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 Subjects -> ELECTRONICS (Total: 156 journals)
 IEEE Transactions on Power Electronics   [SJR: 3.005]   [H-I: 160]   [56 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 0885-8993    Published by IEEE  [191 journals]
• IEEE Power Electronics Society
• PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• IEEE Power Electronics Society
• PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• A Generic and Unified Global-Gyrator Model of Switched-Resonator
Converters
• Authors: Alon Cervera;Mor Mordechai Peretz;Shmuel Ben-Yaakov;
Pages: 8945 - 8952
Abstract: A generic algebraic model of switched-resonator converters is developed and demonstrated by published and new converter configurations data. The model hinges on a newly introduced multiport global-gyrator matrix, of which the classical two-port gyrator is a private case. The main attribute of the skew-symmetrical as well as a Toeplitz global-gyrator matrix is that it expresses the magnitude and directions of the currents as a linear function of the port voltages with a constant gyration factor. The model is verified by previously published data, as well as new experimental and simulation results.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Enhancing the Reliability of Modular Multilevel Converters Using Neutral
Shift
• Authors: Jakub Kucka;Dennis Karwatzki;Axel Mertens;
Pages: 8953 - 8957
Abstract: This letter presents an approach for modular multilevel converters that enables a stable operation with failed nonredundant modules. This is achieved by using a neutral shift with a dedicated power feed-forward control. The feasibility of the approach is verified by simulation.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Hybrid Modulation Concept for Five-Level Active-Neutral-Point-Clamped
Converter
• Authors: Chushan Li;Shuai Wang;Qingxin Guan;David Xu;
Pages: 8958 - 8962
Abstract: In this letter, a hybrid modulation concept consisting of three-level space vector modulation (3L-SVM) and phase-shifted pulse width modulation (PS-PWM) is proposed for five-level active-neutral-point-clamped (5L-ANPC) converter. Under this concept, a simpler 3L-SVM plus PS-PWM scheme is applied to realize 5L modulation, instead of using complex 5L-SVM. The control of neutral voltage, flying capacitor voltage, and the improved dc voltage utilization are all implemented. With the help of the proposed concept, well-developed 3L-SVM schemes can be directly applied to the 5L-ANPC converter, which significantly simplify the gating signal generation. This concept can also be applied to other hybrid clamped 5L converters with two dc-link capacitors. It provides a unique solution, which utilize lower level SVM scheme to control higher level multilevel converters.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Accurate Calorimetric Switching Loss Measurement for 900 V 10 m
$\Omega$ SiC mosfets
• Authors: Jon Azurza Anderson;Christoph Gammeter;Lukas Schrittwieser;Johann W. Kolar;
Pages: 8963 - 8968
Abstract: This letter presents and evaluates three accurate ($\pm$ 20 %) calorimetric switching loss measurement methods, which are capable of measuring hard- and soft-switching losses at high speed (20–25 min/point) compared to other calorimetric methods. A comprehensive switching loss measurement data accuracy analysis is done, setting the benchmark for the accuracy analysis of switching loss data. The high accuracy in the switching loss data is obtained by a high ratio of switching losses to total measured losses in the Device Under Test. This is achieved by using a full-bridge configuration, where the conduction losses are reduced up to 80% in the Device Under Test by utilizing the duty cycle as an additional degree of freedom compared to a half-bridge configuration. Furthermore, the proposed calorimetric methods yield more reliable switching loss data than electrical methods, particularly than the double pulse test. Switching loss data are presented for the 900 V, 75 A, 10 m$\Omega$ SiC mosfets from CREE, that are one of the first discrete SiC mosfets to come with a TO-247-4 package.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• An Adaptive High-Precision OCP Control Scheme for Flyback AC/DC
Converters
• Authors: Qiang Wu;Zhangming Zhu;
Pages: 8969 - 8973
