E-Mail Alert

Add your e-mail address to receive forthcoming issues of this journal:

Journal Browser

Journal Browser

Special Issue "Emerging Power Electronics Technologies for Power Systems and Machine Drives"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Electrical Power and Energy System".

Deadline for manuscript submissions: closed (31 March 2018)

Special Issue Editor

Guest Editor
Prof. Dr. Tomonobu Senjyu

Faculty of Engineering, University of the Ryukyus, 1 Senbaru Nishihara-cho, Nakagami Okinawa 903-0213, Japan
Website | E-Mail
Phone: +81-98-895-8686
Fax: +81 895 8686
Interests: renewable energy; power systems; power electronics; system control; optimization; smart grid; energy storage; smart house; smart city; motor drives; artificial intelligence; electric vehicles

Special Issue Information

Dear Colleagues,

The Guest Editor is inviting submissions for a Special Issue of Energies on the subject area of "Emerging Power Electronics Technologies for Power Systems and Machine Drives". Power Electronic technologies are found in wide range of power systems and machine drives. The application areas of power electronics are small and/or large capacities for electric circuits, e.g., high-voltage DC transmission systems, large capacity energy storage systems, electric vehicles, power conditioners for photovoltaic systems, ship and train traction systems, etc. The applications of power electronic circuits are now increasing throughout various aspects of our lives.

This Special Issue will focus on emerging power electronic topologies, and applications for power systems and motor drives. Topics of interest for publication include, but are not limited to:

• High voltage DC transmission systems;
• Novel renewable energy converter/inverter systems;
• Virtual synchronous generator;
• Electrical machines, drives, systems and applications;
• New topologies for high voltage inverter/converter;
• New applications for power electronics;
• Power electronics in smart grid;
• AC/DC converters and inverters;
• Control and optimization of power electronic circuit;
• Distributed generation for power electronics;
• Recent traction systems for vehicles, trains and ships;
• Demand side electrification and management of power electronics

Prof. Dr. Tomonobu Senjyu
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Power Electronics
  • Power Systems
  • Motor Drives
  • New Topologies for Converters/Inverters
  • High Power Applications

Published Papers (76 papers)

View options order results:
result details:
Displaying articles 1-76
Export citation of selected articles as:

Research

Jump to: Review, Other

Open AccessArticle New Switched-Dual-Source Multilevel Inverter for Symmetrical and Asymmetrical Operation
Energies 2018, 11(4), 984; doi:10.3390/en11040984
Received: 10 March 2018 / Revised: 8 April 2018 / Accepted: 13 April 2018 / Published: 18 April 2018
PDF Full-text (2647 KB) | HTML Full-text | XML Full-text
Abstract
The increasing integration of large solar PV and wind farms into the power grid has fueled, over the past two decades, growing demands for high-power, high-voltage, utility-scale inverters. Multilevel inverters have emerged as the industry’s choice for megawatt-range inverters because of their reduced
[...] Read more.
The increasing integration of large solar PV and wind farms into the power grid has fueled, over the past two decades, growing demands for high-power, high-voltage, utility-scale inverters. Multilevel inverters have emerged as the industry’s choice for megawatt-range inverters because of their reduced voltage stress, capability for generating an almost-sinusoidal voltage, built-in redundancy and other benefits. This paper presents a novel switched-source multilevel inverter (SS MLI) architecture. This new inverter shows superior capabilities when compared to existing topologies. It has reduced voltage stress on the semiconductor, uses fewer switches (i.e., reduced size/weight/cost) and exhibits increased efficiency. The proposed SS MLI is comprised of two voltage sources ( V 1 , V 2 ) and six switches. It is capable of generating five-level output voltage in symmetric mode (i.e., V 1 = V 2 ) and seven-level output voltage in asymmetric mode (i.e., V 1 V 2 ). We present simulations results (using MATLAB®/Simulink®) for five- and seven-level output voltages, and they strongly support the validity of the proposed inverter. These positive results are further supported experimentally using a laboratory prototype. Full article
Figures

Figure 1

Open AccessArticle A Hybrid Filtering Technique-Based PLL Targeting Fast and Robust Tracking Performance under Distorted Grid Conditions
Energies 2018, 11(4), 973; doi:10.3390/en11040973
Received: 28 March 2018 / Revised: 11 April 2018 / Accepted: 12 April 2018 / Published: 18 April 2018
PDF Full-text (10762 KB) | HTML Full-text | XML Full-text
Abstract
In most grid-connected power converter applications, the phase-locked loop (PLL) is probably the most widespread grid synchronization technique, owing to its simple implementation. However, its phase-tracking performance tends to worsen when the grid voltage is under unbalanced and distorted conditions. Many filtering techniques
[...] Read more.
In most grid-connected power converter applications, the phase-locked loop (PLL) is probably the most widespread grid synchronization technique, owing to its simple implementation. However, its phase-tracking performance tends to worsen when the grid voltage is under unbalanced and distorted conditions. Many filtering techniques are utilized to solve this problem, however, at the cost of slowing down the transient response. It is a major challenge for PLL to achieve a satisfactory dynamic performance without degrading its filtering capability. To tackle this challenge, a hybrid filtering technique is proposed in this paper. Our idea is to eliminate the fundamental frequency negative sequence (FFNS) and other harmonic sequences at the prefiltering stage and inner loop of PLL, respectively. Second-order generalized integrators (SOGIs) are used to remove FFNS before the Park transformation. This makes moving average filters (MAFs) eliminate other harmonics with a narrowed window length, which means the time delay that is caused by MAFs is reduced. The entire hybrid filtering technique is included in a quasi-type-1 PLL structure (QT1-PLL), which can provide a rapid dynamic behavior. The small-signal model of the proposed PLL is established. Based on this model, the parameter design guidelines targeting the fast transient response are given. Comprehensive experiments are carried out to confirm the effectiveness of our method. The results show that the settling time of the proposed PLL is less than one grid cycle, which is shorter than most of the widespread PLLs. The harmonic rejection capability is also better than other methods, under both nominal and adverse grid conditions. Full article
Figures

Figure 1

Open AccessArticle Sensorless Control of Dual-Active-Bridge Converter with Reduced-Order Proportional-Integral Observer
Energies 2018, 11(4), 931; doi:10.3390/en11040931
Received: 26 March 2018 / Revised: 9 April 2018 / Accepted: 10 April 2018 / Published: 13 April 2018
PDF Full-text (3224 KB) | HTML Full-text | XML Full-text
Abstract
When controlling a Dual-Active-Bridge (DAB) DC/DC converter, the high frequency terminal current is usually measured for use in the current feedback controller. In order to measure that current, a wide bandwidth sensor accompanied with high-speed amplifiers are required. Furthermore, a high Analog-to-Digital sampling
[...] Read more.
When controlling a Dual-Active-Bridge (DAB) DC/DC converter, the high frequency terminal current is usually measured for use in the current feedback controller. In order to measure that current, a wide bandwidth sensor accompanied with high-speed amplifiers are required. Furthermore, a high Analog-to-Digital sampling rate is also necessary for sampling and processing the measured data. To avoid those expensive requirements, this paper proposes an alternative control method for the DAB converter. In the proposed method, the terminal current is estimated by a reduced-order proportional integral observer. A technique is also proposed to reduce the phase drift effect when the voltages at two terminals are not matched. Afterwards, a combined current feedforward—voltage feedback control system is developed to enhance the system dynamics and to regulate the output voltage. This control system needs only the information of the terminal voltages and no current sensor is required. Experimental results show that the observer can estimate the terminal current very quickly with the accuracy of more than 98 % . In addition, the output voltage is well regulated with a fluctuation of less than ± 2.6 % and a settling time of less than 6.5 ms in the presence of a 30 % load change. Full article
Figures

Figure 1

Open AccessArticle Novel Cathode Design to Improve the ESD Capability of 600 V Fast Recovery Epitaxial Diodes
Energies 2018, 11(4), 832; doi:10.3390/en11040832
Received: 1 February 2018 / Revised: 8 March 2018 / Accepted: 30 March 2018 / Published: 4 April 2018
PDF Full-text (8981 KB) | HTML Full-text | XML Full-text
Abstract
Silicon power diodes are used to design different types of electrical energy systems. Their performance has been improved substantially, as a result of a concentrated research efforts that have taken place in the last two decades. They are considered immune to electrostatic discharge
[...] Read more.
Silicon power diodes are used to design different types of electrical energy systems. Their performance has been improved substantially, as a result of a concentrated research efforts that have taken place in the last two decades. They are considered immune to electrostatic discharge (ESD) failures, since usually they withstand an avalanche energy one order of magnitude higher than that of the ESD. Consequently, few works consider this aspect. However, it was observed that during the mounting of power diodes in automotive systems (e.g., with operators touching and handling the devices), ESD events occur and devices fail. In this paper the ESD capability of 600 V fast recovery epitaxial diode (FRED) is analyzed by means of Technology Computer-Aided Design (TCAD) simulations, theoretical analyses and experimental characterization. Two doping profiles are investigated in order to improve the ESD robustness of a standard device and an optimized doping profile is proposed. The proposed design exhibits a higher ESD robustness and this is due to its superior capability in keeping the current distribution uniform in the structure in a critical condition such as the impact ionization avalanche effect. Both experimental and numerical results validate the proposed design. Full article
Figures

Figure 1

Open AccessArticle An Algorithm for Online Inertia Identification and Load Torque Observation via Adaptive Kalman Observer-Recursive Least Squares
Energies 2018, 11(4), 778; doi:10.3390/en11040778
Received: 29 January 2018 / Revised: 22 March 2018 / Accepted: 26 March 2018 / Published: 28 March 2018
PDF Full-text (91559 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, an on-line parameter identification algorithm to iteratively compute the numerical values of inertia and load torque is proposed. Since inertia and load torque are strongly coupled variables due to the degenerate-rank problem, it is hard to estimate relatively accurate values
[...] Read more.
In this paper, an on-line parameter identification algorithm to iteratively compute the numerical values of inertia and load torque is proposed. Since inertia and load torque are strongly coupled variables due to the degenerate-rank problem, it is hard to estimate relatively accurate values for them in the cases such as when load torque variation presents or one cannot obtain a relatively accurate priori knowledge of inertia. This paper eliminates this problem and realizes ideal online inertia identification regardless of load condition and initial error. The algorithm in this paper integrates a full-order Kalman Observer and Recursive Least Squares, and introduces adaptive controllers to enhance the robustness. It has a better performance when iteratively computing load torque and moment of inertia. Theoretical sensitivity analysis of the proposed algorithm is conducted. Compared to traditional methods, the validity of the proposed algorithm is proved by simulation and experiment results. Full article
Figures

Figure 1a

Open AccessArticle An Efficient Hybrid Filter-Based Phase-Locked Loop under Adverse Grid Conditions
Energies 2018, 11(4), 703; doi:10.3390/en11040703
Received: 25 February 2018 / Revised: 19 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
PDF Full-text (9863 KB) | HTML Full-text | XML Full-text
Abstract
Synchronous-reference-frame phase-locked loop (SRF-PLL) is widely used in grid synchronization applications. However, under unbalanced, distorted and DC offset mixed grid conditions, its performance tends to worsen. In order to improve the filtering capability of SRF-PLL, a modified three-order generalized integrator (MTOGI) with DC
[...] Read more.
Synchronous-reference-frame phase-locked loop (SRF-PLL) is widely used in grid synchronization applications. However, under unbalanced, distorted and DC offset mixed grid conditions, its performance tends to worsen. In order to improve the filtering capability of SRF-PLL, a modified three-order generalized integrator (MTOGI) with DC offset rejection capability based on conventional three order generalized integrator (TOGI) and an enhanced delayed signal cancellation (EDSC) are proposed, then dual modified TOGI (DMTOGI) filtering stage is designed and incorporated into the SRF-PLL control loop with EDSC to form a new hybrid filter-based PLL. The proposed PLL can reject the fundamental frequency negative sequence (FFNS) component, DC offset component, and the rest of harmonic components in SRF-PLL input three-phase voltages at the same time with a simple complexity. The proposed PLL in this paper has a faster transient response due to the EDSC reducing the number of DSC operators. A small-signal model of the proposed PLL is derived. The stability is analyzed and parameter design guidelines are given. Experimental results are included to validate the effectiveness and robustness of the proposed PLL. Full article
Figures

