full-scale three-dimensional (3D) an unsteady state computational fluid dynamics (CFD) model was used. Five operational points with different flow fluxes were numerically investigated by [...] Read more.

In order to simulate the energy efficiency fluctuation behavior of an industrial centrifugal pump with a six-blade impeller, a full-scale three-dimensional (3D) an unsteady state computational fluid dynamics (CFD) model was used. Five operational points with different flow fluxes were numerically investigated by using the Navier–Stokes code with shear-stress transport (SST) k-ω turbulence model. The predicted performance curves agreed well with the test data. A sine function was fitted to the transient calculation results and the results show that the efficiency fluctuates mainly on the blade passing frequency, while the fluctuation level varies with flow rate. Furthermore, high efficiency is not necessarily associated with low fluctuation level. The efficiency fluctuation level is high at part-load points, and becomes relatively low when flow rate exceeds the design value. The effect of change in torque is greater than that of the head lift with respect to fluctuations of efficiency. Based upon the analysis of velocity vector distribution of different impeller phase positions, a hypothesis which considers both the effect of pump’s structural shape and flow fluxes was proposed to explain the above behavior by analyzing the impeller–tongue interaction. This work enriches the theoretical system of flow parameters fluctuation of centrifugal pump, and provides useful insight for the optimal design of centrifugal pumps. Full article

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

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13 pages, 844 KiB

Open AccessArticle

Reliability Assessment of Power Generation Systems Using Intelligent Search Based on Disparity Theory

by Athraa Ali Kadhem, Noor Izzri Abdul Wahab, Ishak Aris, Jasronita Jasni and Ahmed N. Abdalla

Energies 2017, 10(3), 343; https://doi.org/10.3390/en10030343 - 10 Mar 2017

Cited by 17 | Viewed by 4000

The reliability of the generating system adequacy is evaluated based on the ability of the system to satisfy the load demand. In this paper, a novel optimization technique named the disparity evolution genetic algorithm (DEGA) is proposed for reliability assessment of power generation. [...] Read more.

The reliability of the generating system adequacy is evaluated based on the ability of the system to satisfy the load demand. In this paper, a novel optimization technique named the disparity evolution genetic algorithm (DEGA) is proposed for reliability assessment of power generation. Disparity evolution is used to enhance the performance of the probability of mutation in a genetic algorithm (GA) by incorporating features from the paradigm into the disparity theory. The DEGA is based on metaheuristic searching for the truncated sampling of state-space for the reliability assessment of power generation system adequacy. Two reliability test systems (IEEE-RTS-79 and (IEEE-RTS-96) are used to demonstrate the effectiveness of the proposed algorithm. The simulation result shows the DEGA can generate a larger variety of the individuals in an early stage of the next population generation. It is also able to estimate the reliability indices accurately. Full article

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17 pages, 7292 KiB

Open AccessArticle

Consideration of Reactor Installation to Mitigate Voltage Rise Caused by the Connection of a Renewable Energy Generator

by Yeonho Ok, Jaewon Lee and Jaeho Choi

Energies 2017, 10(3), 344; https://doi.org/10.3390/en10030344 - 10 Mar 2017

Cited by 1 | Viewed by 3839

This paper describes the detailed analysis of a reactor application for a power plant to mitigate the voltage rise of a distribution line (DL) caused by the connection of distributed resources (DRs). The maximum capacity of renewable energy generators (REGs) that meets the [...] Read more.

This paper describes the detailed analysis of a reactor application for a power plant to mitigate the voltage rise of a distribution line (DL) caused by the connection of distributed resources (DRs). The maximum capacity of renewable energy generators (REGs) that meets the acceptable voltage rise of a DL and the necessary capacity of the reactor to mitigate that voltage rise according to the different types of REGs are analyzed. The re-coordination of a protection relay and the loss of generation revenue as well as the installation location of a reactor are described. Finally, the ON/OFF conditions of the reactor, such as the magnitudes of the grid voltage and generator voltage, and the duration time of the voltage rise are analyzed. As the voltage rise is mitigated and self-limited in small power plants, it is confirmed that the capacity of the DRs connected to the DL can be increased through a field demonstration. Full article

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

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33 pages, 7189 KiB

Open AccessReview

Application of Nanoparticles in Enhanced Oil Recovery: A Critical Review of Recent Progress

by Xiaofei Sun, Yanyu Zhang, Guangpeng Chen and Zhiyong Gai

Energies 2017, 10(3), 345; https://doi.org/10.3390/en10030345 - 11 Mar 2017

Cited by 512 | Viewed by 31267

The injected fluids in secondary processes supplement the natural energy present in the reservoir to displace oil. The recovery efficiency mainly depends on the mechanism of pressure maintenance. However, the injected fluids in tertiary or enhanced oil recovery (EOR) processes interact with the [...] Read more.

The injected fluids in secondary processes supplement the natural energy present in the reservoir to displace oil. The recovery efficiency mainly depends on the mechanism of pressure maintenance. However, the injected fluids in tertiary or enhanced oil recovery (EOR) processes interact with the reservoir rock/oil system. Thus, EOR techniques are receiving substantial attention worldwide as the available oil resources are declining. However, some challenges, such as low sweep efficiency, high costs and potential formation damage, still hinder the further application of these EOR technologies. Current studies on nanoparticles are seen as potential solutions to most of the challenges associated with these traditional EOR techniques. This paper provides an overview of the latest studies about the use of nanoparticles to enhance oil recovery and paves the way for researchers who are interested in the integration of these progresses. The first part of this paper addresses studies about the major EOR mechanisms of nanoparticles used in the forms of nanofluids, nanoemulsions and nanocatalysts, including disjoining pressure, viscosity increase of injection fluids, preventing asphaltene precipitation, wettability alteration and interfacial tension reduction. This part is followed by a review of the most important research regarding various novel nano-assisted EOR methods where nanoparticles are used to target various existing thermal, chemical and gas methods. Finally, this review identifies the challenges and opportunities for future study regarding application of nanoparticles in EOR processes. Full article

(This article belongs to the Special Issue Nanotechnology for Oil and Gas Applications)

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19 pages, 12209 KiB

Open AccessArticle

Comprehensive Analysis of LCL Filter Interfaced Cascaded H-Bridge Multilevel Inverter-Based DSTATCOM

by Ravikant Pandey, Ravi Nath Tripathi and Tsuyoshi Hanamoto

Energies 2017, 10(3), 346; https://doi.org/10.3390/en10030346 - 12 Mar 2017

Cited by 16 | Viewed by 6826

Three-phase two-level voltage source converters are used for distribution static compensator (DSTATCOM) applications and can be replaced by a multilevel inverter. In this paper, an LCL filter interfaced cascaded H-bridge multilevel inverter-based (CHBMLI) DSTATCOM is simulated and its performance is analyzed considering the [...] Read more.

Three-phase two-level voltage source converters are used for distribution static compensator (DSTATCOM) applications and can be replaced by a multilevel inverter. In this paper, an LCL filter interfaced cascaded H-bridge multilevel inverter-based (CHBMLI) DSTATCOM is simulated and its performance is analyzed considering the system parameters. The analysis considers factors including the switching frequency, modulation index, and filter parameters of a DSTATCOM system. The LCL filter design and analysis for the low switching frequency operation of CHBMLI is proposed in this paper. Phase shift pulse-width modulation is used for the generation of switching signals. The reference current is generated using synchronous reference frame theory (SRFT) for reactive power and harmonic compensations. The simulation model of the CHBMLI-based DSTATCOM system is developed in MATLAB Simulink. The results are demonstrated for a linear/non-linear load under unbalanced conditions, considering the voltage sag and swell in the system due to a disturbance in the load. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2017)

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20 pages, 12570 KiB

Open AccessArticle

Why Electricity Demand Is Highly Income-Elastic in Spain: A Cross-Country Comparison Based on an Index-Decomposition Analysis

by Julián Pérez-García and Julián Moral-Carcedo

Energies 2017, 10(3), 347; https://doi.org/10.3390/en10030347 - 11 Mar 2017

Cited by 5 | Viewed by 5449

Since 1990, Spain has had one of the highest elasticities of electricity demand in the European Union. We provide an in-depth analysis into the causes of this high elasticity, and we examine how these same causes influence electricity demand in other European countries. [...] Read more.

Since 1990, Spain has had one of the highest elasticities of electricity demand in the European Union. We provide an in-depth analysis into the causes of this high elasticity, and we examine how these same causes influence electricity demand in other European countries. To this end, we present an index-decomposition analysis of growth in electricity demand which allows us to identify three key factors in the relationship between gross domestic product (GDP) and electricity demand: (i) structural change; (ii) GDP growth; and (iii) intensity of electricity use. Our findings show that the main differences in electricity demand elasticities across countries and time are accounted for by the fast convergence in residential per capita electricity consumption. This convergence has almost concluded, and we expect the Spanish energy demand elasticity to converge to European standards in the near future. Full article

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18 pages, 1388 KiB

Open AccessArticle

Detoxification of a Lignocellulosic Waste from a Pulp Mill to Enhance Its Fermentation Prospects

by Tamara Llano, Natalia Quijorna and Alberto Coz

Energies 2017, 10(3), 348; https://doi.org/10.3390/en10030348 - 11 Mar 2017

Cited by 28 | Viewed by 5083

Detoxification is required for sugar bioconversion and hydrolyzate valorization within the biorefining concept for biofuel or bio-product production. In this work, the spent sulfite liquor, which is the main residue provided from a pulp mill, has been detoxified. Evaporation, overliming, ionic exchange resins, [...] Read more.

Detoxification is required for sugar bioconversion and hydrolyzate valorization within the biorefining concept for biofuel or bio-product production. In this work, the spent sulfite liquor, which is the main residue provided from a pulp mill, has been detoxified. Evaporation, overliming, ionic exchange resins, and adsorption with activated carbon or black carbon were considered to separate the sugars from the inhibitors in the lignocellulosic residue. Effectiveness in terms of total and individual inhibitor removals, sugar losses and sugar-to-inhibitor removal ratio was determined. The best results were found using the cation exchange Dowex 50WX2 resin in series with the anion exchange Amberlite IRA-96 resin, which resulted in sugar losses of 24.2% with inhibitor removal of 71.3% of lignosulfonates, 84.8% of phenolics, 82.2% acetic acid, and 100% of furfurals. Apart from exchange resins, the results of evaporation, overliming, adsorption with activated carbon and adsorption with black carbon led to total inhibitor removals of 8.6%, 44.9%, 33.6% and 47.6%, respectively. Finally, some fermentation scenarios were proposed in order to evaluate the most suitable technique or combination of techniques that should be implemented in every case. Full article

(This article belongs to the Special Issue Thermo-Chemical Conversion of Waste Biomass)

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12 pages, 5806 KiB

Open AccessArticle

Effects of Syngas Cooling and Biomass Filter Medium on Tar Removal

by Sunil Thapa, Prakashbhai R. Bhoi, Ajay Kumar and Raymond L. Huhnke

Energies 2017, 10(3), 349; https://doi.org/10.3390/en10030349 - 11 Mar 2017

Cited by 53 | Viewed by 9048

Biomass gasification is a proven technology; however, one of the major obstacles in using product syngas for electric power generation and biofuels is the removal of tar. The purpose of this research was to develop and evaluate effectiveness of tar removal methods by [...] Read more.

Biomass gasification is a proven technology; however, one of the major obstacles in using product syngas for electric power generation and biofuels is the removal of tar. The purpose of this research was to develop and evaluate effectiveness of tar removal methods by cooling the syngas and using wood shavings as filtering media. The performance of the wood shavings filter equipped with an oil bubbler and heat exchanger as cooling systems was tested using tar-laden syngas generated from a 20-kW downdraft gasifier. The tar reduction efficiencies of wood shavings filter, wood shavings filter with heat exchanger, and wood shavings filter with oil bubbler were 10%, 61%, and 97%, respectively. Full article

(This article belongs to the Special Issue Woody Biomass for Bioenergy Production)

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18 pages, 1258 KiB

Open AccessArticle

Review of the Life Cycle Greenhouse Gas Emissions from Different Photovoltaic and Concentrating Solar Power Electricity Generation Systems

by Raghava Kommalapati, Akhil Kadiyala, Md. Tarkik Shahriar and Ziaul Huque

Energies 2017, 10(3), 350; https://doi.org/10.3390/en10030350 - 11 Mar 2017

Cited by 70 | Viewed by 9451

This paper contains an extensive review of life cycle assessment (LCA) studies on greenhouse gas emissions (GHG) from different material-based photovoltaic (PV) and working mechanism-based concentrating solar power (CSP) electricity generation systems. Statistical evaluation of the life cycle GHG emissions is conducted to [...] Read more.

This paper contains an extensive review of life cycle assessment (LCA) studies on greenhouse gas emissions (GHG) from different material-based photovoltaic (PV) and working mechanism-based concentrating solar power (CSP) electricity generation systems. Statistical evaluation of the life cycle GHG emissions is conducted to assess the role of different PVs and CSPs in reducing GHG emissions. The widely-used parabolic trough and central receiver CSP electricity generation systems emitted approximately 50% more GHGs than the paraboloidal dish, solar chimney, and solar pond CSP electricity generation systems. The cadmium telluride PVs and solar pond CSPs contributed to minimum life cycle GHGs. Thin-film PVs are also suitable for wider implementation, due to their lower Energy Pay-Back Time (EPBT) periods, in addition to lower GHG emission, in comparison with c-Si PVs. Full article

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18 pages, 8132 KiB

Open AccessArticle

Tomographic Environmental Sections for Environmental Mitigation Devices in Historical Centers

by Roberta Cocci Grifoni, Maria Federica Ottone and Enrico Prenna

Energies 2017, 10(3), 351; https://doi.org/10.3390/en10030351 - 11 Mar 2017

Cited by 5 | Viewed by 4144

Urban heat waves and the overall growing trend in the annual global temperature underline the importance of urban/architectural resilience and the need to reduce energy consumption. By designing urban voids, it is possible to create thermodynamic buffers, i.e., bubbles of controlled atmosphere that [...] Read more.

