Energies

16 pages, 962 KiB

Open AccessArticle

China Building Energy Consumption: Definitions and Measures from an Operational Perspective

by Wei Wei and Ling-Yun He

Energies 2017, 10(5), 582; https://doi.org/10.3390/en10050582 - 25 Apr 2017

Cited by 17 | Viewed by 5256

China building energy consumption (BEC) has been gradually derived and also sparked attention. However, something worth discussing is estimating the BEC based on the definition of life cycle or building operation. In addition, there exists discrepancy in the previous studies and the real [...] Read more.

China building energy consumption (BEC) has been gradually derived and also sparked attention. However, something worth discussing is estimating the BEC based on the definition of life cycle or building operation. In addition, there exists discrepancy in the previous studies and the real status of BEC has not been known well. In order to settle the disputes over the calculation of BEC, this paper establishes an appropriate accounting method of building energy to present the BEC situation in China and lays the foundation for policymakers to develop appropriate energy saving policies. Meanwhile, this study attempts to clarify the BEC to help policymakers assess the effect of environmental policies. Using the method in this document, we find that the energy consumption of buildings just accounts for 15%–16% of the final total energy consumption in China; by contrast, the previous studies usually have double accounting through a top-down approach if central heat supply of buildings was taken into additional consideration. Full article

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25 pages, 5085 KiB

Open AccessEditor’s ChoiceArticle

A Cost Optimized Fully Sustainable Power System for Southeast Asia and the Pacific Rim

by Ashish Gulagi, Dmitrii Bogdanov and Christian Breyer

Energies 2017, 10(5), 583; https://doi.org/10.3390/en10050583 - 25 Apr 2017

Cited by 51 | Viewed by 9657

Abstract

In this paper, a cost optimal 100% renewable energy based system is obtained for Southeast Asia and the Pacific Rim region for the year 2030 on an hourly resolution for the whole year. For the optimization, the region was divided into 15 sub-regions [...] Read more.

In this paper, a cost optimal 100% renewable energy based system is obtained for Southeast Asia and the Pacific Rim region for the year 2030 on an hourly resolution for the whole year. For the optimization, the region was divided into 15 sub-regions and three different scenarios were set up based on the level of high voltage direct current grid connections. The results obtained for a total system levelized cost of electricity showed a decrease from 66.7 €/MWh in a decentralized scenario to 63.5 €/MWh for a centralized grid connected scenario. An integrated scenario was simulated to show the benefit of integrating additional demand of industrial gas and desalinated water which provided the system the required flexibility and increased the efficiency of the usage of storage technologies. This was reflected in the decrease of system cost by 9.5% and the total electricity generation by 5.1%. According to the results, grid integration on a larger scale decreases the total system cost and levelized cost of electricity by reducing the need for storage technologies due to seasonal variations in weather and demand profiles. The intermittency of renewable technologies can be effectively stabilized to satisfy hourly demand at a low cost level. A 100% renewable energy based system could be a reality economically and technically in Southeast Asia and the Pacific Rim with the cost assumptions used in this research and it may be more cost competitive than the nuclear and fossil carbon capture and storage (CCS) alternatives. Full article

(This article belongs to the Special Issue Sustainable Energy Technologies)

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19 pages, 613 KiB

Open AccessReview

Structured Literature Review of Electricity Consumption Classification Using Smart Meter Data

by Alexander Martin Tureczek and Per Sieverts Nielsen

Energies 2017, 10(5), 584; https://doi.org/10.3390/en10050584 - 25 Apr 2017

Cited by 43 | Viewed by 9470

Abstract

Smart meters for measuring electricity consumption are fast becoming prevalent in households. The meters measure consumption on a very fine scale, usually on a 15 min basis, and the data give unprecedented granularity of consumption patterns at household level. A multitude of papers [...] Read more.

Smart meters for measuring electricity consumption are fast becoming prevalent in households. The meters measure consumption on a very fine scale, usually on a 15 min basis, and the data give unprecedented granularity of consumption patterns at household level. A multitude of papers have emerged utilizing smart meter data for deepening our knowledge of consumption patterns. This paper applies a modification of Okoli’s method for conducting structured literature reviews to generate an overview of research in electricity customer classification using smart meter data. The process assessed 2099 papers before identifying 34 significant papers, and highlights three key points: prominent methods, datasets and application. Three important findings are outlined. First, only a few papers contemplate future applications of the classification, rendering papers relevant only in a classification setting. Second; the encountered classification methods do not consider correlation or time series analysis when classifying. The identified papers fail to thoroughly analyze the statistical properties of the data, investigations that could potentially improve classification performance. Third, the description of the data utilized is of varying quality, with only 50% acknowledging missing values impact on the final sample size. A data description score for assessing the quality in data description has been developed and applied to all papers reviewed. Full article

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21 pages, 7592 KiB

Open AccessArticle

A Short-Current Control Method for Constant Frequency Current-Fed Wireless Power Transfer Systems

by Yanling Li, Qichang Duan and Weiyi Li

Energies 2017, 10(5), 585; https://doi.org/10.3390/en10050585 - 25 Apr 2017

Cited by 1 | Viewed by 4068

Abstract

Frequency drift is a serious problem in Current-Fed Wireless Power Transfer (WPT) systems. When the operating frequency is drifting from the inherent Zero Voltage Switching (ZVS) frequency of resonant network, large short currents will appear and damage the switches. In this paper, an [...] Read more.

Frequency drift is a serious problem in Current-Fed Wireless Power Transfer (WPT) systems. When the operating frequency is drifting from the inherent Zero Voltage Switching (ZVS) frequency of resonant network, large short currents will appear and damage the switches. In this paper, an inductance-dampening method is proposed to inhibit short currents and achieve constant-frequency operation. By adding a small auxiliary series inductance in the primary resonant network, short currents are greatly attenuated to a safe level. The operation principle and steady-state analysis of the system are provided. An overlapping time self-regulating circuit is designed to guarantee ZVS running. The range of auxiliary inductances is discussed and its critical value is calculated exactly. The design methodology is described and a design example is presented. Finally, a prototype is built and the experimental results verify the proposed method. Full article

(This article belongs to the Special Issue Wireless Power Transfer and Energy Harvesting Technologies)

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19 pages, 9340 KiB

Open AccessArticle

H∞ Repetitive Control Based on Active Damping with Reduced Computation Delay for LCL-Type Grid-Connected Inverters

by Wei Jin, Yongli Li, Guangyu Sun and Lizhi Bu

Energies 2017, 10(5), 586; https://doi.org/10.3390/en10050586 - 25 Apr 2017

Cited by 27 | Viewed by 5021

Abstract

In the paper, the H∞ repetitive current control scheme based on active damping along with the design method is proposed for three-phase grid-connected inverters with inductor-capacitor-inductor (LCL) filters. The control scheme aims to reduce the harmonic distortion of the output currents and achieve [...] Read more.

In the paper, the H∞ repetitive current control scheme based on active damping along with the design method is proposed for three-phase grid-connected inverters with inductor-capacitor-inductor (LCL) filters. The control scheme aims to reduce the harmonic distortion of the output currents and achieve better efficiency. The design method introduces capacitor-current-feedback active damping into the H∞ controller design process by proposing an equivalent controlled plant. Additionally, based on the discrete model of the controlled plant with variable computation delay, the algebraic expression of the stable region for the feedback coefficient and the computation delay is obtained to avoid system instability caused by the digital control delay. Finally, the stability criterion is proposed to evaluate the stability of the discrete control system with the H∞ repetitive current control scheme. The theoretical analysis and experimental results prove that the control scheme presented in this paper not only can reject the harmonics of output currents, but is robust under the variation of the grid-impedance. Full article

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

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27 pages, 4241 KiB

Open AccessReview

Green and Sustainable Cellular Base Stations: An Overview and Future Research Directions

by Mohammed H. Alsharif, Jeong Kim and Jin Hong Kim

Energies 2017, 10(5), 587; https://doi.org/10.3390/en10050587 - 25 Apr 2017

Cited by 76 | Viewed by 12243

Abstract

Energy efficiency and renewable energy are the main pillars of sustainability and environmental compatibility. This study presents an overview of sustainable and green cellular base stations (BSs), which account for most of the energy consumed in cellular networks. We review the architecture of [...] Read more.

Energy efficiency and renewable energy are the main pillars of sustainability and environmental compatibility. This study presents an overview of sustainable and green cellular base stations (BSs), which account for most of the energy consumed in cellular networks. We review the architecture of the BS and the power consumption model, and then summarize the trends in green cellular network research over the past decade. As its major contribution, this study highlights the uses of renewable energy in cellular communication by: (i) investigating the system model and the potential of renewable energy solutions for cellular BSs; (ii) identifying the potential geographical locations for renewable-energy-powered BSs; (iii) performing case studies on renewable-energy-powered cellular BSs and suggesting future research directions based on our findings; (iv) examining the present deployment of sustainable and green BSs; and (v) studying the barriers that prevent the widespread use of renewable-energy-powered BSs and providing recommendations for future work. Full article

(This article belongs to the Special Issue Sustainable Energy Technologies)

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Graphical abstract

13 pages, 6902 KiB

Open AccessArticle

Space Vector Modulation for an Indirect Matrix Converter with Improved Input Power Factor

by Nguyen Dinh Tuyen and Phan Quoc Dzung

Energies 2017, 10(5), 588; https://doi.org/10.3390/en10050588 - 25 Apr 2017

Cited by 18 | Viewed by 7460

Abstract

Pulse width modulation strategies have been developed for indirect matrix converters (IMCs) in order to improve their performance. In indirect matrix converters, the LC input filter is used to remove input current harmonics and electromagnetic interference problems. Unfortunately, due to the existence of [...] Read more.

Pulse width modulation strategies have been developed for indirect matrix converters (IMCs) in order to improve their performance. In indirect matrix converters, the LC input filter is used to remove input current harmonics and electromagnetic interference problems. Unfortunately, due to the existence of the input filter, the input power factor is diminished, especially during operation at low voltage outputs. In this paper, a new space vector modulation (SVM) is proposed to compensate for the input power factor of the indirect matrix converter. Both computer simulation and experimental studies through hardware implementation were performed to verify the effectiveness of the proposed modulation strategy. Full article

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

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11 pages, 4260 KiB

Open AccessArticle

Evaluation of Interface Defects in Inaccessible Reactor Shrink Fit Nozzle Welds Using Ultrasonic Waves

by Jaesun Lee and Younho Cho

Energies 2017, 10(5), 589; https://doi.org/10.3390/en10050589 - 25 Apr 2017

Cited by 2 | Viewed by 5392

Abstract

This study proposes an effective method to inspect inaccessible nuclear power reactor head nozzles using interface waves that propagate along the shrink fit boundary of a reactor head. The reactor head is relatively thick, which makes it difficult to inspect from the outside [...] Read more.

This study proposes an effective method to inspect inaccessible nuclear power reactor head nozzles using interface waves that propagate along the shrink fit boundary of a reactor head. The reactor head is relatively thick, which makes it difficult to inspect from the outside by conventional ultrasonic testing. However, interface waves can propagate a long distance from a fixed transducer position. The inside of the nuclear reactor has limited access due to the high radiation, so the transducers are located outside the nuclear reactor head, and interface waves propagate into the nuclear reactor to detect defects. A numerical simulation and experiments were carried out to validate the method. Various defect cases that simulate field failures are also presented, and the proposed technique shows satisfactory defect classification. Full article

(This article belongs to the Special Issue Next Generation Reactors and Materials for Advanced Fuel Cycles)

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Graphical abstract

17 pages, 3184 KiB

Open AccessArticle

Probabilistic Power Flow Method Considering Continuous and Discrete Variables

by Xuexia Zhang, Zhiqi Guo and Weirong Chen

Energies 2017, 10(5), 590; https://doi.org/10.3390/en10050590 - 26 Apr 2017

Cited by 5 | Viewed by 5452

Abstract

This paper proposes a probabilistic power flow (PPF) method considering continuous and discrete variables (continuous and discrete power flow, CDPF) for power systems. The proposed method—based on the cumulant method (CM) and multiple deterministic power flow (MDPF) calculations—can deal with continuous variables such [...] Read more.

This paper proposes a probabilistic power flow (PPF) method considering continuous and discrete variables (continuous and discrete power flow, CDPF) for power systems. The proposed method—based on the cumulant method (CM) and multiple deterministic power flow (MDPF) calculations—can deal with continuous variables such as wind power generation (WPG) and loads, and discrete variables such as fuel cell generation (FCG). In this paper, continuous variables follow a normal distribution (loads) or a non-normal distribution (WPG), and discrete variables follow a binomial distribution (FCG). Through testing on IEEE 14-bus and IEEE 118-bus power systems, the proposed method (CDPF) has better accuracy compared with the CM, and higher efficiency compared with the Monte Carlo simulation method (MCSM). Full article

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

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19 pages, 2447 KiB

Open AccessReview

In Situ Stress Measurement Techniques on Li-ion Battery Electrodes: A Review

by Ximing Cheng and Michael Pecht

Energies 2017, 10(5), 591; https://doi.org/10.3390/en10050591 - 27 Apr 2017

Cited by 84 | Viewed by 11980

Abstract

Li-ion batteries experience mechanical stress evolution due in part to Li intercalation into and de-intercalation out of the electrodes, ultimately resulting in performance degradation. In situ measurements of electrode stress can be used to analyze stress generation factors, verify mechanical deformation models, and [...] Read more.

Li-ion batteries experience mechanical stress evolution due in part to Li intercalation into and de-intercalation out of the electrodes, ultimately resulting in performance degradation. In situ measurements of electrode stress can be used to analyze stress generation factors, verify mechanical deformation models, and validate degradation mechanisms. They can also be embedded in Li-ion battery management systems when stress sensors are either implanted in electrodes or attached on battery surfaces. This paper reviews in situ measurement methods of electrode stress based on optical principles, including digital image correlation, curvature measurement, and fiber optical sensors. Their experimental setups, principles, and applications are described and contrasted. This literature review summarizes the current status of these stress measurement methods for battery electrodes and discusses recent developments and trends. Full article

(This article belongs to the Special Issue Advances in Electric Vehicles and Plug-in Hybrid Vehicles 2017)

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16 pages, 3938 KiB

Open AccessArticle

Control Strategy of Single-Phase Three Level Neutral Point Clamped Cascaded Rectifier

by Xiaoqiong He, Xiaolan Lin, Xu Peng, Pengcheng Han, Zeliang Shu and Shibin Gao

Energies 2017, 10(5), 592; https://doi.org/10.3390/en10050592 - 28 Apr 2017

Cited by 10 | Viewed by 4768

Abstract

Single-phase 3-level neutral point clamped cascaded rectifier (3LNPC-CR) has been successfully made its way into traction drive system as a high-voltage traction converter. In this passage, the control issue of the 3LNPC-CR is considered. A transient current control strategy, combined with proportional integral [...] Read more.

Single-phase 3-level neutral point clamped cascaded rectifier (3LNPC-CR) has been successfully made its way into traction drive system as a high-voltage traction converter. In this passage, the control issue of the 3LNPC-CR is considered. A transient current control strategy, combined with proportional integral (PI) controllers, is adopted to achieve unity power factor, satisfactory sinusoidal grid current, regulated overall dc voltage, and even efficient voltage balance between each module. Besides, with regard to the instinct voltage fluctuation problem among dc-link capacitors in one 3-level neutral point clamped (3LNPC) rectifier module, a phase shift carrier space vector pulse width modulation (PSC-SVPWM) worked along with a reasonable redundancy selection scheme is addressed. In addition, two auxiliary balancing circuits for a single-phase 3LNPC rectifier is proposed. The voltage balancing capacity of these internal-module balancing schemes are analyzed and compared. Finally, the control performance of these proposed strategies are verified by simulations and experiments. Full article

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

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12 pages, 4549 KiB

Open AccessArticle

Research on Partial Discharge Source Localization Based on an Ultrasonic Array and a Step-by-Step Over-Complete Dictionary

by Shuguo Gao, Ying Zhang, Qing Xie, Yuqiang Kan, Si Li, Dan Liu and Fangcheng Lü

Energies 2017, 10(5), 593; https://doi.org/10.3390/en10050593 - 29 Apr 2017

Cited by 18 | Viewed by 4820

Abstract

Partial discharge (PD) in electrical equipment is one of the major causes of electrical insulation failures. Fast and accurate positioning of PD sources allows timely elimination of insulation faults. In order to improve the accuracy of PD detection, this paper mainly studies the [...] Read more.

Partial discharge (PD) in electrical equipment is one of the major causes of electrical insulation failures. Fast and accurate positioning of PD sources allows timely elimination of insulation faults. In order to improve the accuracy of PD detection, this paper mainly studies the direction of arrival (DOA) estimation of PD ultrasonic signals based on a step-by-step over-complete dictionary. The simulation results show that the step by step dictionary can improve the operation speed and save signal processing time. Firstly, a step-by-step over-complete dictionary covering all the angles of space is established according to the expression of the steering vector for a matching pursuit direction finding algorithm, which can save computation time. Then, the step-by-step complete dictionary is set up according to the direction vector, and the atomic precision is respectively set to 10°, 1° and 0.1°. The matching pursuit algorithm is used to carry out the sparse representation of the received data X and select the optimal atom from the step-by-step complete dictionary, and the angle information contained in atoms is DOA of the PD sources. According to the direction finding results, combined with the installation location of the ultrasonic array sensor, the spatial position of a partial discharge source can be obtained using the three platform array location method. Finally, a square ultrasonic array sensor is developed, and an experimental platform for the ultrasonic array detection of partial discharges is set up and used to carry out an experimental study. The results show that the DOA estimation method based on a step-by-step over-complete dictionary can improve the direction finding precision, thereby increasing the subsequent positioning accuracy, and the spatial position estimation error of the PD source obtained under laboratory conditions is about 5 cm, making this a feasible method. 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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12 pages, 3027 KiB

Open AccessArticle

Comparison of Solar Radiation Models to Estimate Direct Normal Irradiance for Korea

by Hyun-Jin Lee, Shin-Young Kim and Chang-Yeol Yun

Energies 2017, 10(5), 594; https://doi.org/10.3390/en10050594 - 30 Apr 2017

Cited by 22 | Viewed by 6654

Abstract

Reliable solar radiation data are important for energy simulations in buildings and solar energy systems. Although direct normal irradiance (DNI) is required for simulations, in addition to global horizontal irradiance (GHI), a lack of DNI measurement data is quite often due to high [...] Read more.

Reliable solar radiation data are important for energy simulations in buildings and solar energy systems. Although direct normal irradiance (DNI) is required for simulations, in addition to global horizontal irradiance (GHI), a lack of DNI measurement data is quite often due to high cost and maintenance. Solar radiation models are widely used in order to overcome the limitation, but only a few studies have been devoted to solar radiation data and modeling in Korea. This study investigates the most suitable solar radiation model that converts GHI into DNI for Korea, using measurement data of the city of Daejeon from 2007 to 2009. After ten existing models were evaluated, the Reindl-2 model was selected as the best. A new model was developed for further improvement, and it substantially decreased estimation errors compared to the ten investigated models. The new model was also evaluated for nine major cities other than Daejeon from the standpoint of typical meteorological year (TMY) data, and consistent evaluation results confirmed that the new model is reliably applicable across Korea. Full article

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

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21 pages, 8083 KiB

Open AccessArticle

High-Gain Disturbance Observer-Based Robust Load Frequency Control of Power Systems with Multiple Areas

by Ismi Rosyiana Fitri, Jung-Su Kim and Hwachang Song

Energies 2017, 10(5), 595; https://doi.org/10.3390/en10050595 - 29 Apr 2017

Cited by 15 | Viewed by 4385

Abstract

This paper proposes a high-gain disturbance observer (HDOB)-based controller for load frequency control (LFC) of power systems with multiple areas. The main goal of LFC problem is to maintain the frequency to its nominal value. The objective of this paper is to reject [...] Read more.

This paper proposes a high-gain disturbance observer (HDOB)-based controller for load frequency control (LFC) of power systems with multiple areas. The main goal of LFC problem is to maintain the frequency to its nominal value. The objective of this paper is to reject frequency variations due to abrupt load changes and diverse uncertainties (e.g., inertia and damping parameters, and interconnection topology, etc.) by employing the HDOB for the LFC. The simulation results demonstrate the effectiveness of the proposed HDOB-based LFC by showing that it successfully rejects frequency variations owing to load changes and frequency variations occurring in various locations in interconnected power systems. Besides, it is shown that the proposed LFC can eliminate frequency deviations although there are delays in transmission among the power systems with multiple areas. Full article

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

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16 pages, 2523 KiB

Open AccessArticle

Electricity Production by the Application of a Low Voltage DC-DC Boost Converter to a Continuously Operating Flat-Plate Microbial Fuel Cell

by Young Eun Song, Hitesh C. Boghani, Hong Suck Kim, Byung Goon Kim, Taeho Lee, Byong-Hun Jeon, Giuliano C. Premier and Jung Rae Kim

Energies 2017, 10(5), 596; https://doi.org/10.3390/en10050596 - 29 Apr 2017

Cited by 15 | Viewed by 6634

Abstract

An ultra-low voltage customized DC-DC booster circuit was developed using a LTC3108 converter, and used continuously on a flat-plate microbial fuel cell (FPM) system. The boost converter successfully stepped up the microbial fuel cell (MFC) voltage from ~0.5 V to 3.3 and 5.0 [...] Read more.

An ultra-low voltage customized DC-DC booster circuit was developed using a LTC3108 converter, and used continuously on a flat-plate microbial fuel cell (FPM) system. The boost converter successfully stepped up the microbial fuel cell (MFC) voltage from ~0.5 V to 3.3 and 5.0 V of outputs. The designed circuit and system displayed the dynamic variations of the source FPM as well as the output voltage through the designed three connection points within the booster circuit. The source MFC voltage was interrelated with the booster circuit and its performance, and it adapted to the set points of the booster dynamically. The maximum output power density of the MFC with the DC-DC booster circuit was 8.16 W/m³ compared to the maximum source FPM input power of 14.27 W/m³ at 100 Ω, showing a conversion efficiency of 26–57%, but with a 10-fold higher output than that of the source voltage. The combined LTC3108 with FPM supplied power for electronic devices using synthetic and real domestic wastewater. This report presents a promising strategy for utilizing the electrical energy produced from MFCs, and expands the applicability of bioelectrochemical systems with an improved energy efficiency of the present wastewater treatment system. Full article

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

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Graphical abstract

15 pages, 5431 KiB

Open AccessArticle

A Data-Driven Learning-Based Continuous-Time Estimation and Simulation Method for Energy Efficiency and Coulombic Efficiency of Lithium Ion Batteries

by Yuechen Liu, Linjing Zhang, Jiuchun Jiang, Shaoyuan Wei, Sijia Liu and Weige Zhang

Energies 2017, 10(5), 597; https://doi.org/10.3390/en10050597 - 29 Apr 2017

Cited by 20 | Viewed by 5553

Abstract

Lithium ion (Li-ion) batteries work as the basic energy storage components in modern railway systems, hence estimating and improving battery efficiency is a critical issue in optimizing the energy usage strategy. However, it is difficult to estimate the efficiency of lithium ion batteries [...] Read more.

Lithium ion (Li-ion) batteries work as the basic energy storage components in modern railway systems, hence estimating and improving battery efficiency is a critical issue in optimizing the energy usage strategy. However, it is difficult to estimate the efficiency of lithium ion batteries accurately since it varies continuously under working conditions and is unmeasurable via experiments. This paper offers a learning-based simulation method that employs experimental data to estimate the continuous-time energy efficiency and coulombic efficiency of lithium ion batteries, taking lithium titanate batteries as an example. The state of charge (SOC) regions and discharge current rates are considered as the main variables that may affect the efficiencies. Over eight million empirical datasets are collected during a series of experiments performed to investigate the efficiency variation. A back propagation (BP) neural network efficiency estimation and simulation model is proposed to estimate the continuous-time energy efficiency and coulombic efficiency. The empirical data collected in the experiments are used to train the BP network model, which reveals a test error of 10⁻⁴. With the input of continuous SOC regions and discharge currents, continuous-time efficiency can be estimated by the trained BP network model. The estimated and simulated result is proven to be consistent with the experimental results. Full article

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15 pages, 7843 KiB

Open AccessArticle

Experimental and Theoretical Study of the Interactions between Fe₂O₃/Al₂O₃ and CO

by Zhiyong Liang, Wu Qin and Changqing Dong

Energies 2017, 10(5), 598; https://doi.org/10.3390/en10050598 - 29 Apr 2017

Cited by 16 | Viewed by 4821

Abstract

The behavior of Fe₂O₃/Al₂O₃ particles as oxygen carriers (OCs) for CO chemical looping combustion (CLC) under different reaction temperatures (700 °C, 800 °C, 900 °C, and 1000 °C) were tested in a lab-scale fluidized bed and [...] Read more.

The behavior of Fe₂O₃/Al₂O₃ particles as oxygen carriers (OCs) for CO chemical looping combustion (CLC) under different reaction temperatures (700 °C, 800 °C, 900 °C, and 1000 °C) were tested in a lab-scale fluidized bed and a thermogravimetric analysis (TGA) unit. The results show that the oxygen carrier presents the highest reactivity at 800 °C, even after 30 cycles of redox reaction in a fluidized bed, while more obvious carbon deposition occurred for the case at 700 °C, and agglomeration for the case at 1000 °C. Moreover, the detailed behavior of the prepared Fe₂O₃/Al₂O₃ particle was detected in the TGA apparatus at different reaction temperatures. Furthermore, temperature-programming TGA experiments were performed to investigate the influence of different CO concentrations and CO/CO₂ concentrations on the reaction between CO and OC during the chemical looping combustion processes. Based on these experimental behaviors of the prepared Fe₂O₃/Al₂O₃ during the CLC of CO, the detailed models and electronic properties of the pure and reduced Fe₂O₃/Al₂O₃ supported the slabs, CO adsorption, and oxidation, and the decomposition reactions on these surfaces were revealed using density functional theory (DFT) calculations which went deep into the nature of the synergetic effect of the support of Al₂O₃ on the activity of Fe₂O₃ for the CLC of CO. Full article

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8 pages, 17852 KiB

Open AccessArticle

The Effect of Solvents on the Performance of CH₃NH₃PbI₃ Perovskite Solar Cells

by Pao-Hsun Huang, Yeong-Her Wang, Jhong-Ciao Ke and Chien-Jung Huang

Energies 2017, 10(5), 599; https://doi.org/10.3390/en10050599 - 29 Apr 2017

Cited by 42 | Viewed by 8139

Abstract

The properties of perovskite solar cells (PSCs) fabricated using various solvents was studied. The devices had an indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/CH₃NH₃PbI₃ (fabricated by using various solvents)/fullerene (C₆₀)/bathocuproine (BCP)/silver (Ag) structure. The solvents used were [...] Read more.

The properties of perovskite solar cells (PSCs) fabricated using various solvents was studied. The devices had an indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/CH₃NH₃PbI₃ (fabricated by using various solvents)/fullerene (C₆₀)/bathocuproine (BCP)/silver (Ag) structure. The solvents used were dimethylformamide (DMF), γ-butyrolactone (GBL), dimethyl sulfoxide (DMSO), a mixture of DMSO and DMF (1:1 v/v), and a mixture of DMSO and GBL (DMSO: GBL, 1:1 v/v), respectively. The power conversion efficiency (PCE) of the device fabricated using DMF is zero, which is attributed to the poor coverage of CH₃NH₃PbI₃ film on the substrate. In addition, the PCE of the device made using GBL is only 1.74% due to the low solubility of PbI₂ and CH₃NH₃I. In contrast, the PCE of the device fabricated using the solvents containing DMSO showed better performance. This is ascribed to the high solubilization properties and strong coordination of DMSO. As a result, a PCE of 9.77% was obtained using a mixed DMSO:GBL solvent due to the smooth surface, uniform film coverage on the substrate and the high crystallization of the perovskite structure. Finally, a mixed DMSO: DMF:GBL (5:2:3 v/v/v) solvent that combined the advantages of each solvent was used to fabricate a device, leading to a further improvement of the PCE of the resulting PSC to 10.84%. Full article

(This article belongs to the Special Issue Solid State Lighting)

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25 pages, 3522 KiB

Open AccessArticle

China’s Energy Transition in the Power and Transport Sectors from a Substitution Perspective

by Shangfeng Han, Baosheng Zhang, Xiaoyang Sun, Song Han and Mikael Höök

Energies 2017, 10(5), 600; https://doi.org/10.3390/en10050600 - 29 Apr 2017

Cited by 30 | Viewed by 6504

Abstract

Facing heavy air pollution, China needs to transition to a clean and sustainable energy system, especially in the power and transport sectors, which contribute the highest greenhouse gas (GHG) emissions. The core of an energy transition is energy substitution and energy technology improvement. [...] Read more.

Facing heavy air pollution, China needs to transition to a clean and sustainable energy system, especially in the power and transport sectors, which contribute the highest greenhouse gas (GHG) emissions. The core of an energy transition is energy substitution and energy technology improvement. In this paper, we forecast the levelized cost of electricity (LCOE) for power generation in 2030 in China. Cost-emission effectiveness of the substitution between new energy vehicles and conventional vehicles is also calculated in this study. The results indicate that solar photovoltaic (PV) and wind power will be cost comparative in the future. New energy vehicles are more expensive than conventional vehicles due to their higher manufacturer suggested retail price (MSRP). The cost-emission effectiveness of the substitution between new energy vehicles and conventional vehicles would be $96.7/ton or $114.8/ton. Gasoline prices, taxes, and vehicle insurance will be good directions for policy implementation after the ending of subsidies. Full article

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13 pages, 2499 KiB

Open AccessArticle

Investigating the Effect of Rainfall Parameters on the Self-Cleaning of Polluted Suspension Insulators: Insight from Southern China

by Zidan Jiang, Xingliang Jiang, Zhijin Zhang, Yujun Guo and Yongfu Li

Energies 2017, 10(5), 601; https://doi.org/10.3390/en10050601 - 1 May 2017

Cited by 10 | Viewed by 4445

Abstract

The cleaning effect of heavy rain (the rainfall reaches 5 mm every day) on surface contamination of insulators is more effective than dew, fog, mist, and other light rain conditions which can initiate leakage currents and increase the likelihood of flashover. It is [...] Read more.

The cleaning effect of heavy rain (the rainfall reaches 5 mm every day) on surface contamination of insulators is more effective than dew, fog, mist, and other light rain conditions which can initiate leakage currents and increase the likelihood of flashover. It is well understood that heavy rain can wash away contamination from the surface of high voltage (HV) insulators and thereby reduce the risk of pollution flashover. This study examines the cleaning effect of natural wetting conditions on HV insulators on four 500 kV transmission lines in Hunan Province, China. Historical meteorological data, monthly equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) measurements taken over a period of five years were analyzed to investigate the relationship between rainfall intensity and insulator cleaning. The measured data show that the ESDD/NSDD changes with the seasonal variation, which accumulates in dry season (January–April, about 117–122 days) and is washed off in the wet season (June–October, about 118–127 days). According to the measured data, the ESDD and NSDD on the surface of insulators were affected by the rainfall intensity (in the dry season it is about 1 mm/day and in the wet season it is about 5 mm/day). Based on a comparison of the four study sites, we propose a mathematical model to show the functional relationship between rainfall intensity and insulator self-cleaning capability. The mathematical model’s coefficient of determination (R²) is greater than 0.9 and the effective rate of self-cleaning capability reaches 80%. Full article

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23 pages, 3211 KiB

Open AccessArticle

The Contribution of Non-CO₂ Greenhouse Gas Mitigation to Achieving Long-Term Temperature Goals

by Ajay Gambhir, Tamaryn Napp, Adam Hawkes, Lena Höglund-Isaksson, Wilfried Winiwarter, Pallav Purohit, Fabian Wagner, Dan Bernie and Jason Lowe

Energies 2017, 10(5), 602; https://doi.org/10.3390/en10050602 - 1 May 2017

Cited by 22 | Viewed by 6367

Abstract

This paper analyses the emissions and cost impacts of mitigation of non-CO₂ greenhouse gases (GHGs) at a global level, in scenarios aimed at meeting a range of long-term temperature goals (LTTGs). The study combines an integrated assessment model (TIAM-Grantham) representing CO₂ [...] Read more.

