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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 (88 papers)

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Open AccessArticle Gain Scheduled Torque Compensation of PMSG-Based Wind Turbine for Frequency Regulation in an Isolated Grid
Energies 2018, 11(7), 1623; https://doi.org/10.3390/en11071623
Received: 23 May 2018 / Revised: 17 June 2018 / Accepted: 18 June 2018 / Published: 21 June 2018
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Abstract
Frequency stability in an isolated grid can be easily impacted by sudden load or wind speed changes. Many frequency regulation techniques are utilized to solve this problem. However, there are only few studies designing torque compensation controllers based on power performances in different
[...] Read more.
Frequency stability in an isolated grid can be easily impacted by sudden load or wind speed changes. Many frequency regulation techniques are utilized to solve this problem. However, there are only few studies designing torque compensation controllers based on power performances in different Speed Parts. It is a major challenge for a wind turbine generator (WTG) to achieve the satisfactory compensation performance in different Speed Parts. To tackle this challenge, this paper proposes a gain scheduled torque compensation strategy for permanent magnet synchronous generator (PMSG) based wind turbines. Our main idea is to improve the anti-disturbance ability for frequency regulation by compensating torque based on WTG speed Parts. To achieve higher power reserve in each Speed Part, an enhanced deloading method of WTG is proposed. We develop a new small-signal dynamic model through analyzing the steady-state performances of deloaded WTG in the whole range of wind speed. Subsequently, H theory is leveraged in designing the gain scheduled torque compensation controller to effectively suppress frequency fluctuation. Moreover, since torque compensation brings about untimely power adjustment in over-rated wind speed condition, the conventional speed reference of pitch control system is improved. Our simulation and experimental results demonstrate that the proposed strategy can significantly improve frequency stability and smoothen power fluctuation resulting from wind speed variations. The minimum of frequency deviation with the proposed strategy is improved by up to 0.16 Hz at over-rated wind speed. Our technique can also improve anti-disturbance ability in frequency domain and achieve power balance. Full article
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Open AccessArticle 3-Leg Inverter Control for 2-Phase Outer Rotor Coreless Torque Actuator in Hybrid Multi-D.O.F System
Energies 2018, 11(6), 1611; https://doi.org/10.3390/en11061611
Received: 31 March 2018 / Revised: 6 June 2018 / Accepted: 19 June 2018 / Published: 20 June 2018
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Abstract
Since an existing 3-phase inner rotor torque actuator (TA) has severe torque ripples, it is not appropriate for a gimbal system that requires precise position control. Therefore, a coreless TA is considered to eliminate the core causing torque ripples. In order to compensate
[...] Read more.
Since an existing 3-phase inner rotor torque actuator (TA) has severe torque ripples, it is not appropriate for a gimbal system that requires precise position control. Therefore, a coreless TA is considered to eliminate the core causing torque ripples. In order to compensate for several problems (e.g., problems of production structures and output degradation) when a coreless type is used, the final 2-phase outer rotor is proposed for the low vibration and high power TA in the gimbal system. To control the 2-phase TA applied to such the gimbal system, special inverter control methods, such as bi-directional drive for tilting control and control for output torque improvement, are required. The 2-phase 3-leg inverter is free of DC capacitor voltage unbalance compared to the 2-leg inverter, and is economical because it uses less power switches than the 4-leg inverter. Therefore, the 2-phase 3-leg inverter is applied to drive the 2-phase outer rotor coreless TA of a hybrid gimbal system, and it is verified through simulation. Full article
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Open AccessArticle Application of Synchrosqueezed Wavelet Transforms for Extraction of the Oscillatory Parameters of Subsynchronous Oscillation in Power Systems
Energies 2018, 11(6), 1525; https://doi.org/10.3390/en11061525
Received: 6 May 2018 / Revised: 31 May 2018 / Accepted: 7 June 2018 / Published: 12 June 2018
PDF Full-text (8177 KB) | HTML Full-text | XML Full-text
Abstract
The most classical subsynchronous oscillation (SSO) mode extraction methods have some shortcomings, such as lower mode identification and poor anti-noise properties. Thus, this paper proposes a new time-frequency analysis method, namely, synchrosqueezed wavelet transforms (SWT). SWT combines the advantages of empirical mode decomposition
[...] Read more.