Urban heat waves and the overall growing trend in the annual global temperature underline the importance of urban/architectural resilience and the need to reduce energy consumption. By designing urban voids, it is possible to create thermodynamic buffers, i.e., bubbles of controlled atmosphere that act as mediators between the natural and built environments, between the human body and the surrounding air, between meteorology and physiology (meteorological architecture). Multiple small actions in the urban fabric’s open spaces, such as replacing dark pavements or inserting vegetation and green spaces, are intended to improve outdoor comfort conditions and therefore the resilience of the city itself. This not only benefits the place’s quality, which is intrinsic to the new project, but also the insulating capacity of buildings, which are relieved of an external heat load. The design emphasis therefore changes from solid structures to the climate and weather conditions, which are invisible but perceivable. To design and control these constructed atmopheres, tomographic sections processed with computational fluid dynamics software (tomographic environmental section, TENS) becomes necessary. It allows the effects of an extreme event on an outdoor environment to be evaluated in order to establish the appropriate (adaptive) climate mitigation devices, especially in historical centers where energy retrofits are often discouraged. By fixing boundary conditions after a local intervention, the virtual environment can be simulated and then "sliced" to analyze initial values and verify the design improvements. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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15 pages, 5925 KiB

Open AccessArticle

Pollutant Formation during the Occurrence of Flame Instabilities under Very-Lean Combustion Conditions in a Liquid-Fuel Burner

by Maria Grazia De Giorgi, Stefano Campilongo, Antonio Ficarella, Gianluigi De Falco, Mario Commodo and Andrea D’Anna

Energies 2017, 10(3), 352; https://doi.org/10.3390/en10030352 - 12 Mar 2017

Cited by 19 | Viewed by 5636

Recent advances in gas turbine combustor design are aimed at achieving low exhaust emissions, hence modern aircraft jet engines are designed with lean-burn combustion systems. In the present work, we report an experimental study on lean combustion in a liquid fuel burner, operated [...] Read more.

Recent advances in gas turbine combustor design are aimed at achieving low exhaust emissions, hence modern aircraft jet engines are designed with lean-burn combustion systems. In the present work, we report an experimental study on lean combustion in a liquid fuel burner, operated under a non-premixed (single point injection) regime that mimics the combustion in a modern aircraft engine. The flame behavior was investigated in proximity of the blow-out limit by an intensified high rate Charge-Coupled Device (CCD) camera equipped with different optical filters to selectively record single species chemiluminescence emissions (e.g., OH*, CH*). Analogous filters were also used in combination with photomultiplier (PMT) tubes. Furthermore this work investigates well-mixed lean low NO_x combustion where mixing is good and generation of solid carbon particulate emissions should be very low. An analysis of pollutants such as fine particles and gaseous emissions was also performed. Particle number concentrations and size distributions were measured at the exhaust of the combustion chamber by two different particle size measuring instruments: a scanning mobility particle sizer (SMPS) and an Electrical Low Pressure Impactor (ELPI). NO_x concentration measurements were performed by using a cross-flow modulation chemiluminescence detection system; CO concentration emissions were acquired with a Cross-flow modulation Non-dispersive infrared (NDIR) absorption method. All the measurements were completed by diagnostics of the fundamental combustor parameters. The results herein presented show that at very-lean conditions the emissions of both particulate matter and CO was found to increase most likely due to the occurrence of flame instabilities while the NO_x were observed to reduce. Full article

(This article belongs to the Special Issue Combustion and Propulsion)

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12 pages, 16582 KiB

Open AccessArticle

Analysis of the Vacuum Arc Interruption Process in Aviation Intermediate-Frequency Power Supply Systems

by Yuan Jiang, Jianwen Wu, Mingxuan Chen and Wenlei Huo

Energies 2017, 10(3), 353; https://doi.org/10.3390/en10030353 - 13 Mar 2017

Cited by 6 | Viewed by 4462

In this paper, we present our research into the interruption performance of vacuum circuit breakers in aviation intermediate-frequency (360 Hz to 800 Hz) power supply systems. Intermediate-frequency vacuum arc experiments were carried out in interrupters with a diameter of 41 mm and CuCr50 [...] Read more.

In this paper, we present our research into the interruption performance of vacuum circuit breakers in aviation intermediate-frequency (360 Hz to 800 Hz) power supply systems. Intermediate-frequency vacuum arc experiments were carried out in interrupters with a diameter of 41 mm and CuCr50 alloy contact material. The results show that, as the frequency and peak value of the current increase, both the peak value and rise rate of the intermediate-frequency vacuum arc voltage also increase, and the interruption ability decreases. However, compared to the power frequency current at the same value, the erosion of the contacts is weaker over a shorter arc period. When the vacuum arc reignites, metal droplets are emitted from the contacts. The drive force is from the center of the contact to the edge. If the density of the plasmas and metal vapors and the number of the metal droplets reaches a certain level, the arc may break down, which will cause the interruption to fail. Full article

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15 pages, 7310 KiB

Open AccessArticle

Thermal and Stability Investigation of Phase Change Material Dispersions for Thermal Energy Storage by T-History and Optical Methods

by Maria Gabriela De Paola, Natale Arcuri, Vincenza Calabrò and Marilena De Simone

Energies 2017, 10(3), 354; https://doi.org/10.3390/en10030354 - 13 Mar 2017

Cited by 22 | Viewed by 6598

Glauber’s salt (sodium sulphate decahydrate) is a promising phase change material (PCM) for use in the building sector, thanks to its high enthalpy of fusion associated with a proper phase transition temperature. It also offers economic and environmental advantages because it can be [...] Read more.

Glauber’s salt (sodium sulphate decahydrate) is a promising phase change material (PCM) for use in the building sector, thanks to its high enthalpy of fusion associated with a proper phase transition temperature. It also offers economic and environmental advantages because it can be obtained as a byproduct from the disposal process of lead batteries. However, due to phenomena of phase segregation and supercooling, Glauber’s salt cannot be used in its pure state and requires the addition of rheological modifiers and nucleating agents. In this work, the initial thermal performances of mixtures based on Glauber’s salt with different compositions are compared by using the T-history method and adopting sonication for mixing, and following the same preparation procedure for all the samples. With fixed composition, the effects of the addition sequence of the reagents are also examined. The analysis carried out by optical methods based on light scattering (Turbiscan equipment) allowed us to identify the kinetics of destabilization for each sample and revealed the need to specify in detail the preparation stages of PCMs, in order to make the composition reproducible in the laboratory and on a wider scale. Full article

(This article belongs to the Special Issue 16th CIRIAF National Congress – Sustainable Development, Environment and Human Health Protection)

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17 pages, 20810 KiB

Open AccessArticle

Thermal Analysis of the Driving Component Based on the Thermal Network Method in a Lunar Drilling System and Experimental Verification

by Dewei Tang, Hong Xiao, Fanrui Kong, Zongquan Deng, Shengyuan Jiang and Qiquan Quan

Energies 2017, 10(3), 355; https://doi.org/10.3390/en10030355 - 13 Mar 2017

Cited by 5 | Viewed by 4220

The main task of the third Chinese lunar exploration project is to obtain soil samples that are greater than two meters in length and to acquire bedding information from the surface of the moon. The driving component is the power output unit of [...] Read more.

The main task of the third Chinese lunar exploration project is to obtain soil samples that are greater than two meters in length and to acquire bedding information from the surface of the moon. The driving component is the power output unit of the drilling system in the lander; it provides drilling power for core drilling tools. High temperatures can cause the sensors, permanent magnet, gears, and bearings to suffer irreversible damage. In this paper, a thermal analysis model for this driving component, based on the thermal network method (TNM) was established and the model was solved using the quasi-Newton method. A vacuum test platform was built and an experimental verification method (EVM) was applied to measure the surface temperature of the driving component. Then, the TNM was optimized, based on the principle of heat distribution. Through comparative analyses, the reasonableness of the TNM is validated. Finally, the static temperature field of the driving component was predicted and the “safe working times” of every mode are given. Full article

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

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37 pages, 1354 KiB

Open AccessReview

The Social Costs of Electricity Generation—Categorising Different Types of Costs and Evaluating Their Respective Relevance

by Sascha Samadi

Energies 2017, 10(3), 356; https://doi.org/10.3390/en10030356 - 13 Mar 2017

Cited by 45 | Viewed by 11414

Various electricity generation technologies using different primary energy sources are available. Many published studies compare the costs of these technologies. However, most of those studies only consider plant-level costs and do not fully take into account additional costs that societies may face in [...] Read more.

Various electricity generation technologies using different primary energy sources are available. Many published studies compare the costs of these technologies. However, most of those studies only consider plant-level costs and do not fully take into account additional costs that societies may face in using these technologies. This article reviews the literature on the costs of electricity generation technologies, aiming to determine which types of costs are relevant from a societal point of view when comparing generation technologies. The paper categorises the relevant types of costs, differentiating between plant-level, system and external costs as the main categories. It discusses the relevance of each type of cost for each generation technology. The findings suggest that several low-carbon electricity generation technologies exhibit lower social costs per kWh than the currently dominant technologies using fossil fuels. More generally, the findings emphasise the importance of taking not only plant-level costs, but also system and external costs, into account when comparing electricity generation technologies from a societal point of view. The article intends to inform both policymakers and energy system modellers, the latter who may strive to include all relevant types of costs in their models. Full article

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14 pages, 3858 KiB

Open AccessArticle

Measurement Error Estimation for Capacitive Voltage Transformer by Insulation Parameters

by Bin Chen, Lin Du, Kun Liu, Xianshun Chen, Fuzhou Zhang and Feng Yang

Energies 2017, 10(3), 357; https://doi.org/10.3390/en10030357 - 13 Mar 2017

Cited by 32 | Viewed by 6249

Measurement errors of a capacitive voltage transformer (CVT) are relevant to its equivalent parameters for which its capacitive divider contributes the most. In daily operation, dielectric aging, moisture, dielectric breakdown, etc., it will exert mixing effects on a capacitive divider’s insulation characteristics, leading [...] Read more.

Measurement errors of a capacitive voltage transformer (CVT) are relevant to its equivalent parameters for which its capacitive divider contributes the most. In daily operation, dielectric aging, moisture, dielectric breakdown, etc., it will exert mixing effects on a capacitive divider’s insulation characteristics, leading to fluctuation in equivalent parameters which result in the measurement error. This paper proposes an equivalent circuit model to represent a CVT which incorporates insulation characteristics of a capacitive divider. After software simulation and laboratory experiments, the relationship between measurement errors and insulation parameters is obtained. It indicates that variation of insulation parameters in a CVT will cause a reasonable measurement error. From field tests and calculation, equivalent capacitance mainly affects magnitude error, while dielectric loss mainly affects phase error. As capacitance changes 0.2%, magnitude error can reach −0.2%. As dielectric loss factor changes 0.2%, phase error can reach 5′. An increase of equivalent capacitance and dielectric loss factor in the high-voltage capacitor will cause a positive real power measurement error. An increase of equivalent capacitance and dielectric loss factor in the low-voltage capacitor will cause a negative real power measurement error. Full article

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14 pages, 5092 KiB

Open AccessArticle

Frequency Control Strategy for Black Starts via PMSG-Based Wind Power Generation

by Yi Tang, Jianfeng Dai, Qi Wang and Yixin Feng

Energies 2017, 10(3), 358; https://doi.org/10.3390/en10030358 - 13 Mar 2017

Cited by 23 | Viewed by 6215

The use of wind power generation (WPG) as a source for black starts will significantly enhance the resiliency of power systems and shorten their recovery time from blackouts. Given that frequency stability is the most serious issue during the initial recovery period, virtual [...] Read more.

The use of wind power generation (WPG) as a source for black starts will significantly enhance the resiliency of power systems and shorten their recovery time from blackouts. Given that frequency stability is the most serious issue during the initial recovery period, virtual inertia control can enable wind turbines to provide frequency support to an external system. In this study, a general procedure of WPG participating in black starts is presented, and the key issues are discussed. The adaptability of existing virtual inertia control strategies is analyzed, and improvement work is performed. A new coordinated frequency control strategy is proposed based on the presented improvement work. A local power network with a permanent-magnet synchronous generator (PMSG)-based wind farm is modeled and used to verify the effectiveness of the strategy. Full article

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23 pages, 5466 KiB

Open AccessArticle

Near Wellbore Hydraulic Fracture Propagation from Perforations in Tight Rocks: The Roles of Fracturing Fluid Viscosity and Injection Rate

by Seyed Hassan Fallahzadeh, Md Mofazzal Hossain, Ashton James Cornwell and Vamegh Rasouli

Energies 2017, 10(3), 359; https://doi.org/10.3390/en10030359 - 14 Mar 2017

Cited by 49 | Viewed by 6191

Hydraulic fracture initiation and near wellbore propagation is governed by complex failure mechanisms, especially in cased perforated wellbores. Various parameters affect such mechanisms, including fracturing fluid viscosity and injection rate. In this study, three different fracturing fluids with viscosities ranging from 20 to [...] Read more.

Hydraulic fracture initiation and near wellbore propagation is governed by complex failure mechanisms, especially in cased perforated wellbores. Various parameters affect such mechanisms, including fracturing fluid viscosity and injection rate. In this study, three different fracturing fluids with viscosities ranging from 20 to 600 Pa.s were used to investigate the effects of varying fracturing fluid viscosities and fluid injection rates on the fracturing mechanisms. Hydraulic fracturing tests were conducted in cased perforated boreholes made in tight 150 mm synthetic cubic samples. A true tri-axial stress cell was used to simulate real far field stress conditions. In addition, dimensional analyses were performed to correspond the results of lab experiments to field-scale operations. The results indicated that by increasing the fracturing fluid viscosity and injection rate, the fracturing energy increased, and consequently, higher fracturing pressures were observed. However, when the fracturing energy was transferred to a borehole at a faster rate, the fracture initiation angle also increased. This resulted in more curved fracture planes. Accordingly, a new parameter, called fracturing power, was introduced to relate fracture geometry to fluid viscosity and injection rate. Furthermore, it was observed that the presence of casing in the wellbore impacted the stress distribution around the casing in such a way that the fracture propagation deviated from the wellbore vicinity. Full article

(This article belongs to the Special Issue Hydraulic Fracture Stimulation for the Exploitation of Unconventional Resources in Worldwide)

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26 pages, 3200 KiB

Open AccessArticle

The Deployment of Low Carbon Technologies in Energy Intensive Industries: A Macroeconomic Analysis for Europe, China and India

by Stefan Nabernegg, Birgit Bednar-Friedl, Fabian Wagner, Thomas Schinko, Janusz Cofala and Yadira Mori Clement

Energies 2017, 10(3), 360; https://doi.org/10.3390/en10030360 - 14 Mar 2017

Cited by 26 | Viewed by 8495

Industrial processes currently contribute 40% to global CO₂ emissions and therefore substantial increases in industrial energy efficiency are required for reaching the 2 °C target. We assess the macroeconomic effects of deploying low carbon technologies in six energy intensive industrial sectors (Petroleum, [...] Read more.