This paper analyses the emissions and cost impacts of mitigation of non-CO₂ greenhouse gases (GHGs) at a global level, in scenarios aimed at meeting a range of long-term temperature goals (LTTGs). The study combines an integrated assessment model (TIAM-Grantham) representing CO₂ emissions (and their mitigation) from the fossil fuel combustion and industrial sectors, coupled with a model covering non-CO₂ emissions (GAINS), using the latest global warming potentials from the Intergovernmental Panel on Climate Change’s Fifth Assessment Report. We illustrate that in general non-CO₂ mitigation measures are less costly than CO₂ mitigation measures, with the majority of their abatement potential achievable at US2005$100/tCO₂e or less throughout the 21st century (compared to a marginal CO₂ mitigation cost which is already greater than this by 2030 in the most stringent mitigation scenario). As a result, the total cumulative discounted cost over the period 2010–2100 (at a 5% discount rate) of limiting global average temperature change to 2.5 °C by 2100 is $48 trillion (about 1.6% of cumulative discounted GDP over the period 2010–2100) if only CO₂ from the fossil fuel and industrial sectors is targeted, whereas the cost falls to $17 trillion (0.6% of GDP) by including non-CO₂ GHG mitigation in the portfolio of options—a cost reduction of about 65%. The criticality of non-CO₂ mitigation recommends further research, given its relatively less well-explored nature when compared to CO₂ mitigation. Full article

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13 pages, 8140 KiB

Open AccessArticle

Volume and Mass Measurement of a Burning Wood Pellet by Image Processing

by Sae Byul Kang, Bong Suk Sim and Jong Jin Kim

Energies 2017, 10(5), 603; https://doi.org/10.3390/en10050603 - 1 May 2017

Cited by 16 | Viewed by 6009

Abstract

Wood pellets are a form of solid biomass energy and a renewable energy source. In 2015, the new and renewable energy (NRE) portion of wood pellets was 4.6% of the total primary energy in Korea. Wood pellets account for 6.2% of renewable energy [...] Read more.

Wood pellets are a form of solid biomass energy and a renewable energy source. In 2015, the new and renewable energy (NRE) portion of wood pellets was 4.6% of the total primary energy in Korea. Wood pellets account for 6.2% of renewable energy consumption in Korea, the equivalent of 824,000 TOE (ton of oil equivalent, 10 million kcal). The burning phases of a wood pellet can be classified into three modes: (1) gasification; (2) flame burning and (3) charcoal burning. At each wood pellet burning mode, the volume and weight of the burning wood pellet can drastically change; these parameters are important to understand the wood pellet burning mechanism. We developed a new method for measuring the volume of a burning wood pellet that involves no contact. To measure the volume of a wood pellet, we take pictures of the wood pellet in each burning mode. The volume of a burning wood pellet can then be calculated by image processing. The difference between the calculation method using image processing and the direct measurement of a burning wood pellet in gasification mode is less than 8.8%. In gasification mode in this research, mass reduction of the wood pellet is 37% and volume reduction of the wood pellet is 7%. Whereas in charcoal burning mode, mass reduction of the wood pellet is 10% and volume reduction of the wood pellet is 41%. By measuring volume using image processing, continuous and non-interruptive volume measurements for various solid fuels are possible and can provide more detailed information for CFD (computational fluid dynamics) analysis. Full article

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

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21 pages, 657 KiB

Open AccessArticle

Sliding Mode Control of a Variable- Speed Wind Energy Conversion System Using a Squirrel Cage Induction Generator

by Mohamed Zribi, Muthana Alrifai and Mohamed Rayan

Energies 2017, 10(5), 604; https://doi.org/10.3390/en10050604 - 1 May 2017

Cited by 53 | Viewed by 8005

Abstract

This paper deals with the control of a variable-speed wind energy conversion (WEC) system using a squirrel cage induction generator (SCIG) connected to the grid through a back-to-back three phase (AC-DC-AC) power converter. The sliding mode control technique is used to control the [...] Read more.

This paper deals with the control of a variable-speed wind energy conversion (WEC) system using a squirrel cage induction generator (SCIG) connected to the grid through a back-to-back three phase (AC-DC-AC) power converter. The sliding mode control technique is used to control the WEC system. The objective of the controllers is to force the states of the system to track their desired states. One controller is used to regulate the generator speed and the flux so that maximum power is extracted from the wind. Another controller is used to control the grid side converter, which controls the DC bus voltage and the active and reactive powers injected into the grid. The performance of the controlled wind energy conversion system is verified through MATLAB simulations, which show that the controlled system performs well. Full article

(This article belongs to the Collection Wind Turbines)

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21 pages, 15441 KiB

Open AccessArticle

Management System for Large Li-Ion Battery Packs with a New Adaptive Multistage Charging Method

by Ricardo Velho, Miguel Beirão, Maria Do Rosário Calado, José Pombo, João Fermeiro and Sílvio Mariano

Energies 2017, 10(5), 605; https://doi.org/10.3390/en10050605 - 1 May 2017

Cited by 20 | Viewed by 10492

Abstract

Among the wide diversity of existing technologically mature batteries, lithium-ion (Li-ion) batteries have become popular because of their longevity, high energy density, high efficiency and lack of memory effect. Differential charging of cells with age has turned balancing management systems into an important [...] Read more.

Among the wide diversity of existing technologically mature batteries, lithium-ion (Li-ion) batteries have become popular because of their longevity, high energy density, high efficiency and lack of memory effect. Differential charging of cells with age has turned balancing management systems into an important research subject. This paper proposes a new battery management system (BMS) to improve the capacity usage and lifespan of large Li-ion battery packs and a new charging algorithm based on the traditional multistage method. The main advantages of the proposed system are its versatility and ability to implement different charging and balancing methods in a very accessible way. The combination of charging methods with balancing methods represents an evolution when compared with other works in the literature. 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, 2227 KiB

Open AccessArticle

Optimization of Hybrid Energy Storage Systems at the Building Level with Combined Heat and Power Generation

by Dongmin Yu, Huanan Liu, Gangui Yan, Jing Jiang and Simon Le Blond

Energies 2017, 10(5), 606; https://doi.org/10.3390/en10050606 - 1 May 2017

Cited by 14 | Viewed by 4515

Abstract

The average daily benefit to cost ratio of a building energy storage system is mainly constrained by the battery lifetime. This paper aims to minimize the average daily cost of a hybrid energy storage system (HESS) (comprised of a battery and supercapacitor) by [...] Read more.

The average daily benefit to cost ratio of a building energy storage system is mainly constrained by the battery lifetime. This paper aims to minimize the average daily cost of a hybrid energy storage system (HESS) (comprised of a battery and supercapacitor) by optimizing the battery capacity. A novel optimization model is proposed with the objective to find the minimum average daily investment cost of the HESS. The objective function has two parts: (1) the investment cost formula for the battery is derived as a function of the battery capacity, which has an interdependence with the minimum state of charge (SOC) and the maximum discharge current; (2) the investment cost formula for the supercapacitor is also established as a function of battery capacity by matching the maximum battery power with that of the supercapacitor. Case studies demonstrate several ways to increase the average daily benefit to cost ratio: (1) adopting a suitable control strategy to avoid capacity saturation; (2) reducing the battery SOC to increase the threshold for the maximum discharge current (MDC) saturation; and (3) increasing MDC to raise the threshold for the SOC saturation. Results show that the average daily benefit to cost ratio is doubled compared to previous work. Full article

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

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19 pages, 826 KiB

Open AccessArticle

Harvesting-Aware Energy Management for Environmental Monitoring WSN

by James Rodway and Petr Musilek

Energies 2017, 10(5), 607; https://doi.org/10.3390/en10050607 - 1 May 2017

Cited by 8 | Viewed by 4437

Abstract

Wireless sensor networks can be used to collect data in remote locations, especially when energy harvesting is used to extend the lifetime of individual nodes. However, in order to use the collected energy most effectively, its consumption must be managed. In this work, [...] Read more.

Wireless sensor networks can be used to collect data in remote locations, especially when energy harvesting is used to extend the lifetime of individual nodes. However, in order to use the collected energy most effectively, its consumption must be managed. In this work, forecasts of diurnal solar energies were made based on measurements of atmospheric pressure. These forecasts were used as part of an adaptive duty cycling scheme for node level energy management. This management was realized with a fuzzy logic controller that has been tuned using differential evolution. Controllers were created using one and two days of energy forecasts, then simulated in software. These controllers outperformed a human-created reference controller by taking more measurements while using less reserve energy during the simulated period. The energy forecasts were comparable to other available methods, while the method of tuning the fuzzy controller improved overall node performance. The combination of the two is a promising method of energy management. 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, 4270 KiB

Open AccessArticle

A Data-Driven Method for Energy Consumption Prediction and Energy-Efficient Routing of Electric Vehicles in Real-World Conditions

by Cedric De Cauwer, Wouter Verbeke, Thierry Coosemans, Saphir Faid and Joeri Van Mierlo

Energies 2017, 10(5), 608; https://doi.org/10.3390/en10050608 - 1 May 2017

Cited by 139 | Viewed by 11612

Abstract

Limited driving range remains one of the barriers for widespread adoption of electric vehicles (EVs). To address the problem of range anxiety, this paper presents an energy consumption prediction method for EVs, designed for energy-efficient routing. This data-driven methodology combines real-world measured driving [...] Read more.

Limited driving range remains one of the barriers for widespread adoption of electric vehicles (EVs). To address the problem of range anxiety, this paper presents an energy consumption prediction method for EVs, designed for energy-efficient routing. This data-driven methodology combines real-world measured driving data with geographical and weather data to predict the consumption over any given road in a road network. The driving data are linked to the road network using geographic information system software that allows to separate trips into segments with similar road characteristics. The energy consumption over road segments is estimated using a multiple linear regression (MLR) model that links the energy consumption with microscopic driving parameters (such as speed and acceleration) and external parameters (such as temperature). A neural network (NN) is used to predict the unknown microscopic driving parameters over a segment prior to departure, given the road segment characteristics and weather conditions. The complete proposed model predicts the energy consumption with a mean absolute error (MAE) of 12–14% of the average trip consumption, of which 7–9% is caused by the energy consumption estimation of the MLR model. This method allows for prediction of energy consumption over any route in the road network prior to departure, and enables cost-optimization algorithms to calculate energy efficient routes. The data-driven approach has the advantage that the model can easily be updated over time with changing conditions. Full article

(This article belongs to the Special Issue Advances in Electric Vehicles and Plug-in Hybrid Vehicles 2017)

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15 pages, 916 KiB

Open AccessArticle

An Energy Aware Unified Ant Colony System for Dynamic Virtual Machine Placement in Cloud Computing

by Xiao-Fang Liu, Zhi-Hui Zhan and Jun Zhang

Energies 2017, 10(5), 609; https://doi.org/10.3390/en10050609 - 1 May 2017

Cited by 34 | Viewed by 4911

Abstract

Energy efficiency is a significant topic in cloud computing. Dynamic consolidation of virtual machines (VMs) with live migration is an important method to reduce energy consumption. However, frequent VM live migration may cause a downtime of service. Therefore, the energy save and VM [...] Read more.

Energy efficiency is a significant topic in cloud computing. Dynamic consolidation of virtual machines (VMs) with live migration is an important method to reduce energy consumption. However, frequent VM live migration may cause a downtime of service. Therefore, the energy save and VM migration are two conflict objectives. In order to efficiently solve the dynamic VM consolidation, the dynamic VM placement (DVMP) problem is formed as a multiobjective problem in this paper. The goal of DVMP is to find a placement solution that uses the fewest servers to host the VMs, including two typical dynamic conditions of the assignment of new coming VMs and the re-allocation of existing VMs. Therefore, we propose a unified algorithm based on an ant colony system (ACS), termed the unified ACS (UACS), that works on both conditions. The UACS firstly uses sufficient servers to host the VMs and then gradually reduces the number of servers. With each especial number of servers, the UACS tries to find feasible solutions with the fewest VM migrations. Herein, a dynamic pheromone deposition method and a special heuristic information strategy are also designed to reduce the number of VM migrations. Therefore, the feasible solutions under different numbers of servers cover the Pareto front of the multiobjective space. Experiments with large-scale random workloads and real workload traces are conducted to evaluate the performance of the UACS. Compared with traditional heuristic, probabilistic, and other ACS based algorithms, the proposed UACS presents competitive performance in terms of energy consumption, the number of VM migrations, and maintaining quality of services (QoS) requirements. Full article

(This article belongs to the Special Issue Smart Design, Smart Manufacturing and Industry 4.0)

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13 pages, 1516 KiB

Open AccessFeature PaperReview

Energy-Efficient Through-Life Smart Design, Manufacturing and Operation of Ships in an Industry 4.0 Environment

by Joo Hock Ang, Cindy Goh, Alfredo Alan Flores Saldivar and Yun Li

Energies 2017, 10(5), 610; https://doi.org/10.3390/en10050610 - 29 Apr 2017

Cited by 108 | Viewed by 15991

Abstract

Energy efficiency is an important factor in the marine industry to help reduce manufacturing and operational costs as well as the impact on the environment. In the face of global competition and cost-effectiveness, ship builders and operators today require a major overhaul in [...] Read more.

Energy efficiency is an important factor in the marine industry to help reduce manufacturing and operational costs as well as the impact on the environment. In the face of global competition and cost-effectiveness, ship builders and operators today require a major overhaul in the entire ship design, manufacturing and operation process to achieve these goals. This paper highlights smart design, manufacturing and operation as the way forward in an industry 4.0 (i4) era from designing for better energy efficiency to more intelligent ships and smart operation through-life. The paper (i) draws parallels between ship design, manufacturing and operation processes, (ii) identifies key challenges facing such a temporal (lifecycle) as opposed to spatial (mass) products, (iii) proposes a closed-loop ship lifecycle framework and (iv) outlines potential future directions in smart design, manufacturing and operation of ships in an industry 4.0 value chain so as to achieve more energy-efficient vessels. Through computational intelligence and cyber-physical integration, we envision that industry 4.0 can revolutionise ship design, manufacturing and operations in a smart product through-life process in the near future. Full article

(This article belongs to the Special Issue Smart Design, Smart Manufacturing and Industry 4.0)

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20 pages, 2052 KiB

Open AccessArticle

Statistical Feature Extraction for Fault Locations in Nonintrusive Fault Detection of Low Voltage Distribution Systems

by Hsueh-Hsien Chang and Nguyen Viet Linh

Energies 2017, 10(5), 611; https://doi.org/10.3390/en10050611 - 29 Apr 2017

Cited by 15 | Viewed by 6614

Abstract

This paper proposes statistical feature extraction methods combined with artificial intelligence (AI) approaches for fault locations in non-intrusive single-line-to-ground fault (SLGF) detection of low voltage distribution systems. The input features of the AI algorithms are extracted using statistical moment transformation for reducing the [...] Read more.

This paper proposes statistical feature extraction methods combined with artificial intelligence (AI) approaches for fault locations in non-intrusive single-line-to-ground fault (SLGF) detection of low voltage distribution systems. The input features of the AI algorithms are extracted using statistical moment transformation for reducing the dimensions of the power signature inputs measured by using non-intrusive fault monitoring (NIFM) techniques. The data required to develop the network are generated by simulating SLGF using the Electromagnetic Transient Program (EMTP) in a test system. To enhance the identification accuracy, these features after normalization are given to AI algorithms for presenting and evaluating in this paper. Different AI techniques are then utilized to compare which identification algorithms are suitable to diagnose the SLGF for various power signatures in a NIFM system. The simulation results show that the proposed method is effective and can identify the fault locations by using non-intrusive monitoring techniques for low voltage distribution systems. Full article

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

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17 pages, 9124 KiB

Open AccessArticle

Grain Size Distribution Effect on the Hydraulic Properties of Disintegrated Coal Mixtures

by Dan Ma, Zilong Zhou, Jiangyu Wu, Qiang Li and Haibo Bai

Energies 2017, 10(5), 612; https://doi.org/10.3390/en10050612 - 29 Apr 2017

Cited by 34 | Viewed by 6146

Abstract

In order to better understand groundwater influx and protection in coal mining extraction works, an in-house water flow apparatus coupled with an industrial rock testing system, known as MTS 815.02, were used to study the effects of grain size mixtures on the compaction [...] Read more.

In order to better understand groundwater influx and protection in coal mining extraction works, an in-house water flow apparatus coupled with an industrial rock testing system, known as MTS 815.02, were used to study the effects of grain size mixtures on the compaction and flow properties of disintegrated, or non-cemented, coal samples. From the Reynolds number evaluation of the samples with different grain mixtures, and the relationship between the water flow velocity and pore pressure gradient differences, it was found that seepage through the mixtures are of non-Darcy flow type. The porosity of coal specimens was found to be highly affected by compaction, and the variations of the porosity were also influenced by the samples’ grain size distribution. It was found that the sample porosity decreases with increasing compaction and decreasing grain sizes. Grain crushing during compaction was observed to be the main cause of the appearance of fine grains, and the washing away of fine grains was consequently the main contributing factor for the weight loss due to water seepage. It was observed that during the tests and with the progression of compaction, permeability k decreases and non-Darcy factor β increases with decreasing porosity φ. The k-φ and β-φ plots show that as the sizes of disintegrated coal samples are getting smaller, there are more fluctuations between the porosity values with their corresponding values of k and β. The permeability value of the sample with smallest grains was observed to be considerably lower than that of the sample with largest grains. Non-Darcy behavior could reduce the hydraulic conductivity. It was found that the porosity, grain breakage and hydraulic properties of coal samples are related to grain sizes and compaction levels, as well as to the arrangement of the grains. At high compaction levels, the porosity of disintegrated coal samples decreased strongly, resulting in a significant decrease of the permeability at its full compression state; Non-Darcy flow behavior has the slightest effect in uniform samples, therefore, indicating that disintegrated coal in uniform grain size mixtures could be treated as an aquicluding (water-resisting) stratum. Full article

(This article belongs to the Special Issue Mathematical and Computational Modeling in Geothermal Engineering)

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18 pages, 3350 KiB

Open AccessArticle

A Comparison Study between Two MPPT Control Methods for a Large Variable-Speed Wind Turbine under Different Wind Speed Characteristics

by Dongran Song, Jian Yang, Mei Su, Anfeng Liu, Yao Liu and Young Hoon Joo

Energies 2017, 10(5), 613; https://doi.org/10.3390/en10050613 - 1 May 2017

Cited by 29 | Viewed by 5491

Abstract

Variable speed wind turbines (VSWTs) usually adopt a maximum power point tracking (MPPT) method to optimize energy capture performance. Nevertheless, obtained performance offered by different MPPT methods may be affected by the impact of wind turbine (WT)’s inertia and wind speed characteristics and [...] Read more.

Variable speed wind turbines (VSWTs) usually adopt a maximum power point tracking (MPPT) method to optimize energy capture performance. Nevertheless, obtained performance offered by different MPPT methods may be affected by the impact of wind turbine (WT)’s inertia and wind speed characteristics and it needs to be clarified. In this paper, the tip speed ratio (TSR) and optimal torque (OT) methods are investigated in terms of their performance under different wind speed characteristics on a 1.5 MW wind turbine model. To this end, the TSR control method based on an effective wind speed estimator and the OT control method are firstly presented. Then, their performance is investigated and compared through simulation test results under different wind speeds using Bladed software. Comparison results show that the TSR control method can capture slightly more wind energy at the cost of high component loads than the other one under all wind conditions. Furthermore, it is found that both control methods present similar trends of power reduction that is relevant to mean wind speed and turbulence intensity. From the obtained results, we demonstrate that, to further improve MPPT capability of large VSWTs, other advanced control methods using wind speed prediction information need to be addressed. Full article

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

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13 pages, 2450 KiB

Open AccessArticle

Energy Return on Investment of Canadian Oil Sands Extraction from 2009 to 2015

by Ke Wang, Harrie Vredenburg, Jianliang Wang, Yi Xiong and Lianyong Feng

Energies 2017, 10(5), 614; https://doi.org/10.3390/en10050614 - 2 May 2017

Cited by 14 | Viewed by 14367

Abstract

Oil sands, as unconventional oil, are so essential to both Canada and the world that special attention should be paid to their extraction status, especially their energy efficiency. One of the most commonly used methods to evaluate energy efficiency is the Energy Return [...] Read more.

Oil sands, as unconventional oil, are so essential to both Canada and the world that special attention should be paid to their extraction status, especially their energy efficiency. One of the most commonly used methods to evaluate energy efficiency is the Energy Return on Investment (EROI) analysis. This paper focuses on EROI analysis for both in situ oil sands and mining oil sands over the period of 2009 to 2015. This time period represents an extension to periods previously considered by other analyses. An extended Input-Output model is used to quantify indirect energy input, which has been ignored by previous analyses of oil sands extraction. Results of this paper show that EROI of both mining oil sands (range of value: 3.9–8) and in situ oil sands (range of value: 3.2–5.4) display an upward trend over the past 7 years; EROI of mining oil sands is generally higher, but is more fluctuating than the EROI of in situ oil sands. Compared with EROI of other hydrocarbons, the EROI of oil sands is still quite low, despite the fact that it is increasing gradually. Full article

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

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22 pages, 4038 KiB

Open AccessArticle

Surfactant-Assisted Perovskite Nanofillers Incorporated in Quaternized Poly (Vinyl Alcohol) Composite Membrane as an Effective Hydroxide-Conducting Electrolyte

by Selvaraj Rajesh Kumar, Wei-Ting Ma, Hsin-Chun Lu, Li-Wei Teng, Hung-Chun Hsu, Chao-Ming Shih, Chun-Chen Yang and Shingjiang Jessie Lue

Energies 2017, 10(5), 615; https://doi.org/10.3390/en10050615 - 2 May 2017

Cited by 23 | Viewed by 5311

Abstract

Perovskite LaFeO₃ nanofillers (0.1%) are incorporated into a quaternized poly(vinyl alcohol) (QPVA) matrix for use as hydroxide-conducting membranes in direct alkaline methanol fuel cells (DAMFCs). The as-synthesized LaFeO₃ nanofillers are amorphous and functionalized with cetyltrimethylammonium bromide (CTAB) surfactant. The annealed LaFeO [...] Read more.

Perovskite LaFeO₃ nanofillers (0.1%) are incorporated into a quaternized poly(vinyl alcohol) (QPVA) matrix for use as hydroxide-conducting membranes in direct alkaline methanol fuel cells (DAMFCs). The as-synthesized LaFeO₃ nanofillers are amorphous and functionalized with cetyltrimethylammonium bromide (CTAB) surfactant. The annealed LaFeO₃ nanofillers are crystalline without CTAB. The QPVA/CTAB-coated LaFeO₃ composite membrane shows a defect-free structure while the QPVA/annealed LaFeO₃ film has voids at the interfaces between the soft polymer and rigid nanofillers. The QPVA/CTAB-coated LaFeO₃ composite has lower methanol permeability and higher ionic conductivity than the pure QPVA and QPVA/annealed LaFeO₃ films. We suggest that the CTAB-coated LaFeO₃ provides three functions to the polymeric composite: increasing polymer free volume, ammonium group contributor, and plasticizer to enhance the interfacial compatibility. The composite containing CTAB-coated LaFeO₃ results in superior cell performance. A maximum power density of 272 mW cm⁻² is achieved, which is among the highest power outputs reported for DAMFCs in the literature. Full article

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

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22 pages, 5707 KiB

Open AccessArticle

Research on Control Strategies of an Open-End Winding Permanent Magnet Synchronous Driving Motor (OW-PMSM)-Equipped Dual Inverter with a Switchable Winding Mode for Electric Vehicles

by Liang Chu, Yi-fan Jia, Dong-sheng Chen, Nan Xu, Yan-wei Wang, Xin Tang and Zhe Xu

Energies 2017, 10(5), 616; https://doi.org/10.3390/en10050616 - 2 May 2017

Cited by 32 | Viewed by 8265

Abstract

An open-end winding permanent magnet synchronous motor (PMSM) has a larger range of speed regulation than normal PMSM with the same DC voltage, and the control method is more flexible. It can also manage energy distribution between two power sources without a DC/DC [...] Read more.

An open-end winding permanent magnet synchronous motor (PMSM) has a larger range of speed regulation than normal PMSM with the same DC voltage, and the control method is more flexible. It can also manage energy distribution between two power sources without a DC/DC converter. This paper aims at an electric vehicle equipped with OW-PMSM drive system with dual power sources and dual inverters; based on analyzing the external characteristics of each winding mode, we propose a winding mode switching strategy whose torque saturation judgmental algorithm, which is insensitive to motor’s parameters, could automatically realize upswitching of the winding mode. The proposed multi-level current hysteresis modulation algorithm could set the major power source and switch it at any time in independent mode, which accomplishes energy distribution between two power sources; its two control methods, low switching frequency method and high power difference method, could achieve different energy distribution effects. Simulation results confirm the validity and effectiveness of the winding mode switching strategy and current modulation method. They also show that an electric vehicle under the proposed control methods has better efficiency than one equipped with a traditional OW-PMSM drive system under traditional control. Full article

(This article belongs to the Special Issue Advanced Electrification for Transportation and Built Environment)

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14 pages, 9474 KiB

Open AccessArticle

An Investigation of the Restitution Coefficient Impact on Simulating Sand-Char Mixing in a Bubbling Fluidized Bed

by Xinjun Zhao, Qitai Eri and Qiang Wang

Energies 2017, 10(5), 617; https://doi.org/10.3390/en10050617 - 3 May 2017

Cited by 7 | Viewed by 4856

Abstract

In the present work, the effect of the restitution coefficient on the numerical results for a binary mixture system of sand particles and char particles in a bubbling fluidized bed with a huge difference between the particles in terms of density and volume [...] Read more.

In the present work, the effect of the restitution coefficient on the numerical results for a binary mixture system of sand particles and char particles in a bubbling fluidized bed with a huge difference between the particles in terms of density and volume fraction has been studied based on two-fluid model along with the kinetic theory of granular flow. Results show that the effect of restitution coefficient on the flow characteristics varies in different regions of the bed, which is more evident for the top region of the bed. The restitution coefficient can be categorized into two classes. The restitution coefficients of 0.7 and 0.8 can be included into one class, whereas the restitution coefficient of 0.9 and 0.95 can be included into another class. Moreover, four vortices can be found in the time-averaged flow pattern distribution, which is very different from the result obtained for the binary system with the similar values between particles in density and volume fraction. Full article

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

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17 pages, 1620 KiB

Open AccessArticle

A Network Reconfiguration Method Considering Data Uncertainties in Smart Distribution Networks

by Ke-yan Liu, Wanxing Sheng, Yongmei Liu and Xiaoli Meng

Energies 2017, 10(5), 618; https://doi.org/10.3390/en10050618 - 2 May 2017

Cited by 32 | Viewed by 4979

Abstract

This work presents a method for distribution network reconfiguration with the simultaneous consideration of distributed generation (DG) allocation. The uncertainties of load fluctuation before the network reconfiguration are also considered. Three optimal objectives, including minimal line loss cost, minimum Expected Energy Not Supplied, [...] Read more.

This work presents a method for distribution network reconfiguration with the simultaneous consideration of distributed generation (DG) allocation. The uncertainties of load fluctuation before the network reconfiguration are also considered. Three optimal objectives, including minimal line loss cost, minimum Expected Energy Not Supplied, and minimum switch operation cost, are investigated. The multi-objective optimization problem is further transformed into a single-objective optimization problem by utilizing weighting factors. The proposed network reconfiguration method includes two periods. The first period is to create a feasible topology network by using binary particle swarm optimization (BPSO). Then the DG allocation problem is solved by utilizing sensitivity analysis and a Harmony Search algorithm (HSA). In the meanwhile, interval analysis is applied to deal with the uncertainties of load and devices parameters. Test cases are studied using the standard IEEE 33-bus and PG&E 69-bus systems. Different scenarios and comparisons are analyzed in the experiments. The results show the applicability of the proposed method. The performance analysis of the proposed method is also investigated. The computational results indicate that the proposed network reconfiguration algorithm is feasible. Full article

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

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18 pages, 2198 KiB

Open AccessArticle

Experimental Assessment of a Helical Coil Heat Exchanger Operating at Subcritical and Supercritical Conditions in a Small-Scale Solar Organic Rankine Cycle

by Marija Lazova, Alihan Kaya, Marijn Billiet, Steven Lecompte, Dimitris Manolakos and Michel De Paepe

Energies 2017, 10(5), 619; https://doi.org/10.3390/en10050619 - 4 May 2017

Cited by 8 | Viewed by 5477

Abstract

In this study, the performance of a helical coil heat exchanger operating at subcritical and supercritical conditions is analysed. The counter-current heat exchanger was specially designed to operate at a maximal pressure and temperature of 42 bar and 200 °C, respectively. The small-scale [...] Read more.

In this study, the performance of a helical coil heat exchanger operating at subcritical and supercritical conditions is analysed. The counter-current heat exchanger was specially designed to operate at a maximal pressure and temperature of 42 bar and 200 °C, respectively. The small-scale solar organic Rankine cycle (ORC) installation has a net power output of 3 kWe. The first tests were done in a laboratory where an electrical heater was used instead of the concentrated photovoltaic/thermal (CPV/T) collectors. The inlet heating fluid temperature of the water was 95 °C. The effects of different parameters on the heat transfer rate in the heat exchanger were investigated. Particularly, the performance analysis was elaborated considering the changes of the mass flow rate of the working fluid (R-404A) in the range of 0.20–0.33 kg/s and the inlet pressure varying from 18 bar up to 41 bar. Hence, the variation of the heat flux was in the range of 5–9 kW/m². The results show that the working fluid’s mass flow rate has significant influence on the heat transfer rate rather than the operational pressure. Furthermore, from the comparison between the experimental results with the heat transfer correlations from the literature, the experimental results fall within the uncertainty range for the supercritical analysis but there is a deviation of the investigated subcritical correlations. Full article

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

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25 pages, 7168 KiB

Open AccessReview

A Survey on Smart Agent-Based Microgrids for Resilient/Self-Healing Grids

by Kaveh Dehghanpour, Christopher Colson and Hashem Nehrir

Energies 2017, 10(5), 620; https://doi.org/10.3390/en10050620 - 3 May 2017

Cited by 35 | Viewed by 6413

Abstract

This paper presents an overview of our body of work on the application of smart control techniques for the control and management of microgrids (MGs). The main focus here is on the application of distributed multi-agent system (MAS) theory in multi-objective (MO) power [...] Read more.

This paper presents an overview of our body of work on the application of smart control techniques for the control and management of microgrids (MGs). The main focus here is on the application of distributed multi-agent system (MAS) theory in multi-objective (MO) power management of MGs to find the Pareto-front of the MO power management problem. In addition, the paper presents the application of Nash bargaining solution (NBS) and the MAS theory to directly obtain the NBS on the Pareto-front. The paper also discusses the progress reported on the above issues from the literature. We also present a MG-based power system architecture for enhancing the resilience and self-healing of the system. Full article

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

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23 pages, 3197 KiB

Open AccessArticle

Networked Control of Electric Vehicles for Power System Frequency Regulation with Random Communication Time Delay

by Yunpeng Guo, Liyan Zhang, Junhua Zhao, Fushuan Wen, Abdus Salam, Jianwei Mao and Liang Li

Energies 2017, 10(5), 621; https://doi.org/10.3390/en10050621 - 3 May 2017

Cited by 9 | Viewed by 4830

Abstract

Electric vehicles (EVs) can have noteworthy impact on power system dynamic performance. This paper develops two novel controllers which can take into account the random time delay in the communication channel of the control system. With the designed robust controller, the system can [...] Read more.