Figure 1

Open AccessArticle Research on the Inductance/Capacitance Switch Model for an LCC-HVDC Converter in an AC/DC Hybrid Grid
Energies 2018, 11(4), 692; doi:10.3390/en11040692
Received: 2 March 2018 / Revised: 15 March 2018 / Accepted: 16 March 2018 / Published: 21 March 2018
PDF Full-text (3044 KB) | HTML Full-text | XML Full-text
Abstract
In order to improve the simulation speed of the AC/DC hybrid grid, the inductance/capacitance (L/C) switch model for line-commutated converter of high-voltage direct current (LCC-HVDC) is presented in this study. The time domain modeling method is used to analyze the circuit of L/C
[...] Read more.
In order to improve the simulation speed of the AC/DC hybrid grid, the inductance/capacitance (L/C) switch model for line-commutated converter of high-voltage direct current (LCC-HVDC) is presented in this study. The time domain modeling method is used to analyze the circuit of L/C switch model for the six-pulse system in LCC-HVDC in a switching period. A parameter setting method of L/C switch model is proposed considering the transient response, the steady state performance, switching losses and simulation error of the switch. The inductance/capacitance (L/C) switch model for LCC-HVDC has the advantage of keeping the admittance matrix unchanged regardless of the change of switching state, which improves the simulation efficiency. Finally, the validity of the parameter setting method is verified. Compared with the test results of PSCAD/EMTDC, the accuracy of the proposed LCC-HVDC simulation model is proved. The model is suitable for real-time or offline simulation of AC/DC hybrid grid. Full article
Figures

Figure 1

Open AccessArticle A Fast-Transient Output Capacitor-Less Low-Dropout Regulator Using Active-Feedback and Current-Reuse Feedforward Compensation
Energies 2018, 11(3), 688; doi:10.3390/en11030688
Received: 20 February 2018 / Revised: 10 March 2018 / Accepted: 15 March 2018 / Published: 19 March 2018
PDF Full-text (3696 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, output capacitor-less low-dropout (LDO) regulator using active-feedback and current-reuse feedforward compensation (AFCFC) is presented. The open-loop transfer function was obtained using small-signal modeling. The stability of the proposed LDO was analyzed using pole-zero plots, and it was confirmed by simulations
[...] Read more.
In this paper, output capacitor-less low-dropout (LDO) regulator using active-feedback and current-reuse feedforward compensation (AFCFC) is presented. The open-loop transfer function was obtained using small-signal modeling. The stability of the proposed LDO was analyzed using pole-zero plots, and it was confirmed by simulations that the stability was ensured under the load current of 50 mA. The proposed compensation method increases gain-bandwidth product (GBW) and reduces the on-chip compensation capacitor. The proposed AFCFC technique was applied to a three-stage output capacitor-less LDO. The LDO has a GBW of 5.6 MHz with a small on-chip capacitor of 2.6 pF. Fast-transient time of 450 ns with low quiescent current of 65.8 μA was achieved. The LDO was fabricated in 130 nm CMOS process consuming 180 × 140 μm2 of the silicon area. Full article
Figures

Figure 1

Open AccessArticle A Hybrid Excited Machine with Flux Barriers and Magnetic Bridges
Energies 2018, 11(3), 676; doi:10.3390/en11030676
Received: 23 January 2018 / Revised: 11 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
PDF Full-text (5915 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic
[...] Read more.
In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic torque, no-load magnetic flux linkage, rotor iron losses and back electromotive force is shown. Three different rotor designs are analyzed. Furthermore, the field control characteristics depending on additional DC control coil currents are shown. Full article
Figures

Figure 1

Open AccessArticle Adaptive and Nonlinear Control Techniques Applied to SEPIC Converter in DC-DC, PFC, CCM and DCM Modes Using HIL Simulation
Energies 2018, 11(3), 602; doi:10.3390/en11030602
Received: 31 January 2018 / Revised: 20 February 2018 / Accepted: 24 February 2018 / Published: 9 March 2018
PDF Full-text (3163 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we propose adaptive nonlinear controllers for the Single-Ended Primary Inductance Converter (SEPIC). We also consider four distinct situations: AC-DC, DC-DC, Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM). A comparative analysis between classic linear and nonlinear approaches to regulate
[...] Read more.
In this paper, we propose adaptive nonlinear controllers for the Single-Ended Primary Inductance Converter (SEPIC). We also consider four distinct situations: AC-DC, DC-DC, Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM). A comparative analysis between classic linear and nonlinear approaches to regulate the control loop is made. Three adaptive nonlinear control laws are designed: Feedback Linearization Control (FLC), Passivity-Based Control (PBC) and Interconnection and Damping Assignment Passivity-Based Control (IDAPBC). In order to compare the performance of these control techniques, numerical simulations were made in Software and Hardware in the Loop (HIL) for nominal conditions and operation disturbances. We recommend adaptive controllers for the two different situations: Adaptive Passivity-Based Feedback Linearization Control (APBFLC) for the PFC (Power Factor Correction) AC-DC system and IDAPBC-BB (IDAPBC Based on Boost converter) for the regulator DC-DC system. Full article
Figures

Figure 1

Open AccessArticle Analysis of Non-Isolated Multi-Port Single Ended Primary Inductor Converter or Standalone Applications
Energies 2018, 11(3), 539; doi:10.3390/en11030539
Received: 29 November 2017 / Revised: 3 February 2018 / Accepted: 5 February 2018 / Published: 2 March 2018
PDF Full-text (9783 KB) | HTML Full-text | XML Full-text
Abstract
A non-isolated Multiport Single Ended Primary Inductor Converter (SEPIC) for coordinating photovoltaic sources is developed in this paper. The proposed multiport converter topologies comprise a Single Input Multi yield (SIMO) and Multi Input Multi Output (MIMO). It is having the merits of decreased
[...] Read more.
A non-isolated Multiport Single Ended Primary Inductor Converter (SEPIC) for coordinating photovoltaic sources is developed in this paper. The proposed multiport converter topologies comprise a Single Input Multi yield (SIMO) and Multi Input Multi Output (MIMO). It is having the merits of decreased number of parts and high power density. Steady state analysis verifies the improved situation of both the proposed topologies, which is further checked through simulation results. Full article
Figures

Open AccessArticle Line-to-Line Fault Analysis and Location in a VSC-Based Low-Voltage DC Distribution Network
Energies 2018, 11(3), 536; doi:10.3390/en11030536
Received: 24 January 2018 / Revised: 23 February 2018 / Accepted: 26 February 2018 / Published: 2 March 2018
PDF Full-text (2703 KB) | HTML Full-text | XML Full-text
Abstract
A DC cable short-circuit fault is the most severe fault type that occurs in DC distribution networks, having a negative impact on transmission equipment and the stability of system operation. When a short-circuit fault occurs in a DC distribution network based on a
[...] Read more.
A DC cable short-circuit fault is the most severe fault type that occurs in DC distribution networks, having a negative impact on transmission equipment and the stability of system operation. When a short-circuit fault occurs in a DC distribution network based on a voltage source converter (VSC), an in-depth analysis and characterization of the fault is of great significance to establish relay protection, devise fault current limiters and realize fault location. However, research on short-circuit faults in VSC-based low-voltage DC (LVDC) systems, which are greatly different from high-voltage DC (HVDC) systems, is currently stagnant. The existing research in this area is not conclusive, with further study required to explain findings in HVDC systems that do not fit with simulated results or lack thorough theoretical analyses. In this paper, faults are divided into transient- and steady-state faults, and detailed formulas are provided. A more thorough and practical theoretical analysis with fewer errors can be used to develop protection schemes and short-circuit fault locations based on transient- and steady-state analytic formulas. Compared to the classical methods, the fault analyses in this paper provide more accurate computed results of fault current. Thus, the fault location method can rapidly evaluate the distance between the fault and converter. The analyses of error increase and an improved handshaking method coordinating with the proposed location method are presented. Full article
Figures

Figure 1

Open AccessArticle Adaptive Controller of the Major Functions for Controlling a Drive System with Elastic Couplings
Energies 2018, 11(3), 531; doi:10.3390/en11030531
Received: 23 January 2018 / Revised: 23 February 2018 / Accepted: 27 February 2018 / Published: 1 March 2018
PDF Full-text (1908 KB) | HTML Full-text | XML Full-text
Abstract
In any drive system, there are always couplings between the motor and the load. Since the hardness of these couplings is finite, they have elastic properties, causing unwanted vibration and negatively affecting system quality. When the couplings are springs with nonlinear characteristics, control
[...] Read more.
In any drive system, there are always couplings between the motor and the load. Since the hardness of these couplings is finite, they have elastic properties, causing unwanted vibration and negatively affecting system quality. When the couplings are springs with nonlinear characteristics, control is particularly difficult because it is very difficult or impossible to define the parameters of the controlled object. To solve these difficulties, this article proposes an adaptive controller of the major functions for controlling a drive system with nonlinear elastic couplings of unidentified parameters. For the proposed control system, we measure the response speed of the object, use a Luenberger observer to estimate the state variables of the system, and use an adaptive controller to control the system. The experimental results demonstrate that the control object can be controlled without knowing the parameters: the control quality of the system is very good, close to that of a system with a hard coupling, there is no vibration or overshoot, and the transition time is small. Full article
Figures

Figure 1

Open AccessArticle A Dual Monitoring Technique to Detect Power Quality Transients Based on the Fourth-Order Spectrogram
Energies 2018, 11(3), 503; doi:10.3390/en11030503
Received: 1 February 2018 / Revised: 13 February 2018 / Accepted: 22 February 2018 / Published: 27 February 2018
PDF Full-text (1192 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a higher-order statistics-based approach of detecting transients that uses the fourth-order discrete spectrogram to monitor the power supply in a node of the domestic smart grid. Taking advantage of the mixed time–frequency domain information, the method allows for the transient
[...] Read more.
This paper presents a higher-order statistics-based approach of detecting transients that uses the fourth-order discrete spectrogram to monitor the power supply in a node of the domestic smart grid. Taking advantage of the mixed time–frequency domain information, the method allows for the transient detection and the subsequent identification of the potential area in which the fault takes place. The proposed method is evaluated through real power-line signals from the Spanish electrical grid. Thanks to the peakedness enhancement capability of the higher-order spectra, the results show that the procedure is able to detect low-level transients, which are likely ignored by the traditional detection procedures, where the concern pertains to power reliability (not oriented to micro grids), and this, by analyzing the duration and frequency content of the electrical perturbation, may indicate prospective faulty states of elements in a grid. Easy to implement in a hand-held instrument, the computational strategy has a 5 Hz resolution in the range 0–500 Hz and a 50 Hz resolution in the range of 0–5 kHz, and could be consequently used by technicians in order to allocate new types of transients originated by the distributed energy resources. Four real-life case-studies illustrate the performance. Full article
Figures