The most classical subsynchronous oscillation (SSO) mode extraction methods have some shortcomings, such as lower mode identification and poor anti-noise properties. Thus, this paper proposes a new time-frequency analysis method, namely, synchrosqueezed wavelet transforms (SWT). SWT combines the advantages of empirical mode decomposition (EMD) and wavelet, which has the adaptability of EMD, and improve the ability of anti-mode mixing on EMD and wavelet. Thus, better anti-noise property and higher mode identification can be achieved. Firstly, the SSO signal is transformed by SWT and its time-frequency spectrum is obtained. Secondly, the attenuation characteristic of each intrinsic mode type (IMT) component in its time-frequency spectrum is analyzed by an automatic identification algorithm, and determine which IMT component needs reconstruction. After that, the selected IMT components with divergent characteristic are reconstructed. Thirdly, high-accuracy detection for mode parameter identification is achieved by the Hilbert transform (HT). Simulation and application examples prove the effectiveness of the proposed method. Full article
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Open AccessArticle Calculation of Hybrid Ionized Field of AC/DC Transmission Lines by the Meshless Local Petorv–Galerkin Method
Energies 2018, 11(6), 1521; https://doi.org/10.3390/en11061521
Received: 9 May 2018 / Revised: 31 May 2018 / Accepted: 31 May 2018 / Published: 12 June 2018
PDF Full-text (5267 KB) | HTML Full-text | XML Full-text
Abstract
To save land resources, the construction of the high-voltage direct current (HVDC) and high-voltage alternating current (HVAC) hybrid transmission lines in the same corridor is inevitable. To provide suggestions for the construction of the AC/DC parallel lines, the hybrid ionized field of AC/DC
[...] Read more.
To save land resources, the construction of the high-voltage direct current (HVDC) and high-voltage alternating current (HVAC) hybrid transmission lines in the same corridor is inevitable. To provide suggestions for the construction of the AC/DC parallel lines, the hybrid ionized field of AC/DC transmission lines was calculated by the meshless local Petorv–Galerkin (MLPG) method for the first time. In this method, the radius of local sub-domain is adjusted to the nodes close to the global boundary, but not exactly on the boundary. It can avoid the boundary integral, as well as having simplified calculation. The method was validated by comparing with measured results and calculation results. The MLPG method is beneficial to obtaining high-precision results by constructing the more complex shape function. Finally, a field distribution of the parallel line of about ±800 kV DC/500 kV AC was calculated. Moreover, the influence of different parallel spacing and AC voltage level on the hybrid ionized field was analyzed, which provides theoretical basis for real parallel lines design. Full article
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Open AccessArticle A New Diagnostic Algorithm for Multiple IGBTs Open Circuit Faults by the Phase Currents for Power Inverter in Electric Vehicles
Energies 2018, 11(6), 1508; https://doi.org/10.3390/en11061508
Received: 27 April 2018 / Revised: 5 June 2018 / Accepted: 8 June 2018 / Published: 10 June 2018
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Abstract
In order to simplify the application and improve diagnostic speed of the diagnostics, a novel method to diagnose multiple open circuit faults in insulated gate bipolar transistors (IGBTs) by three-phase currents for power inverter in electric vehicles is presented. The summation of currents
[...] Read more.