Electric vehicles (EVs) can have noteworthy impact on power system dynamic performance. This paper develops two novel controllers which can take into account the random time delay in the communication channel of the control system. With the designed robust controller, the system can utilize EVs to participate in automatic generation control (AGC) processes so as to assist conventional thermal power units to respond rapidly and accurately to load fluctuations, as well as to enhance the capability of a power system to accommodate renewable energy forms such as wind power. Owing to the distributed nature of EVs, a networked control scheme for EVs’ participation in frequency regulation is first proposed in the paper. A closed-loop block diagram, which incorporates EVs and wind power, is then developed. Two controllers are then designed based on rigorous linear matrix inequalities (LMI) theory to ensure the robustness and stability of the system. Finally, comprehensive case studies based on a two-area equivalent of the IEEE 39-bus test system are performed to demonstrate the effectiveness of the proposed methods. Full article

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

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14 pages, 3729 KiB

Open AccessArticle

Development of a Leader-End Reclosing Algorithm Considering Turbine-Generator Shaft Torque

by Gyu-Jung Cho, Ji-Kyung Park, Seung-Hyun Sohn, Se-Jin Chung, Gi-Hyeon Gwon, Yun-Sik Oh and Chul-Hwan Kim

Energies 2017, 10(5), 622; https://doi.org/10.3390/en10050622 - 3 May 2017

Cited by 5 | Viewed by 3752

Abstract

High-speed auto-reclosing is used in power system protection schemes to ensure the stability and reliability of the transmission system; leader-follower auto-reclosing is one scheme type that is widely used. However, when a leader-follower reclosing scheme responds to a permanent fault that affects a [...] Read more.

High-speed auto-reclosing is used in power system protection schemes to ensure the stability and reliability of the transmission system; leader-follower auto-reclosing is one scheme type that is widely used. However, when a leader-follower reclosing scheme responds to a permanent fault that affects a transmission line in the proximity of a generation plant, the reclosing directly impacts the turbine-generator shaft; furthermore, the nature of this impact is dependent upon the selection of the leader reclosing terminal. We therefore analyzed the transient torque of the turbine-generator shaft according to the selection of the leader-follower reclosing end between both ends of the transmission line. We used this analysis to propose an adaptive leader-end reclosing algorithm that removes the stress potential of the transient torque to prevent it from damaging the turbine-generator shaft. We conducted a simulation in actual Korean power systems based on the ElectroMagnetic Transients Program (EMTP) and the Dynamic Link Library (DLL) function in EMTP-RV (Restructured Version) to realize the proposed algorithm. Full article

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12 pages, 3667 KiB

Open AccessArticle

Theoretical and Experimental Evaluation of the Temperature Distribution in a Dry Type Air Core Smoothing Reactor of HVDC Station

by Yu Wang, Xiaoyue Chen, Zhuohong Pan, Hailiang Lu, Xishan Wen, Zhipeng Jiang, Bin Chen and Tuteng Chen

Energies 2017, 10(5), 623; https://doi.org/10.3390/en10050623 - 3 May 2017

Cited by 19 | Viewed by 5599

Abstract

The outdoor ultra-high voltage (UHV) dry-type air-core smoothing reactors (DASR) of High Voltage Direct Current systems are equipped with a rain cover and an acoustic enclosure. To study the convective heat transfer between the DASR and the surrounding air, this paper presents a [...] Read more.

The outdoor ultra-high voltage (UHV) dry-type air-core smoothing reactors (DASR) of High Voltage Direct Current systems are equipped with a rain cover and an acoustic enclosure. To study the convective heat transfer between the DASR and the surrounding air, this paper presents a coupled model of the temperature and fluid field based on the structural features and cooling manner. The resistive losses of encapsulations calculated by finite element method (FEM) were used as heat sources in the thermal analysis. The steady fluid and thermal field of the 3-D reactor model were solved by the finite volume method (FVM), and the temperature distribution characteristics of the reactor were obtained. Subsequently, the axial and radial temperature distributions of encapsulation were investigated separately. Finally, an optical fiber temperature measurement scheme was used for an UHV DASR under natural convection conditions. Comparative analysis showed that the simulation results are in good agreement with the experimental data, which verifies the rationality and accuracy of the numerical calculation. These results can serve as a reference for the optimal design and maintenance of UHV DASRs. Full article

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

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18 pages, 769 KiB

Open AccessArticle

Multi-Objective Dynamic Economic Dispatch with Demand Side Management of Residential Loads and Electric Vehicles

by Mohammad Rasoul Narimani, Maigha, Jhi-Young Joo and Mariesa Crow

Energies 2017, 10(5), 624; https://doi.org/10.3390/en10050624 - 3 May 2017

Cited by 40 | Viewed by 5234

Abstract

In this paper, a multi-objective optimization method based on the normal boundary intersection is proposed to solve the dynamic economic dispatch with demand side management of individual residential loads and electric vehicles. The proposed approach specifically addresses consumer comfort through acceptable appliance deferral [...] Read more.

In this paper, a multi-objective optimization method based on the normal boundary intersection is proposed to solve the dynamic economic dispatch with demand side management of individual residential loads and electric vehicles. The proposed approach specifically addresses consumer comfort through acceptable appliance deferral times and electric vehicle charging requirements. The multi-objectives of minimizing generation costs, emissions, and energy loss in the system are balanced in a Pareto front approach in which a fuzzy decision making method has been implemented to find the best compromise solution based on desired system operating conditions. The normal boundary intersection method is described and validated. Full article

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

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16 pages, 868 KiB

Open AccessArticle

Optimal Allocation of Energy Storage System Considering Multi-Correlated Wind Farms

by Shuli Wen, Hai Lan, Qiang Fu, David C. Yu, Ying-Yi Hong and Peng Cheng

Energies 2017, 10(5), 625; https://doi.org/10.3390/en10050625 - 4 May 2017

Cited by 14 | Viewed by 4290

Abstract

With the increasing penetration of wind power, not only the uncertainties but also the correlation among the wind farms should be considered in the power system analysis. In this paper, Clayton-Copula method is developed to model the multiple correlated wind distribution and a [...] Read more.

With the increasing penetration of wind power, not only the uncertainties but also the correlation among the wind farms should be considered in the power system analysis. In this paper, Clayton-Copula method is developed to model the multiple correlated wind distribution and a new point estimation method (PEM) is proposed to discretize the multi-correlated wind distribution. Furthermore, combining the proposed modeling and discretizing method with Hybrid Multi-Objective Particle Swarm Optimization (HMOPSO), a comprehensive algorithm is explored to minimize the power system cost and the emissions by searching the best placements and sizes of energy storage system (ESS) considering wind power uncertainties in multi-correlated wind farms. In addition, the variations of load are also taken into account. The IEEE 57-bus system is adopted to perform case studies using the proposed approach. The results clearly demonstrate the effectiveness of the proposed algorithm in determining the optimal storage allocations considering multi-correlated wind farms. Full article

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

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23 pages, 13422 KiB

Open AccessArticle

Methane Adsorption Rate and Diffusion Characteristics in Marine Shale Samples from Yangtze Platform, South China

by Wei Dang, Jinchuan Zhang, Xiaoliang Wei, Xuan Tang, Chenghu Wang, Qian Chen and Yue Lei

Energies 2017, 10(5), 626; https://doi.org/10.3390/en10050626 - 4 May 2017

Cited by 23 | Viewed by 4824

Abstract

Knowledge of the gas adsorption rate and diffusion characteristics in shale are very important to evaluate the gas transport properties. However, research on methane adsorption rate characteristics and diffusion behavior in shale is not well established. In this study, high-pressure methane adsorption isotherms [...] Read more.

Knowledge of the gas adsorption rate and diffusion characteristics in shale are very important to evaluate the gas transport properties. However, research on methane adsorption rate characteristics and diffusion behavior in shale is not well established. In this study, high-pressure methane adsorption isotherms and methane adsorption rate data from four marine shale samples were obtained by recording the pressure changes against time at 1-s intervals for 12 pressure steps. Seven pressure steps were selected for modelling, and three pressure steps of low (~0.4 MPa), medium (~4.0 MPa), and high (~7.0 MPa) were selected for display. According to the results of study, the methane adsorption under low pressure attained equilibrium much more quickly than that under medium and high pressure, and the adsorption rate behavior varied between different pressure steps. By fitting the diffusion models to the methane adsorption rate data, the unipore diffusion model based upon unimodal pore size distribution failed to describe the methane adsorption rate, while the bidisperse diffusion model could reasonably describe most of the experimental adsorption rate data, with the exception of sample YY2-1 at high pressure steps. This phenomenon may be related to the restricted assumption on pore size distribution and linear adsorption isotherm. The diffusion parameters α and β/α obtained from the bidisperse model indicated that both macro- and micropore diffusion controlled the methane adsorption rate in shale samples, as well as the relative importance and influence of micropore diffusion and adsorption to adsorption rate and total adsorption increased with increasing pressure. This made the inflection points, or two-stage process, at higher pressure steps not as evident as at low pressure steps, and the adsorption rate curves became less steep with increasing pressure. This conclusion was also supported by the decreasing difference values with increasing pressures between macro- and micropore diffusivities obtained using the bidisperse model, which is roughly from 10⁻³ to 10⁰, and 10⁻³ to 10⁻¹, respectively. Additionally, an evident negative correlation between macropore diffusivities and pressure lower than 3–4 MPa was observed, while the micropore diffusivities only showed a gentle decreasing trend with pressure. A mirror image relationship between the variation in the value of macropore diffusivity and adsorption isotherms was observed, indicating the negative correlation between surface coverage and gas diffusivity. The negative correlation of methane diffusivity with pressure and surface coverage may be related to the increasing degree of pore blockage and the decreasing concentration gradient of methane adsorption. Finally, due to the significant deviation between the unipore model and experimental adsorption rate data, a new estimation method based upon the bidisperse model is proposed here. Full article

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

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16 pages, 513 KiB

Open AccessArticle

A Game Theoretical Approach Based Bidding Strategy Optimization for Power Producers in Power Markets with Renewable Electricity

by Yi Tang, Jing Ling, Tingting Ma, Ning Chen, Xiaofeng Liu and Bingtuan Gao

Energies 2017, 10(5), 627; https://doi.org/10.3390/en10050627 - 4 May 2017

Cited by 13 | Viewed by 4785

Abstract

In a competitive electricity market with substantial involvement of renewable electricity, maximizing profits by optimizing bidding strategies is crucial to different power producers including conventional power plants and renewable ones. This paper proposes a game-theoretic bidding optimization method based on bi-level programming, where [...] Read more.

In a competitive electricity market with substantial involvement of renewable electricity, maximizing profits by optimizing bidding strategies is crucial to different power producers including conventional power plants and renewable ones. This paper proposes a game-theoretic bidding optimization method based on bi-level programming, where power producers are at the upper level and utility companies are at the lower level. The competition among the multiple power producers is formulated as a non-cooperative game in which bidding curves are their strategies, while uniform clearing pricing is considered for utility companies represented by an independent system operator. Consequently, based on the formulated game model, the bidding strategies for power producers are optimized for the day-ahead market and the intraday market with considering the properties of renewable energy; and the clearing pricing for the utility companies, with respect to the power quantity from different power producers, is optimized simultaneously. Furthermore, a distributed algorithm is provided to search the solution of the generalized Nash equilibrium. Finally, simulation results were performed and discussed to verify the feasibility and effectiveness of the proposed non-cooperative game-based bi-level optimization approach. Full article

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

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19 pages, 3349 KiB

Open AccessArticle

Effects of Building Occupancy on Indicators of Energy Efficiency

by Aapo Huovila, Pekka Tuominen and Miimu Airaksinen

Energies 2017, 10(5), 628; https://doi.org/10.3390/en10050628 - 4 May 2017

Cited by 20 | Viewed by 8946

Abstract

The potential to reduce energy consumption in buildings is high. The design phase of the building is very important. In addition, it is vital to understand how to measure the energy efficiency in the building operation phase in order to encourage the right [...] Read more.

The potential to reduce energy consumption in buildings is high. The design phase of the building is very important. In addition, it is vital to understand how to measure the energy efficiency in the building operation phase in order to encourage the right efficiency efforts. In understanding the building energy efficiency, it is important to comprehend the interplay of building occupancy, space efficiency, and energy efficiency. Recent studies found in the literature concerning energy efficiency in office buildings have concentrated heavily on the technical characteristics of the buildings or technical systems. The most commonly used engineering indicator for building energy efficiency is the specific energy consumption (SEC), commonly measured in kWh/m² per annum. While the SEC is a sound way to measure the technical properties of a building and to guide its design, it obviously omits the issues of building occupancy and space efficiency. This paper studies existing energy efficiency indicators and introduces a new indicator for building energy efficiency which takes into account both space and occupancy efficiency. Full article

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15 pages, 3662 KiB

Open AccessArticle

Understanding and Modelling the Effect of Dissolved Metals on Solvent Degradation in Post Combustion CO₂ Capture Based on Pilot Plant Experience

by Sanjana Dhingra, Purvil Khakharia, Alexander Rieder, Ashleigh Cousins, Alicia Reynolds, Jacob Knudsen, Jimmy Andersen, Robin Irons, Jan Mertens, Mohammad Abu Zahra, Peter Van Os and Earl Goetheer

Energies 2017, 10(5), 629; https://doi.org/10.3390/en10050629 - 4 May 2017

Cited by 16 | Viewed by 6217

Abstract

Oxidative degradation is a serious concern for upscaling of amine-based carbon capture technology. Different kinetic models have been proposed based on laboratory experiments, however the kinetic parameters included are limited to those relevant for a lab-scale system and not a capture plant. Besides, [...] Read more.

Oxidative degradation is a serious concern for upscaling of amine-based carbon capture technology. Different kinetic models have been proposed based on laboratory experiments, however the kinetic parameters included are limited to those relevant for a lab-scale system and not a capture plant. Besides, most of the models fail to recognize the catalytic effect of metals. The objective of this work is to develop a representative kinetic model based on an apparent auto-catalytic reaction mechanism between solvent degradation, corrosion and ammonia emissions. Measurements from four different pilot plants: (i) EnBW’s plant at Heilbronn, Germany (ii) TNO’s plant at Maasvlakte, The Netherlands; (iii) CSIRO’s plants at Loy Yang and Tarong, Australia and (iv) DONG Energy’s plant at Esbjerg, Denmark are utilized to propose a degradation kinetic model for 30 wt % ethanolamine (MEA) as the capture solvent. The kinetic parameters of the model were regressed based on the pilot plant campaign at EnBW. The kinetic model was validated by comparing it with the measurements at the remaining pilot campaigns. The model predicted the trends of ammonia emissions and metal concentration within the same order of magnitude. This study provides a methodology to establish a quantitative approach for predicting the onset of unacceptable degradation levels which can be further used to devise counter-measure strategies such as reclaiming and metal removal. Full article

(This article belongs to the Special Issue CO₂ Capture)

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15 pages, 3545 KiB

Open AccessArticle

Design and Implementation of a Data Acquisition System for Combustion Tests

by María Teresa Miranda, Irene Montero, Francisco José Sepúlveda, José Ignacio Arranz and Carmen Victoria Rojas

Energies 2017, 10(5), 630; https://doi.org/10.3390/en10050630 - 4 May 2017

Cited by 2 | Viewed by 4847

Abstract

In recent years, the biomass market has constantly increased. The pellet manufacture industry has started looking for new products, such as wastes from forest, agriculture, and agroindustrial residues, among others, with the potential to be used as biofuels. However, some of these wastes [...] Read more.

In recent years, the biomass market has constantly increased. The pellet manufacture industry has started looking for new products, such as wastes from forest, agriculture, and agroindustrial residues, among others, with the potential to be used as biofuels. However, some of these wastes have some characteristics that make both the combustion process and operating and maintenance conditions of thermal equipment difficult. Thus, further research to optimize the performance and ensure the compliance of the maximum atmospheric levels is needed. In order to carry out these studies, the design and implementation of a supervision, control, and data acquisition system for a domestic pellet boiler was carried out, which makes obtaining further information about the performance of non-conventional biofuels possible. Thus, these biofuels, coming from different sources, underwent different working regimes, facilitating the understanding of the results and the correction of limiting elements. The results from initial tests were reliable and precise, coinciding with the check readings that were done with a thermometer and a combustion gas analyser. Under these conditions, the system designed constitutes a fundamental tool to examine thermal processes with alternative biofuels, with the objective of making the most of different biomass wastes as renewable energy sources. Full article

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

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14 pages, 6210 KiB

Open AccessArticle

Quality Assessment of Biodiesel Blends Proposed by the New Mexican Policy Framework

by Marcos A. Coronado, Gisela Montero, Conrado García, Benjamín Valdez, Ramón Ayala and Armando Pérez

Energies 2017, 10(5), 631; https://doi.org/10.3390/en10050631 - 4 May 2017

Cited by 24 | Viewed by 5549

Abstract

Nowadays, biodiesel is being promoted worldwide as a sustainable and alternative to diesel fuel. However, there is still a lack of a biodiesel market in Mexico. Hence, a new initiative to reform the Mexican biofuels framework by decree includes the production and use [...] Read more.

Nowadays, biodiesel is being promoted worldwide as a sustainable and alternative to diesel fuel. However, there is still a lack of a biodiesel market in Mexico. Hence, a new initiative to reform the Mexican biofuels framework by decree includes the production and use of biodiesel. This regulation can ensure and contribute to the development of the biodiesel market in Mexico. The initiative proposes to start from the B5.8 blend by the end of 2017 and reach the B10 by 2020. Therefore, the objective of the present work was the quality assessment of biodiesel blends proposed by the new Mexican policy framework. The techniques applied were Fourier transform infrared (FT-IR) spectroscopy, X-ray fluorescence analysis, scanning electron microscopy analysis, viscosity, higher heating value, thermogravimetric analysis, refractive index, acid number, specific gravity, flash point, and copper strip corrosion based on ASTM standards. The results indicate that the biodiesel and its blends B5.8 and B10 fulfilled relevant quality specifications established in the ASTM D6751 and EN14214 standards for fuels. However, the fuel blends presented a higher heating value (HHV) diminution. The experimental HHV percentages decrease for the mandatory mixtures compared to diesel were 2.29% (B10), and 0.29% (B5.8). Full article

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

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11 pages, 2640 KiB

Open AccessArticle

Case Study on the Socio-Economic Benefit of Allowing Active Power Curtailment to Postpone Grid Upgrades

by Magne L. Kolstad, Ove Wolfgang and Rolf Håkan Josefsen

Energies 2017, 10(5), 632; https://doi.org/10.3390/en10050632 - 5 May 2017

Cited by 3 | Viewed by 3471

Abstract

The penetration of distributed generation is rapidly increasing in the power system. Traditionally, a fit-and-forget approach has been applied for grid integration of distributed generation, by investing in a grid capacity that can deal with worst-case situations. However, there is now increasing interest [...] Read more.

The penetration of distributed generation is rapidly increasing in the power system. Traditionally, a fit-and-forget approach has been applied for grid integration of distributed generation, by investing in a grid capacity that can deal with worst-case situations. However, there is now increasing interest for the possible cost savings that can be achieved through more active network management. This paper presents a case study on the possible socio-economic benefit of postponing a grid upgrade in an area of surplus generation. Two alternatives for grid integration of an 8 MW run-on-river hydro power plant in the southern part of Norway are investigated: (i) grid upgrade; and (ii) active power curtailment whenever needed to avoid network congestion. This study shows that cost savings corresponding to 13% of the investment cost for the grid upgrade is possible through active power curtailment. Full article

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

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28 pages, 8526 KiB

Open AccessArticle

Wide Area Information-Based Transmission System Centralized Out-of-Step Protection Scheme

by Igor Ivanković, Igor Kuzle and Ninoslav Holjevac

Energies 2017, 10(5), 633; https://doi.org/10.3390/en10050633 - 5 May 2017

Cited by 13 | Viewed by 5373

Abstract

A wide area monitoring system (WAMS) with reliable telecommunication infrastructure can be expanded and enhanced with additional protection and control functionalities using synchronized phasor data measurements. With that aim, we have developed a multifunctional line protection (MFLP) model with both system and back-up [...] Read more.

A wide area monitoring system (WAMS) with reliable telecommunication infrastructure can be expanded and enhanced with additional protection and control functionalities using synchronized phasor data measurements. With that aim, we have developed a multifunctional line protection (MFLP) model with both system and back-up protection functions. Theoretical premises based on transmission and relay protection system knowledge, together with the experience gathered from the operation of existing wide area systems, were used to develop the proposed model. Four main groups of simulation scenarios were defined in order to test the newly implemented functions. The results of the simulation process confirm the assumptions underlying the design of our MFLP module. Simulation results are then used for definition of the protection criteria required for implementation of the wide area protection algorithm in a control center. Conclusions drawn from the protection responses of the proposed algorithm that strengthen the algorithm design process are elaborated in the paper. The main contribution of the paper is the design and development of a centralized MFLP algorithm based on synchronized phasor data that is able to issue a trip command to a circuit breaker before an out-of-step condition occurs. 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, 4162 KiB

Open AccessArticle

Numerical Study of Pressure Fluctuation in a Gas- Liquid Two-Phase Mixed-Flow Pump

by Wenwu Zhang, Zhiyi Yu and Baoshan Zhu

Energies 2017, 10(5), 634; https://doi.org/10.3390/en10050634 - 5 May 2017

Cited by 38 | Viewed by 4989

Abstract

To explore the pressure fluctuation characteristics in a mixed-flow pump handling a gas-liquid two-phase flow, an unsteady simulation was carried out with ANSYS CFX for the whole flow passage when the inlet gas void fraction (IGVF) was 0%, 5%, and 10%, [...] Read more.

To explore the pressure fluctuation characteristics in a mixed-flow pump handling a gas-liquid two-phase flow, an unsteady simulation was carried out with ANSYS CFX for the whole flow passage when the inlet gas void fraction (IGVF) was 0%, 5%, and 10%, respectively. Under pure water conditions (IGVF = 0%), the reliability of the simulation was verified by comparing with the experiment in both aspects of external characteristics and fluctuation. Through the implementation of the fast Fourier transform (FFT) algorithm, the characteristics of the pressure fluctuation in the impeller and the guide vane were obtained at different IGVF conditions. The results demonstrate that pressure fluctuations exist under different IGVF conditions due to the rotor-stator interaction and the gas-liquid phase interaction, and the intensity of the fluctuation is firstly enhanced, and then weakened, along the streamwise direction with the maximum located near the impeller outlet. The relationship between the gas content and the pressure fluctuation was analyzed, and it is shown that the regional pressure fluctuation will be intensified only if the gas content therein reaches a certain level and the local phase interaction is strong. In addition, the pressure fluctuation in both the rotor-stator interaction region and the guide vane may be effectively inhibited under small IGVF conditions. Full article

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20 pages, 12617 KiB

Open AccessArticle

The Impact of Shading Type and Azimuth Orientation on the Daylighting in a Classroom–Focusing on Effectiveness of Façade Shading, Comparing the Results of DA and UDI

by Kyung Sun Lee, Ki Jun Han and Jae Wook Lee

Energies 2017, 10(5), 635; https://doi.org/10.3390/en10050635 - 10 May 2017

Cited by 36 | Viewed by 7922

Abstract

There are many kinds of façade shading designs which provide optimal indoor daylighting conditions. Thus, considering combinations of different types of façade shading systems is an essential aspect in the optimization of daylighting in the building design process. This study explores (1) how [...] Read more.

There are many kinds of façade shading designs which provide optimal indoor daylighting conditions. Thus, considering combinations of different types of façade shading systems is an essential aspect in the optimization of daylighting in the building design process. This study explores (1) how the pattern and different characteristics are evaluated by varying façade shading types and considering their impact on daylighting metrics; and (2) the relative relationships between Daylight Autonomy (DA) and Useful Daylight Illuminance (UDI) with changes of the façade shading types, input parameters, and azimuth orientations. A typical high-school classroom has been chosen as a base model, and seven different façade shading types: vertical louver, horizontal louver, eggcrate louver, overhang, vertical slat, horizontal slat, and light shelf have been applied to eight azimuth orientations for the building. As tools for parametric design and indoor lighting analysis, Design Iterate Validate Adapt (DIVA)-for-Grasshopper has been used to obtain DA and UDI for comparison. Based on the simulation, (1) the effectiveness of the installation of façade shading compared to a non-shading case; and (2) design considerations for façade shading are presented. The result shows that there are some meaningful differences in DA and UDI metrics with the variation of orientation and façade shading types, although all cases of façade shading show some degree of decrease in DA and increase in UDI values. The types of shading devices which produce a dramatic decrease in DA values are the light shelf, horizontal slats, horizontal louvers, and eggcrate louvers. On the contrary, the types of shading devices which produce a dramatic increase in UDI values are the light shelf, horizontal slats, horizontal louvers, and eggcrate louvers. In the case of the vertical and vertical slat shading, the improvements of UDI values are significant in the east and west orientations. This demonstrates that the application and design of shading devices in certain façade orientations should be carefully considered for daylight control. Also, the results show that UDI explains relatively well the daylight performance in the case of the installation of a shading device. Full article

(This article belongs to the Special Issue Solar Energy Application in Buildings)

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20 pages, 4173 KiB

Open AccessReview

Review on Contactless Power Transfer for Electric Vehicle Charging

by Ravikiran Vaka and Ritesh Kumar Keshri

Energies 2017, 10(5), 636; https://doi.org/10.3390/en10050636 - 5 May 2017

Cited by 57 | Viewed by 8682

Abstract

For the past few years the feasibility of contactless power transfer (CPT) is being explored extensively as a future solution for charging electric vehicles (EVs). Studies report that the main obstacles in CPT are low power efficiency, misalignment tolerance, cost, range and charging [...] Read more.

For the past few years the feasibility of contactless power transfer (CPT) is being explored extensively as a future solution for charging electric vehicles (EVs). Studies report that the main obstacles in CPT are low power efficiency, misalignment tolerance, cost, range and charging time anxiety. This paper presents a review based on existing literature of the CPT systems for EV charging. Different cases of CPT technologies, their principle of operation and equivalent circuit based analysis is carried out. A discussion on compensation strategies and their effectiveness are reviewed and discussed. The design of coil systems for some city electric cars has been referenced in general. At the end recommendations and conclusions are made based on the study and analysis of the information available in literature. 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, 1398 KiB

Open AccessReview

Performance Simulation Integrated in Parametric 3D Modeling as a Method for Early Stage Design Optimization—A Review

by Eleftheria Touloupaki and Theodoros Theodosiou

Energies 2017, 10(5), 637; https://doi.org/10.3390/en10050637 - 5 May 2017

Cited by 102 | Viewed by 10816

Abstract

During the last decades, standards on building construction have risen sharply to integrate new, ambitious demands regarding energy efficiency, as well as thermal and optical comfort in the design procedure. Building simulation software assists in the accurate calculation of a hypothetical or existing [...] Read more.

During the last decades, standards on building construction have risen sharply to integrate new, ambitious demands regarding energy efficiency, as well as thermal and optical comfort in the design procedure. Building simulation software assists in the accurate calculation of a hypothetical or existing building’s performance on several aspects; but they are, in their vast majority, assessment-oriented, rather than focused on dynamically supporting the decision-making procedure. During the last two decades, a clear shift of design professionals and academia towards addressing performance issues from the conceptual stages of a building’s design is observed. In this review, the methodology of performance-driven design optimization using computational/parametric design and optimization is presented, and the core literature available on the topic is reviewed in order to identify the current status, different approaches, obstacles, and areas of future research on the subject. The review findings confirm that there is enormous potential for the design of better-performing buildings using this technique, but there are still many obstacles to overcome and areas for future research. Full article

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24 pages, 6391 KiB

Open AccessArticle

Bacteria Foraging Reinforcement Learning for Risk-Based Economic Dispatch via Knowledge Transfer

by Chuanjia Han, Bo Yang, Tao Bao, Tao Yu and Xiaoshun Zhang

Energies 2017, 10(5), 638; https://doi.org/10.3390/en10050638 - 6 May 2017

Cited by 12 | Viewed by 4816

Abstract

This paper proposes a novel bacteria foraging reinforcement learning with knowledge transfer method for risk-based economic dispatch, in which the economic dispatch is integrated with risk assessment theory to represent the uncertainties of active power demand and contingencies during power system operations. Moreover, [...] Read more.

This paper proposes a novel bacteria foraging reinforcement learning with knowledge transfer method for risk-based economic dispatch, in which the economic dispatch is integrated with risk assessment theory to represent the uncertainties of active power demand and contingencies during power system operations. Moreover, a multi-agent collaboration is employed to accelerate the convergence of knowledge matrix, which is decomposed into several lower dimension sub-matrices via a knowledge extension, thus the curse of dimension can be effectively avoided. Besides, the convergence rate of bacteria foraging reinforcement learning is increased dramatically through a knowledge transfer after obtaining the optimal knowledge matrices of source tasks in pre-learning. The performance of bacteria foraging reinforcement learning has been thoroughly evaluated on IEEE RTS-79 system. Simulation results demonstrate that it can outperform conventional artificial intelligence algorithms in terms of global convergence and convergence rate. Full article

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18 pages, 5841 KiB

Open AccessArticle

Design Optimization of a High Power LED Matrix Luminaire

by Jose Luiz F. Barbosa, Dan Simon and Wesley P. Calixto

Energies 2017, 10(5), 639; https://doi.org/10.3390/en10050639 - 5 May 2017

Cited by 11 | Viewed by 5798

Abstract

This work presents a methodology for optimizing the layout and geometry of an

m \times n

high power (HP) light emitting diode (LED) luminaire. Two simulators are used to analyze an LED luminaire model. The first simulator uses the finite element method (FEM) [...] Read more.

This work presents a methodology for optimizing the layout and geometry of an

m \times n

high power (HP) light emitting diode (LED) luminaire. Two simulators are used to analyze an LED luminaire model. The first simulator uses the finite element method (FEM) to analyze the thermal dissipation, and the second simulator uses the ray tracing method for lighting analysis. The thermal and lighting analysis of the luminaire model is validated with an error of less than 10%. The goal of the optimization process is to find a solution that satisfies both thermal dissipation and light efficiency. The optimization goal is to keep the LED temperature at an acceptable level while still obtaining uniform illumination on a target plane. Even though no optical accessories or active cooling systems are used in the model, the results demonstrate that it is possible to obtain satisfactory results even with a limited number of parameters. The optimization results show that it is possible to design luminaires with 4, 6 and up to 8 HP-LEDs, keeping the LED temperature at about 100

^{\circ}

C. However, the best uniformity on a target plane was found by the heuristic algorithm. 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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13 pages, 1034 KiB

Open AccessArticle

Study on the Characteristic Decomposition Components of DC SF₆-Insulated Equipment under Positive DC Partial Discharge

by Min Liu, Ju Tang, Xin Liu, Qiang Yao and Yulong Miao

Energies 2017, 10(5), 640; https://doi.org/10.3390/en10050640 - 5 May 2017

Cited by 13 | Viewed by 3692

Abstract

Pulses with different amplitudes occur when an inner partial discharge fault exists in SF₆-gas-insulated DC high-voltage electrical equipment. SF₆ decomposes following complex physical and chemical processes. Discussing and quantifying the mathematical relationship of pulse discharge quantities to SF₆ decomposition [...] Read more.