Figure 1

Open AccessArticle Analysis of Switching Transients during Energization in Large Offshore Wind Farms
Energies 2018, 11(2), 470; doi:10.3390/en11020470
Received: 24 January 2018 / Revised: 13 February 2018 / Accepted: 19 February 2018 / Published: 23 February 2018
Cited by 1 | PDF Full-text (4323 KB) | HTML Full-text | XML Full-text
Abstract
In order to study switching transients in an offshore wind farm (OWF) collector system, we employ modeling methods of the main components in OWFs, including vacuum circuit breakers (VCBs), submarine cables, and wind turbine transformers (WTTs). In particular, a high frequency (HF) VCB
[...] Read more.
In order to study switching transients in an offshore wind farm (OWF) collector system, we employ modeling methods of the main components in OWFs, including vacuum circuit breakers (VCBs), submarine cables, and wind turbine transformers (WTTs). In particular, a high frequency (HF) VCB model that reflects the prestrike characteristics of VCBs was developed. Moreover, a simplified experimental system of an OWF electric collection system was set up to verify the developed models, and a typical OWF medium voltage (MV) cable collection system was built in PSCAD/EMTDC based on the developed models. Finally, we investigated the influences of both the initial closing phase angle of VCBs and typical system operation scenarios on the amplitude and steepness of transient overvoltages (TOVs) at the high-voltage side of WTTs. Full article
Figures

Figure 1

Open AccessArticle PWM Carrier Displacement in Multi-N-Phase Drives: An Additional Degree of Freedom to Reduce the DC-Link Stress
Energies 2018, 11(2), 443; doi:10.3390/en11020443
Received: 18 November 2017 / Revised: 6 February 2018 / Accepted: 11 February 2018 / Published: 16 February 2018
PDF Full-text (6503 KB) | HTML Full-text | XML Full-text
Abstract
The paper presents a particular Pulse Width Modulation (PWM) strategy to reduce the (Direct Current) DC-link capacitor stress for multi-n-phase drives. A multi-n-phase drive is composed of multiple independent systems of n inverter supplying a multi-n-phase electric machine. The paper focused on the
[...] Read more.
The paper presents a particular Pulse Width Modulation (PWM) strategy to reduce the (Direct Current) DC-link capacitor stress for multi-n-phase drives. A multi-n-phase drive is composed of multiple independent systems of n inverter supplying a multi-n-phase electric machine. The paper focused on the investigation of the best phase shifting between carriers for a triple-3-phase drive compared to the 3-phase counterpart in order to reduce the capacitor bench design point. Simulation and experimental results show as the control technique proposed is able to reduce the value of the DC-link capacitor current in any operating condition including fault case. In this sense, the PWM carrier displacement appears like an additional degree of freedom that can be exploited in multi-n-phase drives but also in multi-motor application. Full article
Figures

Figure 1

Open AccessArticle On the Performance Optimization of Two-Level Three-Phase Grid-Feeding Voltage-Source Inverters
Energies 2018, 11(2), 400; doi:10.3390/en11020400
Received: 11 January 2018 / Revised: 31 January 2018 / Accepted: 5 February 2018 / Published: 9 February 2018
Cited by 1 | PDF Full-text (5403 KB) | HTML Full-text | XML Full-text
Abstract
The performance optimization of the two-level, three-phase, grid-feeding, voltage-source inverter (VSI) is studied in this paper, which adopts an online adaptive switching frequency algorithm (OASF). A new degree of freedom has been added to the employed OASF algorithm for optimal selection of the
[...] Read more.
The performance optimization of the two-level, three-phase, grid-feeding, voltage-source inverter (VSI) is studied in this paper, which adopts an online adaptive switching frequency algorithm (OASF). A new degree of freedom has been added to the employed OASF algorithm for optimal selection of the weighting factor and overall system optimization design. Toward that end, a full mathematical formulation, including the impact of the coupling inductor and the controller response time, is presented. At first, the weighting factor is selected to favor the switching losses, and the controller gains are optimized by minimizing the integral time-weighted absolute error (ITAE) of the output active and reactive power. Different loading and ambient temperature conditions are considered to validate the optimized controller and its fast response through online field programmable gate array (FPGA)-in-the-loop. Then, the weighting factor is optimally selected to reduce the cost of the L-filter and the heat-sink. An optimization problem to minimize the cost design at the worst case of loading condition for grid-feeding VSI is formulated. The results from this optimization problem are the filter inductance, the thermal resistance of the heat-sink, and the optimal switching frequency with the optimal weighting factor. The VSI test-bed using the optimized parameters is used to verify the proposed work experimentally. Adopting the OASF algorithm that employs the optimal weighting factor for grid-feeding VSI, the percentages of the reductions in the slope of the steady state junction temperature profile compared to fixed frequencies of 10 kHz, 14.434 kHz, and 20 kHz are about 6%, 30%, and 18%, respectively. Full article
Figures

Figure 1

Open AccessArticle Step-Up Partial Power DC-DC Converters for Two-Stage PV Systems with Interleaved Current Performance
Energies 2018, 11(2), 357; doi:10.3390/en11020357
Received: 1 December 2017 / Revised: 25 January 2018 / Accepted: 30 January 2018 / Published: 3 February 2018
Cited by 1 | PDF Full-text (2750 KB) | HTML Full-text | XML Full-text
Abstract
This work presents a partial power converter allowing us to obtain, with a single DC-DC converter, the same feature as the classical interleaved operation of two converters. More precisely, the proposed topology performs similarly as the input-parallel output-series (IPOS) configuration reducing the current
[...] Read more.
This work presents a partial power converter allowing us to obtain, with a single DC-DC converter, the same feature as the classical interleaved operation of two converters. More precisely, the proposed topology performs similarly as the input-parallel output-series (IPOS) configuration reducing the current ripple at the input of the system and dividing the individual converters power rating, compared to a single converter. The proposed topology consists of a partial DC-DC converter processing only a fraction of the total power, thus allowing high efficiency. Experimental results are provided to validate the proposed converter topology with a Flyback-based 100 W test bench with a transformer turns ratio n 1 = n 2 . Experimental results show high performances reducing the input current ripple around 30 % , further increasing the conversion efficiency. Full article
Figures

Figure 1

Open AccessArticle Improved Finite-Control-Set Model Predictive Control for Cascaded H-Bridge Inverters
Energies 2018, 11(2), 355; doi:10.3390/en11020355
Received: 25 December 2017 / Revised: 29 January 2018 / Accepted: 31 January 2018 / Published: 2 February 2018
PDF Full-text (20788 KB) | HTML Full-text | XML Full-text
Abstract
In multilevel cascaded H-bridge (CHB) inverters, the number of voltage vectors generated by the inverter quickly increases with increasing voltage level. However, because the sampling period is short, it is difficult to consider all the vectors as the voltage level increases. This paper
[...] Read more.
In multilevel cascaded H-bridge (CHB) inverters, the number of voltage vectors generated by the inverter quickly increases with increasing voltage level. However, because the sampling period is short, it is difficult to consider all the vectors as the voltage level increases. This paper proposes a model predictive control algorithm with reduced computational complexity and fast dynamic response for CHB inverters. The proposed method presents a robust approach to interpret a next step as a steady or transient state by comparing an optimal voltage vector at a present step and a reference voltage vector at the next step. During steady state, only an optimal vector at a present step and its adjacent vectors are considered as a candidate-vector subset. On the other hand, this paper defines a new candidate vector subset for the transient state, which consists of more vectors than those in the subset used for the steady state for fast dynamic speed; however, the vectors are less than all the possible vectors generated by the CHB inverter, for calculation simplicity. In conclusion, the proposed method can reduce the computational complexity without significantly deteriorating the dynamic responses. Full article
Figures

Figure 1

Open AccessArticle Icing Condition Assessment of In-Service Glass Insulators Based on Graphical Shed Spacing and Graphical Shed Overhang
Energies 2018, 11(2), 318; doi:10.3390/en11020318
Received: 10 January 2018 / Revised: 27 January 2018 / Accepted: 29 January 2018 / Published: 2 February 2018
PDF Full-text (3517 KB) | HTML Full-text | XML Full-text
Abstract
Icing on transmission lines might lead to ice flashovers of insulators, collapse of towers, tripping faults of transmission lines, and other accidents. Shed spacing and shed overhang of insulators are clues for evaluating the probability of ice flashover. This paper researches image-processing methods
[...] Read more.
Icing on transmission lines might lead to ice flashovers of insulators, collapse of towers, tripping faults of transmission lines, and other accidents. Shed spacing and shed overhang of insulators are clues for evaluating the probability of ice flashover. This paper researches image-processing methods for the natural icing of in-service glass insulators. Calculation methods of graphical shed spacing and graphical shed overhang are proposed via recognizing the convexity defects of the contours of an icing insulator string based on the GrabCut segmentation algorithm. The experiments are carried out with image data from our climatic chamber and the China Southern Power Grid Disaster (Icing) Warning System of Transmission Lines. The results show that the graphical shed overhang of insulators show evident change due to icing. This method can recognize the most serious icing conditions where the insulator sheds are completely bridged. Also, it can detect bridging positions including the left side, right side, or both sides of the insulator strings in the images. Full article
Figures

Figure 1

Open AccessArticle Development of Automotive Permanent Magnet Alternator with Fully Controlled AC/DC Converter
Energies 2018, 11(2), 274; doi:10.3390/en11020274
Received: 18 November 2017 / Revised: 8 January 2018 / Accepted: 9 January 2018 / Published: 24 January 2018
PDF Full-text (12559 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes the design of a three-phase axial flux permanent magnet alternator (AFPMA) that is characterized with an air-cored stator and two-rotor (ACSTR) configuration. The AFPMA is harnessed with fully controlled AC/DC converter using six bridge Insulated Gate Bipolar Transistor (IGBTs) capable
[...] Read more.
This paper proposes the design of a three-phase axial flux permanent magnet alternator (AFPMA) that is characterized with an air-cored stator and two-rotor (ACSTR) configuration. The AFPMA is harnessed with fully controlled AC/DC converter using six bridge Insulated Gate Bipolar Transistor (IGBTs) capable to deliver a constant DC output power as an attempt to replace the Lundell alternator for automotive applications. First, the design methodology and analysis of the AFPMA is introduced. The most effective parameters, such as rotor diameter, magnet thickness, number of turns, and winding thickness are determined. A smart digital control which facilitates the comparison between the magnitudes of the three-phase input signals instead of finding the zero crossing points is developed. Moreover, custom design comparators are specially designed and developed to generate adaptive signals that are fed into an Arduino Uno microcontroller. Accordingly, the Arduino generates the timely precise pulses that are necessary to maintain the appropriate triggering of the IGBTs. This technique allows the IGBTs to conduct in an adaptive manner to overcome the problem of asymmetrical voltage outputs from the AFPM alternator. The system is also capable of handling the variation in the speed of the AFPMA via the rigor code in Arduino that detects the change in the supply frequency and voltages in a real time process. The system is first analyzed via simulations using MATLAB/Simulink and then experimentally validated at certain speed and loading conditions. The preliminary tests results indicate that such system is capable to provide an efficient solution to satisfy automotive electric power demands. Full article
Figures