Industrial processes currently contribute 40% to global CO₂ emissions and therefore substantial increases in industrial energy efficiency are required for reaching the 2 °C target. We assess the macroeconomic effects of deploying low carbon technologies in six energy intensive industrial sectors (Petroleum, Iron and Steel, Non-metallic Minerals, Paper and Pulp, Chemicals, and Electricity) in Europe, China and India in 2030. By combining the GAINS technology model with a macroeconomic computable general equilibrium model, we find that output in energy intensive industries declines in Europe by 6% in total, while output increases in China by 11% and in India by 13%. The opposite output effects emerge because low carbon technologies lead to cost savings in China and India but not in Europe. Consequently, the competitiveness of energy intensive industries is improved in China and India relative to Europe, leading to higher exports to Europe. In all regions, the decarbonization of electricity plays the dominant role for mitigation. We find a rebound effect in China and India, in the size of 42% and 34% CO₂ reduction, respectively, but not in Europe. Our results indicate that the range of considered low-carbon technology options is not competitive in the European industrial sectors. To foster breakthrough low carbon technologies and maintain industrial competitiveness, targeted technology policy is therefore needed to supplement carbon pricing. Full article

(This article belongs to the Special Issue Low Carbon Economy)

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16 pages, 4361 KiB

Open AccessEditor’s ChoiceArticle

A Top-Down Spatially Resolved Electrical Load Model

by Martin Robinius, Felix ter Stein, Adrien Schwane and Detlef Stolten

Energies 2017, 10(3), 361; https://doi.org/10.3390/en10030361 - 14 Mar 2017

Cited by 20 | Viewed by 6619

The increasing deployment of variable renewable energy sources (VRES) is changing the source regime in the electrical energy sector. However, VRES feed-in from wind turbines and photovoltaic systems is dependent on the weather and only partially predictable. As a result, existing energy sector [...] Read more.

The increasing deployment of variable renewable energy sources (VRES) is changing the source regime in the electrical energy sector. However, VRES feed-in from wind turbines and photovoltaic systems is dependent on the weather and only partially predictable. As a result, existing energy sector models must be re-evaluated and adjusted as necessary. In long-term forecast models, the expansion of VRES must be taken into account so that future local overloads can be identified and measures taken. This paper focuses on one input factor for electrical energy models: the electrical load. We compare two different types to describe this, namely vertical grid load and total load. For the total load, an approach for a spatially-resolved electrical load model is developed and applied at the municipal level in Germany. This model provides detailed information about the load at a quarterly-hour resolution across 11,268 German municipalities. In municipalities with concentrations of energy-intensive industry, high loads are expected, which our simulation reproduces with a good degree of accuracy. Our results also show that municipalities with energy-intensive industry have a higher simulated electric load than neighboring municipalities that do not host energy-intensive industries. The underlying data was extracted from publically accessible sources and therefore the methodology introduced is also applicable to other countries. Full article

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

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16 pages, 15775 KiB

Open AccessArticle

Numerical Study of the Effects of Thermal Barrier Coating and Turbulence Intensity on Cooling Performances of a Nozzle Guide Vane

by Prasert Prapamonthon, Huazhao Xu, Wenshuo Yang and Jianhua Wang

Energies 2017, 10(3), 362; https://doi.org/10.3390/en10030362 - 14 Mar 2017

Cited by 28 | Viewed by 5999

This work presents a numerical investigation of the combined effects of thermal barrier coating (TBC) with mainstream turbulence intensity (Tu) on a modified vane of the real film-cooled nozzle guide vane (NGV) reported by Timko (NASA CR-168289). Using a 3D conjugate [...] Read more.

This work presents a numerical investigation of the combined effects of thermal barrier coating (TBC) with mainstream turbulence intensity (Tu) on a modified vane of the real film-cooled nozzle guide vane (NGV) reported by Timko (NASA CR-168289). Using a 3D conjugate heat transfer (CHT) analysis, the NGVs with and without TBC are simulated at three Tus (Tu = 3.3%, 10% and 20%). The overall cooling effectiveness, TBC effectiveness and heat transfer coefficient are analyzed and discussed. The results indicate the following three interesting phenomena: (1) TBC on the pressure side (PS) is more effective than that on the suction side (SS) due to a fewer number of film holes on the SS; (2) for all three Tus, the variation trends of the overall cooling effectiveness are similar, and TBC plays the positive and negative roles in heat flux at the same time, and significantly increases the overall cooling effectiveness in regions cooled ineffectively by cooling air; (3) when Tu increases, the TBC effect is more significant, for example, at the highest Tu (Tu = 20%) the overall cooling effectiveness can increase as much as 24% in the film cooling ineffective regions, but near the trailing edge (TE) and the exits and downstream of film holes on the SS, this phenomenon is slight. Full article

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15 pages, 10678 KiB

Open AccessArticle

Highly-Efficient and Compact 6 kW/4 × 125 kHz Interleaved DC-DC Boost Converter with SiC Devices and Low-Capacitive Inductors

by Mariusz Zdanowski, Jacek Rabkowski and Roman Barlik

Energies 2017, 10(3), 363; https://doi.org/10.3390/en10030363 - 14 Mar 2017

Cited by 8 | Viewed by 5104

This paper describes a four-leg interleaved DC-DC boost converter built on the basis of Silicon Carbide (SiC) devices (Metal-Oxide Semiconductor Field-Effect Transistors—MOSFETs and Schottky diodes) and improved, low-capacitive magnetic components. A combination of wide-bandgap semiconductors capable of operating at elevated switching frequencies and [...] Read more.

This paper describes a four-leg interleaved DC-DC boost converter built on the basis of Silicon Carbide (SiC) devices (Metal-Oxide Semiconductor Field-Effect Transistors—MOSFETs and Schottky diodes) and improved, low-capacitive magnetic components. A combination of wide-bandgap semiconductors capable of operating at elevated switching frequencies and an interleaving technique brings substantial benefits, such as a cancellation of the input/output current ripples, a reduction of weight, dimensions and increase of power density. The 4 × 125 kHz DC-DC boost converter characterized by a volume of 0.75 dm³ reaches an efficiency above 98.7% at nominal power of 6 kW. A special effort has been made to develop and test inductors with low parasitic capacitance. It is clearly proven that an improved design has an impact on the converter performance, especially on power losses. Reduction of the power losses is higher than 25% in reference to a standard design of the inductors and the efficiency is in excess of 99%. Full article

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

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19 pages, 8998 KiB

Open AccessArticle

Impact of Silicon Carbide Devices on the Dynamic Performance of Permanent Magnet Synchronous Motor Drive Systems for Electric Vehicles

by Xiaofeng Ding, Min Du, Jiawei Cheng, Feida Chen, Suping Ren and Hong Guo

Energies 2017, 10(3), 364; https://doi.org/10.3390/en10030364 - 15 Mar 2017

Cited by 5 | Viewed by 6717

This paper investigates the impact of silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs) on the dynamic performance of permanent magnet synchronous motor (PMSM) drive systems. The characteristics of SiC MOSFETs are evaluated experimentally taking into account temperature variations. Then the [...] Read more.

This paper investigates the impact of silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs) on the dynamic performance of permanent magnet synchronous motor (PMSM) drive systems. The characteristics of SiC MOSFETs are evaluated experimentally taking into account temperature variations. Then the switching characteristics are firstly introduced into the transfer function of a SiC-inverter fed PMSM drive system. The main contribution of this paper is the investigation of the dynamic control performance features such as the fast response, the stability and the robustness of the drive system considering the characteristics of SiC MOSFETs. All the results of the SiC-drive system are compared to the silicon-(Si) insulated gate bipolar transistors (IGBTs) drive system counterpart, and the SiC-drive system manifests a higher dynamic performance than the Si-drive system. The analytical results have been effectively validated by experiments on a test bench. Full article

(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))

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16 pages, 9522 KiB

Open AccessArticle

Neighborhood Effects in Wind Farm Performance: A Regression Approach

by Matthias Ritter, Simone Pieralli and Martin Odening

Energies 2017, 10(3), 365; https://doi.org/10.3390/en10030365 - 16 Mar 2017

Cited by 6 | Viewed by 4235

The optimization of turbine density in wind farms entails a trade-off between the usage of scarce, expensive land and power losses through turbine wake effects. A quantification and prediction of the wake effect, however, is challenging because of the complex aerodynamic nature of [...] Read more.

The optimization of turbine density in wind farms entails a trade-off between the usage of scarce, expensive land and power losses through turbine wake effects. A quantification and prediction of the wake effect, however, is challenging because of the complex aerodynamic nature of the interdependencies of turbines. In this paper, we propose a parsimonious data driven regression wake model that can be used to predict production losses of existing and potential wind farms. Motivated by simple engineering wake models, the predicting variables are wind speed, the turbine alignment angle, and distance. By utilizing data from two wind farms in Germany, we show that our models can compete with the standard Jensen model in predicting wake effect losses. A scenario analysis reveals that a distance between turbines can be reduced by up to three times the rotor size, without entailing substantial production losses. In contrast, an unfavorable configuration of turbines with respect to the main wind direction can result in production losses that are much higher than in an optimal case. Full article

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17 pages, 6030 KiB

Open AccessArticle

Potential of Utilizing Different Natural Cooling Sources to Reduce the Building Cooling Load and Cooling Energy Consumption: A Case Study in Urumqi

by Chong Shen and Xianting Li

Energies 2017, 10(3), 366; https://doi.org/10.3390/en10030366 - 15 Mar 2017

Cited by 18 | Viewed by 5204

Generally, Central Asia is typical for regions with strong solar radiation and various natural cooling sources. The heat gain from the building envelope accounts for a large part of the cooling load there. Thus, the pipe-embedded envelope is receiving attention as a semi-active [...] Read more.

Generally, Central Asia is typical for regions with strong solar radiation and various natural cooling sources. The heat gain from the building envelope accounts for a large part of the cooling load there. Thus, the pipe-embedded envelope is receiving attention as a semi-active system of utilizing natural energy for cooling. In this study, the performance of the pipe-embedded envelope used in Urumqi is numerically investigated. The energy saving potential regarding evaporative cooling and a ground-source heat exchanger (GSHE) is evaluated over a complete summer. The results show that the built-in pipes can reduce 80% of the solar heat gain through windows, with an effectiveness of around 60%. External windows rather than internal windows should be insulated because the air cavity is cool. With respect to the pipe-embedded wall, it becomes a radiant cooling panel absorbing the heat from the room, with an effectiveness around 83%. The seasonal cooling energy is decreased by 25%–50% in a typical office with a pipe-embedded envelope. Offices with a large window-to-wall ratio are acceptable because natural cooling is employed. GSHE performs the best among the selected sources. The effectiveness of evaporative cooling is also satisfactory, with an energy saving rate of 27%. Overall, the pipe-embedded system is suitable for climatic regions like Urumqi. Full article

(This article belongs to the Special Issue The 1st “The Belt and Road Initiative” International Conference on Sustainable Refrigeration and Air Conditioning)

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17 pages, 1167 KiB

Open AccessArticle

Spatial Heterogeneity of Energy-Related CO₂ Emission Growth Rates around the World and Their Determinants during 1990–2014

by Yebing Fang, Limao Wang, Zhoupeng Ren, Yan Yang, Chufu Mou and Qiushi Qu

Energies 2017, 10(3), 367; https://doi.org/10.3390/en10030367 - 15 Mar 2017

Cited by 11 | Viewed by 4078

Understanding the spatial heterogeneity and driving force identification of energy-related CO₂ emissions (ECEs) can help build consensus for mitigating CO₂ emissions and designing appropriate policies. However, previous studies on ECEs that focus on both the global-regional scale and the interaction of [...] Read more.

Understanding the spatial heterogeneity and driving force identification of energy-related CO₂ emissions (ECEs) can help build consensus for mitigating CO₂ emissions and designing appropriate policies. However, previous studies on ECEs that focus on both the global-regional scale and the interaction of factors have been seldom conducted. In this paper, ECE data from 143 countries from 1990 to 2014 were selected to analyze regional differences in ECE growth rates by using the coefficient of variation. Then a geographical detector was used to analyze the key determinant factors on ECE growth rates around the world and in eight types of regions. The results show that: (1) the ECE growth rate in the Organization for Economic Cooperation and Development (OECD) region is low and tended to decrease, while in the non-OECD region it is high and tended to increase; (2) the coefficient of variation and detection factor of ECE growth rates at a regional scale are higher than those at a global scale; (3) in terms of the key determinant factors, population growth rate, growth rate of per capita GDP, and energy intensity growth rate are the three key determinant factors of ECE growth rates in the OECD region and most of the non-OECD regions such as non-OECD European and Eurasian (NO-EE), Asia (NO-AS), non-OECD Americas (NO-AM). The key determinant factors in the African (NO-AF) region are population growth rates and natural gas carbon intensity growth rates. The key determinant factors of the Middle East (NO-ME) are population growth rate, coal carbon intensity growth rate and per capita GDP growth rate; (4) the determinant power of the detection factor, the population growth rate at the global scale and regional scale is the strongest, showing a significant spatial consistency. The determinant power of per capita GDP growth rate and energy intensity growth rate in the OECD region, respectively, rank second and third, also showing a spatial consistency. However, the carbon intensity growth rates of the three fossil fuels contribute little to the growth rate of ECEs, and their spatial coherence is weak; (5) from the perspective of the interaction of detection factors, six detection factors showed bilinear or non-linear enhancement at a global and a regional scale, and the determinant power of the interaction of factors was significantly enhanced; and (6) from the perspective of ecological detection, the growth rate of carbon intensity and the growth rate of natural gas carbon intensity at the global scale and NO-ME region are significantly stronger than other factors, with a significant difference in the spatial distribution of its incidence. Therefore, the OECD region should continue to reduce the growth of energy intensity, and develop alternative energy resources in the future, while those that are plagued by carbon emissions in non-OECD regions should pay more attention to the positive influence of lower population growth rates on reducing the growth rate of energy-related CO₂ emissions. Reducing energy intensity growth rates and reducing, fossil energy consumption carbon intensity. Full article

(This article belongs to the Special Issue Energy Policy and Climate Change 2016)

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20 pages, 4277 KiB

Open AccessArticle

Parameter Optimization on the Uniflow Scavenging System of an OP2S-GDI Engine Based on Indicated Mean Effective Pressure (IMEP)

by Fu-Kang Ma, Jun Wang, Yao-Nan Feng, Yan-Gang Zhang, Tie-Xiong Su, Yi Zhang and Yu-Hang Liu

Energies 2017, 10(3), 368; https://doi.org/10.3390/en10030368 - 15 Mar 2017

Cited by 22 | Viewed by 4925

In this paper, an opposed-piston two-stroke (OP2S) gasoline direct injection (GDI) engine is introduced and its working principles and scavenging process were analyzed. An optimization function was established to optimize the scavenging system parameters, include intake port height, exhaust port height, intake port [...] Read more.