Pulses with different amplitudes occur when an inner partial discharge fault exists in SF₆-gas-insulated DC high-voltage electrical equipment. SF₆ decomposes following complex physical and chemical processes. Discussing and quantifying the mathematical relationship of pulse discharge quantities to SF₆ decomposition component characteristics is helpful to evaluate and predict the insulation fault severity and development trends in SF₆-insulated DC equipment. Numerous simulation experiments on SF₆ decomposition under positive DC partial discharge were performed on a needle-plane model. The DC partial discharge quantities of pulses are obtained, and decomposition characteristics based on the mechanism of SF₆ decomposition are analyzed. Results show that generation, effective generation rate and concentration ratio c(SO₂F₂ + SOF₄)/c(SOF₂ + SO₂) of components increase with partial discharge severity, and the first two act in the following order: SOF₄ > SOF₂ > SO₂F₂ > SO₂ > CF₄ when the discharge quantity level is higher than 238,957 pC. Finally, a coefficient matrix illustrates the mathematical effects of pulses with different discharge quantities on different SF₆ decomposition components. The pulses whose discharge quantity is higher than 50 pC have obvious promotion effects on the formation of decomposition components, whereas the pulses whose discharge quantity lower than 50 pC decrease the positive promotion effects that large discharge pulses have on decomposition components. The higher the effective generation rates are, the greater the partial discharge severity is, and their change laws provide a new method to evaluate and predict insulation fault severity and development trends in DC SF₆-insulated equipment with high reliability and detection 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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14 pages, 2620 KiB

Open AccessArticle

Watching the Smoke Rise Up: Thermal Efficiency, Pollutant Emissions and Global Warming Impact of Three Biomass Cookstoves in Ghana

by George Y. Obeng, Ebenezer Mensah, George Ashiagbor, Owusu Boahen and Daniel J. Sweeney

Energies 2017, 10(5), 641; https://doi.org/10.3390/en10050641 - 6 May 2017

Cited by 31 | Viewed by 8917

Abstract

In Ghana, about 73% of households rely on solid fuels for cooking. Over 13,000 annual deaths are attributed to exposure to indoor air pollution from inefficient combustion. In this study, assessment of thermal efficiency, emissions, and total global warming impact of three cookstoves [...] Read more.

In Ghana, about 73% of households rely on solid fuels for cooking. Over 13,000 annual deaths are attributed to exposure to indoor air pollution from inefficient combustion. In this study, assessment of thermal efficiency, emissions, and total global warming impact of three cookstoves commonly used in Ghana was completed using the International Workshop Agreement (IWA) Water Boiling Test (WBT) protocol. Statistical averages of three replicate tests for each cookstove were computed. Thermal efficiency results were: wood-burning cookstove: 12.2 ± 5.00% (Tier 0); coalpot charcoal stove: 23.3 ± 0.73% (Tier 1–2); and Gyapa charcoal cookstove: 30.00 ± 4.63% (Tier 2–3). The wood-burning cookstove emitted more CO, CO₂, and PM_2.5 than the coalpot charcoal stove and Gyapa charcoal cookstove. The emission factor (EF) for PM_2.5 and the emission rate for the wood-burning cookstove were over four times higher than the coalpot charcoal stove and Gyapa charcoal cookstove. To complete the WBT, the study results showed that, by using the Gyapa charcoal cookstove instead of the wood-burning cookstove, the global warming impact could be potentially reduced by approximately 75% and using the Gyapa charcoal cookstove instead of the coalpot charcoal cookstove by 50%. We conclude that there is the need for awareness, policy, and incentives to enable end-users to switch to, and adopt, Gyapa charcoal cookstoves for increased efficiency and reduced emissions/global warming impact. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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17 pages, 1031 KiB

Open AccessArticle

Determination of the Most Suitable Technology Transfer Strategy for Wind Turbines Using an Integrated AHP-TOPSIS Decision Model

by A. Dinmohammadi and M. Shafiee

Energies 2017, 10(5), 642; https://doi.org/10.3390/en10050642 - 6 May 2017

Cited by 58 | Viewed by 7206

Abstract

The high-speed development of industrial products and goods in the world has caused “technology” to be considered as a crucial competitive advantage for most large organizations. In recent years, developing countries have considerably tended to promote their technological and innovative capabilities through importing [...] Read more.

The high-speed development of industrial products and goods in the world has caused “technology” to be considered as a crucial competitive advantage for most large organizations. In recent years, developing countries have considerably tended to promote their technological and innovative capabilities through importing high-tech equipment owned and operated by developed countries. There are currently a variety of solutions to transfer a particular technology from a developed country. The selection of the most profitable technology transfer strategy is a very complex decision-making problem for technology importers as it involves different technical, environmental, social, and economic aspects. In this study, a hybrid multiple-criteria decision making (MCDM) model based on the analytic hierarchy process (AHP) and the technique for order of preference by similarity to ideal solution (TOPSIS) is proposed to evaluate and prioritise various technology transfer strategies for wind turbine systems. For this purpose, a number of criteria and sub-criteria are defined from the viewpoint of wind energy investors, wind turbine manufacturers, and wind farm operators. The relative importance of criteria and sub-criteria with respect to the ultimate goal are computed using the eigenvalue method and then, the technology transfer alternatives are ranked based on their relative closeness to the ideal solution. The model is finally applied to determine the most suitable wind turbine technology transfer strategy among four options of reverse engineering, technology skills training, turn-key contracts, and technology licensing for the renewable energy sector of Iran, and the results are compared with those obtained by classical decision-making models. Full article

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

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14 pages, 1494 KiB

Open AccessArticle

Optimal Control Based on Maximum Power Point Tracking (MPPT) of an Autonomous Hybrid Photovoltaic/Storage System in Micro Grid Applications

by Ibrahem E. Atawi and Ahmed M. Kassem

Energies 2017, 10(5), 643; https://doi.org/10.3390/en10050643 - 7 May 2017

Cited by 28 | Viewed by 6706

Abstract

This paper investigates how to increase the efficiency of a photovoltaic/energy storage generation unit supplying dynamic loads by regulating and managing both the photovoltaic generator and the storage battery charge-discharge modes. The proposed photovoltaic/energy storage unit is proposed to supply an induction motor [...] Read more.

This paper investigates how to increase the efficiency of a photovoltaic/energy storage generation unit supplying dynamic loads by regulating and managing both the photovoltaic generator and the storage battery charge-discharge modes. The proposed photovoltaic/energy storage unit is proposed to supply an induction motor driven industrial pump with controlled speed and/or a DC motor driven water pump. An optimal proportional-integral-derivative control based on an Artificial Bee Colony Optimization algorithm is used to regulate the photovoltaic generator in case of normal operation or in case of maximum power point tracking (MPPT) and to also control the battery storage charge discharge modes. A vector control based on the proposed optimal control is used to regulate the induction motor rotor speed at its low reference values needed by the industrial pump. First, a total model of the entire system is obtained. The controller performance with the proposed system is studied with both a DC motor and/or induction motor loads. Simulation results show that the proposed photovoltaic/storage generator is able to supply the suggested dynamic loads under different conditions and with good performance. Also, it is noticed that operating the photovoltaic base on maximum power point tracking condition will give about 43% extra generation power than the normal operation case. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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9 pages, 2824 KiB

Open AccessArticle

Effect of Carbon Nanoadditives on Lithium Hydroxide Monohydrate-Based Composite Materials for Low Temperature Chemical Heat Storage

by Xixian Yang, Shijie Li, Hongyu Huang, Jun Li, Noriyuki Kobayashi and Mitsuhiro Kubota

Energies 2017, 10(5), 644; https://doi.org/10.3390/en10050644 - 6 May 2017

Cited by 18 | Viewed by 7066

Abstract

Carbon nanospheres (CNSs) and multi-walled carbon nanotubes (MWCNTs) as nanoadditives were used to modify lithium hydroxide monohydrate for low temperature chemical heat storage application. The lithium hydroxide monohydrate particles were well dispersed on the nanoscale level, and the diameter of nanoparticles was about [...] Read more.

Carbon nanospheres (CNSs) and multi-walled carbon nanotubes (MWCNTs) as nanoadditives were used to modify lithium hydroxide monohydrate for low temperature chemical heat storage application. The lithium hydroxide monohydrate particles were well dispersed on the nanoscale level, and the diameter of nanoparticles was about 20–30 nm in the case of the carbon nanospheres and 50–100 nm the case of the MWCNTs, as shown by transmission electron microscopy characterization results. X-ray diffraction results indicated that the LiOH·H₂O-carbon nano thermochemical composite materials were successfully synthesized. The thermochemical composite materials LiOH·H₂O/CNSs (2020 kJ/kg), LiOH·H₂O/MWCNTs (1804 kJ/kg), and LiOH·H₂O/AC (1236 kJ/kg) exhibited obviously improved heat storage density and higher hydration rate than pure LiOH·H₂O (661 kJ/kg), which was shown by thermogravimetric and differential scanning calorimetric (TG-DSC) analysis. It appears that nanocarbon-modified lithium hydroxide monohydrate thermochemical composite materials have a huge potential for the application of low temperature chemical heat storage. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Thermal Management (TESM2017))

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16 pages, 8079 KiB

Open AccessEditor’s ChoiceArticle

Active Vibration Control of Swash Plate-Type Axial Piston Machines with Two-Weight Notch Least Mean Square/Filtered-x Least Mean Square (LMS/FxLMS) Filters

by Taeho Kim and Monika Ivantysynova

Energies 2017, 10(5), 645; https://doi.org/10.3390/en10050645 - 6 May 2017

Cited by 13 | Viewed by 7452

Abstract

In this paper, swash plate active vibration control techniques were investigated utilizing the weight-limited multi-frequency two-weight notch Least Mean Square (LMS) filter with unit delay compensation and multi-frequency two-weight notch Filtered-x Least Mean Sqaure (FxLMS) filter with offline modeling to achieve adjustable swash [...] Read more.

In this paper, swash plate active vibration control techniques were investigated utilizing the weight-limited multi-frequency two-weight notch Least Mean Square (LMS) filter with unit delay compensation and multi-frequency two-weight notch Filtered-x Least Mean Sqaure (FxLMS) filter with offline modeling to achieve adjustable swash plate vibration reduction at the desired frequency. Simulation studies of the high fidelity pump control system model including realistic swash plate moments are presented to demonstrate the feasibility of the swash plate active vibration control. A 75-cm³/rev swash plate type axial piston pump was modified to implement a high bandwidth pump control system which is required for canceling the swash plate vibration. High speed real-time controllers were proposed and realized using an National Instrument LabVIEW Field Programmable Gate Array (FPGA). Vibration measurements using a tri-axial swash plate acceleration sensor were conducted to show the influence and effectiveness of the proposed swash plate active vibration control system and algorithms. Full article

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

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15 pages, 6132 KiB

Open AccessArticle

Energy Harvesting Based on a Novel Piezoelectric 0.7PbZn_0.3Ti_0.7O₃-0.3Na₂TiO₃ Nanogenerator

by Zainab Radeef, Chong Wen Tong, Ong Zhi Chao and Khoo Shin Yee

Energies 2017, 10(5), 646; https://doi.org/10.3390/en10050646 - 6 May 2017

Cited by 7 | Viewed by 4680

Abstract

Recently, piezoelectric materials have achieved remarkable attention for charging wireless sensor nodes. Among piezoelectric materials, non-ferroelectric materials are more cost effective because they can be prepared without a polarization process. In this study, a non-ferroelectric nanogenerator was manufactured from 0.7PbZn_0.3Ti_0.7 [...] Read more.

Recently, piezoelectric materials have achieved remarkable attention for charging wireless sensor nodes. Among piezoelectric materials, non-ferroelectric materials are more cost effective because they can be prepared without a polarization process. In this study, a non-ferroelectric nanogenerator was manufactured from 0.7PbZn_0.3Ti_0.7O₃-0.3Na₂TiO₃ (PZnT-NT). It was demonstrated that the increment of conductivity via adding the Na₂TiO₃ plays an essential role in increasing the permittivity of the non-ferroelectric nanogenerator and hence improved the generated power density. The dielectric measurements of this material demonstrated high conductivity that quenched the polarization phase. The performance of the device was studied experimentally over a cantilever test rig; the vibrating cantilever (0.4 ms⁻²) was excited by a motor operated at 30 Hz. The generated power successfully illuminated a light emitting diode (LED). The PZnT-NT nanogenerator produced a volume power density of 0.10 μw/mm³ and a surface power density of 10 μw/cm². The performance of the proposed device with a size of (20 × 15 × 1 mm³) was higher in terms of power output than that of the commercial microfiber composite (MFC) (80 × 57 × 0.335 mm3) and piezoelectric bimorph device (70 × 50 × 0.7 mm³). Compared to other existing ferroelectric and non-ferroelectric nanogenerators, the proposed device demonstrated great performance in harvesting the energy at low acceleration and in a low frequency environment Full article

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

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31 pages, 2465 KiB

Open AccessEditor’s ChoiceArticle

Global Energy-Optimal Redundancy Resolution of Hydraulic Manipulators: Experimental Results for a Forestry Manipulator

by Jarmo Nurmi and Jouni Mattila

Energies 2017, 10(5), 647; https://doi.org/10.3390/en10050647 - 6 May 2017

Cited by 31 | Viewed by 8170

Abstract

This paper addresses the energy-inefficiency problem of four-degrees-of-freedom (4-DOF) hydraulic manipulators through redundancy resolution in robotic closed-loop controlled applications. Because conventional methods typically are local and have poor performance for resolving redundancy with respect to minimum hydraulic energy consumption, global energy-optimal redundancy resolution [...] Read more.

This paper addresses the energy-inefficiency problem of four-degrees-of-freedom (4-DOF) hydraulic manipulators through redundancy resolution in robotic closed-loop controlled applications. Because conventional methods typically are local and have poor performance for resolving redundancy with respect to minimum hydraulic energy consumption, global energy-optimal redundancy resolution is proposed at the valve-controlled actuator and hydraulic power system interaction level. The energy consumption of the widely popular valve-controlled load-sensing (LS) and constant-pressure (CP) systems is effectively minimised through cost functions formulated in a discrete-time dynamic programming (DP) approach with minimum state representation. A prescribed end-effector path and important actuator constraints at the position, velocity and acceleration levels are also satisfied in the solution. Extensive field experiments performed on a forestry hydraulic manipulator demonstrate the performance of the proposed solution. Approximately 15–30% greater hydraulic energy consumption was observed with the conventional methods in the LS and CP systems. These results encourage energy-optimal redundancy resolution in future robotic applications of hydraulic manipulators. Full article

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

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16 pages, 6095 KiB

Open AccessArticle

Investigation of Methane Oxy-Fuel Combustion in a Swirl-Stabilised Gas Turbine Model Combustor

by Mao Li, Yiheng Tong, Marcus Thern and Jens Klingmann

Energies 2017, 10(5), 648; https://doi.org/10.3390/en10050648 - 8 May 2017

Cited by 21 | Viewed by 6397

Abstract

CO₂ has a strong impact on both operability and emission behaviours in gas turbine combustors. In the present study, an atmospheric, preheated, swirl-stabilised optical gas turbine model combustor rig was employed. The primary objectives were to analyse the influence of CO₂ [...] Read more.

CO₂ has a strong impact on both operability and emission behaviours in gas turbine combustors. In the present study, an atmospheric, preheated, swirl-stabilised optical gas turbine model combustor rig was employed. The primary objectives were to analyse the influence of CO₂ on the fundamental characteristics of combustion, lean blowout (LBO) limits, CO emission and flame structures. CO₂ dilution effects were examined with three preheating temperatures (396.15, 431.15, and 466.15 K). The fundamental combustion characteristics were studied utilising chemical kinetic simulations. To study the influence of CO₂ on the operational range of the combustor, equivalence ratio (Ф) was varied from stoichiometric conditions to the LBO limits. CO emissions were measured at the exit of the combustor using a water-cooled probe over the entire operational range. The flame structures and locations were characterised by performing CH chemiluminescence imaging. The inverse Abel transformation was used to analyse the CH distribution on the axisymmetric plane of the combustor. Chemical kinetic modelling indicated that the CO₂ resulted in a lower reaction rate compared with the CH₄/air flame. Fundamental combustion properties such as laminar flame speed, ignition delay time and blowout residence time were found to be affected by CO₂. The experimental results revealed that CO₂ dilution resulted in a narrower operational range for the equivalence ratio. It was also found that CO₂ had a strong inhibiting effect on CO burnout, which led to a higher concentration of CO in the combustion exhaust. CH chemiluminescence showed that the CO₂ dilution did not have a significant impact on the flame structure. Full article

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

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16 pages, 3844 KiB

Open AccessArticle

Case Study of an Organic Rankine Cycle (ORC) for Waste Heat Recovery from an Electric Arc Furnace (EAF)

by Steven Lecompte, Oyeniyi A. Oyewunmi, Christos N. Markides, Marija Lazova, Alihan Kaya, Martijn Van den Broek and Michel De Paepe

Energies 2017, 10(5), 649; https://doi.org/10.3390/en10050649 - 7 May 2017

Cited by 66 | Viewed by 13893

Abstract

The organic Rankine cycle (ORC) is a mature technology for the conversion of waste heat to electricity. Although many energy intensive industries could benefit significantly from the integration of ORC technology, its current adoption rate is limited. One important reason for this arises [...] Read more.

The organic Rankine cycle (ORC) is a mature technology for the conversion of waste heat to electricity. Although many energy intensive industries could benefit significantly from the integration of ORC technology, its current adoption rate is limited. One important reason for this arises from the difficulty of prospective investors and end-users to recognize and, ultimately, realise the potential energy savings from such deployment. In recent years, electric arc furnaces (EAF) have been identified as particularly interesting candidates for the implementation of waste heat recovery projects. Therefore, in this work, the integration of an ORC system into a 100 MWe EAF is investigated. The effect of evaluations based on averaged heat profiles, a steam buffer and optimized ORC architectures is investigated. The results show that it is crucial to take into account the heat profile variations for the typical batch process of an EAF. An optimized subcritical ORC system is found capable of generating a net electrical output of 752 kWe with a steam buffer working at 25 bar. If combined heating is considered, the ORC system can be optimized to generate 521 kWe of electricity, while also delivering 4.52 MW of heat. Finally, an increased power output (by 26% with combined heating, and by 39% without combined heating) can be achieved by using high temperature thermal oil for buffering instead of a steam loop; however, the use of thermal oil in these applications has been until now typically discouraged due to flammability concerns. Full article

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

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12 pages, 7586 KiB

Open AccessArticle

A Battery Power Bank with Series-Connected Buck–Boost-Type Battery Power Modules

by Tsung-Hsi Wu, Chin-Sien Moo and Chih-Hao Hou

Energies 2017, 10(5), 650; https://doi.org/10.3390/en10050650 - 8 May 2017

Cited by 12 | Viewed by 6729

Abstract

The operation of a battery power bank with series-connected buck–boost-type battery power modules (BPMs) was investigated in this study. Each BPM consisted of a battery pack with an associated buck–boost converter for individually controlling battery currents. With a proposed discharging scenario, load voltage [...] Read more.

The operation of a battery power bank with series-connected buck–boost-type battery power modules (BPMs) was investigated in this study. Each BPM consisted of a battery pack with an associated buck–boost converter for individually controlling battery currents. With a proposed discharging scenario, load voltage regulation with charge equalization among batteries was performed by controlling the battery currents in accordance with their state-of-charges (SOCs) estimated by real-time battery-loaded voltages detected under the same operating condition. In addition, the fault tolerance was executed to isolate exhausted or faulty batteries from the battery power bank without interrupting the system operation. Experiments were conducted to verify the effectiveness of the discharging scenario for a laboratory battery power bank with four series buck–boost BPMs. Full article

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23 pages, 14171 KiB

Open AccessArticle

2D Numerical Simulation of Improving Wellbore Stability in Shale Using Nanoparticles Based Drilling Fluid

by Jiwei Song, Ye Yuan, Sui Gu, Xianyu Yang, Ye Yue, Jihua Cai and Guosheng Jiang

Energies 2017, 10(5), 651; https://doi.org/10.3390/en10050651 - 9 May 2017

Cited by 22 | Viewed by 6601

Abstract

The past decade has seen increased focus on nanoparticle (NP) based drilling fluid to promote wellbore stability in shales. With the plugging of NP into shale pores, the fluid pressure transmission can be retarded and wellbore stability can be improved. For better understanding [...] Read more.

The past decade has seen increased focus on nanoparticle (NP) based drilling fluid to promote wellbore stability in shales. With the plugging of NP into shale pores, the fluid pressure transmission can be retarded and wellbore stability can be improved. For better understanding of the interaction between shale and NP based drilling fluid based on previous pressure transmission tests (PTTs) on Atoka shale samples, this paper reports the numerical simulation findings of wellbore stability in the presence of NP based drilling fluid, using the 2D fluid-solid coupling model in FLAC3D™ software. The results of previous PTT are discussed first, where the steps of numerical simulation, the simulation on pore fluid pressure transmission, the distribution of stress and the deformation of surrounding rock are presented. The mechanisms of NP in reducing permeability and stabilizing shale are also discussed. Results showed that fluid filtrate from water-based drilling fluid had a strong tendency to invade the shale matrix and increase the likelihood of wellbore instability in shales. However, the pore fluid pressure near wellbore areas could be minimized by plugging silica NP into the nanoscale pores of shales, which is consistent with previous PTT. Pore pressure transmission boundaries could also be restricted with silica NP. Furthermore, the stress differential and shear stress of surrounding rock near the wellbore was reduced in the presence of NP. The plastic yield zone was minimized to improve wellbore stability. The plugging mechanism of NP may be attributed to the electrostatic and electrodynamic interactions between NP and shale surfaces that are governed by Derjaguin-Landau-Verwey-Overbeek (DLVO) forces, which allowed NP to approach shale surfaces and adhere to them. We also found that discretization of the simulation model was beneficial in distinguishing the yield zone distribution of the surrounding rock in shales. The combination of PTT and the 2D numerical simulation offers a better understanding of how NP-based drilling fluid can be developed to address wellbore stability issues in shales. Full article

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

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15 pages, 3581 KiB

Open AccessArticle

Tidal Current Power Resources and Influence of Sea-Level Rise in the Coastal Waters of Kinmen Island, Taiwan

by Wei-Bo Chen, Hongey Chen, Lee-Yaw Lin and Yi-Chiang Yu

Energies 2017, 10(5), 652; https://doi.org/10.3390/en10050652 - 9 May 2017

Cited by 22 | Viewed by 5444

Abstract

The tidal current power (TCP) resource, the impact of TCP extraction on hydrodynamics and the influence of sea-level rise (SLR) on TCP output in the coastal waters of Kinmen Island (Taiwan) are investigated using a state-of-the-art unstructured-grid depth-integrated numerical model. The model was [...] Read more.

The tidal current power (TCP) resource, the impact of TCP extraction on hydrodynamics and the influence of sea-level rise (SLR) on TCP output in the coastal waters of Kinmen Island (Taiwan) are investigated using a state-of-the-art unstructured-grid depth-integrated numerical model. The model was driven by eight tidal constituents extracted from a global tidal prediction model and verified with time series of measured data for tide level and depth-averaged current. The simulations showed reasonable agreement with the observations; the skill index was in the excellent (0.71–0.93) range with regard to simulating tide level and currents. Model predictions indicated that the channel between Kinmen and Lieyu serves as an appropriate site for deploying the tidal turbines because of its higher tidal current and deeper water depth. The bottom friction approach was utilized to compute the average TCP over a spring-neap cycle (i.e., 15 days). Mean TCP reached its maximum to 45.51 kW for a coverage area of 0.036 km² when an additional turbine friction coefficient (C_t) increased to 0.08, and a cut-in speed of 0.5 m/s was used. The annual TCP output was estimated to be 1.08 MW. The impact of TCP extraction on the change in current is significant, with a maximum reduction rate of instant current exceeding 60%, and the extent of influence for the average current is 1.26 km in length and 0.30 km in width for the −0.05 m/s contour line. However, the impact of TCP extraction on the change in tide level is insignificant; the maximum change in amplitude is only 0.73 cm for the K₂ tide. The influence of SLR on the TCP output in Kinmen waters was also estimated. Modeling assessments showed that due to SLR produces faster tidal current, the annual TCP output increased to 1.52 MW, 2.01 MW, 2.48 MW and 2.97 MW under the same cut-in speed and coverage area conditions when SLR 0.25 m, SLR 0.5 m, SLR 0.75 m and SLR 1.0 m were imposed on the model. Full article

(This article belongs to the Special Issue Marine Energy)

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25 pages, 4302 KiB

Open AccessArticle

A Hybrid Dynamic System Assessment Methodology for Multi-Modal Transportation-Electrification

by Thomas J.T. Van der Wardt and Amro M. Farid

Energies 2017, 10(5), 653; https://doi.org/10.3390/en10050653 - 9 May 2017

Cited by 16 | Viewed by 5795

Abstract

In recent years, electrified transportation, be it in the form of buses, trains, or cars have become an emerging form of mobility. Electric vehicles (EVs), especially, are set to expand the amount of electric miles driven and energy consumed. Nevertheless, the question remains [...] Read more.

In recent years, electrified transportation, be it in the form of buses, trains, or cars have become an emerging form of mobility. Electric vehicles (EVs), especially, are set to expand the amount of electric miles driven and energy consumed. Nevertheless, the question remains as to whether EVs will be technically feasible within infrastructure systems. Fundamentally, EVs interact with three interconnected systems: the (physical) transportation system, the electric power grid, and their supporting information systems. Coupling of the two physical systems essentially forms a nexus, the transportation-electricity nexus (TEN). This paper presents a hybrid dynamic system assessment methodology for multi-modal transportation-electrification. At its core, it utilizes a mathematical model which consists of a marked Petri-net model superimposed on the continuous time microscopic traffic dynamics and the electrical state evolution. The methodology consists of four steps: (1) establish the TEN structure; (2) establish the TEN behavior; (3) establish the TEN Intelligent Transportation-Energy System (ITES) decision-making; and (4) assess the TEN performance. In the presentation of the methodology, the Symmetrica test case is used throughout as an illustrative example. Consequently, values for several measures of performance are provided. This methodology is presented generically and may be used to assess the effects of transportation-electrification in any city or area; opening up possibilities for many future studies. Full article

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

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17 pages, 8611 KiB

Open AccessArticle

Study on the Propagation Laws of Hydrofractures Meeting a Faulted Structure in the Coal Seam

by Haiyang Wang, Binwei Xia, Yiyu Lu, Tao Gong and Rui Zhang

Energies 2017, 10(5), 654; https://doi.org/10.3390/en10050654 - 10 May 2017

Cited by 13 | Viewed by 5020

Abstract

Hydraulic fracturing is an important technique for increasing coal seam permeability and productivity of CBM (coalbed methane). As a common type of faulted structure in the coal seam, the fault has a direct impact on the direction and scope of hydrofracture propagation, weakening [...] Read more.

Hydraulic fracturing is an important technique for increasing coal seam permeability and productivity of CBM (coalbed methane). As a common type of faulted structure in the coal seam, the fault has a direct impact on the direction and scope of hydrofracture propagation, weakening fracturing effects. To study the propagation laws of a hydrofracture meeting a fault in the coal seam, based on a two-dimensional model of a hydrofracture meeting a fault, the combined elastic mechanics and fracture mechanics, the propagation mode, critical internal water pressure, and influencing factors were analyzed. A numerical simulation on the propagation laws of hydrofracture meeting a fault was conducted by using the coupling system of flow and solid in the rock failure process analysis (RFPA2D-Flow). The results show that the horizontal crustal stress difference, the intersection angle between hydrofracture and fault plane, and the physical mechanics characteristics of coal-rock bed are the main factors influencing fracture propagation. With a decrease of horizontal crustal stress differences, intersection angle and an increase of roof elasticity modulus, it is easier for the footwall hydrofracture to enter the hanging wall along the bedding plane, forming an effective fracture. When the stress difference is large and the dip angle of fault plane surpasses 45°, the hydrofracture is easy to propagate towards the coal roof and floor by going through the fault plane. At this time, the coal seams of the footwall and the hanging wall should be fractured respectively to ensure fracturing effects, and the support of the roof and floor should be strengthened. The field experiment, theoretical analysis and numerical simulation were consistent in their results, which will contribute to the optimization of hydraulic fracturing and the prediction of hydrofracture in the coal seams containing faults. Full article

(This article belongs to the Special Issue Mathematical and Computational Modeling in Geothermal Engineering)

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13 pages, 4677 KiB

Open AccessArticle

Identification of Non-Stationary Magnetic Field Sources Using the Matching Pursuit Method

by Beata Palczynska

Energies 2017, 10(5), 655; https://doi.org/10.3390/en10050655 - 9 May 2017

Cited by 3 | Viewed by 4068

Abstract

The measurements of electromagnetic field emissions, performed on board a vessel have showed that, in this specific environment, a high level of non-stationary magnetic fields (MFs) is observed. The adaptive time-frequency method can be used successfully to analyze this type of measured signal. [...] Read more.

The measurements of electromagnetic field emissions, performed on board a vessel have showed that, in this specific environment, a high level of non-stationary magnetic fields (MFs) is observed. The adaptive time-frequency method can be used successfully to analyze this type of measured signal. It allows one to specify the time interval in which the individual frequency components of the signal occur. In this paper, the method of identification of non-stationary MF sources based on the matching pursuit (MP) algorithm is presented. It consists of the decomposition of an examined time-waveform into the linear expansion of chirplet atoms and the analysis of the matrix of their parameters. The main feature of the proposed method is the modification of the chirplet’s matrix in a way that atoms, whose normalized energies are lower than a certain threshold, will be rejected. On the time-frequency planes of the spectrograms, obtained separately for each remaining chirlpet, it can clearly identify the time-frequency structures appearing in the examined signal. The choice of a threshold defines the computing speed and precision of the performed analysis. The method was implemented in the virtual application and used for processing real data, obtained from measurements of time-vary MF emissions onboard a ship. 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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13 pages, 784 KiB

Open AccessArticle

Analysis of the Relative Price in China’s Energy Market for Reducing the Emissions from Consumption

by Shumin Jiang, Jingtao Guo, Chen Yang, Zhanwen Ding and Lixin Tian

Energies 2017, 10(5), 656; https://doi.org/10.3390/en10050656 - 9 May 2017

Cited by 4 | Viewed by 3495

Abstract

As a developing country, extensive carbon and sulfur emissions are associated with China’s rapid social and economic development. Chief among them are the emissions from coal and oil consumption. This paper focuses on the demand side, attempting to regulate the range of relative [...] Read more.

As a developing country, extensive carbon and sulfur emissions are associated with China’s rapid social and economic development. Chief among them are the emissions from coal and oil consumption. This paper focuses on the demand side, attempting to regulate the range of relative price of oil to coal at the consumption level. Through the adjustment of the relative price, the goal of reducing the emissions of carbon and sulfur could be achieved in the market of energy consumption. Data regression is applied to investigate the functional relationship between emissions and energy prices. The results indicate that when the coal price is less than 300, the higher relative price leads to less carbon and sulfur emissions; when the coal price is more than 300 and less than 500, there exists an optimal relative price which has the least carbon emissions, and this value is not more than 11.5; when the coal price is more than 500, the smaller relative price is beneficial to decline carbon and sulfur emissions. The changed trend of relative price-sulfur emissions is very similar to relative price-carbon emissions. Compared to the present energy situation in China, the relative price of oil to coal still need to be reduced especially when coal price is more than 500. Full article

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15 pages, 4330 KiB

Open AccessArticle

A Low-Order System Frequency Response Model for DFIG Distributed Wind Power Generation Systems Based on Small Signal Analysis

by Rui Quan and Wenxia Pan

Energies 2017, 10(5), 657; https://doi.org/10.3390/en10050657 - 9 May 2017

Cited by 17 | Viewed by 6373

Abstract

Integrating large amounts of wind power into power systems brings a large influence on the dynamic frequency response characteristic (DFRC). The traditional low-order system frequency response (SFR) model is no longer applicable at the current time. Based on the small signal analysis theory, [...] Read more.