Figure 1

Open AccessArticle A New Method for State of Charge Estimation of Lithium-Ion Batteries Using Square Root Cubature Kalman Filter
Energies 2018, 11(1), 209; doi:10.3390/en11010209
Received: 22 December 2017 / Revised: 2 January 2018 / Accepted: 8 January 2018 / Published: 15 January 2018
PDF Full-text (8277 KB) | HTML Full-text | XML Full-text
Abstract
State of charge (SOC) is a key parameter for lithium-ion battery management systems. The square root cubature Kalman filter (SRCKF) algorithm has been developed to estimate the SOC of batteries. SRCKF calculates 2n points that have the same weights according to cubature
[...] Read more.
State of charge (SOC) is a key parameter for lithium-ion battery management systems. The square root cubature Kalman filter (SRCKF) algorithm has been developed to estimate the SOC of batteries. SRCKF calculates 2n points that have the same weights according to cubature transform to approximate the mean of state variables. After these points are propagated by nonlinear functions, the mean and the variance of the capture can achieve third-order precision of the real values of the nonlinear functions. SRCKF directly propagates and updates the square root of the state covariance matrix in the form of Cholesky decomposition, guarantees the nonnegative quality of the covariance matrix, and avoids the divergence of the filter. Simulink models and the test bench of extended Kalman filter (EKF), Unscented Kalman filter (UKF), cubature Kalman filter (CKF) and SRCKF are built. Three experiments have been carried out to evaluate the performances of the proposed methods. The results of the comparison of accuracy, robustness, and convergence rate with EKF, UKF, CKF and SRCKF are presented. Compared with the traditional EKF, UKF and CKF algorithms, the SRCKF algorithm is found to yield better SOC estimation accuracy, higher robustness and better convergence rate. Full article
Figures

Open AccessArticle Stochastic Model Predictive Fault Tolerant Control Based on Conditional Value at Risk for Wind Energy Conversion System
Energies 2018, 11(1), 193; doi:10.3390/en11010193
Received: 20 December 2017 / Revised: 5 January 2018 / Accepted: 10 January 2018 / Published: 12 January 2018
PDF Full-text (4147 KB) | HTML Full-text | XML Full-text
Abstract
Wind energy has been drawing considerable attention in recent years. However, due to the random nature of wind and high failure rate of wind energy conversion systems (WECSs), how to implement fault-tolerant WECS control is becoming a significant issue. This paper addresses the
[...] Read more.
Wind energy has been drawing considerable attention in recent years. However, due to the random nature of wind and high failure rate of wind energy conversion systems (WECSs), how to implement fault-tolerant WECS control is becoming a significant issue. This paper addresses the fault-tolerant control problem of a WECS with a probable actuator fault. A new stochastic model predictive control (SMPC) fault-tolerant controller with the Conditional Value at Risk (CVaR) objective function is proposed in this paper. First, the Markov jump linear model is used to describe the WECS dynamics, which are affected by many stochastic factors, like the wind. The Markov jump linear model can precisely model the random WECS properties. Second, the scenario-based SMPC is used as the controller to address the control problem of the WECS. With this controller, all the possible realizations of the disturbance in prediction horizon are enumerated by scenario trees so that an uncertain SMPC problem can be transformed into a deterministic model predictive control (MPC) problem. Finally, the CVaR object function is adopted to improve the fault-tolerant control performance of the SMPC controller. CVaR can provide a balance between the performance and random failure risks of the system. The Min-Max performance index is introduced to compare the fault-tolerant control performance with the proposed controller. The comparison results show that the proposed method has better fault-tolerant control performance. Full article
Figures

Figure 1

Open AccessArticle Design and Experimental Verification of a 72/48 Switched Reluctance Motor for Low-Speed Direct-Drive Mining Applications
Energies 2018, 11(1), 192; doi:10.3390/en11010192
Received: 12 December 2017 / Revised: 6 January 2018 / Accepted: 10 January 2018 / Published: 12 January 2018
PDF Full-text (7743 KB) | HTML Full-text | XML Full-text
Abstract
Typically, a geared drive system is used to connect an induction motor of 1500 rpm with a Raymond Pulverizer of 105 rpm in mining applications. This system suffers from low efficiency and a heavy motor drive. This paper proposes a novel design of
[...] Read more.
Typically, a geared drive system is used to connect an induction motor of 1500 rpm with a Raymond Pulverizer of 105 rpm in mining applications. This system suffers from low efficiency and a heavy motor drive. This paper proposes a novel design of a 75 kW, 72/48 switched reluctance motor (SRM) for a low-speed direct-drive as for mining applications. The paper is focused on the design and comparative evaluation of the proposed machine in order to replace a geared drive system whilst providing a high torque low-speed and direct-drive solution. The machine performance is studied and the switching angle configuration of the machine is also optimised. The efficiency of the whole drive system is found to be as high as 90.19%, whereas the geared induction motor drive provides only an efficiency of 59.32% under similar operating conditions. An SRM prototype was built and experimentally tested. Simulation and experimental results show that the drive system has better performance to substitute the induction motor option in mining applications. Full article
Figures

Figure 1

Open AccessArticle A Free-Piston Linear Generator Control Strategy for Improving Output Power
Energies 2018, 11(1), 135; doi:10.3390/en11010135
Received: 9 December 2017 / Revised: 1 January 2018 / Accepted: 2 January 2018 / Published: 5 January 2018
PDF Full-text (6497 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a control strategy to improve the output power for a single-cylinder two-stroke free-piston linear generator (FPLG). The comprehensive simulation model of this FPLG is established and the operation principle is introduced. The factors that affect the output power are analyzed
[...] Read more.
This paper presents a control strategy to improve the output power for a single-cylinder two-stroke free-piston linear generator (FPLG). The comprehensive simulation model of this FPLG is established and the operation principle is introduced. The factors that affect the output power are analyzed theoretically. The characteristics of the piston motion are studied. Considering the different features of the piston motion respectively in acceleration and deceleration phases, a ladder-like electromagnetic force control strategy is proposed. According to the status of the linear electric machine, the reference profile of the electromagnetic force is divided into four ladder-like stages during one motion cycle. The piston motions, especially the dead center errors, are controlled by regulating the profile of the electromagnetic force. The feasibility and advantage of the proposed control strategy are verified through comparison analyses with two conventional control strategies via MatLab/Simulink. The results state that the proposed control strategy can improve the output power by around 7–10% with the same fuel cycle mass. Full article
Figures

Figure 1

Open AccessArticle High Gain Boost Interleaved Converters with Coupled Inductors and with Demagnetizing Circuits
Energies 2018, 11(1), 130; doi:10.3390/en11010130
Received: 15 November 2017 / Revised: 13 December 2017 / Accepted: 3 January 2018 / Published: 5 January 2018
PDF Full-text (7835 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes double interleaved boost converters with high voltage gain and with magnetically coupled inductors, while a third coupled winding is used for magnetic flux reset of the core during converter operation. The topology of the proposal is simple, it does not
[...] Read more.
This paper proposes double interleaved boost converters with high voltage gain and with magnetically coupled inductors, while a third coupled winding is used for magnetic flux reset of the core during converter operation. The topology of the proposal is simple, it does not require many additional components compared to standard interleaved topologies, and it improves the transfer characteristics, as well as system efficiency even for high power levels. The investigation of steady-state operation was undertaken. It was discovered that the proposed converter can be designed for a target application where very high voltage gain is required, while adjustment of voltage gain value can be done through duty-cycle variation or by the turns-ratio modification between individual coils. The 1 kW prototype was designed to test the theoretical analysis. The results demonstrate that the proposed converter achieves very high voltage gain (1:8), while for the designed prototype the peak efficiency reaches >96% even when two additional diodes and one winding were implemented within the converter’s main circuit. The dependency of the output voltage stiffness on load change is minimal. Thus, the presented converter might be a proper solution for applications where tight constant DC-bus voltage is required (a DC-DC converter for inverters). Full article
Figures

Figure 1

Open AccessArticle Numerical Simulations for a Partial Disk MHD Generator Performance
Energies 2018, 11(1), 127; doi:10.3390/en11010127
Received: 15 November 2017 / Revised: 29 December 2017 / Accepted: 31 December 2017 / Published: 4 January 2018
PDF Full-text (5045 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, numerical simulations are carried out to predict the performance of a new designed configuration of the disk magnetohydrodynamic (MHD) generator, which segments the generator into dozens of parts. The behaviors and characteristics of segments are mainly investigated with number of
[...] Read more.
In this paper, numerical simulations are carried out to predict the performance of a new designed configuration of the disk magnetohydrodynamic (MHD) generator, which segments the generator into dozens of parts. The behaviors and characteristics of segments are mainly investigated with number of parts at 24, 36, 60, 72, 90 adopted Large Eddy Simulation (LES). The numerical results declared that these division generators approach more stable plasma ionization and better performance than that of the conventional disk MHD generator at the same working conditions. The optimal value can be reached when the angle is 5–10 degrees (36–72 parts). Due to the division of the generator, the internal resistance is larger than that of the conventional disk channel that causes the reduction of Faraday current, hence the Lorentz force, j θ B , decreased. Therefore, the radial velocity increased and static pressure decreased. Consequently, the reduction of static pressure contributes to improvement to the plasma uniformity and ionization stability. Those features reveal that the designed configuration has the obvious advantage on raising energy conversion efficiency and power output. Full article
Figures

Figure 1

Open AccessArticle Switched Polytopic Controller Applied on a Positive Reconfigurable Power Electronic Converter
Energies 2018, 11(1), 116; doi:10.3390/en11010116
Received: 17 November 2017 / Revised: 27 December 2017 / Accepted: 29 December 2017 / Published: 3 January 2018
PDF Full-text (2041 KB) | HTML Full-text | XML Full-text
Abstract
The reconfigurable power electronic converters (RPECs) are a new generation of systems, which modify their physical configuration in terms of a desired input or output operation characteristic. This kind of converters is very attractive in terms of versatility, compactness, and robustness. They have
[...] Read more.
The reconfigurable power electronic converters (RPECs) are a new generation of systems, which modify their physical configuration in terms of a desired input or output operation characteristic. This kind of converters is very attractive in terms of versatility, compactness, and robustness. They have been proposed in areas such as illumination, transport electrification (TE), eenewable energy (RE), smart grids and the internet of things (IoT). However, the resulting converters operate in switched variable operation-regions, rather than over single operation points. As a result, there is a complexity increment on the modeling and control stage such that traditional techniques are no longer valid. In order to overcome these challenges, this paper proposes a kind of switched polytopic controller (SPC) suitable to stabilize an RPEC. Modeling, control, numerical and practical results are reported. To this end, a 400 W positive synchronous bi-directional buck/boost converter is used as a testbed. It is also shown, that the proposed converter and robust controller accomplish a compact, modular and reliable design during different working configuration, operation points and load changes. Full article
Figures

Figure 1

Open AccessArticle A Practical Approach to Localize Simultaneous Triple Open-Switches for a PWM Inverter-Fed Permanent Magnet Synchronous Machine Drive System
Energies 2018, 11(1), 101; doi:10.3390/en11010101
Received: 12 December 2017 / Revised: 28 December 2017 / Accepted: 31 December 2017 / Published: 2 January 2018
PDF Full-text (9135 KB) | HTML Full-text | XML Full-text
Abstract
In order to overcome the limitations of conventional diagnosis methods, this paper proposes a reliable and practical on-line fault localization scheme for a pulse width modulation (PWM) inverter-fed permanent magnet synchronous machine (PMSM) drive system even when the inverter has simultaneous open faults
[...] Read more.
In order to overcome the limitations of conventional diagnosis methods, this paper proposes a reliable and practical on-line fault localization scheme for a pulse width modulation (PWM) inverter-fed permanent magnet synchronous machine (PMSM) drive system even when the inverter has simultaneous open faults in up to three switches. An open-switch fault is usually initiated by an accidental over-current, or electrical and thermal stresses. This fault may induce crucial secondary damage in the drive system since it is easily propagated and produces a continuous harmful effect on other system components. The open-switch faults in inverters often occur in a very complicated manner. Due to this reason, it was only recently that real-time diagnosis schemes under the open-switch faults in multiple switches have been presented in a few references. However, to alleviate the complexity and exactness issues, most of the conventional diagnosis schemes have considered the open faults only in two simultaneous switches until now, which is not generally the case. Even though the fault detection is simple and immediate, the exact fault localization is not a simple task, especially when there are open faults in three simultaneous switches because different open-switch fault locations may develop the same fault signature. To deal with such a problem, free-wheeling mode detection is introduced in this paper for the purpose of identifying the exact fault group and the faulty switch location. Then main objective of this paper is to realize a reliable fault localization algorithm under the condition of simultaneous open-switches (up to three) on an online basis without requiring any extra hardware or sensors in order that the algorithm can be easily installed in main CPU of a commercial drive system. For this purpose, the open faults in simultaneous switches are categorized into seven different fault groups. The entire system is implemented on a digital controller by using TMS320F28335 digital signal processor (DSP). The experimental results are presented under various open fault conditions to validate the usefulness of the proposed open-switch fault localization scheme. Full article
Figures