In order to simplify the application and improve diagnostic speed of the diagnostics, a novel method to diagnose multiple open circuit faults in insulated gate bipolar transistors (IGBTs) by three-phase currents for power inverter in electric vehicles is presented. The summation of currents with semi-period phase-difference is described in diagnostic variables with exploration of the current information in faulty condition. In contrast with plentiful existing methods which rely on the motor models and control parameters, this algorithm merely requires phase currents. Meanwhile, the normalized way based on the absolute phase currents and variable parameter moving average method are applied to improve the diagnostic speed and independence of load variation, which contributes to the real-time application in the electric vehicles. Experimental results, using a vector-controlled permanent magnet synchronous motor (PMSM) and digital signal processor MC56F8346, are presented to verify the algorithm effectiveness, showing many features, such as applicability for multiple open circuit faults, well-robustness against false alarms, briefness and agility for the diagnosis function. Full article
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Open AccessArticle Analytical Calculation for Multi-Infeed Interaction Factors Considering Control Modes of High Voltage Direct Current Links
Energies 2018, 11(6), 1506; https://doi.org/10.3390/en11061506
Received: 17 May 2018 / Revised: 1 June 2018 / Accepted: 6 June 2018 / Published: 8 June 2018
PDF Full-text (1924 KB) | HTML Full-text | XML Full-text
Abstract
The multi-infeed interaction factor (MIIF) is used extensively in indicating the degree of interaction among high-voltage direct current (HVDC) converters and is currently calculated by simulation methods according to the definition, or by using the equivalent impedance ratio method. The first method is
[...] Read more.
The multi-infeed interaction factor (MIIF) is used extensively in indicating the degree of interaction among high-voltage direct current (HVDC) converters and is currently calculated by simulation methods according to the definition, or by using the equivalent impedance ratio method. The first method is an experimental calculation method and the second method does not account for the effects of HVDC control modes. An analytical calculation method for MIIF considering control modes of HVDC links is proposed in this paper. First, the voltage variation of converter bus in the context of small disturbance is equated by using the bus impedance matrix. In this way the equations for the solution of MIIF considering HVDC control mode are obtained. Subsequently, based on two rational assumptions, the practical analytical calculation expression of MIIF is deduced in detail. The MIIF calculation method proposed in this paper is an improvement of the equivalent impedance ratio method and reflects the main influencing factors of voltage interaction including HVDC control modes. Moreover, the derived analytical expression can give a fundamental insight into parameter dependencies of voltage interaction. Finally, the validity and accuracy of the proposed approach are demonstrated in both dual-infeed HVDC system and actual large-scale power grid. Full article
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Open AccessArticle Study on Reduced Cost of Non-Salient Machine System Using MTPA Angle Pre-Compensation Method Based on EEMF Sensorless Control
Energies 2018, 11(6), 1425; https://doi.org/10.3390/en11061425
Received: 31 March 2018 / Revised: 31 May 2018 / Accepted: 31 May 2018 / Published: 2 June 2018
PDF Full-text (5702 KB) | HTML Full-text | XML Full-text
Abstract
When a consumer chooses a product, one of the most important considerations is price. Therefore, cost reduction is the most important factor when manufacturing a product. This paper has applied the sensorless method to remove the position sensor in an interior permanent magnet
[...] Read more.
When a consumer chooses a product, one of the most important considerations is price. Therefore, cost reduction is the most important factor when manufacturing a product. This paper has applied the sensorless method to remove the position sensor in an interior permanent magnet synchronous motor (IPMSM) system and examined the way to reduce the use of the trigonometric function in order to lower the dependency on a high-end CPU. A sensorless method has been studied to use an extended electromotive force (EEMF) that can increase the degree of freedom of the motor in the IPMSM system. In addition, an observer is applied to the estimated position to stabilize the system. Furthermore, many trigonometric functions are used for driving the IPMSM. Since this trigonometric function requires decimal point operations, that requires a lot of computation time and a high-performance CPU. Therefore, this paper proposes a new method to pre-compensate the maximum torque per ampere (MTPA) angle as a way to reduce the use of the trigonometric functions which makes a high-spec CPU unnecessary. Simulations and experiments are conducted to verify the proposed control algorithm. Full article
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Open AccessArticle Improved Synchronous Machine Rotor Design for the Easy Assembly of Excitation Coils Based on Surrogate Optimization
Energies 2018, 11(5), 1311; https://doi.org/10.3390/en11051311
Received: 10 April 2018 / Revised: 4 May 2018 / Accepted: 16 May 2018 / Published: 21 May 2018
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Abstract
This paper introduces a new rotor design for the easy insertion and removal of rotor windings. The shape of the rotor is optimized based on a surrogate method in order to achieve low power loss under the maximum power output. The synchronous machine
[...] Read more.