In this paper, an opposed-piston two-stroke (OP2S) gasoline direct injection (GDI) engine is introduced and its working principles and scavenging process were analyzed. An optimization function was established to optimize the scavenging system parameters, include intake port height, exhaust port height, intake port circumference ratio, the exhaust port circumference ratio and opposed-piston motion phase difference. The effect of the port height on the effective compression ratio and effective expansion ratio were considered, and indicated mean effective pressure (IMEP) was employed as the optimization objective instead of scavenging efficiency. Orthogonal experiments were employed to reduce the calculation work. The effect of the scavenging parameters on delivery ratio, trapping ratio, scavenging efficiency and indicated thermal efficiency were calculated, and the best parameters were also obtained by the optimization function. The results show that IMEP can be used as the optimization objective in the uniflow scavenging system; intake port height is the main factor to the delivery ratio, while exhaust port height is the main to engine trapping ratio, scavenging efficiency and indicated thermal efficiency; exhaust port height is the most important factor to effect the gas exchange process of OP2S-GDI engine. Full article

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19 pages, 5019 KiB

Open AccessArticle

Pulse Detonation Assessment for Alternative Fuels

by Muhammad Hanafi Azami and Mark Savill

Energies 2017, 10(3), 369; https://doi.org/10.3390/en10030369 - 15 Mar 2017

Cited by 13 | Viewed by 7407

The higher thermodynamic efficiency inherent in a detonation combustion based engine has already led to considerable interest in the development of wave rotor, pulse detonation, and rotating detonation engine configurations as alternative technologies offering improved performance for the next generation of aerospace propulsion [...] Read more.

The higher thermodynamic efficiency inherent in a detonation combustion based engine has already led to considerable interest in the development of wave rotor, pulse detonation, and rotating detonation engine configurations as alternative technologies offering improved performance for the next generation of aerospace propulsion systems, but it is now important to consider their emissions also. To assess both performance and emissions, this paper focuses on the feasibility of using alternative fuels in detonation combustion. Thus, the standard aviation fuels Jet-A, Acetylene, Jatropha Bio-synthetic Paraffinic Kerosene, Camelina Bio-synthetic Paraffinic Kerosene, Algal Biofuel, and Microalgae Biofuel are all asessed under detonation combustion conditions. An analytical model accounting for the Rankine-Hugoniot Equation, Rayleigh Line Equation, and Zel’dovich–von Neumann–Doering model, and taking into account single step chemistry and thermophysical properties for a stoichiometric mixture, is applied to a simple detonation tube test case configuration. The computed pressure rise and detonation velocity are shown to be in good agreement with published literature. Additional computations examine the effects of initial pressure, temperature, and mass flux on the physical properties of the flow. The results indicate that alternative fuels require higher initial mass flux and temperature to detonate. The benefits of alternative fuels appear significant. Full article

(This article belongs to the Special Issue Combustion and Propulsion)

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16 pages, 4435 KiB

Open AccessArticle

Exploring the Micromechanical Sliding Behavior of Typical Quartz Grains and Completely Decomposed Volcanic Granules Subjected to Repeating Shearing

by Chitta Sai Sandeep and Kostas Senetakis

Energies 2017, 10(3), 370; https://doi.org/10.3390/en10030370 - 15 Mar 2017

Cited by 39 | Viewed by 5027

The micromechanical behavior at grain contacts subjected to tangential and normal forces is of major importance in geotechnical engineering research and practice. The development of the discrete element method (DEM) over the past three decades necessitated a more systematic study on the experimental [...] Read more.

The micromechanical behavior at grain contacts subjected to tangential and normal forces is of major importance in geotechnical engineering research and practice. The development of the discrete element method (DEM) over the past three decades necessitated a more systematic study on the experimental grain contact behavior of real soil grains as DEM simulations use as input tangential and normal load–displacement relationships at grain contacts. In this study, experimental results conducted at the City University of Hong Kong are presented exploring the tangential load–displacement behavior of geological materials. The focus of the study is to explore the possible effect of repeating the shearing test to the same grains on the inter-particle coefficient of friction accounting for the level of the applied normal load. Additionally, the study reports on the frictional behavior of different geological materials including quartz sand grains, denoted as Leighton Buzzard sand (LBS) in the study and completely decomposed volcanic granules denoted as CDV. Quartz grains may find applications as proppant in petroleum engineering, whilst the CDV granules consisted of a material taken from a recent landslide in Hong Kong, whose applications are related to debris flow. Through the micromechanical sliding experiments, the inter-particle coefficient of friction was quantified following shearing paths of about 60 to 200 microns. While at the smallest vertical load of 1 N, there was not observed a notable effect of the repeating shearing for the LBS grains, it was noticed that for small to medium vertical loads, between 2 and 5 N, the repeating shearing reduced the friction at the contacts of the LBS grains. This trend was clear between the first and second shearing, but additional cycles did not further alter the frictional response. However, at greater vertical loads, between 7 and 10 N, the results showed a continuous increase in the dynamic inter-particle friction for the LBS grains with repeating shearing. It was also noticed that at 7 and 10 N of vertical load, there was absence of a peak state in the tangential force–displacement plot, whereas a peak state was observed at smaller loads particularly for the first shearing cycle. These observations might be explained by the possible plowing effects at greater vertical loads which resulted in an increase of the inter-particle coefficient of friction when the shearing test was repeated. For the CDV granules, only the first shearing cycle gave a peak state and, in general, the effect of repeating the shearing was small but with an increase of the inter-particle friction from the first to the second cycle. Overall, during the repeating shearing the LBS grains had a dynamic inter-particle coefficient of friction that ranged between about 0.18 and 0.38, but the CDV granules exhibited much greater friction with values that corresponded to the steady state sliding that ranged between 0.54 and 0.66 . The observed trends in the study might be due to mechanisms that take place at the atomic level and the possible more pronounced distortion of the surfaces for the CDV granules which are much softer than the LBS grains. Full article

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

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11 pages, 6362 KiB

Open AccessArticle

Electric Field Simulations and Analysis for High Voltage High Power Medium Frequency Transformer

by Pei Huang, Chengxiong Mao and Dan Wang

Energies 2017, 10(3), 371; https://doi.org/10.3390/en10030371 - 16 Mar 2017

Cited by 15 | Viewed by 7960

The electronic power transformer (EPT) raises concerns for its notable size and volume reduction compared with traditional line frequency transformers. Medium frequency transformers (MFTs) are important components in high voltage and high power energy conversion systems such as EPTs. High voltage and high [...] Read more.

The electronic power transformer (EPT) raises concerns for its notable size and volume reduction compared with traditional line frequency transformers. Medium frequency transformers (MFTs) are important components in high voltage and high power energy conversion systems such as EPTs. High voltage and high power make the reliable insulation design of MFT more difficult. In this paper, the influence of wire type and interleaved winding structure on the electric field distribution of MFT is discussed in detail. The electric field distributions for six kinds of typical non-interleaved windings with different wire types are researched using a 2-D finite element method (FEM). The electric field distributions for one non-interleaved winding and two interleaved windings are also studied using 2-D FEM. Furthermore, the maximum electric field intensities are obtained and compared. The results show that, in this case study, compared with foil conductor, smaller maximum electric field intensity can be achieved using litz wire in secondary winding. Besides, interleaving can increase the maximum electric field intensity when insulation distance is constant. The proposed method of studying the electric field distribution and analysis results are expected to make a contribution to the improvement of electric field distribution in transformers. Full article

(This article belongs to the Collection Smart Grid)

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21 pages, 4859 KiB

Open AccessArticle

Stochastic Residential Harmonic Source Modeling for Grid Impact Studies

by Gu Ye, Michiel Nijhuis, Vladimir Cuk and J.F.G. (Sjef) Cobben

Energies 2017, 10(3), 372; https://doi.org/10.3390/en10030372 - 17 Mar 2017

Cited by 24 | Viewed by 5747

With the introduction of more non-linear loads, e.g., compact fluorescent lamps, electric vehicles, photovoltaics, etc., the need to determine the harmonic impact of the residential load is rising, illustrated by the many studies performed on their harmonic impact. Traditionally, these studies are performed [...] Read more.

With the introduction of more non-linear loads, e.g., compact fluorescent lamps, electric vehicles, photovoltaics, etc., the need to determine the harmonic impact of the residential load is rising, illustrated by the many studies performed on their harmonic impact. Traditionally, these studies are performed for a single new device and single penetration level, neglecting the harmonic interaction between new types of devices, as well as giving little information at which moment in time possible problems may arise. A composite approach to access the impact of harmonic sources on the distribution network is therefore proposed. This method combines a bottom-up stochastic modeling of the residential load with harmonic measurement data and harmonic load-flows all based on a scenario analysis. The method is validated with measurement data and shows a good prediction of the current level of harmonics in a residential neighborhood for the current situation. To demonstrate the applicability of the proposed method, case studies are performed on the IEEE European Low Voltage Test Feeder. These case studies show a marked difference between applying individual device-based models and a composite modeling approach, demonstrating why the proposed approach is an adequate method for the determination of the impact of new devices on the harmonics. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2017)

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16 pages, 8014 KiB

Open AccessArticle

Distributed Control Strategy for Autonomous Operation of Hybrid AC/DC Microgrid

by Jongbok Baek, Wooin Choi and Suyong Chae

Energies 2017, 10(3), 373; https://doi.org/10.3390/en10030373 - 16 Mar 2017

Cited by 27 | Viewed by 6435

This paper proposes a distributed control strategy that considers several source characteristics to achieve reliable and efficient operation of a hybrid ac/dc microgrid. The proposed control strategy has a two-level structure. The primary control layer is based on an adaptive droop method, which [...] Read more.

This paper proposes a distributed control strategy that considers several source characteristics to achieve reliable and efficient operation of a hybrid ac/dc microgrid. The proposed control strategy has a two-level structure. The primary control layer is based on an adaptive droop method, which allows local controllers to operate autonomously and flexibly during disturbances such as fault, load variation, and environmental changes. For efficient distribution of power, a higher control layer adjusts voltage reference points based on optimized energy scheduling decisions. The proposed hybrid ac/dc microgrid is composed of converters and distributed generation units that include renewable energy sources (RESs) and energy storage systems (ESSs). The proposed control strategy is verified in various scenarios experimentally and by simulation. Full article

(This article belongs to the Special Issue Distributed Energy Resources Management)

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33 pages, 3121 KiB

Open AccessArticle

Engineering Smart Grids: Applying Model-Driven Development from Use Case Design to Deployment

by Filip Pröstl Andrén, Thomas I. Strasser and Wolfgang Kastner

Energies 2017, 10(3), 374; https://doi.org/10.3390/en10030374 - 16 Mar 2017

Cited by 39 | Viewed by 9119

The rollout of smart grid solutions has already started and new methods are deployed to the power systems of today. However, complexity is still increasing as focus is moving from a single system, to a system of systems perspective. The results are increasing [...] Read more.

The rollout of smart grid solutions has already started and new methods are deployed to the power systems of today. However, complexity is still increasing as focus is moving from a single system, to a system of systems perspective. The results are increasing engineering efforts and escalating costs. For this reason, new and automated engineering methods are necessary. This paper addresses these needs with a rapid engineering methodology that covers the overall engineering process for smart grid applications—from use case design to deployment. Based on a model-driven development approach, the methodology consists of three main parts: use case modeling, code generation, and deployment. A domain-specific language is introduced supporting the use case design according to the Smart Grid Architecture Model. It is combined with the IEC 61499 distributed control model to improve the function layer design. After a completed use case design, executable code and communication configurations (e.g., IEC 61850) are generated and deployed onto compatible field devices. This paper covers the proposed rapid engineering methodology and a corresponding prototypical implementation which is validated in a laboratory experiment. Compared to other methods the proposed methodology decreases the number of engineering steps and reduces the use case design and implementation complexity. Full article

(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)

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20 pages, 5720 KiB

Open AccessArticle

Lithium-ion Battery Electrothermal Model, Parameter Estimation, and Simulation Environment

by Simone Orcioni, Luca Buccolini, Adriana Ricci and Massimo Conti

Energies 2017, 10(3), 375; https://doi.org/10.3390/en10030375 - 16 Mar 2017

Cited by 38 | Viewed by 7494

The market for lithium-ion batteries is growing exponentially. The performance of battery cells is growing due to improving production technology, but market request is growing even more rapidly. Modeling and characterization of single cells and an efficient simulation environment is fundamental for the [...] Read more.

The market for lithium-ion batteries is growing exponentially. The performance of battery cells is growing due to improving production technology, but market request is growing even more rapidly. Modeling and characterization of single cells and an efficient simulation environment is fundamental for the development of an efficient battery management system. The present work is devoted to defining a novel lumped electrothermal circuit of a single battery cell, the extraction procedure of the parameters of the single cell from experiments, and a simulation environment in SystemC-WMS for the simulation of a battery pack. The electrothermal model of the cell was validated against experimental measurements obtained in a climatic chamber. The model is then used to simulate a 48-cell battery, allowing statistical variations among parameters. The different behaviors of the cells in terms of state of charge, current, voltage, or heat flow rate can be observed in the results of the simulation environment. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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15 pages, 4022 KiB

Open AccessArticle

Wave Energy Assessment along Sicilian Coastline, Based on DEIM Point Absorber

by Vincenzo Franzitta, Pietro Catrini and Domenico Curto

Energies 2017, 10(3), 376; https://doi.org/10.3390/en10030376 - 16 Mar 2017

Cited by 45 | Viewed by 5288

The use of renewable energy sources is one of the most relevant goals to be achieved in order to match the climate protection targets. As a case study, the paper shows the current electrical energy production by sources in the Sicilian context. Among [...] Read more.