Figure 1

Open AccessArticle Power Transformer Spatial Acoustic Radiation Characteristics Analysis under Multiple Operating Conditions
Energies 2018, 11(1), 74; doi:10.3390/en11010074
Received: 15 October 2017 / Revised: 12 December 2017 / Accepted: 18 December 2017 / Published: 1 January 2018
PDF Full-text (5581 KB) | HTML Full-text | XML Full-text
Abstract
Spatial acoustic radiation characteristics analysis is the precondition of reducing the noise influence of outdoor power transformer while multi-physical field coupling method can be applied to quantify and reveal these acoustic characteristics of a running power transformer. In this study, based on the
[...] Read more.
Spatial acoustic radiation characteristics analysis is the precondition of reducing the noise influence of outdoor power transformer while multi-physical field coupling method can be applied to quantify and reveal these acoustic characteristics of a running power transformer. In this study, based on the theoretical analysis about noise generation and dissemination process, an acoustic radiation model about oil-immersed power transformer was established and verified with field test data in time and frequency domain. Then, far-field analysis and directivity analysis were accomplished to characterize acoustic field of power transformer under multiple operating conditions. Finally, the acoustic radiation influence on potential surrounding buildings were analyzed and discussed. The visual results and conclusion provide acoustic guide for the optimal planning and design about both power substation and ambient buildings. Full article
Figures

Figure 1

Open AccessArticle Rotor Position Self-Sensing of SRM Using PSO-RVM
Energies 2018, 11(1), 66; doi:10.3390/en11010066
Received: 31 October 2017 / Revised: 11 December 2017 / Accepted: 20 December 2017 / Published: 1 January 2018
PDF Full-text (3455 KB) | HTML Full-text | XML Full-text
Abstract
The motors’ flux-linkage, current and angle obtained from the system with sensors were chosen as the sample data, and the estimation model of rotor position based on relevance vector machine (RVM) was built by training the sample data. The kernel function parameter in
[...] Read more.
The motors’ flux-linkage, current and angle obtained from the system with sensors were chosen as the sample data, and the estimation model of rotor position based on relevance vector machine (RVM) was built by training the sample data. The kernel function parameter in RVM model was optimized by the particle swarm algorithm in order to increase the fitting precision and generalization ability of RVM model. It achieved higher prediction accuracy with staying at the same on-line testing time as the RVM. And because the short on-line computation, the motor can operate at 3000 r/min in sensorless control with particle swarm optimization-relevance vector machine (PSO-RVM), which is higher than support vector machine (SVM) and neural network (NN). By simulation and experiment on the test motor, it is verified that the proposed estimation model can obtain the angle of full electrical period accurately under low speed and high speed operations in current chopped control and angle position control, which has satisfactory estimation precision. Full article
Figures

Figure 1

Open AccessArticle Design Method for the Coil-System and the Soft Switching Technology for High-Frequency and High-Efficiency Wireless Power Transfer Systems
Energies 2018, 11(1), 7; doi:10.3390/en11010007
Received: 20 October 2017 / Revised: 7 December 2017 / Accepted: 18 December 2017 / Published: 21 December 2017
PDF Full-text (10103 KB) | HTML Full-text | XML Full-text
Abstract
Increasing the resonant frequency of a wireless power transfer (WPT) system effectively improves the power transfer efficiency between the transmit and the receive coils but significantly limits the power transfer capacity with the same coils. Therefore, this paper proposes a coil design method
[...] Read more.
Increasing the resonant frequency of a wireless power transfer (WPT) system effectively improves the power transfer efficiency between the transmit and the receive coils but significantly limits the power transfer capacity with the same coils. Therefore, this paper proposes a coil design method for a series-series (SS) compensated WPT system which can power up the same load with the same DC input voltage & current but with increased resonant frequency. For WPT systems with higher resonant frequencies, a new method of realizing soft-switching by tuning driving frequency is proposed which does not need to change any hardware in the WPT system and can effectively reduce switching losses generated in the inverter. Eighty-five kHz, 200 kHz and 500 kHz WPT systems are built up to validate the proposed methods. Experimental results show that all these three WPT systems can deliver around 3.3 kW power to the same load (15 Ω) with 200 V input voltage and 20 A input current as expected and achieve more than 85% coil-system efficiency and 79% system overall efficiency. With the soft-switching technique, inverter efficiency can be improved from 81.91% to 98.60% in the 500 kHz WPT system. Full article
Figures

Figure 1

Open AccessArticle Multi-Phase Modular Drive System: A Case Study in Electrical Aircraft Applications
Energies 2018, 11(1), 5; doi:10.3390/en11010005
Received: 27 October 2017 / Revised: 8 December 2017 / Accepted: 18 December 2017 / Published: 21 December 2017
PDF Full-text (22107 KB) | HTML Full-text | XML Full-text
Abstract
In this article, an advanced multiphase modular power drive prototype is developed for More Electric Aircraft (MEA). The proposed drive is designed to supply a multi-phase permanent magnet (PM) motor rating 120 kW with 24 slots and 11 pole pairs. The power converter
[...] Read more.
In this article, an advanced multiphase modular power drive prototype is developed for More Electric Aircraft (MEA). The proposed drive is designed to supply a multi-phase permanent magnet (PM) motor rating 120 kW with 24 slots and 11 pole pairs. The power converter of the drive system is based on Silicon Carbide Metal Oxide Semiconductor Field-Effect Transistor (SiC MOSFET) technology to operate at high voltage, high frequency and low reverse recovery current. Firstly, an experimental characterization test is performed for the selected SiC power module in harsh conditions to evaluate the switching energy losses. Secondly, a finite element thermal analysis based on Ansys-Icepak is accomplished to validate the selected cooling system for the power converter. Thirdly, a co-simulation model is developed using Matlab-Simulink and LTspice® to evaluate the SiC power module impact on the performance of a multiphase drive system at different operating conditions. The results obtained show that the dynamic performance and efficiency of the power drive are significantly improved, which makes the proposed system an excellent candidate for future aircraft applications. Full article
Figures

Figure 1

Open AccessArticle A Parallel Restoration for Black Start of Microgrids Considering Characteristics of Distributed Generations
Energies 2018, 11(1), 1; doi:10.3390/en11010001
Received: 7 November 2017 / Revised: 7 December 2017 / Accepted: 15 December 2017 / Published: 21 December 2017
Cited by 1 | PDF Full-text (1197 KB) | HTML Full-text | XML Full-text
Abstract
The black start capability is vital for microgrids, which can potentially improve the reliability of the power grid. This paper proposes a black start strategy for microgrids based on a parallel restoration strategy. Considering the characteristics of distributed generations (DGs), an evaluation model,
[...] Read more.
The black start capability is vital for microgrids, which can potentially improve the reliability of the power grid. This paper proposes a black start strategy for microgrids based on a parallel restoration strategy. Considering the characteristics of distributed generations (DGs), an evaluation model, which is used to assess the black start capability of DGs, is established by adopting the variation coefficient method. Thus, the DGs with good black start capability, which are selected by a diversity sequence method, are restored first in parallel under the constraints of DGs and network. During the selection process of recovery paths, line weight and node importance degree are proposed under the consideration of the node topological importance and the load importance as well as the backbone network restoration time. Therefore, the whole optimization of the reconstructed network is realized. Finally, the simulation results verify the feasibility and effectiveness of the strategy. Full article
Figures

Figure 1

Open AccessArticle Reducing WCET Overestimations by Correcting Errors in Loop Bound Constraints
Energies 2017, 10(12), 2113; doi:10.3390/en10122113
Received: 12 November 2017 / Revised: 3 December 2017 / Accepted: 12 December 2017 / Published: 12 December 2017
PDF Full-text (4663 KB) | HTML Full-text | XML Full-text
Abstract
In order to reduce overestimations of worst-case execution time (WCET), in this article, we firstly report a kind of specific WCET overestimation caused by non-orthogonal nested loops. Then, we propose a novel correction approach which has three basic steps. The first step is
[...] Read more.
In order to reduce overestimations of worst-case execution time (WCET), in this article, we firstly report a kind of specific WCET overestimation caused by non-orthogonal nested loops. Then, we propose a novel correction approach which has three basic steps. The first step is to locate the worst-case execution path (WCEP) in the control flow graph and then map it onto source code. The second step is to identify non-orthogonal nested loops from the WCEP by means of an abstract syntax tree. The last step is to recursively calculate the WCET errors caused by the loose loop bound constraints, and then subtract the total errors from the overestimations. The novelty lies in the fact that the WCET correction is only conducted on the non-branching part of WCEP, thus avoiding potential safety risks caused by possible WCEP switches. Experimental results show that our approach reduces the specific WCET overestimation by an average of more than 82%, and 100% of corrected WCET is no less than the actual WCET. Thus, our approach is not only effective but also safe. It will help developers to design energy-efficient and safe real-time systems. Full article
Figures

Figure 1

Open AccessArticle A Novel Digital Control Method of a Single-Phase Grid-Connected Inverter Based on a Virtual Closed-Loop Circuit and Complex Vector Representation
Energies 2017, 10(12), 2068; doi:10.3390/en10122068
Received: 26 October 2017 / Revised: 26 November 2017 / Accepted: 30 November 2017 / Published: 6 December 2017
PDF Full-text (8348 KB) | HTML Full-text | XML Full-text
Abstract
With the rapid development of renewable energy generation, single-phase grid-connected inverters have been widely applied in modern power systems. Since the power output of the renewable sources is continuously changing, independent active/reactive power control and a rapid current tracking performance is supposed to
[...] Read more.
With the rapid development of renewable energy generation, single-phase grid-connected inverters have been widely applied in modern power systems. Since the power output of the renewable sources is continuously changing, independent active/reactive power control and a rapid current tracking performance is supposed to be achieved in a single-phase grid-connected inverter. However, the poor orthogonal-axis-constructing strategy and the ineffective decoupling in some widely-used controllers have severely weakened the dynamic performance of the single-phase inverter. To deal with the challenges above, this study proposes a comprehensive control strategy for current control in a single-phase grid-connected inverter. In the proposed control strategy, a virtual closed-loop is constructed to improve the dynamic performance and realize independent power control under a synchronous frame. Then, complex vector theory is used to model the virtual closed-loop based single-phase inverter, and a novel digital controller is designed based on zero-pole cancellation and minimum beat control to completely decouple the active/reactive components and achieve a supreme current tracking performance. Experimental results are shown to validate the feasibility of the proposed current controller. Full article
Figures