This paper introduces a new rotor design for the easy insertion and removal of rotor windings. The shape of the rotor is optimized based on a surrogate method in order to achieve low power loss under the maximum power output. The synchronous machine with the new rotor is evaluated in 2-D finite element software and validated by experiments. This rotor shows great potential for reducing the maintenance and repair costs of synchronous machines, making it particularly suited for low-cost mass production markets including gen-sets, steam turbines, wind power generators, and hybrid electric vehicles. Full article
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Open AccessArticle Hybrid Electric Powertrain with Fuel Cells for a Series Vehicle
Energies 2018, 11(5), 1294; https://doi.org/10.3390/en11051294
Received: 18 April 2018 / Revised: 11 May 2018 / Accepted: 15 May 2018 / Published: 18 May 2018
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Abstract
Recent environmental and climate change issues make it imperative to persistently approach research into the development of technologies designed to ensure the sustainability of global mobility. At the European Union level, the transport sector is responsible for approximately 28% of greenhouse gas emissions,
[...] Read more.
Recent environmental and climate change issues make it imperative to persistently approach research into the development of technologies designed to ensure the sustainability of global mobility. At the European Union level, the transport sector is responsible for approximately 28% of greenhouse gas emissions, and 84% of them are associated with road transport. One of the most effective ways to enhance the de-carbonization process of the transport sector is through the promotion of electric propulsion, which involves overcoming barriers related to reduced driving autonomy and the long time required to recharge the batteries. This paper develops and implements a method meant to increase the autonomy and reduce the battery charging time of an electric car to comparable levels of an internal combustion engine vehicle. By doing so, the cost of such vehicles is the only remaining significant barrier in the way of a mass spread of electric propulsion. The chosen method is to hybridize the electric powertrain by using an additional source of fuel; hydrogen gas stored in pressurized cylinders is converted, in situ, into electrical energy by means of a proton exchange membrane fuel cell. The power generated on board can then be used, under the command of a dedicated management system, for battery charging, leading to an increase in the vehicle’s autonomy. Modeling and simulation results served to easily adjust the size of the fuel cell hybrid electric powertrain. After optimization, an actual fuel cell was built and implemented on a vehicle that used the body of a Jeep Wrangler, from which the thermal engine, associated subassemblies, and gearbox were removed. Once completed, the vehicle was tested in traffic conditions and its functional performance was established. Full article
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Open AccessArticle IGBT Dynamic Loss Reduction through Device Level Soft Switching
Energies 2018, 11(5), 1182; https://doi.org/10.3390/en11051182
Received: 30 March 2018 / Revised: 3 May 2018 / Accepted: 7 May 2018 / Published: 8 May 2018
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Abstract
Due to its low conduction loss, hence high current ratings, as well as low cost, Silicon Insulated Gate Bipolar Transistor (Si IGBT) is widely used in high power applications. However, its switching frequency is generally low because of relatively large switching losses. Silicon
[...] Read more.
Due to its low conduction loss, hence high current ratings, as well as low cost, Silicon Insulated Gate Bipolar Transistor (Si IGBT) is widely used in high power applications. However, its switching frequency is generally low because of relatively large switching losses. Silicon carbide Metal-Oxide-Semiconductor Field-Effect Transistor (SiC MOSFET) is much more superior due to their fast switching speed, which is determined by the internal parasitic capacitance instead of the stored charges, like the IGBT. By the combination of SiC MOSFET and Si IGBT, this paper presents a novel series hybrid switching method to achieve IGBT’s dynamic switching loss reduction by switching under Zero Voltage Hard Current (ZVHC) turn-on and Zero Current Hard Voltage (ZCHV) turn-off conditions. Both simulation and experimental results of IGBT are carried out, which shows that the soft switching of IGBT has been achieved both in turn-on and turn-off period. Thus 90% turn-on loss and 57% turn-off loss are reduced. Two different IGBTs’ test results are also provided to study the modulation parameter’s effect on the turn-off switching loss. Furthermore, with the consideration of voltage and current transient states, a new soft switching classification is proposed. At last, another improved modulation and Highly Efficient and Reliable Inverter Concept (HERIC) inverter are given to validate the effectiveness of the device level hybrid soft switching method application. Full article
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Open AccessArticle Optimal Design of a High Efficiency LLC Resonant Converter with a Narrow Frequency Range for Voltage Regulation
Energies 2018, 11(5), 1124; https://doi.org/10.3390/en11051124
Received: 24 March 2018 / Revised: 15 April 2018 / Accepted: 24 April 2018 / Published: 2 May 2018
PDF Full-text (5702 KB) | HTML Full-text | XML Full-text
Abstract
As a key factor in the design of a voltage-adjustable LLC resonant converter, frequency regulation range is very important to the optimization of magnetic components and efficiency improvement. This paper presents a novel optimal design method for LLC resonant converters, which can narrow
[...] Read more.