The use of renewable energy sources is one of the most relevant goals to be achieved in order to match the climate protection targets. As a case study, the paper shows the current electrical energy production by sources in the Sicilian context. Among the renewable energy sources, the paper investigates the wave energy potential along the Sicilian coasts, because of the favorable climate around the island. A point absorber is present in order to exploit this source. Two scenarios are presented, with two different levels of energy production. Full article

(This article belongs to the Special Issue Integration of Renewable Technologies in Water, Electricity, Heating and Cooling Networks)

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16 pages, 5790 KiB

Open AccessFeature PaperArticle

Real-Time Forecasting of EV Charging Station Scheduling for Smart Energy Systems

by Bharatiraja Chokkalingam, Sanjeevikumar Padmanaban, Pierluigi Siano, Ramesh Krishnamoorthy and Raghu Selvaraj

Energies 2017, 10(3), 377; https://doi.org/10.3390/en10030377 - 16 Mar 2017

Cited by 59 | Viewed by 11831

The enormous growth in the penetration of electric vehicles (EVs), has laid the path to advancements in the charging infrastructure. Connectivity between charging stations is an essential prerequisite for future EV adoption to alleviate user’s “range anxiety”. The existing charging stations fail to [...] Read more.

The enormous growth in the penetration of electric vehicles (EVs), has laid the path to advancements in the charging infrastructure. Connectivity between charging stations is an essential prerequisite for future EV adoption to alleviate user’s “range anxiety”. The existing charging stations fail to adopt power provision, allocation and scheduling management. To improve the existing charging infrastructure, data based on real-time information and availability of reserves at charging stations could be uploaded to the users to help them locate the nearest charging station for an EV. This research article focuses on an a interactive user application developed through SQL and PHP platform to allocate the charging slots based on estimated battery parameters, which uses data communication with charging stations to receive the slot availability information. The proposed server-based real-time forecast charging infrastructure avoids waiting times and its scheduling management efficiently prevents the EV from halting on the road due to battery drain out. The proposed model is implemented using a low-cost microcontroller and the system etiquette tested. Full article

(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)

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17 pages, 7789 KiB

Open AccessArticle

A Novel High Step-Up DC-DC Converter with Coupled Inductor and Switched Clamp Capacitor Techniques for Photovoltaic Systems

by Yong-Seng Wong, Jiann-Fuh Chen, Kuo-Bin Liu and Yi-Ping Hsieh

Energies 2017, 10(3), 378; https://doi.org/10.3390/en10030378 - 16 Mar 2017

Cited by 39 | Viewed by 6220

In this study, a novel high step-up DC-DC converter was successfully integrated using coupled inductor and switched capacitor techniques. High step-up DC-DC gain was achieved using a coupled inductor when capacitors charged and discharged energy, respectively. In addition, energy was recovered from the [...] Read more.

In this study, a novel high step-up DC-DC converter was successfully integrated using coupled inductor and switched capacitor techniques. High step-up DC-DC gain was achieved using a coupled inductor when capacitors charged and discharged energy, respectively. In addition, energy was recovered from the leakage inductance of the coupled inductor by using a passive clamp circuit. Therefore, the voltage stress of the main power switch was almost reduced to 1/7 V_o (output voltage). Moreover, the coupled inductor alleviated the reverse-recovery problem of the diode. The proposed circuit efficiency can be further improved and high voltage gain can be achieved. The operation principle and steady-state analysis of the proposed converter were discussed. Finally, a hardware prototype circuit with input voltage of 24 V, output voltage of up to 400 V, and maximum power of 150 W was constructed in a laboratory; the maximum efficiency was almost 96.2%. Full article

(This article belongs to the Special Issue Energy Management, Control, and System Architectures for Electric Vehicle Applications)

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19 pages, 2186 KiB

Open AccessArticle

Limitations and Constraints of Eddy-Current Loss Models for Interior Permanent-Magnet Motors with Fractional-Slot Concentrated Windings

by Hui Zhang and Oskar Wallmark

Energies 2017, 10(3), 379; https://doi.org/10.3390/en10030379 - 16 Mar 2017

Cited by 8 | Viewed by 5087

This paper analyzes and compares models for predicting average magnet losses in interior permanent-magnet motors with fractional-slot concentrated windings due to harmonics in the armature reaction (assuming sinusoidal phase currents). Particularly, loss models adopting different formulations and solutions to the Helmholtz equation to [...] Read more.

This paper analyzes and compares models for predicting average magnet losses in interior permanent-magnet motors with fractional-slot concentrated windings due to harmonics in the armature reaction (assuming sinusoidal phase currents). Particularly, loss models adopting different formulations and solutions to the Helmholtz equation to solve for the eddy currents are compared to a simpler model relying on an assumed eddy-current distribution. Boundaries in terms of magnet dimensions and angular frequency are identified (numerically and using an identified approximate analytical expression) to aid the machine designer whether the more simple loss model is applicable or not. The assumption of a uniform flux-density variation (used in the loss models) is also investigated for the case of V-shaped and straight interior permanent magnets. Finally, predicted volumetric loss densities are exemplified for combinations of slot and pole numbers common in automotive applications. Full article

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18 pages, 3538 KiB

Open AccessArticle

A New Method to Monitor the Primary Neutral Integrity in Multi-Grounded Neutral Systems

by Xiangmin Xie, Yuanyuan Sun, Xun Long and Bingwei Zhang

Energies 2017, 10(3), 380; https://doi.org/10.3390/en10030380 - 16 Mar 2017

Cited by 10 | Viewed by 6332

In the three-phase four-wire system, there are usually multiple grounding points in the primary neutral line due to safety and economic considerations. The rising “neutral to earth voltage (NEV)” caused by a broken primary neutral can threaten the safety of nearby facilities and [...] Read more.

In the three-phase four-wire system, there are usually multiple grounding points in the primary neutral line due to safety and economic considerations. The rising “neutral to earth voltage (NEV)” caused by a broken primary neutral can threaten the safety of nearby facilities and humans; therefore, the integrity of the primary neutral conductor is of vital importance for the multi-grounded neutral (MGN) system. In this paper, a new passive method is proposed to monitor the integrity of the primary neutral line in the MGN system. The method is based on the measured voltage and current data at the service transformer, and there is no need to install any signal generators. Therefore, it causes no disturbance to the utility and customer. In the paper, the equivalent analysis circuit is established and a new parameter is proposed to reflect the neutral condition. The value of the parameter is estimated based on the measured data, and then, the equivalent impedance of the primary neutral groundings can be obtained. On the other hand, the impedance value for the primary neutral under normal operating conditions can be estimated based on the derived analytical formulas. By comparing the monitored primary neutral impedance with its normal value, the broken neutral condition in the primary system can be detected. Different primary neutral broken cases are analyzed in the paper based on the Monte Carlo simulation. The results indicate that the integrity condition in the primary neutral can be accurately monitored by the proposed method. Full article

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

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21 pages, 292 KiB

Open AccessArticle

Does Renewable Energy Drive Sustainable Economic Growth? Multivariate Panel Data Evidence for EU-28 Countries

by Daniel Ştefan Armeanu, Georgeta Vintilă and Ştefan Cristian Gherghina

Energies 2017, 10(3), 381; https://doi.org/10.3390/en10030381 - 17 Mar 2017

Cited by 154 | Viewed by 14340

Energy is crucial to economic progress, but the contemporary worldwide population increase that demands greater energy generated from conventional exhaustible resources, an energy price upsurge, and environmental concerns, imperils sustainable economic growth. Nevertheless, switching to renewable energy produced from naturally replenished resources promotes [...] Read more.

Energy is crucial to economic progress, but the contemporary worldwide population increase that demands greater energy generated from conventional exhaustible resources, an energy price upsurge, and environmental concerns, imperils sustainable economic growth. Nevertheless, switching to renewable energy produced from naturally replenished resources promotes energy security, likewise addressing issues such as global warming and climate change. This paper aims at exploring the influence and causal relation between renewable energy, both overall and by type, and sustainable economic growth of European Union (EU)-28 countries for the period of 2003–2014. We notice that the mean share of renewable energy in the gross final energy consumption is 15%, while the mean share of renewable energy in transport fuel consumption is 3%, which are below the thresholds of 20% and 10%, respectively, as set by the EU Directive 2009/28/EC. By estimating panel data fixed-effects regression models, the results provide support for a positive influence of renewable energy overall, as well as by type, namely biomass, hydropower, geothermal energy, wind power, and solar energy on gross domestic product per capita. However, biomass energy shows the highest influence on economic growth among the rest of renewable energy types. In fact, a 1% increase of the primary production of solid biofuels increases GDP per capita by 0.16%. Besides, cointegrating regressions set on panel fully modified and dynamic ordinary least squares regressions confirm the positive influence related to the primary production of renewable energies on economic growth. A 1% increase in primary production of renewable energies increases GDP per capita by 0.05%–0.06%. However, the results of Granger causality based on panel vector error correction model indicate both in short-run and long-run a unidirectional causal relationship running from sustainable economic growth to the primary production of renewable energies, being supported the conservation hypothesis. Full article

(This article belongs to the Special Issue Contemporary Environmental Paradigms and the Renewable Energy in Rural Economies)

5 pages, 167 KiB

Open AccessEditorial

Smart Home Energy Management

by Giovanni Pau, Mario Collotta, Antonio Ruano and Jiahu Qin

Energies 2017, 10(3), 382; https://doi.org/10.3390/en10030382 - 17 Mar 2017

Cited by 46 | Viewed by 9119

The new challenges on Information and Communication Technologies (ICT) in Automatic Home Systems (AHS) focus on the methods useful to monitor, control, and optimize the data management flow and the use of energy.[...] Full article

(This article belongs to the Special Issue Smart Home Energy Management)

22 pages, 12051 KiB

Open AccessArticle

Process Heat Generation Potential from Solar Concentration Technologies in Latin America: The Case of Argentina

by Isidoro Lillo, Elena Pérez, Sara Moreno and Manuel Silva

Energies 2017, 10(3), 383; https://doi.org/10.3390/en10030383 - 17 Mar 2017

Cited by 44 | Viewed by 7391

This paper evaluates the potential of solar concentration technologies—compound parabolic collector (CPC), linear Fresnel collector (LFC) and parabolic trough collector (PTC)—as an alternative to conventional sources of energy for industrial processes in Latin America, where high levels of solar radiation and isolated areas [...] Read more.

This paper evaluates the potential of solar concentration technologies—compound parabolic collector (CPC), linear Fresnel collector (LFC) and parabolic trough collector (PTC)—as an alternative to conventional sources of energy for industrial processes in Latin America, where high levels of solar radiation and isolated areas without energy supply exist. The analysis is addressed from energy, economic and environmental perspective. A specific application for Argentina in which fourteen locations are analyzed is considered. Results show that solar concentration technologies can be an economically and environmentally viable alternative. Levelized cost of energy (LCOE) ranges between 2.5 and 16.9 c€/kWh/m² and greenhouse gas (GHG) emissions avoided range between 33 and 348 kgCO₂/(m²·year). CPC technology stands out as the most recommendable technology when the working fluid temperature ranges from 373 K to 423 K. As the working fluid temperature increases the differences between the LCOE values of the CPC and LFC technologies decrease. When 523 K is reached LFC technology is the one which presents the lowest LCOE values for all analyzed sites, while the LCOE values of PTC technology are close to CPC technology values. Results show that solar concentration technologies have reached economic and environmental competitiveness levels under certain scenarios, mainly linked to solar resource available, thermal level requirements and solar technology cost. Full article

(This article belongs to the Special Issue Sustainable and Renewable Energy Systems)

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8 pages, 3059 KiB

Open AccessFeature PaperArticle

Simultaneous On-State Voltage and Bond-Wire Resistance Monitoring of Silicon Carbide MOSFETs

by Nick Baker, Haoze Luo and Francesco Iannuzzo

Energies 2017, 10(3), 384; https://doi.org/10.3390/en10030384 - 18 Mar 2017

Cited by 35 | Viewed by 7937

In fast switching power semiconductors, the use of a fourth terminal to provide the reference potential for the gate signal—known as a kelvin-source terminal—is becoming common. The introduction of this terminal presents opportunities for condition monitoring systems. This article demonstrates how the voltage [...] Read more.

In fast switching power semiconductors, the use of a fourth terminal to provide the reference potential for the gate signal—known as a kelvin-source terminal—is becoming common. The introduction of this terminal presents opportunities for condition monitoring systems. This article demonstrates how the voltage between the kelvin-source and power-source can be used to specifically monitor bond-wire degradation. Meanwhile, the drain to kelvin-source voltage can be monitored to track defects in the semiconductor die or gate driver. Through an accelerated aging test on 20 A Silicon Carbide Metal-Oxide-Semiconductor-Field-Effect Transistors (MOSFETs), it is shown that there are opposing trends in the evolution of the on-state resistances of both the bond-wires and the MOSFET die. In summary, after 50,000 temperature cycles, the resistance of the bond-wires increased by up to 2 mΩ, while the on-state resistance of the MOSFET dies decreased by approximately 1 mΩ. The conventional failure precursor (monitoring a single forward voltage) cannot distinguish between semiconductor die or bond-wire degradation. Therefore, the ability to monitor both these parameters due to the presence of an auxiliary-source terminal can provide more detailed information regarding the aging process of a device. Full article

(This article belongs to the Special Issue Semiconductor Power Devices)

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14 pages, 2509 KiB

Open AccessArticle

The Risk of Residential Peak Electricity Demand: A Comparison of Five European Countries

by Jacopo Torriti

Energies 2017, 10(3), 385; https://doi.org/10.3390/en10030385 - 19 Mar 2017

Cited by 19 | Viewed by 6942

The creation of a Europe-wide electricity market combined with the increased intermittency of supply from renewable sources calls for an investigation into the risk of aggregate peak demand. This paper makes use of a risk model to assess differences in time-use data from [...] Read more.