Integrating large amounts of wind power into power systems brings a large influence on the dynamic frequency response characteristic (DFRC). The traditional low-order system frequency response (SFR) model is no longer applicable at the current time. Based on the small signal analysis theory, a set of novel low-order SFR models for doubly-fed induction generator (DFIG) distributed wind power generation systems (DWPGS) are derived under low, medium, and high wind speed conditions, respectively. Time-domain simulations have been conducted on PSCAD/EMTDC, and the novel SFR model is tested and evaluated on a real system. The simulation results from the novel model agree with those from the detailed model. The novel SFR model can also directly show the impact of the initial wind speed and auxiliary frequency controller (AFC) parameters on DFRC, but not on the detailed model. Full article

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29 pages, 2912 KiB

Open AccessArticle

Economic and Thermal Evaluation of Different Uses of an Existing Structure in a Warm Climate

by Delia D’Agostino, Ilaria Zacà, Cristina Baglivo and Paolo Maria Congedo

Energies 2017, 10(5), 658; https://doi.org/10.3390/en10050658 - 9 May 2017

Cited by 27 | Viewed by 3934

Abstract

Accounting for nearly 40% of final energy consumption, buildings are central to European energy policy. The Directive on Energy Performance of Buildings establishes a benchmarking system known as cost-optimality to set minimum energy performance requirements in new and existing buildings. This paper applies [...] Read more.

Accounting for nearly 40% of final energy consumption, buildings are central to European energy policy. The Directive on Energy Performance of Buildings establishes a benchmarking system known as cost-optimality to set minimum energy performance requirements in new and existing buildings. This paper applies the cost-optimal methodology to an existing structure located in the Mediterranean area (Southern Italy). The building is composed of two units that have been considered for different uses: hotel and multi-residential. Several energy efficiency and renewable measures have been implemented both individually and as part of packages of measures. The cost-optimal solution has been identified as able to optimize energy consumption and costs from financial and macroeconomic perspectives. The first reference building (hotel use) shows a maximum reduction of primary energy and CO₂ emission of about 42%, falling within the CasaClima energy class D, while the second reference building (residential use) achieves a value of 88% for primary energy and 85% for CO₂ emissions, falling into class B. Thermal dispersions through the envelope can be limited using a suitable combination of insulating materials while a variety of technical variants are selected, such as VRF (variant refrigerant flow) systems, heat pumps with fan coils associated with controlled mechanical ventilation, solar thermal and photovoltaic. This paper illustrates the development of energy retrofit projects, in order to reach a balance between efficiency measures and costs for a building having two different uses, providing guidance to similar case studies related to a warm climate. Full article

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19 pages, 5300 KiB

Open AccessArticle

A Method for Thermal Dimensioning and for Energy Behavior Evaluation of a Building Envelope PCM Layer by Using the Characteristic Days

by Domenico Mazzeo, Giuseppe Oliveti and Natale Arcuri

Energies 2017, 10(5), 659; https://doi.org/10.3390/en10050659 - 9 May 2017

Cited by 35 | Viewed by 4598

Abstract

Net zero energy buildings (nZEB) require the development of innovative technologies such as the use of phase change materials (PCMs) in walls for the energy requalification of low inertia buildings. The presence of a PCM layer in the external building wall, due to [...] Read more.

Net zero energy buildings (nZEB) require the development of innovative technologies such as the use of phase change materials (PCMs) in walls for the energy requalification of low inertia buildings. The presence of a PCM layer in the external building wall, due to the effect of storage and release of latent energy phenomena, modifies the energy behavior, both during the summer and winter periods. This paper addresses the problem of the definition of the energetic behavior of a layer subject to phase change with periodic non-sinusoidal boundary conditions, characterizing the external walls of air-conditioned buildings. In such conditions, the layer is the site of the formation of one or more bi-phase interfaces, which originate on the boundary surfaces, or are always present and fluctuate within the layer. It is also possible that the layer does not undergo any phase change. The study has been developed by a finite difference numeric calculation model which explicitly determines the number and the position of the bi-phase interfaces that originate in the layer and the temperature and the heat flux fields. The surface heat fluxes are used to evaluate the PCM layer energetic behavior in terms of energy transferred through the boundary surfaces and of stored energy in sensible and latent form. The proposed method employs the characteristic day that it is periodically repeated for all the days of the considered month. The use of the characteristic days drastically reduces the computational burden of the numerical calculation and it allows to obtain guidance on the behaviour of the PCM throughout the year, in accordance with the variability of external climatic conditions, in order to select the PCM with the most suitable thermophysical properties. The methodology developed is applied to PCM layers with different melting temperatures and subject to climatic conditions of two locations, one with a continental climate and the second one with a Mediterranean climate. The results obtained allowed us to identify which PCM is more suitable in improving the energetic performances of building walls in the heating or cooling period during the year. In particular, the energy analysis highlighted that, in both localities, during the winter period: the lowest energy exiting from the indoor environment is ensured by a PCM with a melting temperature of 15 °C; the highest contribution of energy entering the indoor environment, mainly due to solar radiation, is recorded for a PCM with a melting temperature of 26 °C. During the summer period: the lowest value of energy entering the indoor environment is obtained by a PCM with melting temperature of 26 °C; the highest value of energy exiting from the indoor environment is ensured by a melting temperature equal to 20 °C. In both locations, a PCM with a melting temperature intermediate between those of the winter and summer set points of the indoor environment is the best compromise between winter and summer energy needs for an air-conditioned environment, as it allows obtainment of the highest values of the yearly total stored energy. Full article

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

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18 pages, 1536 KiB

Open AccessReview

Measuring Energy Efficiency in China’s Transport Sector

by Han Hao, Feiqi Liu, Zongwei Liu and Fuquan Zhao

Energies 2017, 10(5), 660; https://doi.org/10.3390/en10050660 - 9 May 2017

Cited by 13 | Viewed by 6201

Abstract

Energy efficiency is one of the key factors affecting energy consumption and greenhouse gas (GHG) emissions. By focusing on China’s transport sector, this study comprehensively reviews and compares the energy efficiency performance of passenger vehicles, light-duty commercial vehicles, commercial road transport, commercial water [...] Read more.

Energy efficiency is one of the key factors affecting energy consumption and greenhouse gas (GHG) emissions. By focusing on China’s transport sector, this study comprehensively reviews and compares the energy efficiency performance of passenger vehicles, light-duty commercial vehicles, commercial road transport, commercial water transport, aviation transport and railway transport, and identifies the opportunities for further energy efficiency improvements. It is found that railway transport exhibited the greatest improvement in energy efficiency during the past decade, which was mainly driven by progress in its electrification. Passenger vehicles have also experienced considerable energy efficiency improvements, which can be mainly attributed to the establishment of mandatory fuel consumption standards. In contrast, commercial road transport has shown the least improvement, due to insufficient policy implementations. Based on the analysis, it is recommended that, as China’s present policy framework to improve energy efficiency in the transport sector is generally effective, it should be consistently maintained and successively improved. Electrification represents a major opportunity for improvement of energy efficiency in the transport sector. Such potential should be fully tapped for all transport modes. Greater effort should be put into improving the energy efficiency of commercial road transport. The policy instruments utilized to improve the energy efficiency of heavy-duty vehicles should be as intensive and effective as the policy instruments for passenger vehicles. Full article

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15 pages, 4406 KiB

Open AccessArticle

The Repeatability of Sorption Processes Occurring in the Coal-Methane System during Multiple Measurement Series

by Mateusz Kudasik, Norbert Skoczylas and Anna Pajdak

Energies 2017, 10(5), 661; https://doi.org/10.3390/en10050661 - 10 May 2017

Cited by 32 | Viewed by 3805

Abstract

The aim of this paper was to investigate the repeatability of sorption processes occurring in the coal-methane system during multiple measurement series. For research purposes, three granular samples of coal sorbent were used. The samples were subjected to a series of three measurements, [...] Read more.

The aim of this paper was to investigate the repeatability of sorption processes occurring in the coal-methane system during multiple measurement series. For research purposes, three granular samples of coal sorbent were used. The samples were subjected to a series of three measurements, each time performed under the same conditions. During each series of measurements, the following stages took place: outgassing the sample in a vacuum, and then saturating it with methane under the pressure of 1, 3, and 10 bar. Sorption capacities and the values of effective diffusion coefficients were compared. The studies into the repeatability of measurements of sorption capacities, conducted by means of the IGA-001 (Intelligent Gravimetric Analyzer) gravimetric instrument for three measurement cycles, showed that the obtained measurement discrepancies in relation to the mean value did not exceed 1.23%. The discrepancies in question approximated the measurement uncertainty of the IGA-001 device. The evaluation of the recurrence of determining the values of effective diffusion coefficients showed that the obtained discrepancies were no larger than 10%, which might have resulted from problems with fulfilling most of the assumptions of the applied unipore diffusion model. The authors did not observe any changes of the sorption parameters of hard coal during consecutive cycles of methane saturation. Full article

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

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15 pages, 5711 KiB

Open AccessArticle

Experimental Study on the Influence of the Rotating Cylinder Block and Pistons on Churning Losses in Axial Piston Pumps

by Junhui Zhang, Ying Li, Bing Xu, Min Pan and Fei Lv

Energies 2017, 10(5), 662; https://doi.org/10.3390/en10050662 - 10 May 2017

Cited by 35 | Viewed by 9734

Abstract

Pressure and performance requirements of axial piston pumps and the proportion of churning losses in axial piston pumps increase significantly with increasing speed. To investigate the primary distribution of churning losses in axial piston pumps at various ranges of speed, a test rig [...] Read more.

Pressure and performance requirements of axial piston pumps and the proportion of churning losses in axial piston pumps increase significantly with increasing speed. To investigate the primary distribution of churning losses in axial piston pumps at various ranges of speed, a test rig was set up in which other friction losses can be eliminated, thus making it possible to investigate the net churning losses in an axial piston pump. The influence of the rotating cylinder block and pistons on churning losses is analyzed based on a qualitative evaluation of the various fluid flow regimes at different test speeds in an axial piston pump. The analytical results indicate that pistons have less influence on churning losses than the rotating cylinder block beyond the critical speed in axial piston pumps, because the total energy dissipation transforms laminar viscous friction losses into turbulent shear stress losses. It is concluded that more attention should be given to the effect of the rotating cylinder block on churning losses in axial piston pumps at high rotation speed. Full article

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

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16 pages, 6027 KiB

Open AccessArticle

An Improved Scheme for Voltage Sag Override in Direct Torque Controlled Induction Motor Drives

by Milutin Petronijević, Nebojša Mitrović, Vojkan Kostić and Bojan Banković

Energies 2017, 10(5), 663; https://doi.org/10.3390/en10050663 - 10 May 2017

Cited by 12 | Viewed by 5084

Abstract

This paper analyses symmetrical and unsymmetrical voltage sag effects on the torque and speed deviation in direct torque controlled (DTC) induction motors (IMs) for adjustable speed drives (ASDs). The capability of an ASD for continuous normal operation in case of short supply disturbances [...] Read more.

This paper analyses symmetrical and unsymmetrical voltage sag effects on the torque and speed deviation in direct torque controlled (DTC) induction motors (IMs) for adjustable speed drives (ASDs). The capability of an ASD for continuous normal operation in case of short supply disturbances is essential for high performance drives. In this paper, an updated scheme is proposed for boosting ASD performances during supply disturbances with voltage reduction. Flux weakening is an effective method to overcome the torque-decreasing problem in case of DC-link voltage diminishing. It is also shown that speed reduction is an efficient procedure to obtain the voltage sag insensitivity of an ASD, which is appropriate for the existing industrial applications. Extensive laboratory testing has been conducted to verify the performances and effectiveness of the proposed control algorithm. The suggested method requires only a modification of converter control software or operating speed change without any additional hardware components. Extended tests under various voltage sags events were carried out on a 1.5 kW laboratory drive, and the obtained results have been compared with an industrial DTC drive. Full article

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

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13 pages, 1090 KiB

Open AccessArticle

Bayesian Estimation of Remaining Useful Life for Wind Turbine Blades

by Jannie S. Nielsen and John D. Sørensen

Energies 2017, 10(5), 664; https://doi.org/10.3390/en10050664 - 10 May 2017

Cited by 65 | Viewed by 7003

Abstract

To optimally plan maintenance of wind turbine blades, knowledge of the degradation processes and the remaining useful life is essential. In this paper, a method is proposed for calibration of a Markov deterioration model based on past inspection data for a range of [...] Read more.

To optimally plan maintenance of wind turbine blades, knowledge of the degradation processes and the remaining useful life is essential. In this paper, a method is proposed for calibration of a Markov deterioration model based on past inspection data for a range of blades, and updating of the model for a specific wind turbine blade, whenever information is available from inspections and/or condition monitoring. Dynamic Bayesian networks are used to obtain probabilities of inspection outcomes for a maximum likelihood estimation of the transition probabilities in the Markov model, and are used again when updating the model for a specific blade using observations. The method is illustrated using indicative data from a database containing data from inspections of wind turbine blades. Full article

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

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16 pages, 971 KiB

Open AccessArticle

Adsorption Behaviour of Lactic Acid on Granular Activated Carbon and Anionic Resins: Thermodynamics, Isotherms and Kinetic Studies

by Nirakar Pradhan, Eldon R. Rene, Piet N. L. Lens, Laura Dipasquale, Giuliana D’Ippolito, Angelo Fontana, Antonio Panico and Giovanni Esposito

Energies 2017, 10(5), 665; https://doi.org/10.3390/en10050665 - 10 May 2017

Cited by 56 | Viewed by 7100

Abstract

Solid-liquid extraction (adsorption or ion exchange) is a promising approach for the in situ separation of organic acids from fermentation broths. In this study, a diluted concentration of lactic acid (<10 g/L) separation from a model fermentation broth by granular activated carbon (GAC) [...] Read more.

Solid-liquid extraction (adsorption or ion exchange) is a promising approach for the in situ separation of organic acids from fermentation broths. In this study, a diluted concentration of lactic acid (<10 g/L) separation from a model fermentation broth by granular activated carbon (GAC) as well as weak (Reillex^® 425 or RLX425) and strong (Amberlite^® IRA-400 or AMB400) base anion exchange resins under various operating conditions was experimentally investigated. Thermodynamic analysis showed that the best lactic acid adsorption performances were obtained at a pH below the pK_a value of lactic acid (i.e., 3.86) for GAC and RLX425 by physical adsorption mechanism and above the pK_a value for the AMB400 resin by an ion exchange mechanism, respectively. The adsorption capacity for GAC (38.2 mg/g) was the highest, followed by AMB400 (31.2 mg/g) and RLX425 (17.2 mg/g). As per the thermodynamic analysis, the lactic acid adsorbed onto GAC and RLX425 through a physical adsorption mechanism, whereas the lactic acid adsorbed onto AMB400 with an ion exchange mechanism. The Langmuir adsorption isotherm model (R² > 0.96) and the pseudo-second order kinetic model (R² ~ 1) fitted better to the experimental data than the other models tested. Postulating the conditions for the real fermentation broth (pH: 5.0–6.5 and temperature: 30–80 °C), the resin AMB400 represents an ideal candidate for the extraction of lactic acid during fermentation. Full article

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46 pages, 950 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Mathematical Modelling of Mooring Systems for Wave Energy Converters—A Review

by Josh Davidson and John V. Ringwood

Energies 2017, 10(5), 666; https://doi.org/10.3390/en10050666 - 11 May 2017

Cited by 158 | Viewed by 15105

Abstract

Mathematical analysis is an essential tool for the successful development and operation of wave energy converters (WECs). Mathematical models of moorings systems are therefore a requisite in the overall techno-economic design and operation of floating WECs. Mooring models (MMs) can be applied to [...] Read more.

Mathematical analysis is an essential tool for the successful development and operation of wave energy converters (WECs). Mathematical models of moorings systems are therefore a requisite in the overall techno-economic design and operation of floating WECs. Mooring models (MMs) can be applied to a range of areas, such as WEC simulation, performance evaluation and optimisation, control design and implementation, extreme load calculation, mooring line fatigue life evaluation, mooring design, and array layout optimisation. The mathematical modelling of mooring systems is a venture from physics to numerics, and as such, there are a broad range of details to consider when applying MMs to WEC analysis. A large body of work exists on MMs, developed within other related ocean engineering fields, due to the common requirement of mooring floating bodies, such as vessels and offshore oil and gas platforms. This paper reviews the mathematical modelling of the mooring systems for WECs, detailing the relevant material developed in other offshore industries and presenting the published usage of MMs for WEC analysis. Full article

(This article belongs to the Special Issue Marine Energy)

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28 pages, 6658 KiB

Open AccessArticle

A Self-Tuning Filter-Based Adaptive Linear Neuron Approach for Operation of Three-Level Inverter-Based Shunt Active Power Filters under Non-Ideal Source Voltage Conditions

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

Energies 2017, 10(5), 667; https://doi.org/10.3390/en10050667 - 11 May 2017

Cited by 22 | Viewed by 5717

Abstract

This paper presents a self-tuning filter (STF)-based adaptive linear neuron (ADALINE) reference current generation algorithm to enhance the operation of a three-phase three-level neutral-point diode clamped (NPC) inverter-based shunt active power filter (SAPF) under non-ideal (unbalanced and/or distorted) source voltage conditions. SAPF is [...] Read more.

This paper presents a self-tuning filter (STF)-based adaptive linear neuron (ADALINE) reference current generation algorithm to enhance the operation of a three-phase three-level neutral-point diode clamped (NPC) inverter-based shunt active power filter (SAPF) under non-ideal (unbalanced and/or distorted) source voltage conditions. SAPF is an effective and versatile mitigation tool for current harmonics. As for its controller, ADALINE-based reference current generation algorithmd have widely been applied and proven to work effectively under balanced and purely sinusoidal source voltage conditions. However, no work has been conducted to study its performance under non-ideal source voltage conditions. In this work, a STF-based fundamental voltage extraction algorithm is integrated with an ADALINE algorithm, serving as synchronizer algorithm to ensure in-phase operation of the generated reference current with the non-ideal source voltage. Hence, it completely eliminates any dependency on conventional synchronizer algorithms such as phase-locked loop (PLL) and zero-crossing detector (ZCD). Additionally, the proposed STF-based ADALINE algorithm implements the modified Widrow-Hoff (W-H) weight updating algorithm for fast generation of reference current. Both simulation and experimental works are performed to verify design concept and effectiveness of the proposed algorithm. Comparative study with another recently reported algorithm is performed to investigate the performance improvement achieved by SAPF while using the proposed algorithm. Full article

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

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16 pages, 10897 KiB

Open AccessArticle

Quantitative Evaluation of BIPV Visual Impact in Building Retrofits Using Saliency Models

by Ran Xu, Stephen Wittkopf and Christian Roeske

Energies 2017, 10(5), 668; https://doi.org/10.3390/en10050668 - 10 May 2017

Cited by 16 | Viewed by 11215

Abstract

BIPV (Building Integrated Photovoltaics) integration in urban spaces requires, not only careful technical, but also aesthetic considerations as its visual impact is seen as a kind of environmental effect. To manage this effect, different methods were developed to measure it; however, most existing [...] Read more.

BIPV (Building Integrated Photovoltaics) integration in urban spaces requires, not only careful technical, but also aesthetic considerations as its visual impact is seen as a kind of environmental effect. To manage this effect, different methods were developed to measure it; however, most existing evaluation methods are either based on subjective speculations and have no continuous criteria standards, or they do not show much relevance to neuropsychological findings. This paper presents an alternative and complementary method for evaluating the BIPV visual impact using the saliency method with an objective, quantitative and neuropsychological-based approach. The application of the method was tested and is discussed in the context of an example case study in Switzerland. Several different BIPV designs were developed for the case study, purposely in ways that made it difficult to rank their visual impacts with one’s subjective instinct. Using the proposed saliency method; however, the differences in BIPV visual impact across all designs could be identified, demonstrated and calculated sensitively. Potential applications of this proposed method include being a helping tool in deciding which BIPV design causes the least or most visual impact among others. Additionally, when combined with solar cadaster, the method enables a comprehensive estimation of BIPV potential in urban areas from both technical and societal aspects. Full article

(This article belongs to the Special Issue Solar Energy Application in Buildings)

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21 pages, 7320 KiB

Open AccessArticle

Coordinated Control Strategy for a Hybrid Wind Farm with DFIG and PMSG under Symmetrical Grid Faults

by Jiawei Li, Jun Yao, Xin Zeng, Ruikuo Liu, Depeng Xu and Caisheng Wang

Energies 2017, 10(5), 669; https://doi.org/10.3390/en10050669 - 11 May 2017

Cited by 14 | Viewed by 6028

Abstract

This paper presents a coordinated control strategy for a hybrid wind farm with doubly-fed induction generator (DFIG)- and direct-driven permanent-magnet synchronous generator (PMSG)-based wind turbines under symmetrical grid faults. The proposed low-voltage ride-through (LVRT) strategy is based on a novel current allocation principle [...] Read more.

This paper presents a coordinated control strategy for a hybrid wind farm with doubly-fed induction generator (DFIG)- and direct-driven permanent-magnet synchronous generator (PMSG)-based wind turbines under symmetrical grid faults. The proposed low-voltage ride-through (LVRT) strategy is based on a novel current allocation principle and is implemented for individual DFIG- or PMSG-based wind turbines. No communication equipment between different wind power generators is required. By monitoring the local voltages and active power outputs of the corresponding wind generators, the proposed control strategy can control the hybrid wind farm to provide the maximum reactive power to support the grid voltage during a symmetrical grid fault. As a result, the reduction in the active power output from the hybrid wind farm can be decreased, which also helps avoid generator over-speed issues and supply active power support for the power grid. In addition, the reactive current upper limits of DFIG- and PMSG-based sub-wind farms are investigated by considering different active power outputs and different grid voltage dip depths, and the feasible regions of the two types of sub-wind farms for meeting the LVRT requirements are further studied. Finally, the effectiveness of the proposed coordinated LVRT control strategy for the hybrid wind farm is validated by simulation and experimental results. Full article

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

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16 pages, 555 KiB

Open AccessFeature PaperArticle

Energy Trading and Pricing in Microgrids with Uncertain Energy Supply: A Three-Stage Hierarchical Game Approach

by Kai Ma, Shubing Hu, Jie Yang, Chunxia Dou and Josep M. Guerrero

Energies 2017, 10(5), 670; https://doi.org/10.3390/en10050670 - 11 May 2017

Cited by 14 | Viewed by 5520

Abstract

This paper studies an energy trading and pricing problem for microgrids with uncertain energy supply. The energy provider with the renewable energy (RE) generation (wind power) determines the energy purchase from the electricity markets and the pricing strategy for consumers to maximize its [...] Read more.

This paper studies an energy trading and pricing problem for microgrids with uncertain energy supply. The energy provider with the renewable energy (RE) generation (wind power) determines the energy purchase from the electricity markets and the pricing strategy for consumers to maximize its profit, and then the consumers determine their energy demands to maximize their payoffs. The hierarchical game is established between the energy provider and the consumers. The energy provider is the leader and the consumers are the followers in the hierarchical game. We consider two types of consumers according to their response to the price, i.e., the price-taking consumers and the price-anticipating consumers. We derive the equilibrium point of the hierarchical game through the backward induction method. Comparing the two types of consumers, we study the influence of the types of consumers on the equilibrium point. In particular, the uncertainty of the energy supply from the energy provider is considered. Simulation results show that the energy provider can obtain more profit using the proposed decision-making scheme. Full article

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

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23 pages, 7563 KiB

Open AccessArticle

Robustness Improvement of Superconducting Magnetic Energy Storage System in Microgrids Using an Energy Shaping Passivity-Based Control Strategy

by Rui Hou, Huihui Song, Thai-Thanh Nguyen, Yanbin Qu and Hak-Man Kim

Energies 2017, 10(5), 671; https://doi.org/10.3390/en10050671 - 11 May 2017

Cited by 18 | Viewed by 6191

Abstract

Superconducting magnetic energy storage (SMES) systems, in which the proportional-integral (PI) method is usually used to control the SMESs, have been used in microgrids for improving the control performance. However, the robustness of PI-based SMES controllers may be unsatisfactory due to the high [...] Read more.

Superconducting magnetic energy storage (SMES) systems, in which the proportional-integral (PI) method is usually used to control the SMESs, have been used in microgrids for improving the control performance. However, the robustness of PI-based SMES controllers may be unsatisfactory due to the high nonlinearity and coupling of the SMES system. In this study, the energy shaping passivity (ESP)-based control strategy, which is a novel nonlinear control based on the methodology of interconnection and damping assignment (IDA), is proposed for robustness improvement of SMES systems. A step-by-step design of the ESP-based method considering the robustness of SMES systems is presented. A comparative analysis of the performance between ESP-based and PI control strategies is shown. Simulation and experimental results prove that the ESP-based strategy achieves the stronger robustness toward the system parameter uncertainties than the conventional PI control. Besides, the use of ESP-based control method can reduce the eddy current losses of a SMES system due to the significant reduction of 2nd and 3rd harmonics of superconducting coil DC current. Full article

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

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21 pages, 2811 KiB

Open AccessArticle

An Elastic Charging Service Fee-Based Load Guiding Strategy for Fast Charging Stations

by Shu Su, Hang Zhao, Hongzhi Zhang and Xiangning Lin

Energies 2017, 10(5), 672; https://doi.org/10.3390/en10050672 - 11 May 2017

Cited by 6 | Viewed by 4221

Abstract

Compared with the traditional slow charging loads, random integration of large scale fast charging loads will exert more serious impacts on the security of power network operation. Besides, to maximize social benefits, effective scheduling strategies guiding fast charging behaviors should be formulated rather [...] Read more.

Compared with the traditional slow charging loads, random integration of large scale fast charging loads will exert more serious impacts on the security of power network operation. Besides, to maximize social benefits, effective scheduling strategies guiding fast charging behaviors should be formulated rather than simply increasing infrastructure construction investments on the power grid. This paper first analyzes the charging users’ various responses to an elastic charging service fee, and introduces the index of charging balance degree to a target region by considering the influence of fast charging loads on the power grid. Then, a multi-objective optimization model of the fast charging service fee is constructed, whose service fee can be further optimized by employing a fuzzy programming method. Therefore, both users’ satisfaction degree and the equilibrium of charging loads can be maintained simultaneously by reasonably guiding electric vehicles (EVs) to different fast charging stations. The simulation results demonstrate the effectiveness of the proposed dynamic charging service pricing and the corresponding fast charging load guidance strategy. 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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13 pages, 5948 KiB

Open AccessArticle

A Single-Loop Repetitive Voltage Controller with an Active Damping Control Technique

by Younghoon Cho, Byeng-Joo Byen, Han-Sol Lee and Kwan-Yuhl Cho

Energies 2017, 10(5), 673; https://doi.org/10.3390/en10050673 - 11 May 2017

Cited by 6 | Viewed by 5016

Abstract

This paper proposes a single-loop repetitive voltage control strategy which incorporates the active damping control feature for single-phase uninterruptible power supply (UPS) applications. The proposed method reduces the effect of the LC resonant peak, which limits the control bandwidth and deteriorates the stability [...] Read more.

This paper proposes a single-loop repetitive voltage control strategy which incorporates the active damping control feature for single-phase uninterruptible power supply (UPS) applications. The proposed method reduces the effect of the LC resonant peak, which limits the control bandwidth and deteriorates the stability of the entire control loop by effectively increasing the damping component. Due to the increased stability margin, a repetitive controller working together with a proportional-resonant (PR) controller can be easily adopted. Moreover, the voltage error is minimized even under severe non-linear load conditions. It is confirmed that the proposed single-loop controller achieves excellent and stable voltage regulation performance by evaluating the entire loop-gain of the system and the output impedance. Both the simulation and the experimental results for a 1.5 kW UPS inverter show agree well with the analyses, and the excellence of the proposed method has been verified. Full article

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

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15 pages, 1152 KiB

Open AccessArticle

Multi-Objective Optimization of Hybrid Renewable Energy System Using an Enhanced Multi-Objective Evolutionary Algorithm

by Mengjun Ming, Rui Wang, Yabing Zha and Tao Zhang

Energies 2017, 10(5), 674; https://doi.org/10.3390/en10050674 - 11 May 2017

Cited by 83 | Viewed by 8777

Abstract

Due to the scarcity of conventional energy resources and the greenhouse effect, renewable energies have gained more attention. This paper proposes methods for multi-objective optimal design of hybrid renewable energy system (HRES) in both isolated-island and grid-connected modes. In each mode, the optimal [...] Read more.

Due to the scarcity of conventional energy resources and the greenhouse effect, renewable energies have gained more attention. This paper proposes methods for multi-objective optimal design of hybrid renewable energy system (HRES) in both isolated-island and grid-connected modes. In each mode, the optimal design aims to find suitable configurations of photovoltaic (PV) panels, wind turbines, batteries and diesel generators in HRES such that the system cost and the fuel emission are minimized, and the system reliability/renewable ability (corresponding to different modes) is maximized. To effectively solve this multi-objective problem (MOP), the multi-objective evolutionary algorithm based on decomposition (MOEA/D) using localized penalty-based boundary intersection (LPBI) method is proposed. The algorithm denoted as MOEA/D-LPBI is demonstrated to outperform its competitors on the HRES model as well as a set of benchmarks. Moreover, it effectively obtains a good approximation of Pareto optimal HRES configurations. By further considering a decision maker’s preference, the most satisfied configuration of the HRES can be identified. Full article

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

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20 pages, 2678 KiB

Open AccessArticle

A Hierarchical Optimization Model for a Network of Electric Vehicle Charging Stations

by Cuiyu Kong, Raka Jovanovic, Islam Safak Bayram and Michael Devetsikiotis

Energies 2017, 10(5), 675; https://doi.org/10.3390/en10050675 - 11 May 2017

Cited by 54 | Viewed by 8421

Abstract

Charging station location decisions are a critical element in mainstream adoption of electric vehicles (EVs). The consumer confidence in EVs can be boosted with the deployment of carefully-planned charging infrastructure that can fuel a fair number of trips. The charging station (CS) location [...] Read more.

Charging station location decisions are a critical element in mainstream adoption of electric vehicles (EVs). The consumer confidence in EVs can be boosted with the deployment of carefully-planned charging infrastructure that can fuel a fair number of trips. The charging station (CS) location problem is complex and differs considerably from the classical facility location literature, as the decision parameters are additionally linked to a relatively longer charging period, battery parameters, and available grid resources. In this study, we propose a three-layered system model of fast charging stations (FCSs). In the first layer, we solve the flow capturing location problem to identify the locations of the charging stations. In the second layer, we use a queuing model and introduce a resource allocation framework to optimally provision the limited grid resources. In the third layer, we consider the battery charging dynamics and develop a station policy to maximize the profit by setting maximum charging levels. The model is evaluated on the Arizona state highway system and North Dakota state network with a gravity data model, and on the City of Raleigh, North Carolina, using real traffic data. The results show that the proposed hierarchical model improves the system performance, as well as the quality of service (QoS), provided to the customers. The proposed model can efficiently assist city planners for CS location selection and system design. Full article

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

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23 pages, 1929 KiB

Open AccessArticle

Design of Nonlinear Robust Damping Controller for Power Oscillations Suppressing Based on Backstepping-Fractional Order Sliding Mode

by Cheng Liu, Guowei Cai, Jiwei Gao and Deyou Yang

Energies 2017, 10(5), 676; https://doi.org/10.3390/en10050676 - 15 May 2017

Cited by 7 | Viewed by 4649

Abstract

In this paper, a novel nonlinear robust damping controller is proposed to suppress power oscillation in interconnected power systems. The proposed power oscillation damping controller exhibits good nonlinearity and robustness. It can consider the strong nonlinearity of power oscillation and uncertainty of its [...] Read more.