Abstract: Flyback topology has been widely used in low-power applications due to its simplicity, wide input voltage range, low cost, and low standby power. However, conventional over current protection (OCP) control scheme in flyback converters cannot meet the high precision constant current (CC) requirement in battery charger and LED applications. The proposed adaptive high-precision OCP control scheme can be widely used in ac/dc flyback converters to improve their CC accuracy. It consists of an OCP-Comp circuit and a Vpump circuit to detect the primary current in current cycle and adjust it in next cycle adaptively. The proposed OCP control scheme has been implemented in a controller IC adding no extra pin and achieves a significant improvement in output current accuracy compared to conventional OCP schemes. Test results show that the output current variation of the proposed prototype is less than ±0.6% when the input line voltage changes from 85 to 265 Vac.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• New Tunable Piezoelectric Transformers and Their Application in
DC–DC Converters
• Authors: Mudit Khanna;Rolando Burgos;Qiong Wang;Khai D. T. Ngo;Alfredo Vazquez Carazo;
Pages: 8974 - 8978
Abstract: This paper introduces a new tunable piezoelectric transformer (TPT) and demonstrates its operation in a dc–dc converter application. Piezoelectric transformers (PTs) have been conventionally used in high-voltage, low-power applications such as electronic ballasts. Recently, radial type PTs have been developed for higher power ac–dc and dc–dc step down applications. Based on the latter, a new TPT has been developed featuring an auxiliary secondary terminal to control the voltage gain of the transformer. This results in some exciting characteristics from a dc–dc converter standpoint, like an adjustable frequency response of the TPT, and fixed frequency control of the converter with no-cross talk between the primary and secondary in the control circuit. This paper introduces the design concept behind TPT-based dc–dc converters, and proposes a control scheme for their implementation. Experimental results with a 30 W, 220:55 V converter unit are shown to validate these concepts.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• A Transition Arm Modular Multilevel Universal Pulse-Waveform Generator for
Electroporation Applications
• Authors: Mohamed A. Elgenedy;Ahmed Darwish;Shehab Ahmed;Barry W. Williams;
Pages: 8979 - 8991
Abstract: High-voltage (HV) pulses are used in electroporation to subject pulsed electric field (PEF) onto a sample under treatment. Pulse-waveform shape, voltage magnitude, pulse duration, and pulse repetition rate are the basic controllable variables required for particular PEF application. In practice, a custom-made pulse generator is dedicated for each PEF application with limited flexibility in changing these variables. In this paper, a universal pulse-waveform generator (UPG) is proposed, where the controller software algorithm can manipulate a basic generated multilevel pulse waveform to emulate many different PEF pulse waveforms. The commonly used PEF HV pulse waveforms can be generated as bipolar or monopolar with controllable pulse durations, repetition times, and voltage magnitudes. The UPG has the ability to generate multilevel pulses that have controllable $dv/dt$, which allows reduction of the electromagnetic interference generated by the converter. The UPG topology is based on half-bridge modular multilevel converter (HB-MMC) cells forming two transition arms in conjunction with two bistate arms, together creating an H-bridge. The HB-MMC cell capacitors provide a controllable energy source which charge from the dc input supply and discharge across the load, while the two bistate arms allow charging the HB-MMC cell capacitors. Hence, the UPG topology offers modularity, redundancy, and scalability. The HB-MMC individual cell capacitance is low and the cell voltages are balanced by employing the sorting and rotating algorithm used in conventional HB-MMC topologies for HV dc transmission applications. The viability of the proposed UPG converter is validated by MATLAB/Simulink simulation and scaled-down experimentation.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Design and Analysis of a Novel ZVZCT Boost Converter With Coupling Effect
• Authors: Xi Zhang;Wei Qian;Zhe Li;
Pages: 8992 - 9000
Abstract: In this paper, a new zero voltage zero current transition (ZVZCT) boost DC–DC converter using a coupled inductor is proposed. This topology provides the main switch ZVZCT for the turn-on and zero voltage switching (ZVS) for the turn-off. Moreover, the auxiliary switch turns on at zero current switching (ZCS) and turns off at ZVS. The main diode turns on with ZVT and turns off with ZCS, and other diodes also operate under soft-switching conditions. Besides, due to the coupling effect, the proposed converter improves efficiency additionally since resonant energy in the resonance tank could be transferred to the output, and the circulating current can be limited as well. The soft-switching can be realized in almost all the load rang. In this design, there always exist energy releasing circuits to conduct magnetic flux leakage currents, such that the surge currents are eliminated and switch current stress can be accordingly reduced. All the devices resonate in a unique direction within less than half of a resonance period, so power losses with respect to the resonance can be decreased. In this paper, the converter design and operation principles of the converter are given. It also has been verified by a 1-kW experimental prototype with switching frequency of 100 kHz, and the related experimental results are presented.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Isolated Bidirectional Grid-Tied Three-Phase AC–DC Power Conversion