The creation of a Europe-wide electricity market combined with the increased intermittency of supply from renewable sources calls for an investigation into the risk of aggregate peak demand. This paper makes use of a risk model to assess differences in time-use data from residential end-users in five different European electricity markets. Drawing on the Multinational Time-Use Survey database, it assesses risk in relation to the probability of electrical appliance use within households for five European countries. Findings highlight in which countries and for which activities the risk of aggregate peak demand is higher and link smart home solutions (automated load control, dynamic pricing and smart appliances) to different levels of peak demand risk. Full article

(This article belongs to the Special Issue Solar Technologies for Buildings)

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15 pages, 635 KiB

Open AccessArticle

Equivalent Electrical Circuits of Thermoelectric Generators under Different Operating Conditions

by Saima Siouane, Slaviša Jovanović and Philippe Poure

Energies 2017, 10(3), 386; https://doi.org/10.3390/en10030386 - 18 Mar 2017

Cited by 33 | Viewed by 8277

Energy harvesting has become a promising and alternative solution to conventional energy generation patterns to overcome the problem of supplying autonomous electrical systems. More particularly, thermal energy harvesting technologies have drawn a major interest in both research and industry. Thermoelectric Generators (TEGs) can [...] Read more.

Energy harvesting has become a promising and alternative solution to conventional energy generation patterns to overcome the problem of supplying autonomous electrical systems. More particularly, thermal energy harvesting technologies have drawn a major interest in both research and industry. Thermoelectric Generators (TEGs) can be used in two different operating conditions, under constant temperature gradient or constant heat flow. The commonly used TEG electrical model, based on a voltage source in series with an electrical resistance, shows its limitations especially under constant heat flow conditions. Here, the analytical electrical modeling, taking into consideration the internal and contact thermal resistances of a TEG under constant temperature gradient and constant heat flow conditions, is first given. To give further insight into the electrical behavior of a TEG module in different operating conditions, we propose a new and original way of emulating the above analytical expressions with usual electronics components (voltage source, resistors, diode), whose values are determined with the TEG’s parameters. Note that such a TEG emulation is particularly suited when designing the electronic circuitry commonly associated to the TEG, to realize both Maximum Power Point Tracking and output voltage regulation. First, the proposed equivalent electrical circuits are validated through simulation with a SPICE environment in static operating conditions using only one value of either temperature gradient or heat flow. Then, they are also analyzed in dynamic operating conditions where both temperature gradient and heat flow are considered as time-varying functions. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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20 pages, 2646 KiB

Open AccessArticle

Effects of Energy Storage Systems Grid Code Requirements on Interface Protection Performances in Low Voltage Networks

by Fabio Bignucolo, Alberto Cerretti, Massimiliano Coppo, Andrea Savio and Roberto Turri

Energies 2017, 10(3), 387; https://doi.org/10.3390/en10030387 - 18 Mar 2017

Cited by 30 | Viewed by 6154

The ever-growing penetration of local generation in distribution networks and the large diffusion of energy storage systems (ESSs) foreseen in the near future are bound to affect the effectiveness of interface protection systems (IPSs), with negative impact on the safety of medium voltage [...] Read more.

The ever-growing penetration of local generation in distribution networks and the large diffusion of energy storage systems (ESSs) foreseen in the near future are bound to affect the effectiveness of interface protection systems (IPSs), with negative impact on the safety of medium voltage (MV) and low voltage (LV) systems. With the scope of preserving the main network stability, international and national grid connection codes have been updated recently. Consequently, distributed generators (DGs) and storage units are increasingly called to provide stabilizing functions according to local voltage and frequency. This can be achieved by suitably controlling the electronic power converters interfacing small-scale generators and storage units to the network. The paper focuses on the regulating functions required to storage units by grid codes currently in force in the European area. Indeed, even if such regulating actions would enable local units in participating to network stability under normal steady-state operating conditions, it is shown through dynamic simulations that they may increase the risk of unintentional islanding occurrence. This means that dangerous operating conditions may arise in LV networks in case dispersed generators and storage systems are present, even if all the end-users are compliant with currently applied connection standards. Full article

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11 pages, 1356 KiB

Open AccessArticle

Using Grass Cuttings from Sports Fields for Anaerobic Digestion and Combustion

by Meike Nitsche, Frank Hensgen and Michael Wachendorf

Energies 2017, 10(3), 388; https://doi.org/10.3390/en10030388 - 18 Mar 2017

Cited by 17 | Viewed by 5239

Sports fields provide a recreation space for citizens, but also generate grass biomass, which is cut weekly during the main seasons and therefore could be used in energy generation (combustion or anaerobic digestion). To evaluate the technical suitability of the grass cuttings, silage [...] Read more.

Sports fields provide a recreation space for citizens, but also generate grass biomass, which is cut weekly during the main seasons and therefore could be used in energy generation (combustion or anaerobic digestion). To evaluate the technical suitability of the grass cuttings, silage was produced from four sports fields during one vegetation period and investigated for relevant properties. Potential methane yield was determined with batch tests. Mean methane yield was 291.86 l_N·kg⁻¹ VS_added (VS, volatile solid). Neutral detergent fiber concentration was low (44.47% DM, dry matter), yet mineral concentration was high in comparison to grass types cut at a lower frequency. Concentrations of Cl, N, and S, which may lead to unfavorable emissions, fouling, and corrosion during combustion, were too high for an unproblematic combustion process. This was still the case even after applying a mineral-reducing pretreatment, which generates a fiber-rich press cake and a press fluid rich in easy soluble substances. Digestion of the press fluid led to methane yields of 340.10 l_N·kg⁻¹ VS_added and the press cake had a higher heating value of 19.61 MJ·kg⁻¹ DM, which is close to that of coniferous wood. It can be concluded that biomass from sports fields could be a suitable co-substrate in bio-energy generation. Full article

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

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30 pages, 6270 KiB

Open AccessArticle

Performance Improvement for Two-Stage Single-Phase Grid-Connected Converters Using a Fast DC Bus Control Scheme and a Novel Synchronous Frame Current Controller

by Bingzhang Li, Shenghua Huang and Xi Chen

Energies 2017, 10(3), 389; https://doi.org/10.3390/en10030389 - 18 Mar 2017

Cited by 19 | Viewed by 5966

Two-stage single-phase grid-connected converters are widely used in renewable energy applications. Due to the presence of a second harmonic ripple across the DC bus voltage, it is very challenging to design the DC bus voltage control scheme in single-phase grid-connected inverters. The DC [...] Read more.

Two-stage single-phase grid-connected converters are widely used in renewable energy applications. Due to the presence of a second harmonic ripple across the DC bus voltage, it is very challenging to design the DC bus voltage control scheme in single-phase grid-connected inverters. The DC bus voltage controller must filter the ripple and balance a tradeoff between low harmonic distortion and high bandwidth. This paper presents a fast DC bus voltage controller, which uses a second order digital finite impulse response (FIR) notch filter in conjunction with input power feedforward scheme to ensure the steady-state and dynamic performance. To gain the input power without extra hardware, a Kalman filter is incorporated to estimate the DC bus input current. At the same time, a modulation compensation strategy is implemented to eliminate the nonlinearity of the grid current control loop, which is caused by the DC bus voltage ripple. Moreover, a novel synchronous frame current controller for single-phase systems is also introduced, and its equivalent model in stationary frame has been derived. Simulation and experimental results are provided to verify the effective of the proposed control scheme. Full article

(This article belongs to the Special Issue Grid-Connected Photovoltaic Systems)

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22 pages, 8277 KiB

Open AccessEditor’s ChoiceArticle

Online Reliable Peak Charge/Discharge Power Estimation of Series-Connected Lithium-Ion Battery Packs

by Bo Jiang, Haifeng Dai, Xuezhe Wei, Letao Zhu and Zechang Sun

Energies 2017, 10(3), 390; https://doi.org/10.3390/en10030390 - 19 Mar 2017

Cited by 29 | Viewed by 7717

The accurate peak power estimation of a battery pack is essential to the power-train control of electric vehicles (EVs). It helps to evaluate the maximum charge and discharge capability of the battery system, and thus to optimally control the power-train system to meet [...] Read more.

The accurate peak power estimation of a battery pack is essential to the power-train control of electric vehicles (EVs). It helps to evaluate the maximum charge and discharge capability of the battery system, and thus to optimally control the power-train system to meet the requirement of acceleration, gradient climbing and regenerative braking while achieving a high energy efficiency. A novel online peak power estimation method for series-connected lithium-ion battery packs is proposed, which considers the influence of cell difference on the peak power of the battery packs. A new parameter identification algorithm based on adaptive ratio vectors is designed to online identify the parameters of each individual cell in a series-connected battery pack. The ratio vectors reflecting cell difference are deduced strictly based on the analysis of battery characteristics. Based on the online parameter identification, the peak power estimation considering cell difference is further developed. Some validation experiments in different battery aging conditions and with different current profiles have been implemented to verify the proposed method. The results indicate that the ratio vector-based identification algorithm can achieve the same accuracy as the repetitive RLS (recursive least squares) based identification while evidently reducing the computation cost, and the proposed peak power estimation method is more effective and reliable for series-connected battery packs due to the consideration of cell difference. Full article

(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))

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23 pages, 4751 KiB

Open AccessArticle

Assessment Analysis and Forecasting for Security Early Warning of Energy Consumption Carbon Emissions in Hebei Province, China

by Yi Liang, Dongxiao Niu, Haichao Wang and Hanyu Chen

Energies 2017, 10(3), 391; https://doi.org/10.3390/en10030391 - 19 Mar 2017

Cited by 12 | Viewed by 5180

Against the backdrop of increasingly serious global climate change and the development of the low-carbon economy, the coordination between energy consumption carbon emissions (ECCE) and regional population, resources, environment, economy and society has become an important subject. In this paper, the research focuses [...] Read more.

Against the backdrop of increasingly serious global climate change and the development of the low-carbon economy, the coordination between energy consumption carbon emissions (ECCE) and regional population, resources, environment, economy and society has become an important subject. In this paper, the research focuses on the security early warning of ECCE in Hebei Province, China. First, an assessment index system of the security early warning of ECCE is constructed based on the pressure-state-response (P-S-R) model. Then, the variance method and linearity weighted method are used to calculate the security early warning index of ECCE. From the two dimensions of time series and spatial pattern, the security early warning conditions of ECCE are analyzed in depth. Finally, with the assessment analysis of the data from 2000 to 2014, the prediction of the security early warning of carbon emissions from 2015 to 2020 is given, using a back propagation neural network based on a kidney-inspired algorithm (KA-BPNN) model. The results indicate that: (1) from 2000 to 2014, the security comprehensive index of ECCE demonstrates a fluctuating upward trend in general and the trend of the alarm level is “Severe warning”–“Moderate warning”–“Slight warning”; (2) there is a big spatial difference in the security of ECCE, with relatively high-security alarm level in the north while it is relatively low in the other areas; (3) the security index shows the trend of continuing improvement from 2015 to 2020, however the security level will remain in the state of “Semi-secure” for a long time and the corresponding alarm is still in the state of “Slight warning”, reflecting that the situation is still not optimistic. Full article

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20 pages, 4349 KiB

Open AccessArticle

Techno-Economic Evaluation of a Stand-Alone Power System Based on Solar Power/Batteries for Global System for Mobile Communications Base Stations

by Mohammed H. Alsharif

Energies 2017, 10(3), 392; https://doi.org/10.3390/en10030392 - 19 Mar 2017

Cited by 27 | Viewed by 5966

Energy consumption in cellular networks is receiving significant attention from academia and the industry due to its significant potential economic and ecological influence. Energy efficiency and renewable energy are the main pillars of sustainability and environmental compatibility. Technological advancements and cost reduction for [...] Read more.

Energy consumption in cellular networks is receiving significant attention from academia and the industry due to its significant potential economic and ecological influence. Energy efficiency and renewable energy are the main pillars of sustainability and environmental compatibility. Technological advancements and cost reduction for photovoltaics are making cellular base stations (BSs; a key source of energy consumption in cellular networks) powered by solar energy sources a long-term promising solution for the mobile cellular network industry. This paper addresses issues of deployment and operation of two solar-powered global system for mobile communications (GSM) BSs that are being deployed at present (GSM BS 2/2/2 and GSM BS 4/4/4). The study is based on the characteristics of South Korean solar radiation exposure. The optimum criteria as well as economic and technical feasibility for various BSs are analyzed using a hybrid optimization model for electric renewables. In addition, initial capital, replacement, operations, maintenance, and total net present costs for various solar-powered BSs are discussed. Furthermore, the economic feasibility of the proposed solar system is compared with conventional energy sources in urban and remote areas. Full article

(This article belongs to the Special Issue Energy Production Systems)

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13 pages, 3251 KiB

Open AccessArticle

International Electronical Committee (IEC) 61850 Mapping with Constrained Application Protocol (CoAP) in Smart Grids Based European Telecommunications Standard Institute Machine-to-Machine (M2M) Environment

by In-Jae Shin, Byung-Kwen Song and Doo-Seop Eom

Energies 2017, 10(3), 393; https://doi.org/10.3390/en10030393 - 20 Mar 2017

Cited by 22 | Viewed by 12101

As power systems develop rapidly into smarter and more flexible configurations, so too must the communication technologies that support them. Machine-to-machine (M2M) communication in power systems enables information collection by combining sensors and communication protocols. In doing so, M2M technology supports communication between [...] Read more.

As power systems develop rapidly into smarter and more flexible configurations, so too must the communication technologies that support them. Machine-to-machine (M2M) communication in power systems enables information collection by combining sensors and communication protocols. In doing so, M2M technology supports communication between machines to improve power quality and protection coordination. When functioning in a “smart grid” environment, M2M has been labelled by the European Telecommunications Standard Institute (ETSI). International Electronical Committee (IEC) 61850 as the most important standard in power network systems. As evidence, this communication platform has been used for device data collection/control in substation automation systems and distribution automation systems. If the IEC 61850 information model were to be combined with a set of contemporary web protocols, the potential benefits would be enormous. Therefore, a constrained application protocol (CoAP) has been adopted to create an ETSI M2M communication architecture. CoAP is compared with other protocols (MQTT, SOAP) to demonstrate the validity of using it. This M2M communication technology is applied in an IEC61850, and use the OPNET Modeler 17.1 to demonstrate intercompatibility of CoAP Gateway. The proposed IEC 61850 and CoAP mapping scheme reduces the mapping time and improves throughput. CoAP is useful in the ETSI M2M environment where device capability is able to be limited. Full article

(This article belongs to the Collection Smart Grid)

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16 pages, 5202 KiB

Open AccessEditor’s ChoiceArticle

Neuro-Fuzzy Wavelet Based Adaptive MPPT Algorithm for Photovoltaic Systems

by Syed Zulqadar Hassan, Hui Li, Tariq Kamal, Uğur Arifoğlu, Sidra Mumtaz and Laiq Khan

Energies 2017, 10(3), 394; https://doi.org/10.3390/en10030394 - 20 Mar 2017

Cited by 52 | Viewed by 7457

An intelligent control of photovoltaics is necessary to ensure fast response and high efficiency under different weather conditions. This is often arduous to accomplish using traditional linear controllers, as photovoltaic systems are nonlinear and contain several uncertainties. Based on the analysis of the [...] Read more.