In this paper, a novel nonlinear robust damping controller is proposed to suppress power oscillation in interconnected power systems. The proposed power oscillation damping controller exhibits good nonlinearity and robustness. It can consider the strong nonlinearity of power oscillation and uncertainty of its model. First, through differential homeomorphic mapping, a mathematical model of the system can be transformed into the Brunovsky standard. Next, an extended state observer (ESO) estimated and compensated for model errors and external disturbances as well as uncertain factors to achieve dynamic linearization of the nonlinear model. A power oscillation damping controller for interconnected power systems was designed on a backstepping-fractional order sliding mode variable structure control theory (BFSMC). Compared with traditional methods, the controller exhibits good dynamic performance and strong robustness. Simulations involving a four-generator two-area and partial test system of Northeast China were conducted under various disturbances to prove the effectiveness and robustness of the proposed damping control method. Full article

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

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16 pages, 5367 KiB

Open AccessArticle

Electromagnetic Performance Evaluation of an Outer-Rotor Flux-Switching Permanent Magnet Motor Based on Electrical-Thermal Two-Way Coupling Method

by Zhengming Shu, Xiaoyong Zhu, Li Quan, Yi Du and Chang Liu

Energies 2017, 10(5), 677; https://doi.org/10.3390/en10050677 - 12 May 2017

Cited by 11 | Viewed by 5998

Abstract

Flux-switching permanent magnet (FSPM) motors have gained increasing attention in electric vehicles (EVs) applications due to the advantages of high power density and high efficiency. However, the heat sources of both permanent magnet (PM) and armature winding are located on the limited stator [...] Read more.

Flux-switching permanent magnet (FSPM) motors have gained increasing attention in electric vehicles (EVs) applications due to the advantages of high power density and high efficiency. However, the heat sources of both permanent magnet (PM) and armature winding are located on the limited stator space in the FSPM motors, which may result in the PM overheating and irreversible demagnetization caused by temperature rise, and it is often ignored in the conventional thermal analysis. In this paper, a new electrical-thermal two-way coupling design method is proposed to analyze the electromagnetic performances, where the change of PM material characteristics under different temperatures is taken into consideration. First, the motor topology and design equations are introduced. Second, the demagnetization curves of PM materials under different temperatures are modeled due to PM materials are sensitive to the temperature. Based on the electrical-thermal two-way coupling method, the motor performances are evaluated in detail, such as the load PM flux linkage and output torque. The motor is then optimized, and the electromagnetic performances between initial and improved motors are compared. Finally, a prototype motor is manufactured, and the results are validated by experimental measurements. Full article

(This article belongs to the Special Issue Advances in Electric Vehicles and Plug-in Hybrid Vehicles 2017)

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16 pages, 9456 KiB

Open AccessArticle

Study on the Effect of Flame Instability on the Flame Structural Characteristics of Hydrogen/Air Mixtures Based on the Fast Fourier Transform

by Fu-Sheng Li, Guo-Xiu Li, Yan-Huan Jiang, Hong-Meng Li and Zuo-Yu Sun

Energies 2017, 10(5), 678; https://doi.org/10.3390/en10050678 - 12 May 2017

Cited by 19 | Viewed by 4550

Abstract

In this study, the effect of flame intrinsic instability on the flame structural characteristics of hydrogen/air mixtures premixed at various equivalence ratios were experimentally investigated from the macroscopic and microscopic perspectives, respectively. The correlation degree and the relative deformation degree were defined to [...] Read more.

In this study, the effect of flame intrinsic instability on the flame structural characteristics of hydrogen/air mixtures premixed at various equivalence ratios were experimentally investigated from the macroscopic and microscopic perspectives, respectively. The correlation degree and the relative deformation degree were defined to quantitatively study the global flame structural characteristics. Peak detection was used to capture the characteristic length of the flame and fast Fourier transform was adopted to study the components of the fluctuation of the flame front. The results show that with the development of flames, the wrinkles in the flame front increase and the correlation degree of the flame decreases. The relative deformation degree of the flame first decreases and then increases. When the equivalence ratio is 0.6, the average characteristic length initially exhibits an increasing trend, followed by a decreasing trend. The average characteristic length scale gradually increases, and the growth rate gradually decreases when the equivalence ratio ranges from 0.70 to 0.99. With the increase in the wavenumber, the amplitude of the corresponding disturbance exhibited an increasing trend followed by a decreasing one. With the development of the flame, the maximum amplitude of the disturbance shows a reverse trend, i.e., first decreasing and then increasing. The disturbances with smaller wavelengths could be further developed. Full article

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

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19 pages, 1487 KiB

Open AccessArticle

State of Charge Estimation for Lithium-Ion Battery Based on Nonlinear Observer: An H_∞ Method

by Qiao Zhu, Neng Xiong, Ming-Liang Yang, Rui-Sen Huang and Guang-Di Hu

Energies 2017, 10(5), 679; https://doi.org/10.3390/en10050679 - 12 May 2017

Cited by 61 | Viewed by 6589

Abstract

This work is focused on the state of charge (SOC) estimation of a lithium-ion battery based on a nonlinear observer. First, the second-order resistor-capacitor (RC) model of the battery pack is introduced by utilizing the physical behavior of the battery. Then, for the [...] Read more.

This work is focused on the state of charge (SOC) estimation of a lithium-ion battery based on a nonlinear observer. First, the second-order resistor-capacitor (RC) model of the battery pack is introduced by utilizing the physical behavior of the battery. Then, for the nonlinear function of the RC model, a one-sided Lipschitz condition is proposed to ensure that the nonlinear function can play a positive role in the observer design. After that, a nonlinear observer design criterion is presented based on the

H_{\infty}

method, which is formulated as linear matrix inequalities (LMIs). Compared with existing nonlinear observer-based SOC estimation methods, the proposed observer design criterion does not depend on any estimates of the unknown variables. Consequently, the convergence of the proposed nonlinear observer is guaranteed for any operating conditions. Finally, both the static and dynamic experimental cases are given to show the efficiency of the proposed nonlinear observer by comparing with the classic extended Kalman filter (EKF). Full article

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15 pages, 2609 KiB

Open AccessArticle

Stability Analysis of the Cyber Physical Microgrid System under the Intermittent DoS Attacks

by Rong Fu, Xiaojuan Huang, Jun Sun, Zhenkai Zhou, Decheng Chen and Yingjun Wu

Energies 2017, 10(5), 680; https://doi.org/10.3390/en10050680 - 12 May 2017

Cited by 26 | Viewed by 5446

Abstract

Recent research has demonstrated the vulnerabilities of cyber physical microgrid to different rates of denial-of-service (DoS) attacks, which send internal requests to degrade the victim’s performance. However, the interaction between the attacks and the security of microgrid remains largely unknown. In this paper, [...] Read more.

Recent research has demonstrated the vulnerabilities of cyber physical microgrid to different rates of denial-of-service (DoS) attacks, which send internal requests to degrade the victim’s performance. However, the interaction between the attacks and the security of microgrid remains largely unknown. In this paper, we address two fundamental questions: (1) What is the impact of intermittent DoS (IDoS) attacks on the security of cyber physical microgrid and (2) how can we analyze the stability of the cyber physical microgrid under IDoS attacks? To tackle these problems, we firstly model the cyber physical microgrid system considering the IDoS attacks on the network server. Based on the model, the interaction between the cyber system and the physical system is analyzed. Then, the impacts of IDoS attacks on the security of the cyber physical microgrid system are studied. It shows that the attack may lead to the system level oscillation with the information variation during the attack period. Therefore, a risk assessment method is proposed to investigate the stability of the cyber physcial microgrid system under IDoS attacks. Lastly, the proposed methodology is verified by simulation results. Full article

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

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13 pages, 5009 KiB

Open AccessArticle

Enhancing Insulating Performances of Presspaper by Introduction of Nanofibrillated Cellulose

by Jianwen Huang, Yuanxiang Zhou, Longyu Dong, Zhongliu Zhou and Xiangjun Zeng

Energies 2017, 10(5), 681; https://doi.org/10.3390/en10050681 - 12 May 2017

Cited by 13 | Viewed by 5285

Abstract

This study explores the possibility of enhancing both mechanical and breakdown properties of insulating presspaper by the introduction of an organic nano additive. Four different concentrations of nanofibrillated cellulose (NFC) were taken into account: 0.5 wt %, 2.5 wt %, 5 wt %, [...] Read more.

This study explores the possibility of enhancing both mechanical and breakdown properties of insulating presspaper by the introduction of an organic nano additive. Four different concentrations of nanofibrillated cellulose (NFC) were taken into account: 0.5 wt %, 2.5 wt %, 5 wt %, and 10 wt %. Presspaper containing no NFC was also prepared as a reference. Obtained samples were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Mechanical properties and breakdown behaviors were measured. Results show that the addition of 10 wt % NFC to softwood fibers can achieve the best performance. Tensile strength of reference presspaper is 109 MPa, whereas that of presspaper modified by 10 wt % NFC is 136 MPa, resulting in a 25% increase. The improved tensile strength can be attributed to the increased density and inter fiber bond strength. More importantly, presspaper reinforced by 10 wt % NFC can also achieve enhanced AC and DC breakdown strengths, which are 19% and 21% higher than those of the reference presspaper. It is concluded that NFC is likely to be a promising nano additive for cellulose insulation. 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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15 pages, 11164 KiB

Open AccessArticle

Effects of Variable Diffuser Vanes on Performance of a Centrifugal Compressor with Pressure Ratio of 8.0

by Mohsen Ebrahimi, Qiangqiang Huang, Xiao He and Xinqian Zheng

Energies 2017, 10(5), 682; https://doi.org/10.3390/en10050682 - 12 May 2017

Cited by 38 | Viewed by 9118

Abstract

In numerous applications, centrifugal compressors are required to provide a high pressure ratio with good efficiency while also working in a wide operating range. This is a challenge because as pressure ratio increases, efficiency and operating range inevitably decline. This paper studies the [...] Read more.

In numerous applications, centrifugal compressors are required to provide a high pressure ratio with good efficiency while also working in a wide operating range. This is a challenge because as pressure ratio increases, efficiency and operating range inevitably decline. This paper studies the effects of a variable geometry diffuser on the performance and operating range of a centrifugal compressor with high pressure ratios of up to 8.0. The numerical method employed three-dimensional Reynolds-averaged Navier-Stokes simulations. An analysis of the matching of the vaned diffuser with the impeller for different working conditions and diffuser vane angles is presented. The results show that improved matching of the adjusted diffuser increased efficiency by 4.5%. The range extension mechanism of the variable diffuser is explained, and it is shown that adjusting the vane angle by +6° to −6° extended the operating range of the compressor by up to 30.0% for pressure ratios between 5.0 and 6.0. The interaction between diffuser and impeller was examined, and the independent characteristic of the impeller is illustrated. The connection between the incidence angle at the leading edge of the impeller and flow separation near the tip of the impeller is discussed. Full article

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

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16 pages, 910 KiB

Open AccessArticle

Assessment of Energy Storage Operation in Vertically Integrated Utility and Electricity Market

by Zora Luburić, Hrvoje Pandžić and Tomislav Plavšić

Energies 2017, 10(5), 683; https://doi.org/10.3390/en10050683 - 12 May 2017

Cited by 4 | Viewed by 5015

Abstract

The aim of this paper is to compare the operational pattern of an energy storage system (ESS) in a vertically-integrated utility and in a deregulated market environment for different levels of wind integration. As the main feature of a vertically-integrated utility is a [...] Read more.

The aim of this paper is to compare the operational pattern of an energy storage system (ESS) in a vertically-integrated utility and in a deregulated market environment for different levels of wind integration. As the main feature of a vertically-integrated utility is a centralized decision-making process, all of the investment and operating decisions are made with a single goal of minimizing the overall system operating costs. As a result, an ESS in such an environment is operated in a way that is optimal for the overall system economics. On the other hand, the system operator in a deregulated market has less power over the system resources, and commitment and dispatch decisions are a result of the market clearing procedure. In this setting, the ESS owner aims at maximizing its profit, which might not be in line with minimizing overall system operating costs or maximizing social welfare. To compare the ESS operation in these two environments, we analyze the storage operation in two different settings. The first one is a standard unit commitment model with the addition of centrally-controlled storage. The second one is a bilevel model, where the upper level is a coordinated ESS profit maximization problem, while the lower level a simulated market clearing. The case study is performed on a standardized IEEE RTS-96 system. The results show a reduction in the generation dispatch cost, online generation capacity and wind curtailment for both models. Moreover, ESS significantly increases social welfare in the market-based 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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17 pages, 11244 KiB

Open AccessArticle

Numerical Investigation of the Effects of Split Injection Strategies on Combustion and Emission in an Opposed-Piston, Opposed-Cylinder (OPOC) Two-Stroke Diesel Engine

by Lei Zhang, Tiexiong Su, Yangang Zhang, Fukang Ma, Jinguan Yin and Yaonan Feng

Energies 2017, 10(5), 684; https://doi.org/10.3390/en10050684 - 12 May 2017

Cited by 8 | Viewed by 7616

Abstract

In opposed-piston, opposed-cylinder (OPOC) two-stroke diesel engines, the relative movement rules of opposed-pistons, combustion chamber components and injector position are different from those of conventional diesel engines. In this study, the combustion and emission characteristics of the OPOC which is equipped with a [...] Read more.

In opposed-piston, opposed-cylinder (OPOC) two-stroke diesel engines, the relative movement rules of opposed-pistons, combustion chamber components and injector position are different from those of conventional diesel engines. In this study, the combustion and emission characteristics of the OPOC which is equipped with a common-rail injection system are investigated by experimental and numerical simulation. Different split injection strategies involving different pilot injection/fuel mass ratios and injection intervals were compared with a single injection strategy. The numerical simulation was applied to calculate and analyze the effect of split injection strategies on the combustion and emission after validation with the same experimental result (single injection strategy). Results showed that using split injection had a significant beneficial effect on the combustion process, because of the acceleration effect that enhances the air-fuel mixture. Additionally, the temperature of the split injection strategies was higher than that of single strategy, leading to the nitrogen oxides (NO_x) increasing and soot decreasing. In addition, it has been found that the split injection condition with a smaller pilot injection/fuel mass ratio and a medium injection interval performed better than the single injection condition in terms of the thermo-atmosphere utilization and space utilization. Full article

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17 pages, 3668 KiB

Open AccessArticle

Modeling and Validation of a Diesel Engine with Turbocharger for Hardware-in-the-Loop Applications

by Jinguan Yin, Tiexiong Su, Zhuowei Guan, Quanhong Chu, Changjiang Meng, Li Jia, Jun Wang and Yangang Zhang

Energies 2017, 10(5), 685; https://doi.org/10.3390/en10050685 - 13 May 2017

Cited by 13 | Viewed by 5813

Abstract

This paper presents a simulator model of a diesel engine with a turbocharger for hardware-in-the-loop (HIL) applications, which is used to obtain engine performance data to study the engine performance under faulty conditions, to assist engineers in diagnosis and estimation, and to assist [...] Read more.

This paper presents a simulator model of a diesel engine with a turbocharger for hardware-in-the-loop (HIL) applications, which is used to obtain engine performance data to study the engine performance under faulty conditions, to assist engineers in diagnosis and estimation, and to assist engineers in model-based calibration (MBC). The whole diesel engine system is divided into several functional blocks: air block, injection block, cylinder block, crankshaft block, cooling block, lubrication block, and accessory block. The diesel engine model is based on physical level, semi-physical level and mathematical level concepts, and developed by Matlab/Simulink. All the model parameters are estimated using weighted least-squares optimization and the tuning process details are presented. Since the sub-model coupling may cause errors, the validation process is then given to make the model more accurate. The results show that the tuning process is important for the functional blocks and the validation process is useful for the accuracy of the whole engine model. Subsequently, this program could be used as a plant model for MBC, to develop and test engine control units (ECUs) on HIL equipment for the purpose of improving ECU performance. Full article

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

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22 pages, 8018 KiB

Open AccessArticle

Assessment of Large Scale Photovoltaic Power Generation from Carport Canopies

by Abdulsalam S. Alghamdi, AbuBakr S. Bahaj and Yue Wu

Energies 2017, 10(5), 686; https://doi.org/10.3390/en10050686 - 13 May 2017

Cited by 31 | Viewed by 8878

Abstract

Reliance on fossil fuel-driven energy supply is a major contributor to global emissions. In order to stay within the Paris Agreement’s temperature rise limits, current and growing energy consumption will need to be significantly underpinned by deployment of low/non-carbon power generation. This work [...] Read more.

Reliance on fossil fuel-driven energy supply is a major contributor to global emissions. In order to stay within the Paris Agreement’s temperature rise limits, current and growing energy consumption will need to be significantly underpinned by deployment of low/non-carbon power generation. This work promotes power generation at the megawatt scale from solar photovoltaics (PV) systems deployed in untapped car parking areas, which are estimated to represent up to ~6.6% of the urban footprint within cities. The methodology developed is globally applicable to support PV development, including site selection and PV array configuration. It is underpinned by a case study in a university campus, which has a similar footprint as assigned in cities for vehicle parking. The methodology demonstrates that less than 1% of the available parking spaces are affected by shadows from surrounding buildings or vegetation. The work shows that by utilising such parking areas within the selected campus a PV installation with a capacity of ~36.4 MWp, which can generate ~66.2 GWh of electricity annually, would be feasible. Financial analysis based on multiple scenarios indicates that a 50% return on investment is achievable over 25 years at an export tariff of USD ¢4.5/kWh, which is commensurate with the latest granted bids for a similar export tariff. Full article

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

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25 pages, 6231 KiB

Open AccessFeature PaperArticle

Reducing Fuel Consumption in Hydraulic Excavators—A Comprehensive Analysis

by Milos Vukovic, Roland Leifeld and Hubertus Murrenhoff

Energies 2017, 10(5), 687; https://doi.org/10.3390/en10050687 - 12 May 2017

Cited by 58 | Viewed by 13175

Abstract

Mobile machines, especially excavators, still consume considerable amounts of fuel during their operating lifetimes. This is not only undesirable in economic terms but also adversely affects our environment. The following paper discusses methods to lower fuel consumption by conducting a comprehensive analysis of [...] Read more.

Mobile machines, especially excavators, still consume considerable amounts of fuel during their operating lifetimes. This is not only undesirable in economic terms but also adversely affects our environment. The following paper discusses methods to lower fuel consumption by conducting a comprehensive analysis of the components comprising a hydraulic excavator and the cycles these machines perform. One of the main aims is to emphasise that a design centred on the standard definitions of efficiency, especially hydraulic efficiency, can be rather misleading. A new approach using a novel fuel consumption model, based on the Willans approximation, coupled with the concepts of fixed and variable fuel consumption is introduced and validated using real test data obtained from an 18 t excavator. The new methodology can be used to help uncover simpler methods to improve today’s machines. Full article

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

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11 pages, 3165 KiB

Open AccessArticle

New Insight of Maximum Transferred Power by Matching Capacitance of a Wireless Power Transfer System

by Chunyan Xiao, Yufeng Liu, Dingning Cheng and Kangzheng Wei

Energies 2017, 10(5), 688; https://doi.org/10.3390/en10050688 - 13 May 2017

Cited by 17 | Viewed by 4878

Abstract

Most research on wireless power transfer (WPT) has been focused on how to achieve a high-efficiency power transfer. Our study found that under the impedance matching for achieving maximum WPT efficiency, the power transferred to the load cannot reach the maximum when a [...] Read more.

Most research on wireless power transfer (WPT) has been focused on how to achieve a high-efficiency power transfer. Our study found that under the impedance matching for achieving maximum WPT efficiency, the power transferred to the load cannot reach the maximum when a WPT system is supplied by an AC voltage source with constant amplitude. However, the load power or the voltage across the load is essential for a low-power electric device such as the implanted medical device where the transfer efficiency is not the priority to be considered. The paper presents a method for achieving maximum power on the load by matching capacitance in a WPT system with given two-coupled-coils. Three sets of matching capacitances for extreme load power were deduced based on the circuit model considering the coil's resistance, and all these three matching make the WPT system operate at the resonant state. Two sets can make the system achieve the global maximum of load power. One set can make the system achieve the local maximum of load power and reach the power transfer efficiency next to 1. Experimental results verified the theoretical calculations. The results can contribute to the compensation design of a practical WPT system for transferring the maximum power to the load. Full article

(This article belongs to the Special Issue Wireless Power Transfer and Energy Harvesting Technologies)

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14 pages, 3125 KiB

Open AccessArticle

Modeling the Performance of a New Speed Adjustable Compound Supercharging Diesel Engine Working under Plateau Conditions

by Meng Xia, Changlu Zhao, Fujun Zhang and Ying Huang

Energies 2017, 10(5), 689; https://doi.org/10.3390/en10050689 - 17 May 2017

Cited by 7 | Viewed by 4783

Abstract

In order to improve the diesel engine performance under plateau (high altitude) conditions, a new Speed Adjustable Compound (SAC) supercharging method is proposed. A simulation model based on a six-cylinder V-type turbocharged intercooler diesel engine is built on the GT-POWER platform, and then [...] Read more.

In order to improve the diesel engine performance under plateau (high altitude) conditions, a new Speed Adjustable Compound (SAC) supercharging method is proposed. A simulation model based on a six-cylinder V-type turbocharged intercooler diesel engine is built on the GT-POWER platform, and then simulation-based research is carried out. A genetic algorithm (GA) is used to identify the best operation parameters, including the supercharger speed and fuel injection quantity under steady state conditions. Transient performance is obtained through starting process simulation of a vehicle with SAC engine on the MATLAB/Simulink GT-POWER co-simulation platform. Both the steady and transient performance of the SAC engine are compared with those of the original engine. Results show that the torque of the SAC engine at full load is significantly increased when the engine speed n < 1600 r/min. The increment of the maximum torque can reach up to 31% at 1000 r/min compared to that of the original engine, while the peak torque is increased by 9%. The fuel consumption deterioration is restricted within 5%. What’s more, the SAC engine can help reducing the acceleration time by 20% during tip-in pedal events during the vehicle starting process. Full article

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

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15 pages, 2224 KiB

Open AccessArticle

Economics and Resources Analysis of the Potential Use of Reprocessing Options by a Medium Sized Nuclear Reactor Fleet

by Iván Merino Rodríguez, Francisco Álvarez-Velarde, Aris V. Skarbeli and Enrique M. González-Romero

Energies 2017, 10(5), 690; https://doi.org/10.3390/en10050690 - 13 May 2017

Cited by 1 | Viewed by 3907

Abstract

Reprocessing of irradiated nuclear fuel is or has been implemented in several countries with significant numbers of nuclear power plants and installed capacity. In this work, a set of scenarios has been analyzed to find the key variables for the implementation of reprocessing [...] Read more.

Reprocessing of irradiated nuclear fuel is or has been implemented in several countries with significant numbers of nuclear power plants and installed capacity. In this work, a set of scenarios has been analyzed to find the key variables for the implementation of reprocessing in medium sized fleets. The inventories of the Spanish nuclear fuel cycle scenario were chosen as representative, considering two different reactor lifetimes and reprocessing strategies, with the aim of burning the maximum amount of the Pu mass generated in the cycle. The simulations of the scenarios were performed with the TR_EVOL code developed at CIEMAT. Results show that the lifetime of the reactors has an impact in the possible reduction in the Pu amount. Some scenarios show a shortage of Pu available for mixed uranium-plutonium oxide (MOX) fuel fabrication coming from the reprocessing of UO₂ spent fuel. This work has verified that, for medium sized fuel cycle scenarios, the parameters with the most importance are the reprocessing cost and natural uranium cost. A smaller impact in the comparison is also found for the cost of the final disposal and the possibility of valuing the surplus Pu and reprocessed uranium existent at the end of the cycle. Full article

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

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15 pages, 3525 KiB

Open AccessArticle

An On-Board Remaining Useful Life Estimation Algorithm for Lithium-Ion Batteries of Electric Vehicles

by Xiaoyu Li, Xing Shu, Jiangwei Shen, Renxin Xiao, Wensheng Yan and Zheng Chen

Energies 2017, 10(5), 691; https://doi.org/10.3390/en10050691 - 14 May 2017

Cited by 62 | Viewed by 5784

Abstract

Battery remaining useful life (RUL) estimation is critical to battery management and performance optimization of electric vehicles (EVs). In this paper, we present an effective way to estimate RUL online by using the support vector machine (SVM) algorithm. By studying the characteristics of [...] Read more.

Battery remaining useful life (RUL) estimation is critical to battery management and performance optimization of electric vehicles (EVs). In this paper, we present an effective way to estimate RUL online by using the support vector machine (SVM) algorithm. By studying the characteristics of the battery degradation process, the rising of the terminal voltage and changing characteristics of the voltage derivative (DV) during the charging process are introduced as the training variables of the SVM algorithm to determine the battery RUL. The SVM is then applied to build the battery degradation model and predict the battery real cycle numbers. Experimental results prove that the built battery degradation model shows higher accuracy and less computation time compared with those of the neural network (NN) method, thereby making it a potential candidate for realizing online RUL estimation in a battery management system (BMS). Full article

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

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14 pages, 6118 KiB

Open AccessArticle

Study on the Thermal and Dielectric Properties of SrTiO₃/Epoxy Nanocomposites

by Xiaoxing Zhang, Hao Wen, Xiaoyu Chen, Yunjian Wu and Song Xiao

Energies 2017, 10(5), 692; https://doi.org/10.3390/en10050692 - 15 May 2017

Cited by 22 | Viewed by 6688

Abstract

SrTiO₃/epoxy nanocomposites are prepared using the facile solution-processing technique by incorporating SrTiO₃ nanoparticles with different weight fractions into the epoxy resin host. The morphology of the nanoparticles and composites, as well as the thermal conduction characteristics and electrical properties of [...] Read more.

SrTiO₃/epoxy nanocomposites are prepared using the facile solution-processing technique by incorporating SrTiO₃ nanoparticles with different weight fractions into the epoxy resin host. The morphology of the nanoparticles and composites, as well as the thermal conduction characteristics and electrical properties of the composites were investigated via conventional testing methods. The thermal conductivity increased along with the SrTiO₃ weight fractions, and the thermal conductivity of the SrTiO₃/epoxy composite with 40 wt % weight fraction increased to 0.52 W/mK. The dielectric constant increased along with the weight fractions and decreased along with frequency, thereby suggesting that the interfacial and dipole polarization do not follow the changes in the electrical field direction at high frequency. The dielectric constants at 1 kHz frequency increased along with temperature. Surface breakdown tests illustrated further improvements in the thermal and electrical properties of the composites. In the same time span of 40 s, the 40 wt % nanocomposite demonstrated a rapid temperature decline rate of 6.77 °C/s, which was 47% faster than that of the pure epoxy sample. The surface breakdown voltage also increased along with the weight fractions. The functional composites can solve the key problem in the intelligentization, miniaturization, and high-efficiency of the gas-insulated switchgear, which warrants further research. 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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19 pages, 10720 KiB

Open AccessArticle

Presentation and Performance Evaluation of a Novel Stator-Permanent-Magnet Hybrid Stepping Motor

by Binglin Lu and Yanliang Xu

Energies 2017, 10(5), 693; https://doi.org/10.3390/en10050693 - 15 May 2017

Cited by 2 | Viewed by 6097

Abstract

In this paper, a new type of hybrid stepping motor (HSM) with permanent magnets (PMs) embedded in the stator, namely the stator-permanent-magnet hybrid stepping motor (SHSM), is presented. It has the same operation principles as the traditional HSM, with a 2-D distributed magnetic [...] Read more.

In this paper, a new type of hybrid stepping motor (HSM) with permanent magnets (PMs) embedded in the stator, namely the stator-permanent-magnet hybrid stepping motor (SHSM), is presented. It has the same operation principles as the traditional HSM, with a 2-D distributed magnetic field nature and superiorities such as simpler rotor structure, easier PM cooling, higher torque and power density, and higher power grade. Its structural topology and operation principles are initially presented. Then an investigation on the performance comparison between the HSM and the SHSM, in terms of PM flux density, PM torque, detent torque, positional holding accuracy, stator core saturation issue, PM flux leakage, and PM utilization rate is carried out theoretically to make an assessment of the performance superiorities of the SHSM. A prototype of a 2-phase 8-pole 50-rotor-tooth SHSM is fabricated and experimentally compared with the HSM by using finite element analysis (FEA) to verify the motor’s operational feasibility and the theoretical analysis. The FEA and experimental results show that the proposed SHSM has performance advantages such as higher torque density, higher power grade, and higher pull-out torque, holding torque, and torque-speed property, although it has performance defects such as higher torque ripple and relatively lower positional holding accuracy in the open-loop operation than the conventional HSM. Consequently, this novel SHSM is more suitable for electromechanical energy conversion applications rather than positioning mechanisms, especially taking into account the open-loop control advantage. Full article

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

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16 pages, 2527 KiB

Open AccessArticle

A Novel Hybrid Model Based on Extreme Learning Machine, k-Nearest Neighbor Regression and Wavelet Denoising Applied to Short-Term Electric Load Forecasting

by Weide Li, Demeng Kong and Jinran Wu

Energies 2017, 10(5), 694; https://doi.org/10.3390/en10050694 - 16 May 2017

Cited by 36 | Viewed by 5482

Abstract

Electric load forecasting plays an important role in electricity markets and power systems. Because electric load time series are complicated and nonlinear, it is very difficult to achieve a satisfactory forecasting accuracy. In this paper, a hybrid model, Wavelet Denoising-Extreme Learning Machine optimized [...] Read more.

Electric load forecasting plays an important role in electricity markets and power systems. Because electric load time series are complicated and nonlinear, it is very difficult to achieve a satisfactory forecasting accuracy. In this paper, a hybrid model, Wavelet Denoising-Extreme Learning Machine optimized by k-Nearest Neighbor Regression (EWKM), which combines k-Nearest Neighbor (KNN) and Extreme Learning Machine (ELM) based on a wavelet denoising technique is proposed for short-term load forecasting. The proposed hybrid model decomposes the time series into a low frequency-associated main signal and some detailed signals associated with high frequencies at first, then uses KNN to determine the independent and dependent variables from the low-frequency signal. Finally, the ELM is used to get the non-linear relationship between these variables to get the final prediction result for the electric load. Compared with three other models, Extreme Learning Machine optimized by k-Nearest Neighbor Regression (EKM), Wavelet Denoising-Extreme Learning Machine (WKM) and Wavelet Denoising-Back Propagation Neural Network optimized by k-Nearest Neighbor Regression (WNNM), the model proposed in this paper can improve the accuracy efficiently. New South Wales is the economic powerhouse of Australia, so we use the proposed model to predict electric demand for that region. The accurate prediction has a significant meaning. Full article

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

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14 pages, 6908 KiB

Open AccessArticle

Influence of Prewhirl Angle and Axial Distance on Energy Performance and Pressure Fluctuation for a Centrifugal Pump with Inlet Guide Vanes

by Yabin Liu, Lei Tan, Ming Liu, Yue Hao and Yun Xu

Energies 2017, 10(5), 695; https://doi.org/10.3390/en10050695 - 15 May 2017

Cited by 59 | Viewed by 6148

Abstract

The energy performance and pressure fluctuations in a centrifugal pump with inlet guide vanes (IGVs) are investigated experimentally and numerically in a prewhirl angle range of −24° to 24° and in an axial distance range of 280 mm, 380 mm, and 460 mm. [...] Read more.