Open AccessArticle Loss Model and Efficiency Analysis of Tram Auxiliary Converter Based on a SiC Device
Energies 2017, 10(12), 2018; doi:10.3390/en10122018
Received: 9 October 2017 / Revised: 25 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
PDF Full-text (11098 KB) | HTML Full-text | XML Full-text
Abstract
Currently, the auxiliary converter in the auxiliary power supply system of a modern tram adopts Si IGBT as its switching device and with the 1700 V/225 A SiC MOSFET module commercially available from Cree, an auxiliary converter using all SiC devices is now
[...] Read more.
Currently, the auxiliary converter in the auxiliary power supply system of a modern tram adopts Si IGBT as its switching device and with the 1700 V/225 A SiC MOSFET module commercially available from Cree, an auxiliary converter using all SiC devices is now possible. A SiC auxiliary converter prototype is developed during this study. The author(s) derive the loss calculation formula of the SiC auxiliary converter according to the system topology and principle and each part loss in this system can be calculated based on the device datasheet. Then, the static and dynamic characteristics of the SiC MOSFET module used in the system are tested, which aids in fully understanding the performance of the SiC devices and provides data support for the establishment of the PLECS loss simulation model. Additionally, according to the actual circuit parameters, the PLECS loss simulation model is set up. This simulation model can simulate the actual operating conditions of the auxiliary converter system and calculate the loss of each switching device. Finally, the loss of the SiC auxiliary converter prototype is measured and through comparison it is found that the loss calculation theory and PLECS loss simulation model is valuable. Furthermore, the thermal images of the system can prove the conclusion about loss distribution to some extent. Moreover, these two methods have the advantages of less variables and fast calculation for high power applications. The loss models may aid in optimizing the switching frequency and improving the efficiency of the system. Full article
Figures

Figure 1

Open AccessArticle A Three-Phase Four-Leg Inverter-Based Active Power Filter for Unbalanced Current Compensation Using a Petri Probabilistic Fuzzy Neural Network
Energies 2017, 10(12), 2005; doi:10.3390/en10122005
Received: 20 October 2017 / Revised: 26 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
PDF Full-text (19056 KB) | HTML Full-text | XML Full-text
Abstract
A three-phase four-leg inverter-based shunt active power filter (APF) is proposed to compensate three-phase unbalanced currents under unbalanced load conditions in grid-connected operation in this study. Since a DC-link capacitor is required on the DC side of the APF to release or absorb
[...] Read more.
A three-phase four-leg inverter-based shunt active power filter (APF) is proposed to compensate three-phase unbalanced currents under unbalanced load conditions in grid-connected operation in this study. Since a DC-link capacitor is required on the DC side of the APF to release or absorb the instantaneous apparent power, the regulation control of the DC-link voltage of the APF is important especially under load variation. In order to improve the regulation control of the DC-link voltage of the shunt APF under variation of three-phase unbalanced load and to compensate the three-phase unbalanced currents effectively, a novel Petri probabilistic fuzzy neural network (PPFNN) controller is proposed to replace the traditional proportional-integral (PI) controller in this study. Furthermore, the network structure and online learning algorithms of the proposed PPFNN are represented in detail. Finally, the effectiveness of the three-phase four-leg inverter-based shunt APF with the proposed PPFNN controller for the regulation of the DC-link voltage and compensation of the three-phase unbalanced current has been demonstrated by some experimental results. Full article
Figures

Figure 1

Open AccessArticle Dynamic Power Dispatch Considering Electric Vehicles and Wind Power Using Decomposition Based Multi-Objective Evolutionary Algorithm
Energies 2017, 10(12), 1991; doi:10.3390/en10121991
Received: 27 October 2017 / Revised: 17 November 2017 / Accepted: 22 November 2017 / Published: 1 December 2017
Cited by 1 | PDF Full-text (6067 KB) | HTML Full-text | XML Full-text
Abstract
The intermittency of wind power and the large-scale integration of electric vehicles (EVs) bring new challenges to the reliability and economy of power system dispatching. In this paper, a novel multi-objective dynamic economic emission dispatch (DEED) model is proposed considering the EVs and
[...] Read more.
The intermittency of wind power and the large-scale integration of electric vehicles (EVs) bring new challenges to the reliability and economy of power system dispatching. In this paper, a novel multi-objective dynamic economic emission dispatch (DEED) model is proposed considering the EVs and uncertainties of wind power. The total fuel cost and pollutant emission are considered as the optimization objectives, and the vehicle to grid (V2G) power and the conventional generator output power are set as the decision variables. The stochastic wind power is derived by Weibull probability distribution function. Under the premise of meeting the system energy and user’s travel demand, the charging and discharging behavior of the EVs are dynamically managed. Moreover, we propose a two-step dynamic constraint processing strategy for decision variables based on penalty function, and, on this basis, the Multi-Objective Evolutionary Algorithm Based on Decomposition (MOEA/D) algorithm is improved. The proposed model and approach are verified by the 10-generator system. The results demonstrate that the proposed DEED model and the improved MOEA/D algorithm are effective and reasonable. Full article
Figures

Figure 1

Open AccessArticle Model-Based Predictive Current Control Method with Constant Switching Frequency for Single-Phase Voltage Source Inverters
Energies 2017, 10(11), 1927; doi:10.3390/en10111927
Received: 24 October 2017 / Revised: 10 November 2017 / Accepted: 16 November 2017 / Published: 21 November 2017
PDF Full-text (8428 KB) | HTML Full-text | XML Full-text
Abstract
Voltage source inverters operated by predictive control methods generally lead to a variable switching frequency, because predictive control methods generate switching operation based on an optimal voltage state selected at every sampling period. Varying switching frequencies make it difficult to design output filters
[...] Read more.
Voltage source inverters operated by predictive control methods generally lead to a variable switching frequency, because predictive control methods generate switching operation based on an optimal voltage state selected at every sampling period. Varying switching frequencies make it difficult to design output filters of voltage source inverters. This paper proposes a predictive control algorithm with a constant switching frequency for the load current control of single-phase voltage source inverters. This method selects two future optimal voltage states used in the subsequent sampling period, which are a zero-voltage state and a future optimal voltage state, based on the slope of the reference current at each sampling period. After selecting the two future voltages, the proposed method distributes them to produce a constant switching frequency and symmetric switching pattern. The performance of the proposed method is validated with both simulation and experimental results for single-phase voltage source inverters. Full article
Figures

Figure 1

Open AccessArticle Enhanced Regenerative Braking Strategies for Electric Vehicles: Dynamic Performance and Potential Analysis
Energies 2017, 10(11), 1875; doi:10.3390/en10111875
Received: 13 October 2017 / Revised: 7 November 2017 / Accepted: 13 November 2017 / Published: 15 November 2017
PDF Full-text (14892 KB) | HTML Full-text | XML Full-text
Abstract
A regenerative braking system and hydraulic braking system are used in conjunction in the majority of electric vehicles worldwide. We propose a new regenerative braking distribution strategy that is based on multi-input fuzzy control logic while considering the influences of the battery’s state
[...] Read more.
A regenerative braking system and hydraulic braking system are used in conjunction in the majority of electric vehicles worldwide. We propose a new regenerative braking distribution strategy that is based on multi-input fuzzy control logic while considering the influences of the battery’s state of charge, the brake strength and the motor speed. To verify the braking performance and recovery economy, this strategy was applied to a battery electric vehicle model and compared with two other improved regenerative braking strategies. The performance simulation was performed using standard driving cycles (NEDC, LA92, and JP1015) and a real-world-based urban cycle in China. The tested braking strategies satisfied the general safety requirements of Europe (as specified in ECE-13H), and the emergency braking scenario and economic potential were tested. The simulation results demonstrated the differences in the braking force distribution performance of these three regenerative braking strategies, the feasibility of the braking methods for the proposed driving cycles and the energy economic potential of the three strategies. Full article
Figures

Figure 1

Open AccessArticle Case Library Construction Technology of Energy Loss in Distribution Networks Considering Regional Differentiation Theory
Energies 2017, 10(11), 1861; doi:10.3390/en10111861
Received: 28 September 2017 / Revised: 5 November 2017 / Accepted: 10 November 2017 / Published: 14 November 2017
PDF Full-text (3379 KB) | HTML Full-text | XML Full-text
Abstract
The grid structures, load levels, and running states of distribution networks in different supply regions are known as the influencing factors of energy loss. In this paper, the case library of energy loss is constructed to differentiate the crucial factors of energy loss
[...] Read more.
The grid structures, load levels, and running states of distribution networks in different supply regions are known as the influencing factors of energy loss. In this paper, the case library of energy loss is constructed to differentiate the crucial factors of energy loss in the different supply regions. First of all, the characteristic state values are selected as the representation of the cases based on the analysis of energy loss under various voltage classes and in different types of regions. Then, the methods of Grey Relational Analysis and the K-Nearest Neighbor are utilized to implement the critical technologies of case library construction, including case representation, processing, analysis, and retrieval. Moreover, the analysis software of the case library is designed based on the case library construction technology. Some case studies show that there are many differences and similarities concerning the factors that influence the energy loss in different types of regions. In addition, the most relevant sample case can be retrieved from the case library. Compared with the traditional techniques, constructing a case library provides a new way to find out the characteristics of energy loss in different supply regions and constitutes differentiated loss-reducing programs. Full article
Figures

Figure 1

Open AccessArticle Research on Single-Phase PWM Converter with Reverse Conducting IGBT Based on Loss Threshold Desaturation Control
Energies 2017, 10(11), 1845; doi:10.3390/en10111845
Received: 15 September 2017 / Revised: 3 November 2017 / Accepted: 5 November 2017 / Published: 12 November 2017
PDF Full-text (5518 KB) | HTML Full-text | XML Full-text
Abstract
In the application of vehicle power supply and distributed power generation, there are strict requirements for the pulse width modulation (PWM) converter regarding power density and reliability. When compared with the conventional insulated gate bipolar transistor (IGBT) module, the Reverse Conducting-Insulated Gate Bipolar
[...] Read more.
In the application of vehicle power supply and distributed power generation, there are strict requirements for the pulse width modulation (PWM) converter regarding power density and reliability. When compared with the conventional insulated gate bipolar transistor (IGBT) module, the Reverse Conducting-Insulated Gate Bipolar Transistor (RC-IGBT) with the same package has a lower thermal resistance and higher current tolerance. By applying the gate desaturation control, the reverse recovery loss of the RC-IGBT diode may be reduced. In this paper, a loss threshold desaturation control method is studied to improve the output characteristics of the single-phase PWM converter with a low switching frequency. The gate desaturation control characteristics of the RC-IGBT’s diode are studied. A proper current limit is set to avoid the ineffective infliction of the desaturation pulse, while the bridge arm current crosses zero. The expectation of optimized loss decrease is obtained, and the better performance for the RC-IGBTs of the single-phase PWM converter is achieved through the optimized desaturation pulse distribution. Finally, the improved predictive current control algorithm that is applied to the PWM converter with RC-IGBTs is simulated, and is operated and tested on the scaled reduced power platform. The results prove that the gate desaturation control with the improved predictive current algorithm may effectively improve the RC-IGBT’s characteristics, and realize the stable output of the PWM converter. Full article
Figures