As a key factor in the design of a voltage-adjustable LLC resonant converter, frequency regulation range is very important to the optimization of magnetic components and efficiency improvement. This paper presents a novel optimal design method for LLC resonant converters, which can narrow the frequency variation range and ensure high efficiency under the premise of a required gain achievement. A simplified gain model was utilized to simplify the calculation and the expected efficiency was initially set as 96.5%. The restricted area of parameter optimization design can be obtained by taking the intersection of the gain requirement, the efficiency requirement, and three restrictions of ZVS (Zero Voltage Switch). The proposed method was verified by simulation and experiments of a 150 W prototype. The results show that the proposed method can achieve ZVS from full-load to no-load conditions and can reach 1.6 times the normalized voltage gain in the frequency variation range of 18 kHz with a peak efficiency of up to 96.3%. Moreover, the expected efficiency is adjustable, which means a converter with a higher efficiency can be designed. The proposed method can also be used for the design of large-power LLC resonant converters to obtain a wide output voltage range and higher efficiency. Full article
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Open AccessArticle Triple Line-Voltage Cascaded VIENNA Converter Applied as the Medium-Voltage AC Drive
Energies 2018, 11(5), 1079; https://doi.org/10.3390/en11051079
Received: 5 April 2018 / Revised: 23 April 2018 / Accepted: 24 April 2018 / Published: 27 April 2018
PDF Full-text (5183 KB) | HTML Full-text | XML Full-text
Abstract
A novel rectifier based on a triple line-voltage cascaded VIENNA converter (LVC-VC) was proposed. Compared to the conventional cascaded H-bridge converters, the switch voltage stress is lower, and the numbers of switches and dc capacitors are fewer under similar operating conditions in the
[...] Read more.
A novel rectifier based on a triple line-voltage cascaded VIENNA converter (LVC-VC) was proposed. Compared to the conventional cascaded H-bridge converters, the switch voltage stress is lower, and the numbers of switches and dc capacitors are fewer under similar operating conditions in the proposed new multilevel converter. The modeling and control for the LVC-VC ware presented. Based on the analysis of the operation principle of the new converter, the power factor correction of the proposed converter was realized by employing a traditional one-cycle control strategy. The minimum average value and maximum harmonic components of the dc-link voltages of the three VIENNA rectifier modules ware calculated. Three VIENNA dc-link voltages were unbalanced under the unbalanced load conditions, so the zero sequence current was injected to the three inner currents for balancing three VIENNA dc-link voltages. Simulation and the results of the experiment verified the availability of the new proposed multilevel converter and the effectiveness of the corresponding control strategy applied. Full article
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Open AccessArticle New Switched-Dual-Source Multilevel Inverter for Symmetrical and Asymmetrical Operation
Energies 2018, 11(4), 984; https://doi.org/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
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Open AccessArticle A Hybrid Filtering Technique-Based PLL Targeting Fast and Robust Tracking Performance under Distorted Grid Conditions
Energies 2018, 11(4), 973; https://doi.org/10.3390/en11040973
Received: 28 March 2018 / Revised: 11 April 2018 / Accepted: 12 April 2018 / Published: 18 April 2018
PDF Full-text (10896 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
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Open AccessArticle Sensorless Control of Dual-Active-Bridge Converter with Reduced-Order Proportional-Integral Observer
Energies 2018, 11(4), 931; https://doi.org/10.3390/en11040931
Received: 26 March 2018 / Revised: 9 April 2018 / Accepted: 10 April 2018 / Published: 13 April 2018
PDF Full-text (3276 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
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Open AccessArticle Novel Cathode Design to Improve the ESD Capability of 600 V Fast Recovery Epitaxial Diodes
Energies 2018, 11(4), 832; https://doi.org/10.3390/en11040832
Received: 1 February 2018 / Revised: 8 March 2018 / Accepted: 30 March 2018 / Published: 4 April 2018
PDF Full-text (8979 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
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Open AccessArticle An Algorithm for Online Inertia Identification and Load Torque Observation via Adaptive Kalman Observer-Recursive Least Squares
Energies 2018, 11(4), 778; https://doi.org/10.3390/en11040778
Received: 29 January 2018 / Revised: 22 March 2018 / Accepted: 26 March 2018 / Published: 28 March 2018
PDF Full-text (91556 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
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Open AccessArticle An Efficient Hybrid Filter-Based Phase-Locked Loop under Adverse Grid Conditions
Energies 2018, 11(4), 703; https://doi.org/10.3390/en11040703
Received: 25 February 2018 / Revised: 19 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
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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
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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
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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; https://doi.org/10.3390/en11040692
Received: 2 March 2018 / Revised: 15 March 2018 / Accepted: 16 March 2018 / Published: 21 March 2018
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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