Using Series-Resonant Converter Modules and a Three-Phase Unfolder
• Authors: W. Warren Chen;Regan Zane;Luca Corradini;
Pages: 9001 - 9012
Abstract: Power-bidirectional converters are used to integrate energy storage with both dc and ac distribution grids. A modular bidirectional dc–dc converter system consisting of multiple dual-bridge series resonant converter (DBSRC) modules can be reconfigured to extend the system operating range. This paper proposes a modular three-phase ac–dc converter system by adding a line-frequency unfolder to series-connected outputs of two DBSRC modules. The DBSRC modules are controlled to output time-varying currents, which are then reconstructed into sinusoidal ac currents by the unfolder. Compared with a conventional two-stage system with a dc–dc converter and a two-level voltage-source inverter, the DBSRC–unfolder system has smaller dc-link capacitance, negligible unfolder switching loss, reduced line filter size, and faster dynamic response. The system operation and performance are verified on a 1-kW experimental prototype.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Single-Phase PLLs: A Review of Recent Advances
• Authors: Saeed Golestan;Josep M. Guerrero;Juan C. Vasquez;
Pages: 9013 - 9030
Abstract: Single-phase phase-locked loops (PLLs) are popular for the synchronization and control of single-phase grid-connected converters. They are also widely used for monitoring and diagnostic purposes in the power and energy areas. In recent years, a large number of single-phase PLLs with different structures and properties have been proposed in the literature. The main aim of this paper is to provide a review of these PLLs. To this end, the single-phase PLLs are first classified into two major categories: 1) power-based PLLs and 2) quadrature signal generation-based PLLs. The members of each category are then described and their pros and cons are discussed. This paper provides a deep insight into characteristics of different single-phase PLLs, and therefore, can be considered as a reference for researchers and engineers.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Reactive Power Compensation and Negative-Sequence Current Suppression
System for Electrical Railways With YNvd-Connected Balance
Transformer—Part II: Implementation and Verification
• Authors: Bin Xie;Zhiwen Zhang;Yong Li;Sijia Hu;Longfu Luo;Christian Rehtanz;Olav Krause;
Pages: 9031 - 9042
Abstract: This part mainly focuses on the implementation and verification of the reactive power compensation and negative-sequence current suppression system with YNvd-connected balance transformer, by means of simulation and experiment. The system model is presented, and a current control method, which explores the dissipation characteristic of the proposed system under two-phase rotating frame, is analyzed. Then, a stability analysis of this control is made, considering the deviations of system parameters and the time delay caused by the low-pass filter. Besides, dc-link overall control and balance control are investigated, and the self-balance ability of multiple dc links is briefly discussed. Both the simulation and experimental results verify the effectiveness of the proposed system topology, compensation strategy, and control method.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• A Bridge-Type Fault Current Limiter for Energy Management of AC/DC
Microgrids
Pages: 9043 - 9050
Abstract: This paper proposes a novel structure for fault current limiter (FCL), which not only controls the magnitude of fault current, but also is enable to power management in normal and fault condition of utility. The main capabilities of the proposed structure, which is able to connect both ac and dc systems, are controlling the dc reactor current for fault current magnitude control, and management and control of power flow from ac system to dc system. A boost converter is utilized in the proposed structure, that its output is connected to a dc bus, in order to control the dc reactor current. The proposed FCL, which ensures a high protection level of the system, has no impact on utility voltage and load currents. A boost converter is utilized to provide an almost sinusoidal input current. The simulation and experimental results are presented to clarify the theory and feasibility of the proposed FCL, which manifest simple structure of the circuit and show feasibility of the proposed FCL.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Analysis and Implementation of a High-Performance-Integrated KY Converter