Figure 1

Open AccessArticle New Approach for Optimal Location and Parameters Setting of UPFC for Enhancing Power Systems Stability under Contingency Analysis
Energies 2017, 10(11), 1738; doi:10.3390/en10111738
Received: 13 September 2017 / Revised: 22 October 2017 / Accepted: 23 October 2017 / Published: 30 October 2017
Cited by 1 | PDF Full-text (10474 KB) | HTML Full-text | XML Full-text
Abstract
Operation of power system within specified limits of voltage and frequency are the major concerns in power system stability studies. As power system is always prone to disturbances, which consequently affect the voltage instability and optimal power flow, and therefore risks the power
[...] Read more.
Operation of power system within specified limits of voltage and frequency are the major concerns in power system stability studies. As power system is always prone to disturbances, which consequently affect the voltage instability and optimal power flow, and therefore risks the power systems stability and security. In this paper, a novel technique based on the “Artificial Algae Algorithm” (AAA) is introduced, to identify the optimal location and the parameters setting of Unified Power Flow Controller (UPFC) under N-1 contingency criterion. In the first part, we have carried out a contingency operation and ranking process for the most parlous lines outage contingencies while taking the transmission lines overloading (NOLL) and voltage violation of buses (NVVB) as a performance parameter (PP = NOLL + NVVB). As UPFC possesses too much prohibitive cost and larger size, its optimal location and size must be identified before the actual deployment. In the second part, we have applied a novel AAA technique to identify the optimal location and parameters setting of UPFC under the discovered contingencies. The simulations have been executed on IEEE 14 bus and 30 bus networks. The results reveals that the location of UPFC is significantly optimized using AAA technique, which has improved the stability and security of the power system by curtailing the overloaded transmission lines and limiting the voltage violations of buses. Full article
Figures

Figure 1

Open AccessArticle Core Loss Analysis of Interior Permanent Magnet Synchronous Machines under SVPWM Excitation with Considering Saturation
Energies 2017, 10(11), 1716; doi:10.3390/en10111716
Received: 22 September 2017 / Revised: 10 October 2017 / Accepted: 16 October 2017 / Published: 26 October 2017
Cited by 1 | PDF Full-text (5446 KB) | HTML Full-text | XML Full-text
Abstract
Core loss is one of the significant factors affecting the high power density of permanent magnet machines; thus, it is necessary to consider core loss in machine design. This paper presents a novel method for calculating the core loss of permanent magnet synchronous
[...] Read more.
Core loss is one of the significant factors affecting the high power density of permanent magnet machines; thus, it is necessary to consider core loss in machine design. This paper presents a novel method for calculating the core loss of permanent magnet synchronous machines under space vector pulse width modulation (SVPWM) excitation, taking magnetic saturation and cross coupling into account. In order to accurately obtain the direct and quadrature (d-q) axis, current in the given load condition, the permanent magnet motor model under SVPWM excitation has been modified, so as to consider the influence of magnetic saturation and cross coupling effects on the d-q axis flux-linkage. Based on the magnetic field distribution caused by permanent magnet and armature reactions, the stator core loss can be calculated with the core loss analytical model, corresponding to the rotational magnetic field. In this study, the method has been applied to analyze core loss in an interior permanent magnet synchronous machine, and has been validated by the experimental results. The influence of pole/slot number combinations on core loss in the same on-load condition is also investigated. This study provides a potential method to guide motor design optimization. Full article
Figures

Figure 1

Open AccessArticle Torque Coordination Control during Braking Mode Switch for a Plug-in Hybrid Electric Vehicle
Energies 2017, 10(11), 1684; doi:10.3390/en10111684
Received: 15 September 2017 / Revised: 13 October 2017 / Accepted: 16 October 2017 / Published: 25 October 2017
PDF Full-text (4315 KB) | HTML Full-text | XML Full-text
Abstract
Hybrid vehicles usually have several braking systems, and braking mode switches are significant events during braking. It is difficult to coordinate torque fluctuations caused by mode switches because the dynamic characteristics of braking systems are different. In this study, a new type of
[...] Read more.
Hybrid vehicles usually have several braking systems, and braking mode switches are significant events during braking. It is difficult to coordinate torque fluctuations caused by mode switches because the dynamic characteristics of braking systems are different. In this study, a new type of plug-in hybrid vehicle is taken as the research object, and braking mode switches are divided into two types. The control strategy of type one is achieved by controlling the change rates of clutch hold-down and motor braking forces. The control strategy of type two is achieved by simultaneously changing the target braking torque during different mode switch stages and controlling the motor to participate in active coordination control. Finally, the torque coordination control strategy is modeled in MATLAB/Simulink, and the results show that the proposed control strategy has a good effect in reducing the braking torque fluctuation and vehicle shocks during braking mode switches. Full article
Figures

Figure 1

Open AccessArticle A Novel Topology of Hybrid HVDC Circuit Breaker for VSC-HVDC Application
Energies 2017, 10(10), 1675; doi:10.3390/en10101675
Received: 19 September 2017 / Revised: 17 October 2017 / Accepted: 19 October 2017 / Published: 23 October 2017
PDF Full-text (2951 KB) | HTML Full-text | XML Full-text
Abstract
The use of high voltage direct current (HVDC) circuit breakers (CBs) with the capabilities of bidirectional fault interruption, reclosing, and rebreaking can improve the reliable and safe operation of HVDC grids. Although several topologies of CBs have been proposed to perform these capabilities,
[...] Read more.
The use of high voltage direct current (HVDC) circuit breakers (CBs) with the capabilities of bidirectional fault interruption, reclosing, and rebreaking can improve the reliable and safe operation of HVDC grids. Although several topologies of CBs have been proposed to perform these capabilities, the limitation of these topologies is either high on-state losses or long time interruption in the case bidirectional fault current interruption. Long time interruption results in the large magnitude of the fault current in the voltage source converter based HVDC (VSC-HVDC) system due to the high rate of rise of fault current. This paper proposes a new topology of hybrid CB (HCB) with lower conduction loss and lower interruption time to solve the problems. The proposed topology is based on the inverse current injection method, which uses the capacitor to enforce the fault current to zero. In the case of the bidirectional fault current interruption, the capacitor does not change its polarity after identifying the direction of fault current, which can reduce the interruption time accordingly. A switching control algorithm for the proposed topology is presented in detail. Different operation modes of proposed HCB, such as normal current mode, breaking fault current mode, discharging, and reversing capacitor voltage modes after clearing the fault, are considered in the proposed algorithm. The proposed topology with the switching control algorithm is tested in a simulation-based system. Different simulation scenarios such as temporary and permanent faults are carried out to verify the performance of the proposed topology. The simulation is performed in the Matlab/Simulink environment. Full article
Figures

Figure 1

Open AccessArticle Grid-Connected Control Strategy of Five-level Inverter Based on Passive E-L Model
Energies 2017, 10(10), 1657; doi:10.3390/en10101657
Received: 20 September 2017 / Revised: 16 October 2017 / Accepted: 18 October 2017 / Published: 19 October 2017
PDF Full-text (3584 KB) | HTML Full-text | XML Full-text
Abstract
At present, the research on five-level inverters mainly involves the modulation algorithm and topology, and few articles study the five-level inverter from the control strategy. In this paper, the nonlinear passivity-based control (PBC) method is proposed for single-phase uninterruptible power supply inverters. The
[...] Read more.
At present, the research on five-level inverters mainly involves the modulation algorithm and topology, and few articles study the five-level inverter from the control strategy. In this paper, the nonlinear passivity-based control (PBC) method is proposed for single-phase uninterruptible power supply inverters. The proposed PBC method is based on an energy shaping and damping injection idea, which is performed to regulate the energy flow of an inverter to a desired level and to assure global asymptotic stability, respectively. Furthermore, this paper presents a control algorithm based on the theory of passivity that gives an inverter in a photovoltaic system additional functions: power factor correction, harmonic currents compensation, and the ability to stabilize the system under varying injection damping. Finally, the effectiveness of the PBC method in terms of both stability and harmonic distortion is verified by the simulation and experiments under resistive and inductive loads. Full article
Figures

Figure 1

Open AccessArticle A Method for the Realization of an Interruption Generator Based on Voltage Source Converters
Energies 2017, 10(10), 1642; doi:10.3390/en10101642
Received: 9 August 2017 / Revised: 19 September 2017 / Accepted: 11 October 2017 / Published: 19 October 2017
PDF Full-text (10669 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we described the structure and working principle of an interruption generator based on voltage source converters (VSCs). The main circuit parameters of the VSCs are determined according to the target of power transfer capability, harmonic suppression, and dynamic response capability.
[...] Read more.
In this paper we described the structure and working principle of an interruption generator based on voltage source converters (VSCs). The main circuit parameters of the VSCs are determined according to the target of power transfer capability, harmonic suppression, and dynamic response capability. A state feedback linearization method in nonlinear differential geometry theory was used for dq axis current decoupling, based on the mathematical model used in the dq coordinate system of VSCs. The direct current control strategy was adopted to achieve the independent regulation of active power and reactive power. The proportional integral (PI) link was used to optimize the dynamic performance of the controller, and PI parameters were adjusted. Disturbance voltage waves were generated by the regular sampling method. PSCAD/EMTDC simulation results and physical prototype experiments showed that the device could generate various disturbance voltage waveforms steadily, and had good dynamic and steady-state performance. Full article
Figures

Figure 1

Open AccessArticle Integrated BMS-MMC Balancing Technique Highlighted by a Novel Space-Vector Based Approach for BEVs Application
Energies 2017, 10(10), 1628; doi:10.3390/en10101628
Received: 27 September 2017 / Revised: 11 October 2017 / Accepted: 12 October 2017 / Published: 17 October 2017
PDF Full-text (2415 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a new mathematical model of modular multilevel converters for battery electric vehicles with space-vectors enabling a critical analysis of cell balancing for the battery management system. In particular, the requirements for power balancing and the actual number of degrees of
[...] Read more.
This paper proposes a new mathematical model of modular multilevel converters for battery electric vehicles with space-vectors enabling a critical analysis of cell balancing for the battery management system. In particular, the requirements for power balancing and the actual number of degrees of freedom of the control are investigated. The paper shows that the traditional approach of cell balancing is a special case of the proposed control methodology. Numerical analyses with Matlab/Simulink™ highlight the reasons of the slow response of the standard balancing technique for specific operating conditions of the battery electric vehicle. The paper suggests potential improvements that could be introduced through the proposed generalised approach. Full article
Figures

Figure 1

Open AccessArticle Thrust Force Ripple Reduction of Two C-Core Linear Flux-Switching Permanent Magnet Machines of High Thrust Force Capability
Energies 2017, 10(10), 1608; doi:10.3390/en10101608
Received: 11 August 2017 / Revised: 10 October 2017 / Accepted: 11 October 2017 / Published: 14 October 2017
PDF Full-text (4711 KB) | HTML Full-text | XML Full-text
Abstract
Linear flux-switching permanent magnetic (LFSPM) machines are good choices for long stroke applications. These machines deliver high thrust force density in addition to the machine structure where permanent magnetics (PMs) and windings are all on the short mover. For LFSPM machines, their performance
[...] Read more.
Linear flux-switching permanent magnetic (LFSPM) machines are good choices for long stroke applications. These machines deliver high thrust force density in addition to the machine structure where permanent magnetics (PMs) and windings are all on the short mover. For LFSPM machines, their performance is always affected by big thrust force ripple. In this paper, for two C-core LFSPM machines of high thrust force capability, including a 6/13 C-core LFSPM (6/13LFSPM-C) machine and a sandwiched C-core LFSPM (SLFSPM-C) machine, and a thrust force ripple reduction method is proposed. The proposed method is developed by reducing the slot effect component of the cogging force based on staggered stator tooth, and suppressing the thrust force ripple caused by unbalanced three phase back-electromagnetic forces (EMFs) based on two end PMs. Based on finite element analysis (FEA) results, both C-core LFSPM machines can achieve small thrust force ripples as well as high sinusoidal back-EMFs, and at the same time, maintain high thrust force capability with the proposed method. It was also found that, the improved SLFSPM-C machine exhibited the same thrust force capability as the improved 6/13LFSPM-C machine, but with a much smaller thrust force ripple. Full article
Figures