An intelligent control of photovoltaics is necessary to ensure fast response and high efficiency under different weather conditions. This is often arduous to accomplish using traditional linear controllers, as photovoltaic systems are nonlinear and contain several uncertainties. Based on the analysis of the existing literature of Maximum Power Point Tracking (MPPT) techniques, a high performance neuro-fuzzy indirect wavelet-based adaptive MPPT control is developed in this work. The proposed controller combines the reasoning capability of fuzzy logic, the learning capability of neural networks and the localization properties of wavelets. In the proposed system, the Hermite Wavelet-embedded Neural Fuzzy (HWNF)-based gradient estimator is adopted to estimate the gradient term and makes the controller indirect. The performance of the proposed controller is compared with different conventional and intelligent MPPT control techniques. MATLAB results show the superiority over other existing techniques in terms of fast response, power quality and efficiency. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2017)

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19 pages, 10909 KiB

Open AccessFeature PaperArticle

Wind Turbine Power Curve Design for Optimal Power Generation in Wind Farms Considering Wake Effect

by Jie Tian, Dao Zhou, Chi Su, Mohsen Soltani, Zhe Chen and Frede Blaabjerg

Energies 2017, 10(3), 395; https://doi.org/10.3390/en10030395 - 20 Mar 2017

Cited by 27 | Viewed by 7430

In modern wind farms, maximum power point tracking (MPPT) is widely implemented. Using the MPPT method, each individual wind turbine is controlled by its pitch angle and tip speed ratio to generate the maximum active power. In a wind farm, the upstream wind [...] Read more.

In modern wind farms, maximum power point tracking (MPPT) is widely implemented. Using the MPPT method, each individual wind turbine is controlled by its pitch angle and tip speed ratio to generate the maximum active power. In a wind farm, the upstream wind turbine may cause power loss to its downstream wind turbines due to the wake effect. According to the wake model, downstream power loss is also determined by the pitch angle and tip speed ratio of the upstream wind turbine. By optimizing the pitch angle and tip speed ratio of each wind turbine, the total active power of the wind farm can be increased. In this paper, the optimal pitch angle and tip speed ratio are selected for each wind turbine by the exhausted search. Considering the estimation error of the wake model, a solution to implement the optimized pitch angle and tip speed ratio is proposed, which is to generate the optimal control curves for each individual wind turbine off-line. In typical wind farms with regular layout, based on the detailed analysis of the influence of pitch angle and tip speed ratio on the total active power of the wind farm by the exhausted search, the optimization is simplified with the reduced computation complexity. By using the optimized control curves, the annual energy production (AEP) is increased by 1.03% compared to using the MPPT method in a case-study of a typical eighty-turbine wind farm. Full article

(This article belongs to the Collection Wind Turbines)

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16 pages, 3008 KiB

Open AccessArticle

An Improved Multi-Infeed Effective Short-Circuit Ratio for AC/DC Power Systems with Massive Shunt Capacitors Installed

by Shiwu Liao, Wei Yao, Xiaomeng Ai, Jinyu Wen, Qing Liu, Yanhong Jiang, Jian Zhang and Jingzhe Tu

Energies 2017, 10(3), 396; https://doi.org/10.3390/en10030396 - 20 Mar 2017

Cited by 10 | Viewed by 5359

The multi-infeed effective short-circuit ratio (MESCR) is widely used in indicating the strength of multi-infeed AC/DC power systems. However, when the widely used MESCR was adopted to evaluate the stability margin of the Eastern China Grid including three infeed ultra-high-voltage DC (UHVDC) and [...] Read more.

The multi-infeed effective short-circuit ratio (MESCR) is widely used in indicating the strength of multi-infeed AC/DC power systems. However, when the widely used MESCR was adopted to evaluate the stability margin of the Eastern China Grid including three infeed ultra-high-voltage DC (UHVDC) and five high-voltage DC transmission lines in 2016, the MESCR result indicated the system was strong enough but in fact occasionally collapses after the N-1 contingency. To determine the reason for this conflict, this paper theoretically analyzes the limitations of the existing MESCR. The theoretical analysis reveals that when a large amount of capacitor compensations are concentratively installed in the system, the conventional MESCR will not be able to reflect the capacitor compensations’ influence on the system stability, and no matter how many capacitors are installed or where the capacitors are installed, the MESCR almost retains the same value; namely, the MESCR is saturated in such systems. To address the saturation problem of conventional MESCR, this paper proposes an improved multi-infeed effective short-circuit ratio (IMESCR) which considers the influences of all capacitor compensations by converting all capacitors installed throughout the system to virtual capacitors at the DC inverter station. Case studies are carried out based on the New England 39-bus system and the Eastern China Grid, respectively. The simulation results verify the theoretical analysis of the MESCR’s limitations in evaluating the stability of power systems with massive capacitors installed, and proves that the proposed IMESCR could accurately indicate the strength of AC/DC power systems. Therefore, the proposed IMESCR provides a new index for evaluating the stability margin of power systems with massive capacitor compensations installed. Full article

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

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11 pages, 3100 KiB

Open AccessArticle

Thermal Stability of Modified Insulation Paper Cellulose Based on Molecular Dynamics Simulation

by Chao Tang, Song Zhang, Qian Wang, Xiaobo Wang and Jian Hao

Energies 2017, 10(3), 397; https://doi.org/10.3390/en10030397 - 20 Mar 2017

Cited by 15 | Viewed by 5230

In this paper, polysiloxane is used to modify insulation paper cellulose, and molecular dynamics methods are used to evaluate the glass transition temperature and mechanical properties of the paper before and after the modification. Analysis of the static mechanical performance of the model [...] Read more.

In this paper, polysiloxane is used to modify insulation paper cellulose, and molecular dynamics methods are used to evaluate the glass transition temperature and mechanical properties of the paper before and after the modification. Analysis of the static mechanical performance of the model shows that, with increasing temperature, the elastic modulus of both the modified and unmodified cellulose models decreases gradually. However, the elastic modulus of the modified model is greater than that of the unmodified model. Using the specific volume method and calculation of the mean square displacement of the models, the glass transition temperature of the modified cellulose model is found to be 48 K higher than that of the unmodified model. Finally, the changes in the mechanical properties and glass transition temperature of the model are analyzed by energy and free volume theory. The glass transition temperatures of the unmodified and modified cellulose models are approximately 400 K and 450 K, respectively. These results are consistent with the conclusions obtained from the specific volume method and the calculation of the mean square displacement. It can be concluded that the modification of insulation paper cellulose with polysiloxane will effectively improve its thermal stability. Full article

(This article belongs to the Special Issue Selected Papers from 2016 IEEE International Conference on High Voltage Engineering (ICHVE 2016))

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18 pages, 4381 KiB

Open AccessFeature PaperArticle

Experimental Results on a Wireless Wattmeter Device for the Integration in Home Energy Management Systems

by Eduardo M. G. Rodrigues, Radu Godina, Miadreza Shafie-khah and João P. S. Catalão

Energies 2017, 10(3), 398; https://doi.org/10.3390/en10030398 - 20 Mar 2017

Cited by 13 | Viewed by 7213

This paper presents a home area network (HAN)-based domestic load energy consumption monitoring prototype device as part of an advanced metering system (AMS). This device can be placed on individual loads or configured to measure several loads as a whole. The wireless communication [...] Read more.

This paper presents a home area network (HAN)-based domestic load energy consumption monitoring prototype device as part of an advanced metering system (AMS). This device can be placed on individual loads or configured to measure several loads as a whole. The wireless communication infrastructure is supported on IEEE 805.12.04 radios that run a ZigBee stack. Data acquisition concerning load energy transit is processed in real time and the main electrical parameters are then transmitted through a RF link to a wireless terminal unit, which works as a data logger and as a human-machine interface. Voltage and current sensing are implemented using Hall effect principle-based transducers, while C code is developed on two 16/32-bit microcontroller units (MCUs). The main features and design options are then thoroughly discussed. The main contribution of this paper is that the proposed metering system measures the reactive energy component through the Hilbert transform for low cost measuring device systems. Full article

(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)

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14 pages, 698 KiB

Open AccessArticle

Development of Brazilian Biodiesel Sector from the Perspective of Stakeholders

by Bárbara Françoise Cardoso, Pery Francisco Assis Shikida and Adele Finco

Energies 2017, 10(3), 399; https://doi.org/10.3390/en10030399 - 20 Mar 2017

Cited by 12 | Viewed by 3922

In Brazil, the main program with respect to biodiesel is the National Program of Biodiesel Production and Use (NPBP). It is also considered the regulation mark of biodiesel production in Brazil and its directives are social inclusion and regional development. Considering these directives, [...] Read more.

In Brazil, the main program with respect to biodiesel is the National Program of Biodiesel Production and Use (NPBP). It is also considered the regulation mark of biodiesel production in Brazil and its directives are social inclusion and regional development. Considering these directives, this paper aims to analyse the perspective of biodiesel sector stakeholders in Brazil to understand whether NPBP directives are in consonance with the reality of the sector for its development. A questionnaire was created with 48 questions in order to understand the importance of 13 variables for the stakeholders, and the responses were treated by factor analysis (FA). The results showed the existence of a trade-off related to technological advances in biodiesel production that confronts NPBP directives, that is, the biodiesel sector tends not to evolve in terms of the use of advanced technologies. If policies change so as to develop the biodiesel sector using advanced technologies, NPBP should change its directives in order to involve family farmers in another way in the Brazilian economy. Full article

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17 pages, 5204 KiB

Open AccessArticle

A Droop Control Based Three Phase Bidirectional AC-DC Converter for More Electric Aircraft Applications

by Xiancheng Zheng, Fei Gao, Husan Ali and Huamei Liu

Energies 2017, 10(3), 400; https://doi.org/10.3390/en10030400 - 20 Mar 2017

Cited by 10 | Viewed by 6165

This paper addresses the design and implementation of a droop controlled three phase bidirectional AC-DC converter for more electric aircraft (MEA) applications. A unified control strategy using a droop characteristic is presented to achieve the bidirectional power flow between the AC and DC [...] Read more.

This paper addresses the design and implementation of a droop controlled three phase bidirectional AC-DC converter for more electric aircraft (MEA) applications. A unified control strategy using a droop characteristic is presented to achieve the bidirectional power flow between the AC and DC source while maintaining a stable DC output voltage. Based on the rigorous control design, the converter is capable of operating over a wide frequency range with a unity power factor. The key findings obtained from the theoretical analysis are confirmed by simulation studies and further validated by a scaled down laboratory prototype. The practical results show good performance of the bidirectional converter and demonstrate the effectiveness of the proposed control strategies. Full article

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

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26 pages, 9922 KiB

Open AccessArticle

Methodology for Determination of the Number of Equipment Malfunctions Due to Voltage Sags

by Alena Otcenasova, Roman Bodnar, Michal Regula, Marek Hoger and Michal Repak

Energies 2017, 10(3), 401; https://doi.org/10.3390/en10030401 - 20 Mar 2017

Cited by 10 | Viewed by 5326

This article deals with the assessment of the reliability of sensitive equipment due to voltage sags. The most frequent problems of power quality are voltage sags. Equipment that cannot withstand short-term voltage sag is defined as sensitive device. Sensitivity of such equipment can [...] Read more.

This article deals with the assessment of the reliability of sensitive equipment due to voltage sags. The most frequent problems of power quality are voltage sags. Equipment that cannot withstand short-term voltage sag is defined as sensitive device. Sensitivity of such equipment can be described by the voltage–tolerance curves. A device (generator) to generate voltage sags (also interruptions) with duration at least 1 ms has been designed and developed for this purpose. Equipment sensitive to voltage sags was tested using this generator. Overall, five types of sensitive equipment were tested: personal computers, fluorescent lamps, drives with speed control, programmable logic controllers, and contactors. The measured sensitivity curves of these devices have been used to determine the number of trips (failures) due to voltage sags. Two probabilistic methods (general probability method and cumulative probability method) to determine probability of equipment failure occurrence are used. These methods were applied to real node in the distribution system with its actual performance of voltage sags/swells. The calculations also contain different levels of sensitivity of the sensitive equipment. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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18 pages, 26136 KiB

Open AccessArticle

High Frequency Dual-Buck Full-Bridge Inverter Utilizing a Dual-Core MCU and Parallel Algorithm for Renewable Energy Applications

by Zhun Meng, Yi-Feng Wang, Liang Yang and Wei Li

Energies 2017, 10(3), 402; https://doi.org/10.3390/en10030402 - 21 Mar 2017

Cited by 6 | Viewed by 6007

A high frequency dual-buck full-bridge inverter for small power renewable energy applications is proposed in this paper. The implementation of the wide band gap SiC (Silicon Carbide) power device contributes to the high switching frequency of 400 kHz. This high frequency contributes to [...] Read more.

A high frequency dual-buck full-bridge inverter for small power renewable energy applications is proposed in this paper. The implementation of the wide band gap SiC (Silicon Carbide) power device contributes to the high switching frequency of 400 kHz. This high frequency contributes to reduced converter volume as well as improved power density, which greatly strengthens its portability and application range. For the control strategy, a voltage-current dual loop controller is employed. A three-pole-three-zero (3P3Z) compensator is applied in the current loop in order to track the current reference without static error. A voltage loop two-pole two-zero (2P2Z) compensator is used to generate the current reference for stabilizing the DC bus voltage. Not only is the inner current loop analyzed in detail, which includes the modeling of the equivalent inductor-capacitor-inductor (LCL)-type inverter and the design of the 3P3Z compensator, but also the outer voltage loop is discussed, the model of which is established based on the energy balance. Furthermore, a feedback linearization method is adopted to simplify the duty cycle calculation and helps to accelerate the control speed. A second-order generalized integrator software phase lock loop (SOGI-SPLL) is employed to obtain the phase angle and to synchronize the inverter output current with the grid voltage. A parallel structure algorithm is conducted based on a dual-core microcontroller unit (MCU) for the first time to control the high frequency inverter. This approach avoids the contradiction between the high frequency operation and the limited computing capacity of the conventional single-core MCUs. The software structure, time-consuming distribution, and interactive communication method are analyzed in detailed. Finally, this paper verifies the feasibility of the theoretical analyses through simulation and experiments based on a 1 kW prototype. Full article

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17 pages, 4120 KiB

Open AccessArticle

Power Controlling, Monitoring and Routing Center Enabled by a DC-Transformer †

by Syed Ashad Mustufa Younus, Matteo Nardello, Pietro Tosato and Davide Brunelli

Energies 2017, 10(3), 403; https://doi.org/10.3390/en10030403 - 21 Mar 2017

Cited by 2 | Viewed by 5709

The penetration of various types of renewable sources and on-site storage devices have recently focused attention towards DC power distribution in consumer grids to achieve the target of zero/positive energy buildings and communities. To achieve this target, the most important component is the [...] Read more.