The energy performance and pressure fluctuations in a centrifugal pump with inlet guide vanes (IGVs) are investigated experimentally and numerically in a prewhirl angle range of −24° to 24° and in an axial distance range of 280 mm, 380 mm, and 460 mm. The reliability and accuracy of the numerical method are validated by the satisfactory agreement between the experimental data and numerical results. Prewhirl regulation with IGVs can significantly increase the energy performance and broaden the efficient operation range for the centrifugal pump due to the improvement of flow pattern at the impeller inlet. The prewhirl angle has an obvious impact on pump energy performance, and the maximum amplitudes of pressure fluctuations on the blade leading edge of the pressure and suction sides decrease by 69% and 89%, respectively. The axial distance has a slight impact on pump energy performance, but the maximum amplitudes of pressure fluctuations drop by 35.4% on the blade leading edge of pressure side when the axial distance extends from 280 mm to 460 mm. Full article

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14 pages, 340 KiB

Open AccessArticle

An Efficient Reactive Power Control Method for Power Network Systems with Solar Photovoltaic Generators Using Sparse Optimization

by Yu Li and Masato Ishikawa

Energies 2017, 10(5), 696; https://doi.org/10.3390/en10050696 - 16 May 2017

Cited by 5 | Viewed by 4478

Abstract

With the incremental introduction of solar photovoltaic (PV) generators into existing power systems, and their fast-growing share in the gross electricity generation, system voltage stability has become a critical issue. One of the major concerns is voltage fluctuation, due to large and random [...] Read more.

With the incremental introduction of solar photovoltaic (PV) generators into existing power systems, and their fast-growing share in the gross electricity generation, system voltage stability has become a critical issue. One of the major concerns is voltage fluctuation, due to large and random penetration of solar PV generators. To suppress severe system voltage deviation, reactive power control of the photovoltaic system inverter has been widely proposed in recent works; however, excessive use of reactive power control would increase both initial and operating costs. In this paper, a method for efficient allocation and control of reactive power injection using the sparse optimization technique is proposed. Based on a constrained linearized model describing the influence of reactive power injection on voltage magnitude change, the objective of this study is formulated as an optimization problem, which aims to find the best reactive power injection that minimizes the whole system voltage variation. Two types of formulations are compared: the first one is the conventional least-square optimization, while the second one is adopted from a sparse optimization technique, called the constrained least absolute shrinkage and selection operator (LASSO) method. The constrained LASSO method adds

ℓ^{1}

-norm penalty to the total reactive power injection, which contributes to the suppression of the number of control nodes with non-zero reactive power injection. The authors analyzed the effectiveness of the constrained LASSO method using the IEEE 39-bus and 57-bus power network as benchmark examples, under various PV power generation and allocation patterns. The simulation results show that the constrained LASSO method automatically selects the minimum number of inverters required for voltage regulation at the current operating point. Full article

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

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11 pages, 5399 KiB

Open AccessArticle

A High-Power-Density Single-Phase Rectifier Based on Three-Level Neutral-Point Clamped Circuits

by Tao Zhou, Zeliang Shu, Hongjian Lin, Deng Luo, Yajun Chen and Xiaoxiao Guo

Energies 2017, 10(5), 697; https://doi.org/10.3390/en10050697 - 16 May 2017

Cited by 3 | Viewed by 5500

Abstract

A single-phase three-level converter is suitable for medium-power applications, with an interface voltage that is higher than that of a traditional two-level configuration. The three-level neutral-point clamped converter is adopted using four switches in each bridge arm, which, compared to a two-level rectifier, [...] Read more.

A single-phase three-level converter is suitable for medium-power applications, with an interface voltage that is higher than that of a traditional two-level configuration. The three-level neutral-point clamped converter is adopted using four switches in each bridge arm, which, compared to a two-level rectifier, leads to less voltage stress, a lower switching frequency, and switching loss on switches. The transient current control strategy is designed to control the active power. The single-phase space vector pulse width modulation (SVPWM) with a voltage balance strategy is designed to solve the neutral point voltage fluctuation problem and keep the dc-link voltage stable. A 1.3 kW high-power-density prototype based on SiC MOSFET was built and tested. The experimental results verified the high performance of steady-state and dynamic responses. Full article

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

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28 pages, 10287 KiB

Open AccessArticle

A Modular Multilevel Converter with Power Mismatch Control for Grid-Connected Photovoltaic Systems

by Turgay Duman, Shilpa Marti, M. A. Moonem, Azas Ahmed Rifath Abdul Kader and Hariharan Krishnaswami

Energies 2017, 10(5), 698; https://doi.org/10.3390/en10050698 - 17 May 2017

Cited by 23 | Viewed by 6883

Abstract

A modular multilevel power converter configuration for grid connected photovoltaic (PV) systems is proposed. The converter configuration replaces the conventional bulky line frequency transformer with several high frequency transformers, potentially reducing the balance of systems cost of PV systems. The front-end converter for [...] Read more.

A modular multilevel power converter configuration for grid connected photovoltaic (PV) systems is proposed. The converter configuration replaces the conventional bulky line frequency transformer with several high frequency transformers, potentially reducing the balance of systems cost of PV systems. The front-end converter for each port is a neutral-point diode clamped (NPC) multi-level dc-dc dual-active bridge (ML-DAB) which allows maximum power point tracking (MPPT). The integrated high frequency transformer provides the galvanic isolation between the PV and grid side and also steps up the low dc voltage from PV source. Following the ML-DAB stage, in each port, is a NPC inverter. N number of NPC inverters’ outputs are cascaded to attain the per-phase line-to-neutral voltage to connect directly to the distribution grid (i.e., 13.8 kV). The cascaded NPC (CNPC) inverters have the inherent advantage of using lower rated devices, smaller filters and low total harmonic distortion required for PV grid interconnection. The proposed converter system is modular, scalable, and serviceable with zero downtime with lower foot print and lower overall cost. A novel voltage balance control at each module based on power mismatch among N-ports, have been presented and verified in simulation. Analysis and simulation results are presented for the N-port converter. The converter performance has also been verified on a hardware prototype. Full article

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

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13 pages, 1172 KiB

Open AccessArticle

Photovoltaic Array Fault Detection by Automatic Reconfiguration

by Dong Ji, Cai Zhang, Mingsong Lv, Ye Ma and Nan Guan

Energies 2017, 10(5), 699; https://doi.org/10.3390/en10050699 - 16 May 2017

Cited by 36 | Viewed by 7633

Abstract

Photovoltaic (PV) system output electricity is related to PV cells’ conditions, with the PV faults decreasing the efficiency of the PV system and even causing a possible source of fire. In industrial production, PV fault detection is typically laborious manual work. In this [...] Read more.

Photovoltaic (PV) system output electricity is related to PV cells’ conditions, with the PV faults decreasing the efficiency of the PV system and even causing a possible source of fire. In industrial production, PV fault detection is typically laborious manual work. In this paper, we present a method that can automatically detect PV faults. Based on the observation that different faults will have different impacts on a PV system, we propose a method that systematically and iteratively reconfigures the PV array until the faults are located based on the specific current-voltage (I-V) curve of the (sub-)array. Our method can detect several main types of faults including open-circuit faults, mismatch faults, short circuit faults, etc. We evaluate our methods by Matlab/Simulink-based simulation. The results show that the proposed methods can accurately detect and classify the different faults occurring in a PV system. Full article

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

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31 pages, 1115 KiB

Open AccessArticle

The Optimal Road Grade Design for Minimizing Ground Vehicle Energy Consumption

by Junhui Liu, Lei Feng and Zhiwu Li

Energies 2017, 10(5), 700; https://doi.org/10.3390/en10050700 - 16 May 2017

Cited by 10 | Viewed by 5111

Abstract

Reducing energy consumption of ground vehicles is a paramount pursuit in academia and industry. Even though the road infrastructural has a significant influence on vehicular fuel consumption, the majority of the R&D efforts are dedicated to improving vehicles. Little investigation has been made [...] Read more.

Reducing energy consumption of ground vehicles is a paramount pursuit in academia and industry. Even though the road infrastructural has a significant influence on vehicular fuel consumption, the majority of the R&D efforts are dedicated to improving vehicles. Little investigation has been made in the optimal design of the road infrastructure to minimize the total fuel consumption of all vehicles running on it. This paper focuses on this overlooked design problem and the design parameters of the optimal road infrastructure is the profile of road grade angle between two fixed points. We assume that all vehicles on the road follow a given acceleration profile between the two given points. The mean value of the energy consumptions of all vehicles running on the road is defined as the objective function. The optimization problem is solved both analytically by Pontryagin’s minimum principle and numerically by dynamic programming. The two solutions agree well. A large number of Monte Carlo simulations show that the vehicles driving on the road with the optimal road grade consume up to 31.7% less energy than on a flat road. Finally, a rough cost analysis justifies the economic advantage of building the optimal road profile. Full article

(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)

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20 pages, 5941 KiB

Open AccessArticle

Dynamic Charging of Electric Vehicle with Negligible Power Transfer Fluctuation

by Md Morshed Alam, Saad Mekhilef, Mehdi Seyedmahmoudian and Ben Horan

Energies 2017, 10(5), 701; https://doi.org/10.3390/en10050701 - 16 May 2017

Cited by 28 | Viewed by 5227

Abstract

High-efficiency inductive power transfer (IPT) with low misalignment effects is a key issue in the dynamic charging of electric vehicle (EV) systems. In this study, an advanced concept of analysis and design of transmitter and receiver coils with a special coil assembly is [...] Read more.

High-efficiency inductive power transfer (IPT) with low misalignment effects is a key issue in the dynamic charging of electric vehicle (EV) systems. In this study, an advanced concept of analysis and design of transmitter and receiver coils with a special coil assembly is proposed for the dynamic charging of EVs. In each transmitter coil, large rectangular section is series connected with two zigzag-shaped small rectangular sections. These small sections are back-to-back series connected and located inside the large rectangular section. An adjacent pair of proposed transmitter coils with back-to-back series connection named extended double D (DD)-shaped transmitter is used throughout this paper. The major contribution in the case of the extended DD transmitter is negligible power transfer fluctuation, regardless of any horizontal misalignment of the receiver coil. Justification of the coil design is performed based on its load independent voltage gain and power transfer fluctuation characteristics. Experimental results prove that the power transfer fluctuation with load independent voltage gain is within ±6%, and the efficiency is approximately 93% under horizontal misalignment of receiver coil with an air gap of 140 mm. Finally, a new coil design set with a special arrangement has been proposed to maintain nearly uniform coupling factor and negligible power transfer fluctuation. Full article

(This article belongs to the Special Issue Advances in Electric Vehicles and Plug-in Hybrid Vehicles 2017)

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12 pages, 5251 KiB

Open AccessArticle

Scale-Model Experiments for the Surface Wave Influence on a Submerged Floating Ocean-Current Turbine

by Katsutoshi Shirasawa, Junichiro Minami and Tsumoru Shintake

Energies 2017, 10(5), 702; https://doi.org/10.3390/en10050702 - 16 May 2017

Cited by 13 | Viewed by 6918

Abstract

In order to harness the kinetic energy of marine currents, we propose a novel ocean-current turbine with a horizontal axis. The turbine can be moored to the seabed and function similarly to kites in a water flow. To operate such turbines in a [...] Read more.

In order to harness the kinetic energy of marine currents, we propose a novel ocean-current turbine with a horizontal axis. The turbine can be moored to the seabed and function similarly to kites in a water flow. To operate such turbines in a marine current, the resulting rotor torque needs to be canceled. Therefore, the proposed turbine is designed with a float at its top and a counterweight at its bottom. Thus far, we have verified the turbine stability and blade performance through towing experiments. As the next step, we constructed a scale-model turbine to confirm the mooring system. This experiment was performed at a circulating water channel with wave-making facilities. The influence of waves on the floating body was also investigated. In this paper, we report the behavior of the scale-model turbine moored to the tank bottom and discuss the influence of surface waves. Full article

(This article belongs to the Special Issue Marine Energy)

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15 pages, 2485 KiB

Open AccessArticle

A Numerical Study on the Impact of Grouting Material on Borehole Heat Exchangers Performance in Aquifers

by Luca Alberti, Adriana Angelotti, Matteo Antelmi and Ivana La Licata

Energies 2017, 10(5), 703; https://doi.org/10.3390/en10050703 - 17 May 2017

Cited by 34 | Viewed by 5285

Abstract

U-pipes for ground source heat pump (GSHP) installations are generally inserted in vertical boreholes back-filled with pumpable grouts. Grout thermal conductivity is a crucial parameter, dominating the borehole thermal resistance and impacting the heat exchanger efficiency. In order to seal the borehole and [...] Read more.

U-pipes for ground source heat pump (GSHP) installations are generally inserted in vertical boreholes back-filled with pumpable grouts. Grout thermal conductivity is a crucial parameter, dominating the borehole thermal resistance and impacting the heat exchanger efficiency. In order to seal the borehole and prevent leakages of the heat carrier fluid, grouting materials are also hydraulically impermeable, so that groundwater flow inside the borehole is inhibited. The influence of groundwater flow on the borehole heat exchangers (BHE) performance has recently been highlighted by several authors. However groundwater impact and grouting materials influence are usually evaluated separately, disregarding any combined effect. Therefore simulation is used to investigate the role of the thermal and hydraulic conductivities of the grout when the BHE operates in an aquifer with a relevant groundwater flow. Here 3 main cases for a single U-pipe in a sandy aquifer are compared. In Case 1 the borehole is back-filled with the surrounding soil formation, while a thermally enhanced grout and a low thermal conductivity grout are considered in Case 2 and Case 3 respectively. Simulations are carried out maintaining the inlet temperature constant in order to reproduce the yearly operation of the GSHP system. For each of the 3 cases three different groundwater flow velocities are considered. The results show that a high thermal conductivity grout further enhances the effects of a significant groundwater flow. The conditions when neglecting the grout material in the numerical model does not lead to relevant errors are also identified. Full article

(This article belongs to the Special Issue Low Enthalpy Geothermal Energy)

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15 pages, 2321 KiB

Open AccessArticle

A Failure Probability Calculation Method for Power Equipment Based on Multi-Characteristic Parameters

by Hang Liu, Youyuan Wang, Yi Yang, Ruijin Liao, Yujie Geng and Liwei Zhou

Energies 2017, 10(5), 704; https://doi.org/10.3390/en10050704 - 17 May 2017

Cited by 12 | Viewed by 5801

Abstract

Although traditional fault diagnosis methods can qualitatively identify the failure modes for power equipment, it is difficult to evaluate the failure probability quantitatively. In this paper, a failure probability calculation method for power equipment based on multi-characteristic parameters is proposed. After collecting the [...] Read more.

Although traditional fault diagnosis methods can qualitatively identify the failure modes for power equipment, it is difficult to evaluate the failure probability quantitatively. In this paper, a failure probability calculation method for power equipment based on multi-characteristic parameters is proposed. After collecting the historical data of different fault characteristic parameters, the distribution functions and the cumulative distribution functions of each parameter, which are applied to dispersing the parameters and calculating the differential warning values, are calculated by using the two-parameter Weibull model. To calculate the membership functions of parameters for each failure mode, the Apriori algorithm is chosen to mine the association rules between parameters and failure modes. After that, the failure probability of each failure mode is obtained by integrating the membership functions of different parameters by a weighted method, and the important weight of each parameter is calculated by the differential warning values. According to the failure probability calculation result, the series model is established to estimate the failure probability of the equipment. Finally, an application example for two 220 kV transformers is presented to show the detailed process of the method. Compared with traditional fault diagnosis methods, the calculation results not only identify the failure modes correctly, but also reflect the failure probability changing trend of the equipment accurately. 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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15 pages, 6328 KiB

Open AccessArticle

Design of a Bearingless Outer Rotor Induction Motor

by Yuxin Sun, Jingwei Tang and Kai Shi

Energies 2017, 10(5), 705; https://doi.org/10.3390/en10050705 - 17 May 2017

Cited by 17 | Viewed by 6546

Abstract

A bearingless induction (BI) motor with an outer rotor for flywheel energy storage systems is proposed due to the perceived advantages of simple rotor structure, non-contact support and high speed operation. Firstly, the configuration and operation principle of the proposed motor are described. [...] Read more.

A bearingless induction (BI) motor with an outer rotor for flywheel energy storage systems is proposed due to the perceived advantages of simple rotor structure, non-contact support and high speed operation. Firstly, the configuration and operation principle of the proposed motor are described. Then several leading dimensional parameters are optimally calculated for achieving the maximum average values and the minimum ripples of torque output and suspension force. Finally, by using the finite element method, the characteristics and performance of the proposed machine are analyzed and verified. Full article

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24 pages, 17018 KiB

Open AccessArticle

Performance Analysis of a Four-Switch Three-Phase Grid-Side Converter with Modulation Simplification in a Doubly-Fed Induction Generator-Based Wind Turbine (DFIG-WT) with Different External Disturbances

by Kai Ni, Yihua Hu, Yang Liu and Chun Gan

Energies 2017, 10(5), 706; https://doi.org/10.3390/en10050706 - 18 May 2017

Cited by 25 | Viewed by 5604

Abstract

This paper investigates the performance of a fault-tolerant four-switch three-phase (FSTP) grid-side converter (GSC) in a doubly-fed induction generator-based wind turbine (DFIG-WT). The space vector pulse width modulation (SVPWM) technique is simplified and unified duty ratios are used for controlling the FSTP GSC. [...] Read more.

This paper investigates the performance of a fault-tolerant four-switch three-phase (FSTP) grid-side converter (GSC) in a doubly-fed induction generator-based wind turbine (DFIG-WT). The space vector pulse width modulation (SVPWM) technique is simplified and unified duty ratios are used for controlling the FSTP GSC. Steady DC-bus voltage, sinusoidal three-phase grid currents and unity power factor are obtained. In addition, the balance of capacitor voltages is accomplished based on the analysis of current flows at the midpoint of DC bus in different operational modes. Besides, external disturbances such as fluctuating wind speed and grid voltage sag are considered to test its fault-tolerant ability. Furthermore, the effects of fluctuating wind speed on the performance of DFIG-WT system are explained according to an approximate expression of the turbine torque. The performance of the proposed FSTP GSC is simulated in Matlab/Simulink 2016a based on a detailed 1.5 MW DFIG-WT Simulink model. Experiments are carried out on a 2 kW platform by using a discrete signal processor (DSP) TMS320F28335 controller to validate the reliability of DFIG-WT for the cases with step change of the stator active power and grid voltage sag, respectively. Full article

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

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13 pages, 5288 KiB

Open AccessArticle

ITO-Free Transparent Organic Solar Cell with Distributed Bragg Reflector for Solar Harvesting Windows

by Yuelin Peng, Lushuai Zhang, Nongyi Cheng and Trisha L. Andrew

Energies 2017, 10(5), 707; https://doi.org/10.3390/en10050707 - 17 May 2017

Cited by 18 | Viewed by 8787

Abstract

We demonstrated an indium tin oxide (ITO)-free, highly transparent organic solar cell with the potential to be integrated into window panes for energy harvesting purposes. A transparent, conductive ZnO/Ag/ZnO multilayer electrode and a Ag:Ca thin film electrode were used in this transparent device [...] Read more.

We demonstrated an indium tin oxide (ITO)-free, highly transparent organic solar cell with the potential to be integrated into window panes for energy harvesting purposes. A transparent, conductive ZnO/Ag/ZnO multilayer electrode and a Ag:Ca thin film electrode were used in this transparent device as the bottom and top electrode, respectively. To further improve the transmittance of the solar cell, the thickness of the top ZnO layer was investigated both experimentally and with simulations. An average visible transmittance of >60% was reached, with a maximum transmittance of 73% at 556 nm. Both top and bottom illumination of the solar cell generated comparable power conversion efficiencies, which indicates the wide application of this solar cell structure. In addition, we fabricated distributed Bragg reflector mirrors with sputtered SiO₂ and TiO₂, which efficiently increased the power conversion efficiency over 20% for the solar cells on glass and poly(ethylene terephthalate) (PET) substrates. Full article

(This article belongs to the Special Issue Solar Energy Application in Buildings)

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13 pages, 2334 KiB

Open AccessArticle

Bifurcation Phenomena Studies of a Voltage Controlled Buck-Inverter Cascade System

by Xiaofei Li, Chunsen Tang, Xin Dai, Aiguo Patrick Hu and Sing Kiong Nguang

Energies 2017, 10(5), 708; https://doi.org/10.3390/en10050708 - 18 May 2017

Cited by 3 | Viewed by 4366

Abstract

This paper studies the complex bifurcation phenomena of a voltage-controlled Buck-inverter cascade system. A state-flow chart is drawn to illustrate the complex relations among the linear operating modes. Combined with the state transition function of each mode, the time response of the system [...] Read more.

This paper studies the complex bifurcation phenomena of a voltage-controlled Buck-inverter cascade system. A state-flow chart is drawn to illustrate the complex relations among the linear operating modes. Combined with the state transition function of each mode, the time response of the system can be obtained. For period-one steady state, the periodic mapping function and its fixed point are further derived, on the basis of which the Jacobi matrix is developed and its maximum eigenvalue is analyzed to understand the bifurcation diagram. By globally analyzing the state space using this cell mapping method, the coexistence of attractors is revealed in the Buck-inverter system. All theoretical results have been verified experimentally on a prototype system. The results obtained can be used for guiding the design and analysis of the Buck-inverter system. The analyzing method can be helpful for studying other power electronics systems with compound topologies. Full article

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

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15 pages, 5193 KiB

Open AccessArticle

Research on the Optimal Charging Strategy for Li-Ion Batteries Based on Multi-Objective Optimization

by Haitao Min, Weiyi Sun, Xinyong Li, Dongni Guo, Yuanbin Yu, Tao Zhu and Zhongmin Zhao

Energies 2017, 10(5), 709; https://doi.org/10.3390/en10050709 - 17 May 2017

Cited by 43 | Viewed by 7156

Abstract

Charging performance affects the commercial application of electric vehicles (EVs) significantly. This paper presents an optimal charging strategy for Li-ion batteries based on the voltage-based multistage constant current (VMCC) charging strategy. In order to satisfy the different charging demands of the EV users [...] Read more.

Charging performance affects the commercial application of electric vehicles (EVs) significantly. This paper presents an optimal charging strategy for Li-ion batteries based on the voltage-based multistage constant current (VMCC) charging strategy. In order to satisfy the different charging demands of the EV users for charging time, charged capacity and energy loss, the multi-objective particle swarm optimization (MOPSO) algorithm is employed and the influences of charging stage number, charging cut-off voltage and weight factors of different charging goals are analyzed. Comparison experiments of the proposed charging strategy and the traditional normal and fast charging strategies are carried out. The experimental results demonstrate that the traditional normal and fast charging strategies can only satisfy a small range of EV users’ charging demand well while the proposed charging strategy can satisfy the whole range of the charging demand well. The relative increase in charging performance of the proposed charging strategy can reach more than 80% when compared to the normal and fast charging dependently. Full article

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

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14 pages, 2582 KiB

Open AccessArticle

The Potential of Thermal Plasma Gasification of Olive Pomace Charcoal

by Andrius Tamošiūnas, Ajmia Chouchène, Pranas Valatkevičius, Dovilė Gimžauskaitė, Mindaugas Aikas, Rolandas Uscila, Makrem Ghorbel and Mejdi Jeguirim

Energies 2017, 10(5), 710; https://doi.org/10.3390/en10050710 - 17 May 2017

Cited by 42 | Viewed by 6458

Abstract

Annually, the olive oil industry generates a significant amount of by-products, such as olive pomace, olive husks, tree prunings, leaves, pits, and branches. Therefore, the recovery of these residues has become a major challenge in Mediterranean countries. The utilization of olive industry residues [...] Read more.

Annually, the olive oil industry generates a significant amount of by-products, such as olive pomace, olive husks, tree prunings, leaves, pits, and branches. Therefore, the recovery of these residues has become a major challenge in Mediterranean countries. The utilization of olive industry residues has received much attention in recent years, especially for energy purposes. Accordingly, this primary experimental study aims at investigating the potential of olive biomass waste for energy recovery in terms of synthesis gas (or syngas) production using the thermal arc plasma gasification method. The olive charcoal made from the exhausted olive solid waste (olive pomace) was chosen as a reference material for primary experiments with known composition from the performed proximate and ultimate analysis. The experiments were carried out at various operational parameters: raw biomass and water vapour flow rates and the plasma generator power. The producer gas involved principally CO, H₂, and CO₂ with the highest concentrations of 41.17%, 13.06%, and 13.48%, respectively. The produced synthesis gas has a lower heating value of 6.09 MJ/nm³ at the H₂O/C ratio of 3.15 and the plasma torch had a power of 52.2 kW. Full article

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

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16 pages, 993 KiB

Open AccessEditor’s ChoiceArticle

Economic Assessment of Network-Constrained Transactive Energy for Managing Flexible Demand in Distribution Systems

by Junjie Hu, Guangya Yang and Yusheng Xue

Energies 2017, 10(5), 711; https://doi.org/10.3390/en10050711 - 18 May 2017

Cited by 10 | Viewed by 4866

Abstract

The increasing number of distributed energy resources such as electric vehicles and heat pumps connected to power systems raises operational challenges to the network operator, for example, introducing grid congestion and voltage deviations in the distribution network level if their operations are not [...] Read more.

The increasing number of distributed energy resources such as electric vehicles and heat pumps connected to power systems raises operational challenges to the network operator, for example, introducing grid congestion and voltage deviations in the distribution network level if their operations are not properly coordinated. Coordination and control of a large number of distributed energy resources requires innovative approaches. In this paper, we follow up on a recently proposed network-constrained transactive energy (NCTE) method for scheduling of electric vehicles and heat pumps within a retailer’s aggregation at distribution system level. We extend this method with: (1) a new modeling technique that allows the resulting congestion price to be directly interpreted as a locational marginal pricing in the system; (2) an explicit analysis of the benefits and costs of different actors when using the NCTE method in the system, given the high penetration of distributed energy resources. This paper firstly describes the NCTE-based distribution system that introduces a new interacting scheme for actors at the distribution system level. Then, technical modeling and economic interpretation of the NCTE-based distribution system are described. Finally, we show the benefits and costs of different actors within the NCTE-based distribution system. Full article

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

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16 pages, 3997 KiB

Open AccessArticle

Hydrodynamic Investigation of an Oscillating Buoy Wave Energy Converter Integrated into a Pile-Restrained Floating Breakwater

by Xuanlie Zhao, Dezhi Ning, Chongwei Zhang and Haigui Kang

Energies 2017, 10(5), 712; https://doi.org/10.3390/en10050712 - 18 May 2017

Cited by 55 | Viewed by 7410

Abstract

An analytical model is developed based on linear potential flow theory and matching eigenfunction expansion technique to investigate the hydrodynamics of a two-dimensional floating structure. This structure is an integration system consisting of a breakwater and an oscillating buoy wave energy converter (WEC). [...] Read more.

An analytical model is developed based on linear potential flow theory and matching eigenfunction expansion technique to investigate the hydrodynamics of a two-dimensional floating structure. This structure is an integration system consisting of a breakwater and an oscillating buoy wave energy converter (WEC). It is constrained to heave motion, and linear power take-off (PTO) damping is used to calculate the absorbed power. The proposed model is verified against the published results. The proposed integrated structure is compared with the fixed structure and free heave-motion structure, respectively. The hydrodynamic properties of the integrated structure with the optimal PTO damping i.e., the transmission coefficient, reflection coefficient, capture width ratio (CWR), and heave response amplitude operator (RAO), are investigated. The effect of the PTO damping on the performance of the integrated system is also evaluated. Results indicate that with the proper adjustment of the PTO damping, the proposed integrated system can produce power efficiently. Meanwhile, the function of coastal protection can be compared with that of the fixed structure. Full article

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

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19 pages, 26823 KiB

Open AccessArticle

Improved Capacitor Voltage Feedforward for Three-Phase LCL-Type Grid-Connected Converter to Suppress Start-Up Inrush Current

by Shiying Zhou, Xudong Zou, Donghai Zhu, Li Tong and Yong Kang

Energies 2017, 10(5), 713; https://doi.org/10.3390/en10050713 - 18 May 2017

Cited by 13 | Viewed by 5617

Abstract

Three-phase active damping LCL-type grid-connected converters are usually used in distributed power generation systems. However, serious inrush current will be aroused when the grid-connected converter starts, especially in rectifier mode, if no effective control method is taken. The point of common coupling (PCC) [...] Read more.

Three-phase active damping LCL-type grid-connected converters are usually used in distributed power generation systems. However, serious inrush current will be aroused when the grid-connected converter starts, especially in rectifier mode, if no effective control method is taken. The point of common coupling (PCC) voltage feedforward is usually used to suppress start-up inrush current. Unfortunately, it will introduce a positive feedback loop related to the grid current and grid impedance under weak grid conditions, and therefore, the grid current will be distorted and the system stability margin will be significantly reduced. To solve the above problems, this paper proposes a simple method based on a d-axis fundamental positive-sequence component of filter capacitor voltage feedforward, without extra sensors and software resources. With the proposed method, it is possible to suppress the start-up inrush current and maintain the grid current quality and system stability under weak grid conditions. The mechanism of start-up inrush current and the effectiveness of the method for inrush current suppression are analyzed in detail. Then, the influences of different feedforward methods on system stability are analyzed under weak grid conditions by the impedance model of grid-connected converter. Finally, experimental results verify the validity of the proposed method. Full article

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

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13 pages, 4472 KiB

Open AccessArticle

Insulation Resistance Monitoring Algorithm for Battery Pack in Electric Vehicle Based on Extended Kalman Filtering

by Chuanxue Song, Yulong Shao, Shixin Song, Silun Peng, Fang Zhou, Cheng Chang and Da Wang

Energies 2017, 10(5), 714; https://doi.org/10.3390/en10050714 - 18 May 2017

Cited by 27 | Viewed by 8856

Abstract

To improve the accuracy of insulation monitoring between the battery pack and chassis of electric vehicles, we established a serial battery pack model composed of first-order resistor-capacitor (RC) circuit battery cells. We then designed a low-voltage, low-frequency insulation monitoring model based on this [...] Read more.

To improve the accuracy of insulation monitoring between the battery pack and chassis of electric vehicles, we established a serial battery pack model composed of first-order resistor-capacitor (RC) circuit battery cells. We then designed a low-voltage, low-frequency insulation monitoring model based on this serial battery pack model. An extended Kalman filter (EKF) was designed for this non-linear system to filter the measured results, thus mitigating the influence of noise. Experimental and simulation results show that the proposed monitoring model and extended Kalman filtering algorithm for insulation resistance monitoring present satisfactory estimation accuracy and robustness. Full article

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

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10 pages, 3133 KiB

Open AccessArticle

A SVPWM to Eliminate Common-Mode Voltage for Multilevel Inverters

by Xiongmin Tang, Chengjing Lai, Zheng Liu and Miao Zhang

Energies 2017, 10(5), 715; https://doi.org/10.3390/en10050715 - 18 May 2017

Cited by 13 | Viewed by 4896

Abstract

This paper presents a new space vector pulse width modulation (SVPWM) to eliminate common-mode voltage (CMV) for multilevel inverters. The proposed SVPWM is performed in a new coordinate system, in which the converter voltage vectors have only integer entries and the absolute coordinate [...] Read more.