• Authors: Ying Zhang;Dan Li;Hao Lu;Shiquan Fan;Zeqiang Chen;Yan Wang;Li Geng;
Pages: 9051 - 9064
Abstract: Boost converter often exhibits large output voltage ripples and slow transient response due to the pulsating output capacitor current and the right-half-plane zero in transfer function from duty ratio to output voltage. On the contrary, a KY converter shows small output voltage ripples and fast transient response compared with the boost converter thanks to its buck-converter-like characteristics. In this study, a comprehensive study of an integrated KY converter considering parasitic resistance is presented as design guidelines for its IC implementation, and various aspects of KY converter versus boost converter are also analyzed to show its advantages. In particular, optimum transistor sizes, power losses, and output voltage ripples are analyzed in depth. The designs of power components including energy-transferring capacitor, inductor, and filter capacitor are discussed. Theoretical derivations of load and line regulations are also provided. The designed KY converter has been fabricated with standard 0.18-µm CMOS process and the total chip area is 1.93 mm2 including pads. The output voltage is 2.5 V with the regulated supply voltage ranging from 1.55 to 1.8 V, at switching frequency of 1 MHz. The output voltage ripples are 10 mV. Maximum efficiency of 95.7% is obtained at load current of 55 mA and supply voltage of 1.8 V. Efficiency is no less than 92.9% for load current as low as 30 mA. Even with simple compensation scheme employed, the output voltage settles within 48 µs when loading a step current of 150 mA.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Selective Compensation of Distortion, Unbalanced and Reactive Power of a
Thyristor-Controlled LC -Coupling Hybrid Active Power Filter (TCLC-HAPF)
• Authors: Lei Wang;Chi-Seng Lam;Man-Chung Wong;
Pages: 9065 - 9077
Abstract: When the load generated harmonic, unbalanced, and reactive power is beyond the limited capacity of a thyristor-controlled LC-coupling hybrid active power filter (TCLC-HAPF), the TCLC-HAPF with the conventional control methods cannot provide satisfactory compensation performance. In this paper, a selective compensation control method of harmonic distortion, unbalanced and reactive power of the TCLC-HAPF is proposed, which can function even at different voltage conditions (e.g., voltage dip, voltage fault, etc.). First, the proposed control method decomposes the load power into fundamental positive-sequence reactive power, fundamental negative-sequence power (unbalanced power), and harmonic power. Then, the decomposed reactive, unbalanced, and harmonic power can be selectively or fully compensated based on the capacity of the TCLC-HAPF. Finally, simulation and experimental results are provided to verify the effectiveness of the proposed selective compensation control method for the TCLC-HAPF.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• An Active Trap Filter for Switching Harmonic Attenuation of
Low-Pulse-Ratio Inverters
• Authors: Haofeng Bai;Xiongfei Wang;Poh Chiang Loh;Frede Blaabjerg;
Pages: 9078 - 9092
Abstract: Switching harmonic attenuation has always been challenging for inverters used in high-power conversion applications, where ratio of switching to fundamental frequency is low. Addition of multiple LC-trap filters is no doubt a feasible cost-effective method, which has increasingly been used, but generally susceptible to filter parameter variations and harmonic resonances. This paper hence presents an alternative active trap filter (ATF), based on a series-LC-filtered inverter, for attenuating switching harmonics in a flexible, while yet not cost burdensome, approach. A direct impedance synthesis method has also been proposed for the ATF to better enforce its active switching harmonic bypassing ability. Compared with conventional schemes for controlling active power filters, the proposed method is more readily implemented, since it requires neither current reference generation nor high-bandwidth current control loop. Moreover, the use of a series LC filter at its ac side helps the ATF to reduce its inverter voltage and power ratings. Compensated frequency range of the ATF can hence be enlarged by using a comparably higher switching frequency and a proper step-by-step design procedure to be presented in this paper. Simulation and experimental results have confirmed the design procedures, and hence expected performance of the ATF.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Extension of Soft-Switching Region of Dual-Active-Bridge Converter by a