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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
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Open AccessArticle A Fast-Transient Output Capacitor-Less Low-Dropout Regulator Using Active-Feedback and Current-Reuse Feedforward Compensation
Energies 2018, 11(3), 688; https://doi.org/10.3390/en11030688
Received: 20 February 2018 / Revised: 10 March 2018 / Accepted: 15 March 2018 / Published: 19 March 2018
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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
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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
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Open AccessArticle A Hybrid Excited Machine with Flux Barriers and Magnetic Bridges
Energies 2018, 11(3), 676; https://doi.org/10.3390/en11030676
Received: 23 January 2018 / Revised: 11 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
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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
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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
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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; https://doi.org/10.3390/en11030602
Received: 31 January 2018 / Revised: 20 February 2018 / Accepted: 24 February 2018 / Published: 9 March 2018
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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
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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
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Open AccessArticle Analysis of Non-Isolated Multi-Port Single Ended Primary Inductor Converter or Standalone Applications
Energies 2018, 11(3), 539; https://doi.org/10.3390/en11030539
Received: 29 November 2017 / Revised: 3 February 2018 / Accepted: 5 February 2018 / Published: 2 March 2018
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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
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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
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Open AccessArticle Line-to-Line Fault Analysis and Location in a VSC-Based Low-Voltage DC Distribution Network
Energies 2018, 11(3), 536; https://doi.org/10.3390/en11030536
Received: 24 January 2018 / Revised: 23 February 2018 / Accepted: 26 February 2018 / Published: 2 March 2018
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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
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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
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Open AccessArticle Adaptive Controller of the Major Functions for Controlling a Drive System with Elastic Couplings
Energies 2018, 11(3), 531; https://doi.org/10.3390/en11030531
Received: 23 January 2018 / Revised: 23 February 2018 / Accepted: 27 February 2018 / Published: 1 March 2018
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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
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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
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Open AccessArticle A Dual Monitoring Technique to Detect Power Quality Transients Based on the Fourth-Order Spectrogram
Energies 2018, 11(3), 503; https://doi.org/10.3390/en11030503
Received: 1 February 2018 / Revised: 13 February 2018 / Accepted: 22 February 2018 / Published: 27 February 2018
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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
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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
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Open AccessArticle Analysis of Switching Transients during Energization in Large Offshore Wind Farms
Energies 2018, 11(2), 470; https://doi.org/10.3390/en11020470
Received: 24 January 2018 / Revised: 13 February 2018 / Accepted: 19 February 2018 / Published: 23 February 2018
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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
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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
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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; https://doi.org/10.3390/en11020443
Received: 18 November 2017 / Revised: 6 February 2018 / Accepted: 11 February 2018 / Published: 16 February 2018
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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
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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
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Open AccessArticle On the Performance Optimization of Two-Level Three-Phase Grid-Feeding Voltage-Source Inverters
Energies 2018, 11(2), 400; https://doi.org/10.3390/en11020400
Received: 11 January 2018 / Revised: 31 January 2018 / Accepted: 5 February 2018 / Published: 9 February 2018
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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
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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
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Open AccessArticle Step-Up Partial Power DC-DC Converters for Two-Stage PV Systems with Interleaved Current Performance
Energies 2018, 11(2), 357; https://doi.org/10.3390/en11020357
Received: 1 December 2017 / Revised: 25 January 2018 / Accepted: 30 January 2018 / Published: 3 February 2018
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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