This paper presents a new space vector pulse width modulation (SVPWM) to eliminate common-mode voltage (CMV) for multilevel inverters. The proposed SVPWM is performed in a new coordinate system, in which the converter voltage vectors have only integer entries and the absolute coordinate increment between adjacent vectors is equal to 1. The location of the reference vector, detection of the nearest three CMV vectors, and duty cycles of the nearest three CMV vectors are all obtained by simple calculations, no lookup table is needed and the SVPWM is computationally fast. Compared with earlier pulse width modulations (PWMs), the realization of the CMV vectors is very simple, and the CMV of multilevel inverters are limited to zero with any modulation index. Because the SVPWM is independent of the level number of the inverter, the proposed SVPWM is suitable for any level of inverter. This paper also thoroughly compares the proposed SVPWM with prior PWMs. Experimental results are also given in the paper. Full article

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

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11 pages, 2820 KiB

Open AccessArticle

The Investigation of High Quality PEDOT:PSS Film by Multilayer-Processing and Acid Treatment

by Po-Wen Sze, Kuan-Wei Lee, Pin-Chiao Huang, Dei-Wei Chou, Bing-Siang Kao and Chien-Jung Huang

Energies 2017, 10(5), 716; https://doi.org/10.3390/en10050716 - 18 May 2017

Cited by 26 | Viewed by 9557

Abstract

In this study, we have investigated the performance of multilayer films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) treated with one of the perfluorinated carboxylic acids, named trifluoroacetic acid (TFA). According to the increased density of the PEDOT chain under unit area conditions, the sheet resistance (R [...] Read more.

In this study, we have investigated the performance of multilayer films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) treated with one of the perfluorinated carboxylic acids, named trifluoroacetic acid (TFA). According to the increased density of the PEDOT chain under unit area conditions, the sheet resistance (R_sq) has improved from 300 to 65 Ω/sq through additional processing of PEDOT:PSS from single layer to multilayer. After the further treatment with TFA, however, the R_sq of the multilayer PEDOT:PSS was enhanced to 45 Ω/sq, leading to the decline of film thickness from 400 to 270 nm. Both conductivity and work function based on X-ray photoelectron spectroscopy results have built a breakthrough by double-processing because of the higher density of conductive PEDOT chains and the increase of 0.4 eV alternatives to typical indium tin oxide substrate, respectively. This improvement is contributed to the development of more effective transparent electrodes. Full article

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21 pages, 13316 KiB

Open AccessArticle

Determination of Equivalent Thermal Conductivity of Window Spacers in Consideration of Condensation Prevention and Energy Saving Performance

by Mi-Su Shin, Kyu-Nam Rhee, Ji-Yong Yu and Gun-Joo Jung

Energies 2017, 10(5), 717; https://doi.org/10.3390/en10050717 - 18 May 2017

Cited by 12 | Viewed by 7464

Abstract

This study investigated the impact of thermally improved spacers (TISs) on the condensation prevention and energy saving performances of residential windows. The temperature factor and total U-value were analyzed with the two-box model, by which the TISs are represented with the equivalent thermal [...] Read more.

This study investigated the impact of thermally improved spacers (TISs) on the condensation prevention and energy saving performances of residential windows. The temperature factor and total U-value were analyzed with the two-box model, by which the TISs are represented with the equivalent thermal conductivity. The results showed that the TISs could increase the temperature factor by up to 12%, and this significantly improved the condensation prevention performance. In addition, it was proved that the TIS enables the prevention of the condensation at an outdoor temperature that is 4.2 °C to 15.7 °C lower compared with the conventional spacer. Also, it was shown that the TISs reduce the total U-value by an amount from 0.07 W/m²K to 0.12 W/m²K, implying that the heat loss through the window is reduced by a rate from 2.8% to 8.2%. In addition, the results of the whole building energy simulation proved that the TISs can reduce the annual heating-energy consumption by a rate from 3.0% to 6.3%. The results were then used for the development of monographs to determine the equivalent thermal conductivity of a window spacer that can meet the performance criteria in terms of condensation prevention and energy saving. Full article

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24 pages, 3149 KiB

Open AccessArticle

Waste Heat Recovery from Marine Gas Turbines and Diesel Engines

by Marco Altosole, Giovanni Benvenuto, Ugo Campora, Michele Laviola and Alessandro Trucco

Energies 2017, 10(5), 718; https://doi.org/10.3390/en10050718 - 18 May 2017

Cited by 46 | Viewed by 12727

Abstract

The paper presents the main results of a research project directed to the development of mathematical models for the design and simulation of combined Gas Turbine-Steam or Diesel-Steam plants for marine applications. The goal is to increase the energy conversion efficiency of both [...] Read more.

The paper presents the main results of a research project directed to the development of mathematical models for the design and simulation of combined Gas Turbine-Steam or Diesel-Steam plants for marine applications. The goal is to increase the energy conversion efficiency of both gas turbines and diesel engines, adopted in ship propulsion systems, by recovering part of the thermal energy contained in the exhaust gases through Waste Heat Recovery (WHR) dedicated installations. The developed models are used to identify the best configuration of the combined plants in order to optimize, for the different applications, the steam plant layout and the performance of WHR plant components. This research activity has allowed to obtain significant improvements in terms of energy conversion efficiency, but also on other important issues: dimensions and weights of the installations, ship load capacity, environmental compatibility, investment and operating costs. In particular, the main results of the present study can be summarized as follows: (a) the quantitative assessment of the advantages (and limits) deriving by the application of a Combined Gas And Steam (COGAS) propulsion system to a large container ship, in substitution of the traditional two-stroke diesel engine; (b) the proposal of optimized WHR propulsion and power systems for an oil tanker, for which a quantitative evaluation is given of the attainable advantages, in terms of fuel consumption and emissions reduction, in comparison with more traditional solutions. Full article

(This article belongs to the Special Issue Waste Heat Recovery)

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28 pages, 12899 KiB

Open AccessArticle

A Multistage DC-DC Step-Up Self-Balanced and Magnetic Component-Free Converter for Photovoltaic Applications: Hardware Implementation

by Mahajan Sagar Bhaskar, Sanjeevikumar Padmanaban and Frede Blaabjerg

Energies 2017, 10(5), 719; https://doi.org/10.3390/en10050719 - 18 May 2017

Cited by 58 | Viewed by 9592

Abstract

This article presents a self-balanced multistage DC-DC step-up converter for photovoltaic applications. The proposed converter topology is designed for unidirectional power transfer and provides a doable solution for photovoltaic applications where voltage is required to be stepped up without magnetic components (transformer-less and [...] Read more.

This article presents a self-balanced multistage DC-DC step-up converter for photovoltaic applications. The proposed converter topology is designed for unidirectional power transfer and provides a doable solution for photovoltaic applications where voltage is required to be stepped up without magnetic components (transformer-less and inductor-less). The output voltage obtained from renewable sources will be low and must be stepped up by using a DC-DC converter for photovoltaic applications. 2 K diodes and 2 K capacitors along with two semiconductor control switch are used in the K-stage proposed converter to obtain an output voltage which is (K + 1) times the input voltage. The conspicuous features of proposed topology are: (i) magnetic component free (transformer-less and inductor-less); (ii) continuous input current; (iii) low voltage rating semiconductor devices and capacitors; (iv) modularity; (v) easy to add a higher number of levels to increase voltage gain; (vi) only two control switches with alternating operation and simple control. The proposed converter is compared with recently described existing transformer-less and inductor-less power converters in term of voltage gain, number of devices and cost. The application of the proposed circuit is discussed in detail. The proposed converter has been designed with a rated power of 60 W, input voltage is 24 V, output voltage is 100 V and switching frequency is 100 kHz. The performance of the converter is verified through experimental and simulation results. Full article

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15 pages, 12140 KiB

Open AccessArticle

Mapping Urban Heat Demand with the Use of GIS-Based Tools

by Artur Wyrwa and Yi-kuang Chen

Energies 2017, 10(5), 720; https://doi.org/10.3390/en10050720 - 19 May 2017

Cited by 20 | Viewed by 6642

Abstract

This article presents a bottom-up approach for calculation of the useful heat demand for space heating and hot water preparation using geo-referenced datasets for buildings at the city level. This geographic information system (GIS) based approach was applied in the case study for [...] Read more.

This article presents a bottom-up approach for calculation of the useful heat demand for space heating and hot water preparation using geo-referenced datasets for buildings at the city level. This geographic information system (GIS) based approach was applied in the case study for the city of Krakow, where on the one hand the district heat network is well developed, while on the other hand there are still substantial number of buildings burning solid fuels in individual boilers and stoves, causing air pollution. The calculated heat demand was aggregated in the grid with 100 m × 100 m spatial resolution to deliver the heat map depicting the current situation for 21 buildings types. The results show that the residential buildings, in particular one- and multi-family buildings, have the highest share in overall demand for heat. By combining the results with location of the district heat (DH) network, the potential areas in its close vicinity that have sufficient heat demand density for developing the net were pointed out. Future evolution in heat demand for space heating in one-family houses was evaluated with the use of deterministic method employing building stock model. The study lays a foundation for planning the development of the heating system at the city level. Full article

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19 pages, 4324 KiB

Open AccessArticle

The Role of Shearing Energy and Interfacial Gibbs Free Energy in the Emulsification Mechanism of Waxy Crude Oil

by Zhihua Wang, Xinyu Lin, Zhenhua Rui, Mengmeng Xu and Shuyi Zhan

Energies 2017, 10(5), 721; https://doi.org/10.3390/en10050721 - 19 May 2017

Cited by 33 | Viewed by 6654

Abstract

Crude oil is generally produced with water, and the water cut produced by oil wells is increasingly common over their lifetime, so it is inevitable to create emulsions during oil production. However, the formation of emulsions presents a costly problem in surface process [...] Read more.

Crude oil is generally produced with water, and the water cut produced by oil wells is increasingly common over their lifetime, so it is inevitable to create emulsions during oil production. However, the formation of emulsions presents a costly problem in surface process particularly, both in terms of transportation energy consumption and separation efficiency. To deal with the production and operational problems which are related to crude oil emulsions, especially to ensure the separation and transportation of crude oil-water systems, it is necessary to better understand the emulsification mechanism of crude oil under different conditions from the aspects of bulk and interfacial properties. The concept of shearing energy was introduced in this study to reveal the driving force for emulsification. The relationship between shearing stress in the flow field and interfacial tension (IFT) was established, and the correlation between shearing energy and interfacial Gibbs free energy was developed. The potential of the developed correlation model was validated using the experimental and field data on emulsification behavior. It was also shown how droplet deformation could be predicted from a random deformation degree and orientation angle. The results indicated that shearing energy as the energy produced by shearing stress working in the flow field is the driving force activating the emulsification behavior. The deformation degree and orientation angle of dispersed phase droplet are associated with the interfacial properties, rheological properties and the experienced turbulence degree. The correlation between shearing stress and IFT can be quantified if droplet deformation degree vs. droplet orientation angle data is available. When the water cut is close to the inversion point of waxy crude oil emulsion, the interfacial Gibbs free energy change decreased and the shearing energy increased. This feature is also presented in the special regions where the suddenly changed flow field can be formed. Hence, the shearing energy is an effective form that can show the contribution of kinetic energy for the oil-water mixtures to interfacial Gibbs free energy in emulsification process, and the emulsification mechanism of waxy crude oil-water emulsions was further explained from the theoretical level. Full article

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

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17 pages, 4008 KiB

Open AccessArticle

An Innovative Adaptive Control System to Regulate Microclimatic Conditions in a Greenhouse

by Giuseppina Nicolosi, Roberto Volpe and Antonio Messineo

Energies 2017, 10(5), 722; https://doi.org/10.3390/en10050722 - 19 May 2017

Cited by 51 | Viewed by 7882

Abstract

In the recent past home automation has been expanding its objectives towards new solutions both inside the smart home and in its outdoor spaces, where several new technologies are available. This work has developed an approach to integrate intelligent microclimatic greenhouse control into [...] Read more.

In the recent past home automation has been expanding its objectives towards new solutions both inside the smart home and in its outdoor spaces, where several new technologies are available. This work has developed an approach to integrate intelligent microclimatic greenhouse control into integrated home automation. Microclimatic control of greenhouses is a critical issue in agricultural practices, due to often common sudden daily variation of climatic conditions, and to its potentially detrimental effect on plant growth. A greenhouse is a complex thermodynamic system where indoor temperature and relative humidity have to be closely monitored to facilitate plant growth and production. This work shows an adaptive control system tailored to regulate microclimatic conditions in a greenhouse, by using an innovative combination of soft computing applications. In particular, a neural network solution has been proposed in order to forecast the climatic behavior of greenhouse, while a parallel fuzzy scheme approach is carried out in order to adjust the air speed of fan-coil and its temperature. The proposed combined approach provides a better control of greenhouse climatic conditions due to the system’s capability to base instantaneous solutions both on real measured variables and on forecasted climatic change. Several simulation campaigns were carried out to perform accurate neural network and fuzzy schemes, aimed at obtaining respectively a minimum forecasted error value and a more appropriate fuzzification and de-fuzzification process. A Matlab/Simulink solution implemented with a combined approach and its relevant obtained performance is also shown in present study, demonstrating that through controlled parameters it will be possible to maintain a better level of indoor climatic conditions. In the present work we prove how with a forecast of outside temperature at the next time-instant and rule-based controller monitoring of cooling or heating air temperatures and air velocities of devices that regulate the indoor micro-climate inside, a better adjustment of the conditions of comfort for crops is achievable. Full article

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22 pages, 2291 KiB

Open AccessArticle

A Study on the Conduction Mechanism and Evaluation of the Comprehensive Efficiency of Photovoltaic Power Generation in China

by Jinpeng Liu, Yun Long and Xiaohua Song

Energies 2017, 10(5), 723; https://doi.org/10.3390/en10050723 - 19 May 2017

Cited by 19 | Viewed by 5583

Abstract

In the context of the global potential energy crisis and aggravating regional environmental pollution, Chinese photovoltaic power generation still faces the key problems of sustainable development, even given its favorable background in large-scale exploitation. Scientific evaluation of the comprehensive efficiency of photovoltaic power [...] Read more.

In the context of the global potential energy crisis and aggravating regional environmental pollution, Chinese photovoltaic power generation still faces the key problems of sustainable development, even given its favorable background in large-scale exploitation. Scientific evaluation of the comprehensive efficiency of photovoltaic power generation is of great significance because it will improve investment decision-making and enhance management level, evaluate the development conditions of photovoltaic power generation and then promote sustainable development capability. The concept of “comprehensive efficiency” is proposed in this paper on the basis of the resource development of solar energy and exploitation of photovoltaic power generation. A system dynamics model is used to study the conduction mechanism of the comprehensive efficiency of photovoltaic power generation. This paper collects data from 2005 to 2015 as research models, establishes the evaluation model of the comprehensive efficiency of photovoltaic power generation and conducts empirical analysis based on a super-efficient data envelopment analysis (SE-DEA) model. With the evaluation results, this paper puts forward political suggestions as to the optimization of the comprehensive efficiency of photovoltaic power generation. The research results may provide policy-oriented references on the sustainable development of photovoltaic power generation and give theoretical guidance on the scientific evaluation and diagnosis of photovoltaic power generation efficiency. Full article

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

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22 pages, 6370 KiB

Open AccessArticle

Anomaly Detection in Gas Turbine Fuel Systems Using a Sequential Symbolic Method

by Fei Li, Hongzhi Wang, Guowen Zhou, Daren Yu, Jiangzhong Li and Hong Gao

Energies 2017, 10(5), 724; https://doi.org/10.3390/en10050724 - 20 May 2017

Cited by 11 | Viewed by 5634

Abstract

Anomaly detection plays a significant role in helping gas turbines run reliably and economically. Considering the collective anomalous data and both sensitivity and robustness of the anomaly detection model, a sequential symbolic anomaly detection method is proposed and applied to the gas turbine [...] Read more.

Anomaly detection plays a significant role in helping gas turbines run reliably and economically. Considering the collective anomalous data and both sensitivity and robustness of the anomaly detection model, a sequential symbolic anomaly detection method is proposed and applied to the gas turbine fuel system. A structural Finite State Machine is used to evaluate posterior probabilities of observing symbolic sequences and the most probable state sequences they may locate. Hence an estimation-based model and a decoding-based model are used to identify anomalies in two different ways. Experimental results indicate that both models have both ideal performance overall, but the estimation-based model has a strong robustness ability, whereas the decoding-based model has a strong accuracy ability, particularly in a certain range of sequence lengths. Therefore, the proposed method can facilitate well existing symbolic dynamic analysis- based anomaly detection methods, especially in the gas turbine domain. Full article

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

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18 pages, 8292 KiB

Open AccessArticle

A Switching Frequency Optimized Space Vector Pulse Width Modulation (SVPWM) Scheme for Cascaded Multilevel Inverters

by Xiongmin Tang, Junhui Zhang, Zheng Liu and Miao Zhang

Energies 2017, 10(5), 725; https://doi.org/10.3390/en10050725 - 21 May 2017

Cited by 6 | Viewed by 5432

Abstract

This paper presents a novel switching frequency optimized space vector pulse width modulation (SVPWM) scheme for cascaded multilevel inverters. The proposed SVPWM is developed in a α′β′ coordinate system, in which the voltage vectors have only integer entries and the absolute increment of [...] Read more.

This paper presents a novel switching frequency optimized space vector pulse width modulation (SVPWM) scheme for cascaded multilevel inverters. The proposed SVPWM is developed in a α′β′ coordinate system, in which the voltage vectors have only integer entries and the absolute increment of coordinate values between adjacent vectors is equal to dc-bus voltage of power cells (1 pu). The new SVPWM scheme is built with three categories of switching paths. During each switching path, the change of one phase voltage is limited in 1 pu. This contributes to decrease the number of commutations of switches. The proposed SVPWM scheme is validated on a 7-level cascaded inverter and the results show that it significantly outperforms traditional SVPWM schemes in terms of decreasing the number of switch commutations. Full article

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

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25 pages, 3889 KiB

Open AccessArticle

Effects of Support Structures in an LES Actuator Line Model of a Tidal Turbine with Contra-Rotating Rotors

by Angus C. W. Creech, Alistair G. L. Borthwick and David Ingram

Energies 2017, 10(5), 726; https://doi.org/10.3390/en10050726 - 19 May 2017

Cited by 29 | Viewed by 5913

Abstract

Computational fluid dynamics is used to study the impact of the support structure of a tidal turbine on performance and the downstream wake characteristics. A high-fidelity computational model of a dual rotor, contra-rotating tidal turbine in a large channel domain is presented, with [...] Read more.

Computational fluid dynamics is used to study the impact of the support structure of a tidal turbine on performance and the downstream wake characteristics. A high-fidelity computational model of a dual rotor, contra-rotating tidal turbine in a large channel domain is presented, with turbulence modelled using large eddy simulation. Actuator lines represent the turbine blades, permitting the analysis of transient flow features and turbine diagnostics. The following four cases are considered: the flow in an unexploited, empty channel; flow in a channel containing the rotors; flow in a channel containing the support structure; and flow in a channel with both rotors and support structure. The results indicate that the support structure contributes significantly to the behaviour of the turbine and to turbulence levels downstream, even when the rotors are upstream. This implies that inclusion of the turbine structure, or some parametrisation thereof, is a prerequisite for the realistic prediction of turbine performance and reliability, particularly for array layouts where wake effects become significant. Full article

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18 pages, 6656 KiB

Open AccessArticle

Simulation Modeling Method and Experimental Investigation on the Uniflow Scavenging System of an Opposed-Piston Folded-Cranktrain Diesel Engine

by Fukang Ma, Zhenfeng Zhao, Yangang Zhang, Jun Wang, Yaonan Feng, Tiexiong Su, Yi Zhang and Yuhang Liu

Energies 2017, 10(5), 727; https://doi.org/10.3390/en10050727 - 20 May 2017

Cited by 10 | Viewed by 5933

Abstract

The scavenging process for opposed-piston folded-cranktrain (OPFC) diesel engines can be described by the time evolution of the in-cylinder and exhaust chamber residual gas rates. The relation curve of in-cylinder and exhaust chamber residual gas rate is called scavenging profile, which is calculated [...] Read more.

The scavenging process for opposed-piston folded-cranktrain (OPFC) diesel engines can be described by the time evolution of the in-cylinder and exhaust chamber residual gas rates. The relation curve of in-cylinder and exhaust chamber residual gas rate is called scavenging profile, which is calculated through the changes of in-cylinder and exhaust chamber gas compositions determined by computational fluid dynamics (CFD) simulation. The scavenging profile is used to calculate the scavenging process by mono-dimensional (1D) simulation. The tracer gas method (TGM) is employed to validate the accuracy of the scavenging profile. At the same time, the gas exchange performance under different intake and exhaust state parameters was examined based on the TGM. The results show that the scavenging process from 1D simulation and experiment match well, which means the scavenging model obtained by CFD simulation performs well and validation of its effectiveness by TGM is possible. The difference between intake and exhaust pressure has a significant positive effect on the gas exchange performance and trapped gas mass, but the pressure difference has little effect on the scavenging efficiency and the trapped air mass if the delivery ratio exceeds 1.4. Full article

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13 pages, 1361 KiB

Open AccessArticle

A Feasibility Study on Hydrate-Based Technology for Transporting CO₂ from Industrial to Agricultural Areas

by Seiji Matsuo, Hiroki Umeda, Satoshi Takeya and Toyohisa Fujita

Energies 2017, 10(5), 728; https://doi.org/10.3390/en10050728 - 20 May 2017

Cited by 8 | Viewed by 5023

Abstract

Climate change caused by global warming has become a serious issue in recent years. The main purpose of this study was to evaluate the effectiveness of the above system to quantitatively supply CO₂ or CO₂ hydrate from industrial to agricultural areas. [...] Read more.

Climate change caused by global warming has become a serious issue in recent years. The main purpose of this study was to evaluate the effectiveness of the above system to quantitatively supply CO₂ or CO₂ hydrate from industrial to agricultural areas. In this analysis, several transportation methods, namely, truck, hydrate tank lorry, and pipeline, were considered. According to this analysis, the total CO₂ supply costs including transportation ranged from 15 to 25 yen/kg-CO₂ when the transportation distance was 50 km or less. The cost of the hydrate-based method increased with the transport distance in contrast to the liquefied CO₂ approach. However, the technology of supplying CO₂ hydrate had merit by using a local cooling technique for cooling specific parts of agricultural products. Full article

(This article belongs to the Special Issue Methane Hydrate Research and Development)

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15 pages, 5532 KiB

Open AccessArticle

Incorporating Charging/Discharging Strategy of Electric Vehicles into Security-Constrained Optimal Power Flow to Support High Renewable Penetration

by Kyungsung An, Kyung-Bin Song and Kyeon Hur

Energies 2017, 10(5), 729; https://doi.org/10.3390/en10050729 - 20 May 2017

Cited by 31 | Viewed by 7627

Abstract

This research aims to improve the operational efficiency and security of electric power systems at high renewable penetration by exploiting the envisioned controllability or flexibility of electric vehicles (EVs); EVs interact with the grid through grid-to-vehicle (G2V) and vehicle-to-grid (V2G) services to ensure [...] Read more.

This research aims to improve the operational efficiency and security of electric power systems at high renewable penetration by exploiting the envisioned controllability or flexibility of electric vehicles (EVs); EVs interact with the grid through grid-to-vehicle (G2V) and vehicle-to-grid (V2G) services to ensure reliable and cost-effective grid operation. This research provides a computational framework for this decision-making process. Charging and discharging strategies of EV aggregators are incorporated into a security-constrained optimal power flow (SCOPF) problem such that overall energy cost is minimized and operation within acceptable reliability criteria is ensured. Particularly, this SCOPF problem has been formulated for Jeju Island in South Korea, in order to lower carbon emissions toward a zero-carbon island by, for example, integrating large-scale renewable energy and EVs. On top of conventional constraints on the generators and line flows, a unique constraint on the system inertia constant, interpreted as the minimum synchronous generation, is considered to ensure grid security at high renewable penetration. The available energy constraint of the participating EV associated with the state-of-charge (SOC) of the battery and market price-responsive behavior of the EV aggregators are also explored. Case studies for the Jeju electric power system in 2030 under various operational scenarios demonstrate the effectiveness of the proposed method and improved operational flexibility via controllable EVs. Full article

(This article belongs to the Special Issue Theory and Application of Computational Intelligence in Electric Vehicles and their Integration within Smart Energy Networks)

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17 pages, 1729 KiB

Open AccessArticle

A New Methodology for Building-Up a Robust Model for Heliostat Field Flux Characterization

by Nicolás C. Cruz, José D. Álvarez, Juana L. Redondo, Jesús Fernández-Reche, Manuel Berenguel, Rafael Monterreal and Pilar M. Ortigosa

Energies 2017, 10(5), 730; https://doi.org/10.3390/en10050730 - 20 May 2017

Cited by 5 | Viewed by 6049

Abstract

The heliostat field of solar central receiver systems (SCRS) is formed by hundreds, even thousands, of working heliostats. Their adequate configuration and control define a currently active research line. For instance, automatic aiming methodologies of existing heliostat fields are being widely studied. In [...] Read more.

The heliostat field of solar central receiver systems (SCRS) is formed by hundreds, even thousands, of working heliostats. Their adequate configuration and control define a currently active research line. For instance, automatic aiming methodologies of existing heliostat fields are being widely studied. In general, control techniques require a model of the system to be controlled in order to obtain an estimation of its states. However, this kind of information may not be available or may be hard to obtain for every plant to be studied. In this work, an innovative methodology for data-based analytical heliostat field characterization is proposed and described. It formalizes the way in which the behavior of a whole field can be derived from the study of its more descriptive parts. By successfully applying this procedure, the instantaneous behavior of a field could be expressed by a reduced set of expressions that can be seen as a field descriptor. It is not intended to replace real experimentation but to enhance researchers’ autonomy to build their own reliable and portable synthetic datasets at preliminary stages of their work. The methodology proposed in this paper is successfully applied to a virtual field. Only 30 heliostats out of 541 were studied to characterize the whole field. For the validation set, the average difference in power between the flux maps directly fitted from the measured information and the estimated ones is only of 0.67% (just 0.10946 kW/m² of root-mean-square error, on average, between them). According to these results, a consistent field descriptor can be built by applying the proposed methodology, which is hence ready for use. Full article

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

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29 pages, 2310 KiB

Open AccessReview

A Critical Review on Processes and Energy Profile of the Australian Meat Processing Industry

by Ihsan Hamawand, Anas Ghadouani, Jochen Bundschuh, Sara Hamawand, Raed A. Al Juboori, Sayan Chakrabarty and Talal Yusaf

Energies 2017, 10(5), 731; https://doi.org/10.3390/en10050731 - 20 May 2017

Cited by 24 | Viewed by 9533

Abstract

This review article addresses wastewater treatment methods in the red meat processing industry. The focus is on conventional chemicals currently in use for abattoir wastewater treatment and energy related aspects. In addition, this article discusses the use of cleaning and sanitizing agents at [...] Read more.

This review article addresses wastewater treatment methods in the red meat processing industry. The focus is on conventional chemicals currently in use for abattoir wastewater treatment and energy related aspects. In addition, this article discusses the use of cleaning and sanitizing agents at the meat processing facilities and their effect on decision making in regard to selecting the treatment methods. This study shows that cleaning chemicals are currently used at a concentration of 2% to 3% which will further be diluted with the bulk wastewater. For example, for an abattoir that produces 3500 m³/day wastewater and uses around 200 L (3%) acid and alkaline chemicals, the final concentration of these chemical will be around 0.00017%. For this reason, the effects of these chemicals on the treatment method and the environment are very limited. Chemical treatment is highly efficient in removing soluble and colloidal particles from the red meat processing industry wastewater. Actually, it is shown that, if chemical treatment has been applied, then biological treatment can only be included for the treatment of the solid waste by-product and/or for production of bioenergy. Chemical treatment is recommended in all cases and especially when the wastewater is required to be reused or released to water streams. This study also shows that energy consumption for chemical treatment units is insignificant while efficient compared to other physical or biological units. A combination of a main (ferric chloride) and an aid coagulant has shown to be efficient and cost-effective in treating abattoir wastewater. The cost of using this combination per cubic meter wastewater treated is 0.055 USD/m³ compared to 0.11 USD/m³ for alum and the amount of sludge produced is 77% less than that produced by alum. In addition, the residues of these chemicals in the wastewater and the sludge have a positive or no impact on biological processes. Energy consumption from a small wastewater treatment plant (WWTP) installed to recycle wastewater for a meet facility can be around $500,000. Full article

(This article belongs to the Special Issue Energy and Water, Current and Future Crisis)

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19 pages, 6579 KiB

Open AccessArticle

Fast Calculation Model and Theoretical Analysis of Rotor Unbalanced Magnetic Pull for Inter-Turn Short Circuit of Field Windings of Non-Salient Pole Generators

by Guangtao Zhang, Junyong Wu and Liangliang Hao

Energies 2017, 10(5), 732; https://doi.org/10.3390/en10050732 - 20 May 2017

Cited by 14 | Viewed by 7065

Abstract

Inter-turn short circuit of field windings (ISCFW) may cause the field current of a generator to increase, output reactive power to decrease, and unit vibration to intensify, seriously affecting its safe and stable operation. Full integration of mechanical and electrical characteristics can improve [...] Read more.

Inter-turn short circuit of field windings (ISCFW) may cause the field current of a generator to increase, output reactive power to decrease, and unit vibration to intensify, seriously affecting its safe and stable operation. Full integration of mechanical and electrical characteristics can improve the sensitivity of online monitoring, and detect the early embryonic period fault of small turns. This paper studies the calculations and variations of unbalanced magnetic pull (UMP), of which the excitation source of rotor vibration is the basis and key to online fault monitoring. In grid load operation, ISCFW are first calculated with the multi-loop method, so as to obtain the numerical solutions of the stator and the rotor currents during the fault. Next, the air-gap magnetic field of the ISCFW is analyzed according to the actual composition modes of the motor loops in the fault, so as to obtain the analytic expressions of the air-gap magnetic motive force (MMF) and magnetic density. The UMP of the rotor is obtained by solving the integral of the Maxwell stress. The correctness of the electric quantity calculation is verified by the ISCFW experiment, conducted in a one pair-pole non-salient pole model machine. On this basis, comparing the simulation analysis with the calculation results of the model in this paper not only verifies the accuracy of the electromagnetic force calculation, but also proves that the latter has the advantages of a short time consumption and high efficiency. Finally, the influencing factors and variation law of UMP are analyzed by means of an analytic model. This develops a base for the online monitoring of ISCFW with the integration of mechanical and electrical information. Full article

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18 pages, 5345 KiB

Open AccessArticle

Modeling and Optimization of a CoolingTower-Assisted Heat Pump System

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

Energies 2017, 10(5), 733; https://doi.org/10.3390/en10050733 - 20 May 2017

Cited by 9 | Viewed by 6529

Abstract

To minimize the total energy consumption of a cooling tower-assisted heat pump (CTAHP) system in cooling mode, a model-based control strategy with hybrid optimization algorithm for the system is presented in this paper. An existing experimental device, which mainly contains a closed wet [...] Read more.

To minimize the total energy consumption of a cooling tower-assisted heat pump (CTAHP) system in cooling mode, a model-based control strategy with hybrid optimization algorithm for the system is presented in this paper. An existing experimental device, which mainly contains a closed wet cooling tower with counter flow construction, a condenser water loop and a water-to-water heat pump unit, is selected as the study object. Theoretical and empirical models of the related components and their interactions are developed. The four variables, viz. desired cooling load, ambient wet-bulb temperature, temperature and flow rate of chilled water at the inlet of evaporator, are set to independent variables. The system power consumption can be minimized by optimizing input powers of cooling tower fan, spray water pump, condenser water pump and compressor. The optimal input power of spray water pump is determined experimentally. Implemented on MATLAB, a hybrid optimization algorithm, which combines the Limited memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm with the greedy diffusion search (GDS) algorithm, is incorporated to solve the minimization problem of energy consumption and predict the system’s optimal set-points under quasi-steady-state conditions. The integrated simulation tool is validated against experimental data. The results obtained demonstrate the proposed operation strategy is reliable, and can save energy by 20.8% as compared to an uncontrolled system under certain testing conditions. Full article

(This article belongs to the Special Issue Solar Energy Application in Buildings)

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