Tunable Resonant Tank
• Authors: M. Yaqoob;K. H. Loo;Y. M. Lai;
Pages: 9093 - 9104
Abstract: Hard-switching-induced switching loss can contribute significantly to the power loss of an isolated bidirectional dual-active-bridge (DAB) dc–dc converter operating at high frequency. An $LC$-type series resonant DAB converter based on a switch-controlled-inductor (SCI) is proposed to mitigate the loss arising from hard switching under wide-range variations in output voltage and current. Zero-voltage switching is achieved at the primary side (high voltage), while at the secondary side (low voltage), zero-current switching is preferred to reduce excessive ringing due to circulating current and switching loss. In order to achieve reduced conduction loss, a nominal operating point is chosen where the root-mean-square resonant tank current is the minimum. To validate the proposed topology and modulation scheme, an $LC$-type series resonant DAB converter based on SCI operating at 100 kHz is designed to interface a 400-V dc bus to a supercapacitor-based energy storage. Simulation and experimental results validate the effectiveness of the proposed topology for charging/discharging a supercapacitor with an output voltage variation of between 10 and 48 V and a maximum rated power of 480 W. A maximum efficiency of 94.6% is achieved using the proposed topology and modulation scheme.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Analysis of the Behavior of Undamped and Unstable High-Frequency Resonance
in a DFIG System
• Authors: Yipeng Song;Frede Blaabjerg;
Pages: 9105 - 9116
Abstract: As the wind power generation develops, the doubly fed induction generator (DFIG) based wind power system may suffer subsynchronous resonance and high-frequency resonance (HFR) in the series and parallel compensated weak network. The principle and frequency of HFR have been discussed using the Bode diagram as an analysis tool. However, the HFR can be categorized into two different types: undamped HFR (which exists in steady state) and unstable HFR (which eventually results in complete instability and divergence), both of them are not investigated before. Since both the undamped HFR and unstable HFR are critical to the output wind power quality as well as the safe and reliable operation of the DFIG system, it is meaningful to discuss them using the Nyquist criterion from two perspectives: 1) determining either the undamped HFR or the unstable HFR occurs; and 2) estimating the amplitude of the undamped HFR. The influence factors, including the weak network shunt capacitance and the current PI controller parameters, are discussed when estimating the amplitude of the undamped HFR. The experimental and simulation results of a 7.5 kW down-scaled DFIG setup are provided to validate the analysis of the undamped HFR and unstable HFR.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• A Control Approach for a Small-Scale PMSG-Based WECS in the Whole Wind
Speed Range
Pages: 9117 - 9130
Abstract: In this paper, an overall power control strategy is proposed for control of a fixed-pitch small-scale wind energy conversion system operating at both underrated and overrated wind speeds. At underrated wind speeds, the dynamical behavior of the rotor is considered, and the optimal reference torque is generated without the need of wind speed sensors through a robust variable structure observer with the aim of maximum power point tracking. At overrated wind speed, the flux-weakening strategy is invoked to let the machine exploit maximum electrical torque under given current and voltage constraints. As a new approach, the optimal reference flux magnitude together with a reference torque angle is provided by online numerically solving an optimization problem in the whole wind speed range. Moreover, a space-vector-modulation -based direct torque control (SVM-DTC) is used to track the provided references for flux magnitude and torque angle. In particular, the SVM-DTC is composed of a reference voltage vector calculator providing a desired voltage vector. The effectiveness of the proposed overall power control strategy is verified not only by applying the strategy to a commercial 10-kW wind turbine simulated in MATLAB/Simulink, but also by experimental results derived from a developed laboratory setup.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Single-Stage Three-Phase Grid-Tied PV System With Universal Filtering
Capability Applied to DG Systems and AC Microgrids
• Authors: Leonardo Bruno Garcia Campanhol;Sérgio Augusto Oliveira da Silva;Azauri Albano de Oliveira;Vinícius Dário Bacon;
Pages: 9131 - 9142