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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
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Open AccessArticle Improved Finite-Control-Set Model Predictive Control for Cascaded H-Bridge Inverters
Energies 2018, 11(2), 355; https://doi.org/10.3390/en11020355
Received: 25 December 2017 / Revised: 29 January 2018 / Accepted: 31 January 2018 / Published: 2 February 2018
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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
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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
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Open AccessArticle Icing Condition Assessment of In-Service Glass Insulators Based on Graphical Shed Spacing and Graphical Shed Overhang
Energies 2018, 11(2), 318; https://doi.org/10.3390/en11020318
Received: 10 January 2018 / Revised: 27 January 2018 / Accepted: 29 January 2018 / Published: 2 February 2018
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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
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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
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Open AccessArticle Development of Automotive Permanent Magnet Alternator with Fully Controlled AC/DC Converter
Energies 2018, 11(2), 274; https://doi.org/10.3390/en11020274
Received: 18 November 2017 / Revised: 8 January 2018 / Accepted: 9 January 2018 / Published: 24 January 2018
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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
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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
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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; https://doi.org/10.3390/en11010209
Received: 22 December 2017 / Revised: 2 January 2018 / Accepted: 8 January 2018 / Published: 15 January 2018
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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
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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
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Open AccessArticle Stochastic Model Predictive Fault Tolerant Control Based on Conditional Value at Risk for Wind Energy Conversion System
Energies 2018, 11(1), 193; https://doi.org/10.3390/en11010193
Received: 20 December 2017 / Revised: 5 January 2018 / Accepted: 10 January 2018 / Published: 12 January 2018
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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
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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
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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; https://doi.org/10.3390/en11010192
Received: 12 December 2017 / Revised: 6 January 2018 / Accepted: 10 January 2018 / Published: 12 January 2018
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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
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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
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Open AccessArticle A Free-Piston Linear Generator Control Strategy for Improving Output Power
Energies 2018, 11(1), 135; https://doi.org/10.3390/en11010135
Received: 9 December 2017 / Revised: 1 January 2018 / Accepted: 2 January 2018 / Published: 5 January 2018
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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
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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
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Open AccessArticle High Gain Boost Interleaved Converters with Coupled Inductors and with Demagnetizing Circuits
Energies 2018, 11(1), 130; https://doi.org/10.3390/en11010130
Received: 15 November 2017 / Revised: 13 December 2017 / Accepted: 3 January 2018 / Published: 5 January 2018
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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
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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
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Open AccessArticle Numerical Simulations for a Partial Disk MHD Generator Performance
Energies 2018, 11(1), 127; https://doi.org/10.3390/en11010127
Received: 15 November 2017 / Revised: 29 December 2017 / Accepted: 31 December 2017 / Published: 4 January 2018
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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
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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
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Open AccessArticle Switched Polytopic Controller Applied on a Positive Reconfigurable Power Electronic Converter
Energies 2018, 11(1), 116; https://doi.org/10.3390/en11010116
Received: 17 November 2017 / Revised: 27 December 2017 / Accepted: 29 December 2017 / Published: 3 January 2018
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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
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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
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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; https://doi.org/10.3390/en11010101
Received: 12 December 2017 / Revised: 28 December 2017 / Accepted: 31 December 2017 / Published: 2 January 2018
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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
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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
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