Figure 1

Open AccessArticle Position and Speed Estimation of Permanent Magnet Machine Sensorless Drive at High Speed Using an Improved Phase-Locked Loop
Energies 2017, 10(10), 1571; doi:10.3390/en10101571
Received: 4 September 2017 / Revised: 26 September 2017 / Accepted: 27 September 2017 / Published: 11 October 2017
Cited by 1 | PDF Full-text (12230 KB) | HTML Full-text | XML Full-text
Abstract
In conventional position sensorless permanent magnet (PM) machine drives, the rotor position is obtained from the phase-locked loop (PLL) with the regulation of spatial signal in estimated back electromotive force (EMF) voltages. Due to the sinusoidal distribution of back-EMF voltages, a small-signal approximation
[...] Read more.
In conventional position sensorless permanent magnet (PM) machine drives, the rotor position is obtained from the phase-locked loop (PLL) with the regulation of spatial signal in estimated back electromotive force (EMF) voltages. Due to the sinusoidal distribution of back-EMF voltages, a small-signal approximation is assumed in the PLL in order to estimate the position. That is, the estimated position is almost equal to the actual position per sample instant. However, at high speed when the ratio of sampling frequency, fsample, over the rotor operating frequency, fe, is low, this approximation might not be valid during the speed and load transient. To overcome this limitation, a position estimation is proposed specifically for the high-speed operation of a PM machine drive. A discrete-time EMF voltage estimator is developed to obtain the machine spatial signal. In addition, an arctangent calculation is cascaded to the PLL in order to remove this small-signal approximation for better sensorless drive performance. By using the discrete-time EMF estimation and modified PLL, the drive is able to maintain the speed closed-loop at 36 krpm with only 4.2 sampling points per electrical cycle on a PM machine, according to experimental results. Full article
Figures

Figure 1

Open AccessArticle A Stable and Fast-Transient Performance Switched-Mode Power Amplifier for a Power Hardware in the Loop (PHIL) System
Energies 2017, 10(10), 1569; doi:10.3390/en10101569
Received: 21 July 2017 / Revised: 24 September 2017 / Accepted: 27 September 2017 / Published: 11 October 2017
PDF Full-text (9158 KB) | HTML Full-text | XML Full-text
Abstract
Power Hardware in the Loop (PHIL) systems are used to test a power system with the help of combined software and hardware. Generally, to construct a PHIL system, a switched-mode power amplifier that has a stable performance is used, because of their large,
[...] Read more.
Power Hardware in the Loop (PHIL) systems are used to test a power system with the help of combined software and hardware. Generally, to construct a PHIL system, a switched-mode power amplifier that has a stable performance is used, because of their large, linear signal control-to-output characteristics. However, the fundamental limitations of a switch-mode power amplifier (PA) are the dynamic performance and output bandwidth. In this paper, a compound controller has been used for the rectifier part of a PA, which can ensure the stability of a PA under transient or fault operating conditions. Moreover, a compound controller, which involves a feed-forward controller, a proportional controller and a repetitive controller, is proposed in the inverter part of a PA, and it can be used for PHIL applications. Experimental results are obtained under various operating conditions, such as transient responses under load step change, and output voltage bandwidth testing for a PHIL system, it is concluded that a proposed switched-mode power amplifier is useful for the PHIL system. Full article
Figures

Figure 1

Open AccessArticle A Harmonic Resonance Suppression Strategy for a High-Speed Railway Traction Power Supply System with a SHE-PWM Four-Quadrant Converter Based on Active-Set Secondary Optimization
Energies 2017, 10(10), 1567; doi:10.3390/en10101567
Received: 19 September 2017 / Revised: 28 September 2017 / Accepted: 2 October 2017 / Published: 11 October 2017
PDF Full-text (6099 KB) | HTML Full-text | XML Full-text
Abstract
Pulse width modulation (PWM) technology is widely used in traction converters for high-speed railways. The harmonic distribution caused by PWM is quite extensive, and increases the possibility of grid–train coupling resonance in the traction power supply system (TPSS). This paper first analyzes the
[...] Read more.
Pulse width modulation (PWM) technology is widely used in traction converters for high-speed railways. The harmonic distribution caused by PWM is quite extensive, and increases the possibility of grid–train coupling resonance in the traction power supply system (TPSS). This paper first analyzes the mechanism of resonance, when the characteristic harmonic frequency of a four-quadrant converter (4QC) current that injects into the traction grid matches the resonant frequency of the traction grid, which may result in resonance in the system. To suppress resonance, this paper adopts specific harmonic elimination–pulse width modulation (SHE-PWM) technology combined with a transient direct current control strategy to eliminate the harmonics in the resonant frequency, which may suppress the grid–train coupling resonance. Due to the fact that the SHE-PWM process with multiple switching angles contains complex transcendental equations, the initial value is difficult to provide, and is difficult to solve using ordinary iterative algorithms. In this paper, an active-set secondary optimization method is used to solve the equation. The algorithm has the benefits of low dependence on initial values, fast convergence and high solution accuracy. Finally, the feasibility of the resonant suppression algorithm is verified by means of Matlab simulation. Full article
Figures

Figure 1

Open AccessArticle A New Control Method for a Bi-Directional Phase-Shift-Controlled DC-DC Converter with an Extended Load Range
Energies 2017, 10(10), 1532; doi:10.3390/en10101532
Received: 21 July 2017 / Revised: 29 September 2017 / Accepted: 29 September 2017 / Published: 10 October 2017
Cited by 1 | PDF Full-text (4137 KB) | HTML Full-text | XML Full-text
Abstract
Phase-shifted converters are practically important to provide high conversion efficiencies through soft-switching techniques. However, the limitation on a resonant inductor current in the converters often leads to a non-fulfillment of the requirement of minimum load current. This paper presents a new power electronics
[...] Read more.
Phase-shifted converters are practically important to provide high conversion efficiencies through soft-switching techniques. However, the limitation on a resonant inductor current in the converters often leads to a non-fulfillment of the requirement of minimum load current. This paper presents a new power electronics control technique to enable the dual features of bi-directional power flow and an extended load range for soft-switching in phase-shift-controlled DC-DC converters. The proposed technique utilizes two identical full bridge converters and inverters in conjunction with a new control logic for gate-driving signals to facilitate both Zero Current Switching (ZCS) and Zero Voltage Switching (ZVS) in a single phase-shift-controlled DC-DC converter. The additional ZCS is designed for light load conditions at which the minimum load current cannot be attained. The bi-directional phase-shift-controlled DC-DC converter can implement the function of synchronous rectification. Its fast dynamic response allows for quick energy recovery during the regenerative braking of traction systems in electrified trains. Full article
Figures

Figure 1

Open AccessArticle Effects of Nonlinearity in Input Filter on the Dynamic Behavior of an Interleaved Boost PFC Converter
Energies 2017, 10(10), 1530; doi:10.3390/en10101530
Received: 12 August 2017 / Revised: 22 September 2017 / Accepted: 25 September 2017 / Published: 2 October 2017
PDF Full-text (4551 KB) | HTML Full-text | XML Full-text
Abstract
A power factor correction (PFC) converter with interleaved multi-channel topology is gaining increasing attention due to its ability in reducing input and output current ripples, but an Electromagnetic Interference (EMI) noise filter is still required for suppressing the large high-frequency switching noise that
[...] Read more.
A power factor correction (PFC) converter with interleaved multi-channel topology is gaining increasing attention due to its ability in reducing input and output current ripples, but an Electromagnetic Interference (EMI) noise filter is still required for suppressing the large high-frequency switching noise that could potentially degrade the input power quality of the supplying grid and cause malfunctions to other grid-connected systems. In this paper, a magnetic modeling of an interleaved PFC converter with an input differential mode (DM) EMI filter has been successfully implemented, which considers the nonlinear behavior of the inductive component in the EMI filter. The Jiles-Atherton (J-A) model is applied to describe the filtering inductor whose core displays saturation and hysteresis. The simulation results are verified with the experimental test. Full article
Figures

Figure 1

Open AccessArticle Feature Selection for Partial Discharge Severity Assessment in Gas-Insulated Switchgear Based on Minimum Redundancy and Maximum Relevance
Energies 2017, 10(10), 1516; doi:10.3390/en10101516
Received: 5 September 2017 / Revised: 22 September 2017 / Accepted: 26 September 2017 / Published: 1 October 2017
Cited by 1 | PDF Full-text (1783 KB) | HTML Full-text | XML Full-text
Abstract
Scientific evaluation of partial discharge (PD) severity in gas-insulation switchgear (GIS) can assist in mastering the insulation condition of in-service GIS. Limited theoretical research on the laws of PD deterioration leads to a finite number of evaluation features extracted and subjective features selected
[...] Read more.
Scientific evaluation of partial discharge (PD) severity in gas-insulation switchgear (GIS) can assist in mastering the insulation condition of in-service GIS. Limited theoretical research on the laws of PD deterioration leads to a finite number of evaluation features extracted and subjective features selected for PD severity assessment. Therefore, this study proposes a minimum-redundancy maximum-relevance (mRMR) algorithm-based feature optimization selection method to realize the scientific and reasonable choice of PD severity features. PD ultra-high frequency data of varying severities are produced by simulating four typical insulation defects in GIS, which are then collected in the lab. A 16-dimension feature set describing PD original characteristics is abstracted in phase-resolved partial discharge (PRPD) mode, and the more informative evaluation feature set characterizing PD severity is further excavated by the mRMR method. Finally, a support vector machine (SVM) algorithm is employed as the classifier for intelligent evaluation to compare the evaluation effects of PD severity between the feature set selected by mRMR and the feature set is composed of discharge times, amplitude value, and time intervals obtained traditionally based on discharge change theory. The proposed comparison test showed the effectiveness of the mRMR method in informative feature selection and the accuracy of PD severity assessment for all defined defects. Full article
Figures

Figure 1

Open AccessArticle An Improved Commutation Prediction Algorithm to Mitigate Commutation Failure in High Voltage Direct Current
Energies 2017, 10(10), 1481; doi:10.3390/en10101481
Received: 20 July 2017 / Revised: 12 September 2017 / Accepted: 18 September 2017 / Published: 25 September 2017
Cited by 2 | PDF Full-text (3774 KB) | HTML Full-text | XML Full-text
Abstract
Commutation failure is a common fault for line-commutated converters in the inverter. To reduce the possibility of commutation failure, many prediction algorithms based on alternating current (AC) voltage detection have already been implemented in high voltage direct current (HVDC) control and protection systems.
[...] Read more.
Commutation failure is a common fault for line-commutated converters in the inverter. To reduce the possibility of commutation failure, many prediction algorithms based on alternating current (AC) voltage detection have already been implemented in high voltage direct current (HVDC) control and protection systems. Nevertheless, there are currently no effective methods to prevent commutation failure due to transformer excitation surge current. In this paper, an improved commutation failure prediction algorithm based on the harmonic characteristics of the converter bus voltage during transformer charging is proposed. Meanwhile, a sliding-window iterative algorithm of discrete Fourier transformation (DFT) is developed for detecting the voltage harmonic in real time. This method is proved to be an effective solution, which prevents commutation failure in cases of excitation surge current, through experimental analysis. This method is already implemented into TianShan-ZhongZhou (TianZhong) ± 800 kV ultra high voltage direct current (UHVDC) system. Full article