Abstract: This paper proposes a single-stage three-phase four-wire grid-connected photovoltaic (PV) system operating with a dual compensating strategy and feedforward control loop (FFCL). Besides injection of active power into the grid, the PV system operates as a unified power quality conditioner (UPQC), suppressing load harmonic currents and compensating reactive power. Furthermore, regulated, balanced, and harmonic-free output voltages are provided to the load. Since the PV-UPQC is based on a dual compensation strategy, the series converter operates as a sinusoidal current source, whereas the parallel converter operates as a sinusoidal voltage source. Thus, seamless transition can be achieved from the interconnected to the islanding operation modes, and vice versa, without load voltage transients. Moreover, to overcome problems associated with sudden solar irradiation changes, fast power balance involving the PV array and the grid is obtained, since the FFCL acts on the generation of the series inverter current references. As a result, the dynamic responses of both inverter currents and dc-bus voltage are improved. Detailed analysis involving the active power flow through the inverters is performed allowing proper understanding of the PV-UPQC operation. Experimental results are presented to evaluate both dynamic and static performances of the PV-UPQC tied to the electrical distribution system.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Step-Up DC–DC Converters: A Comprehensive Review of Voltage-Boosting
Techniques, Topologies, and Applications
• Authors: Mojtaba Forouzesh;Yam P. Siwakoti;Saman A. Gorji;Frede Blaabjerg;Brad Lehman;
Pages: 9143 - 9178
Abstract: DC–DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc–dc converters, this paper aims to comprehensively review and classify various step-up dc–dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc–dc converters are presented and summarized with comparative study of different voltage-boosting techniques.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Analysis and Experiments on a Single-Inductor Half-Bridge LED Driver With
Magnetic Control
• Authors: José Marcos Alonso;Marina S. Perdigão;Marco A. Dalla Costa;Gilberto Martínez;René Osorio;
Pages: 9179 - 9190
Abstract: This paper presents the analysis and experiments of a variable inductor (VI) based LED driver for dc grid lighting applications. The proposed driver requires only a series inductor and a transformer as major components to drive the LED lamp from a half-bridge inverter. By introducing a VI as the series inductor, the LED current can be controlled independently from any other parameter, which makes it possible to drive and regulate several LED branches from the same half-bridge output. Other advantages of the proposed converter include inherent open-circuit and short-circuit protections, zero-voltage switching for the bridge transistor and zero-current switching for the output rectifier diodes, simple dynamics, possibility of analog and pulse width modulation dimming, constant switching frequency operation, and high efficiency. The converter is thoroughly analyzed and modeled for both steady-state and dynamic operation. As another novelty of this paper, the dynamic response of the VI has been studied and taken into account to obtain the complete transfer function of the VI-controlled system. In addition, some housekeeping issues that usually arise when dealing with VI, e.g., how to drive the VI bias winding, are solved in this work. Experimental results provided from a 50 W laboratory prototype demonstrate the correctness of the performed analysis and the good possibilities of the proposed converter.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• A Passive-Impedance-Matching Technology to Achieve Automatic Current
Sharing for a Multiphase Resonant Converter
• Authors: Hongliang Wang;Yang Chen;Yan-Fei Liu;
Pages: 9191 - 9209
Abstract: A passive-impedance-matching (PIM) technology is proposed to achieve automatic current sharing for multiphase resonant converters through matching the input impedance of each phase. The series inductors (or series capacitors) of each phase are connected in parallel to achieve a couple of virtual resistors including positive and negative resistors and variably series inductors (or capacitors). A virtual positive (or negative) resistor increases (or decreases) the input impedance of the respective phase, and the variably series inductors can also compensate the component tolerance such that the impedance of each phase is matched. The current-sharing performance of the common-inductor two-phase LLC resonant converter (as one example) is evaluated under the first-harmonic-approximation assumption. The virtual positive and negative resistors and variably virtual inductors are calculated. The proposed method can share the primary resonant current and the load current for all phases without any additional circuit and control strategy. The PIM technology is extended to other resonant converter topologies, including common-inductor or common-capacitor series-resonant converter, LCC, CLL resonant converter, etc. A 600-W 12-V common-inductor two-phase LLC resonant converter prototype is built to verify the feasibility and demonstrate advantages of PIM technology.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Passive Regenerative and Dissipative Snubber Cells for Isolated SEPIC