The penetration of various types of renewable sources and on-site storage devices have recently focused attention towards DC power distribution in consumer grids to achieve the target of zero/positive energy buildings and communities. To achieve this target, the most important component is the DC consumer grid architecture which can integrate not only renewable sources and storage, but also enable the implementation in any conventional AC distribution network without any significant upgrade. To this end, a unique DC Transformer enabled DC microgrid architecture is presented in this paper. The architecture, called PCmRC (power controlling monitoring routing center) is proposed to manage distributed energy sources and storage at any stage and also directly interconnects the DC consumer grid with the conventional AC power grid. This paper also investigates detailed control algorithms of each component and the DC Transformer topology in addition to proposing four unique stages of grid operational modes to enhance the overall grid stability in any operational condition. The main objectives are to maximize the exploitation of renewable sources, to decrease reliance on fossil fuels, to boost the overall efficiency of the grid by reducing the power conversion losses and demand side management in all possible forms. The simulation platform is designed in MATLAB/Simulink. Simulation results of several types of case studies show the effectiveness of the proposed power distribution and management model. Full article

(This article belongs to the Collection Smart Grid)

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13 pages, 3505 KiB

Open AccessArticle

Energy Management of Parallel-Connected Cells in Electric Vehicles Based on Fuzzy Logic Control

by Chuanxue Song, Yulong Shao, Shixin Song, Cheng Chang, Fang Zhou, Silun Peng and Feng Xiao

Energies 2017, 10(3), 404; https://doi.org/10.3390/en10030404 - 21 Mar 2017

Cited by 22 | Viewed by 6537

Inconsistencies that are associated with parallel-connected cells used in electric vehicles induce varied states of charge (SOCs) in each cell. Thus, loop current in the battery pack is inevitable, and this reduces overall capacity, energy utilization rate, and pack lifetime. However, [...] Read more.

Inconsistencies that are associated with parallel-connected cells used in electric vehicles induce varied states of charge (SOCs) in each cell. Thus, loop current in the battery pack is inevitable, and this reduces overall capacity, energy utilization rate, and pack lifetime. However, no method is available to address loop current. To reduce loop current and the resulting battery inconsistency, a parallel-connected cell pack (PCCP) model that considers thermal effects is established, and a novel Simscape model that is based on PCCP is successfully constructed. Furthermore, the strategy of parallel-connected cell energy management (PCCEM) is proposed to utilize fuzzy logic control (FLC) strategy, which automatically adjusts the number of cells in a circuit in accordance with the load demand, and turns on the first N switches in the corresponding SOC order. The New European Driving Cycle (NEDC) driving cycle simulation shows that the PCCEM strategy considerably reduces loop current and improves the consistency of battery performance and the utilization rate of battery power. Full article

(This article belongs to the Special Issue Energy Management, Control, and System Architectures for Electric Vehicle Applications)

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11 pages, 2806 KiB

Open AccessArticle

Environmental Potential of Using Coal-Processing Waste as the Primary and Secondary Fuel for Energy Providers

by Galina Nyashina, Jean Claude Legros and Pavel Strizhak

Energies 2017, 10(3), 405; https://doi.org/10.3390/en10030405 - 21 Mar 2017

Cited by 34 | Viewed by 4765

The main anthropogenic emissions (CO, CO₂, NO_x, SO_x) produced by the processing (combustion) of wastes (coal filter cakes) were measured directly for the first time. The research considered the most widespread coal filter cakes: those of nonbaking, [...] Read more.

The main anthropogenic emissions (CO, CO₂, NO_x, SO_x) produced by the processing (combustion) of wastes (coal filter cakes) were measured directly for the first time. The research considered the most widespread coal filter cakes: those of nonbaking, low-caking, coking, flame, and gas coals. These filter cakes are regarded as promising components for the technologies of coal-water slurry (CWS) and coal-water slurry containing petrochemicals (CWSP). According to our estimates, the annual increment of such wastes in the world is as high as 100 million tons. Consequently, the effective utilization of these wastes in the power industry is of high interest. The evaluation of hazardous emissions from the combustion of such wastes shows that filter cakes produce a similar amount of CO and CO₂ as the initially-used coals but filter cakes are more cost-effective. We have established that CWS and CWSP technologies can be used to reduce NO_x and SO_x emissions. To reduce CO and CO₂ emissions when burning filter cakes, we need to switch to low-temperature combustion. Lowering the combustion temperature of filter cakes from 850 °C down to 650 °C decreases the underburning insignificantly while decreasing CO and CO₂ emissions by 30–40%. Full article

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22 pages, 7488 KiB

Open AccessArticle

Research on Unstructured Text Data Mining and Fault Classification Based on RNN-LSTM with Malfunction Inspection Report

by Daqian Wei, Bo Wang, Gang Lin, Dichen Liu, Zhaoyang Dong, Hesen Liu and Yilu Liu

Energies 2017, 10(3), 406; https://doi.org/10.3390/en10030406 - 21 Mar 2017

Cited by 78 | Viewed by 7597

This paper documents the condition-based maintenance (CBM) of power transformers, the analysis of which relies on two basic data groups: structured (e.g., numeric and categorical) and unstructured (e.g., natural language text narratives) which accounts for 80% of data required. However, unstructured data comprised [...] Read more.

This paper documents the condition-based maintenance (CBM) of power transformers, the analysis of which relies on two basic data groups: structured (e.g., numeric and categorical) and unstructured (e.g., natural language text narratives) which accounts for 80% of data required. However, unstructured data comprised of malfunction inspection reports, as recorded by operation and maintenance of the power grid, constitutes an abundant untapped source of power insights. This paper proposes a method for malfunction inspection report processing by deep learning, which combines the text data mining–oriented recurrent neural networks (RNN) with long short-term memory (LSTM). In this paper, the effectiveness of the RNN-LSTM network for modeling inspection data is established with a straightforward training strategy in which we replicate targets at each sequence step. Then, the corresponding fault labels are given in datasets, in order to calculate the accuracy of fault classification by comparison with the original data labels and output samples. Experimental results can reflect how key parameters may be selected in the configuration of the key variables to achieve optimal results. The accuracy of the fault recognition demonstrates that the method we proposed can provide a more effective way for grid inspection personnel to deal with unstructured data. Full article

(This article belongs to the Special Issue Optimal and Neural Network Control for Renewables and Electric Power and Energy Systems)

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11 pages, 1094 KiB

Open AccessArticle

On the Source of Oscillatory Behaviour during Switching of Power Enhancement Mode GaN HEMTs

by Loizos Efthymiou, Gianluca Camuso, Giorgia Longobardi, Terry Chien, Max Chen and Florin Udrea

Energies 2017, 10(3), 407; https://doi.org/10.3390/en10030407 - 21 Mar 2017

Cited by 24 | Viewed by 6878

With Gallium Nitride (GaN) device technology for power electronics applications being ramped up for volume production, an increasing amount of research is now focused on the performance of GaN power devices in circuits. In this study, an enhancement mode GaN high electron mobility [...] Read more.

With Gallium Nitride (GaN) device technology for power electronics applications being ramped up for volume production, an increasing amount of research is now focused on the performance of GaN power devices in circuits. In this study, an enhancement mode GaN high electron mobility transistor (HEMT) is switched in a clamped inductive switching configuration with the aim of investigating the source of oscillatory effects observed. These arise as a result of the increased switching speed capability of GaN devices compared to their silicon counterparts. The study identifies the two major mechanisms (Miller capacitance charge and parasitic common source inductance) that can lead to ringing behaviour during turn-off and considers the effect of temperature on the latter. Furthermore, the experimental results are backed by SPICE modelling to evaluate the contribution of different circuit components to oscillations. The study concludes with good design techniques that can suppress the effects discussed. Full article

(This article belongs to the Special Issue Semiconductor Power Devices)

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20 pages, 8106 KiB

Open AccessArticle

A Short-Term Load Forecasting Model with a Modified Particle Swarm Optimization Algorithm and Least Squares Support Vector Machine Based on the Denoising Method of Empirical Mode Decomposition and Grey Relational Analysis

by Dongxiao Niu and Shuyu Dai

Energies 2017, 10(3), 408; https://doi.org/10.3390/en10030408 - 21 Mar 2017

Cited by 61 | Viewed by 5464

As an important part of power system planning and the basis of economic operation of power systems, the main work of power load forecasting is to predict the time distribution and spatial distribution of future power loads. The accuracy of load forecasting will [...] Read more.

As an important part of power system planning and the basis of economic operation of power systems, the main work of power load forecasting is to predict the time distribution and spatial distribution of future power loads. The accuracy of load forecasting will directly influence the reliability of the power system. In this paper, a novel short-term Empirical Mode Decomposition-Grey Relational Analysis-Modified Particle Swarm Optimization-Least Squares Support Vector Machine (EMD-GRA-MPSO-LSSVM) load forecasting model is proposed. The model uses the de-noising method combining empirical mode decomposition and grey relational analysis to process the original load series and forecasts the processed subsequences by the algorithm of modified particle swarm optimization and least square support vector machine. Then, the final forecasting results can be obtained after reconstructing the forecasting series. This paper takes the Jibei area as an example to produce an empirical analysis for load forecasting. The model input includes the hourly load one week before the forecasting day and the daily maximum temperature, daily minimum temperature, daily average temperature, relative humidity, wind force, date type of the forecasting day. The model output is the hourly load of the forecasting day. The models of BP neural network, SVM (Support vector machine), LSSVM (Least squares support vector machine), PSO-LSSVM (Particle swarm optimization-Least squares support vector machine), MPSO-LSSVM (Modified particle swarm optimization-Least squares support vector machine), EMD-MPSO-LSSVM are selected to compare with the model of EMD-GRA-MPSO-LSSVM using the same sample. The comparison results verify that the short-term load forecasting model of EMD-GRA-MPSO-LSSVM proposed in this paper is superior to other models and has strong generalization ability and robustness. It can achieve good forecasting effect with high forecasting accuracy, providing a new idea and reference for accurate short-term load forecasting. Full article

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7 pages, 1954 KiB

Open AccessArticle

Doping-Induced Isotopic Mg¹¹B₂ Bulk Superconductor for Fusion Application

by Qi Cai, Qianying Guo, Yongchang Liu, Zongqing Ma, Huijun Li, Wenbin Qiu, Dipak Patel, Hyunseock Jie, Jung Ho Kim, Mehmet Somer, Ekrem Yanmaz, Arnaud Devred, Vladimir Luzin, Amanullah Fatehmulla, Wazirzada Aslam Farooq, Daniel Gajda, Yoshio Bando, Yusuke Yamauchi, Subrata Pradhan and Md. Shahriar A. Hossain

Energies 2017, 10(3), 409; https://doi.org/10.3390/en10030409 - 21 Mar 2017

Cited by 23 | Viewed by 5222

Superconducting wires are widely used for fabricating magnetic coils in fusion reactors. Superconducting magnet system represents a key determinant of the thermal efficiency and the construction/operating costs of such a reactor. In consideration of the stability of ¹¹B against fast neutron irradiation [...] Read more.

Superconducting wires are widely used for fabricating magnetic coils in fusion reactors. Superconducting magnet system represents a key determinant of the thermal efficiency and the construction/operating costs of such a reactor. In consideration of the stability of ¹¹B against fast neutron irradiation and its lower induced radioactivation properties, MgB₂ superconductor with ¹¹B serving as the boron source is an alternative candidate for use in fusion reactors with a severe high neutron flux environment. In the present work, the glycine-doped Mg¹¹B₂ bulk superconductor was synthesized from isotopic ¹¹B powder to enhance the high field properties. The critical current density was enhanced (10³ A·cm⁻² at 20 K and 5 T) over the entire field in contrast with the sample prepared from natural boron. Full article

(This article belongs to the Special Issue Fusion Power)

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15 pages, 4243 KiB

Open AccessArticle

Accurate and Efficient Torque Control of an Interior Permanent Magnet Synchronous Motor in Electric Vehicles Based on Hall-Effect Sensors

by Lei Yu, Youtong Zhang and Wenqing Huang

Energies 2017, 10(3), 410; https://doi.org/10.3390/en10030410 - 21 Mar 2017

Cited by 15 | Viewed by 7791

Abstract: In this paper, an effective method to achieve accurate and efficient torque control of an interior permanent magnet synchronous motor (IPMSM) in electric vehicles, based on low-resolution Hall-effect sensors, is proposed. The high-resolution rotor position is estimated by a proportional integral [...] Read more.

Abstract: In this paper, an effective method to achieve accurate and efficient torque control of an interior permanent magnet synchronous motor (IPMSM) in electric vehicles, based on low-resolution Hall-effect sensors, is proposed. The high-resolution rotor position is estimated by a proportional integral (PI) regulator using the deviation between actual output power and reference output power. This method can compensate for the Hall position sensor mounting error, and estimate rotor position continuously and accurately. The permanent magnetic flux linkage is also estimated based on a current PI controller. Other important parameters, such as the d-axis and q-axis inductances, stator resistance, and energy loss, are measured offline by experiments. The measured parameters are saved as lookup tables which cover the entire current operating range at different current levels. Based on these accurate parameters, a maximum torque per ampere (MTPA) control strategy, combined with the feedforward parameter iteration method, can be achieved for accurate and efficient torque control. The effectiveness of the proposed method is verified by both simulation and experimental results. Full article

(This article belongs to the Special Issue Energy Management, Control, and System Architectures for Electric Vehicle Applications)

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