Converters: Analysis, Design, and Comparison
• Authors: Gabriel Tibola;Erik Lemmen;Jorge L. Duarte;Ivo Barbi;
Pages: 9210 - 9222
Abstract: An isolated converter such as SEPIC has high voltage stress on the main switch due to transformer leakage inductance. To solve this issue, active or passive clamp action is necessary. The common passive solution based on an RCD snubber is simple but impractical when the value of the leakage inductance is significant. On the other hand, passive regenerative solutions generally compromise the isolation, making the search for a suitable snubber a challenge. In this paper, an effective passive regenerative snubber cell for isolated SEPIC converters operating in DCM or CCM is presented. It is intended to improve the converter efficiency by transferring the energy stored in the transformer leakage inductance to the output. The analysis is presented in detail for DCM and extended to CCM together with a practical design procedure. In order to compare with the RCD, the analysis and design of a conventional cell are presented as well. To validate the proposal and quantify its feasibility, experimental results are performed for both dissipative and regenerative snubbers on a 100 W, 100 V, input and 50 V output voltage converter operating first in DCM and later in CCM.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• An Expandable Two-Phase Interleaved Ultrahigh Step-Down Converter With
Automatic Current Balance
• Authors: K. I. Hwu;W. Z. Jiang;P. Y. Wu;
Pages: 9223 - 9237
Abstract: In the high step-down voltage applications, the dc–dc converter with a high step-down voltage conversion ratio is usually used. Recently, a high step-down converter, named ultrahigh step-down converter, has been presented. As compared with the nonisolated tapped-inductor buck converter, the ultrahigh step-down converter has not only a higher voltage step-down gain but also a lower voltage spike. On the other hand, in the high-current applications, a multiple phase structure is preferable. Therefore, in this paper, a novel expandable two-phase interleaved ultrahigh step-down converter with automatic current balance is presented, which is derived from the existing single-phase ultrahigh step-down converter. There are four main advantages of the proposed converter. First, the step-down voltage gain is improved. Therefore, the turns ratio of each phase can be decreased. Second, due to the charge balance of the energy-transferring capacitor, the proposed two-phase ultrahigh step-down converter possesses an automatic current balance. Third, as compared with a single-phase ultrahigh step-down converter, the output current ripple can be reduced. Fourth, the phase number of the proposed converter can be expanded. Finally, the basic operating principle of the proposed converter is analyzed, and a prototype is constructed to verify its effectiveness by some experimental results.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Optimum Third Current Harmonic During Nondead Zone and Its Control
Implementation to Improve PF for DCM Buck PFC Converter
• Authors: Kai Yao;Xufeng Zhou;Fei Yang;Siwen Yang;Cheng Cao;Chunyan Mao;
Pages: 9238 - 9248
Abstract: A buck power factor correction (PFC) converter is widely used in low-power applications for its high efficiency in the entire universal input voltage range. However, because of the inherent dead zone, the input power factor (PF) is not high. A buck PFC converter operating in a discontinuous conduction mode is introduced. When the duty cycle is constant during the line cycle, the input current contains a large amount of negative third harmonic, especially at a low input voltage. By proposing an optimum third harmonic injection during the nondead zone and its control implementation, a higher PF and a lower output voltage ripple within the entire universal input voltage range are achieved. The experimental verifications are carried out on a 120-W prototype with universal input.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Current Integral Method for Fine Commutation Tuning of Sensorless
Brushless DC Motor
• Authors: An-Chen Lee;Chia-Juei Fan;Guan-Hong Chen;
Pages: 9249 - 9266
Abstract: This paper presents a method for fine commutation tuning of brushless direct current (BLDC) motor. First, we analyze the phase current waveform under commutation error and nonideal back-EMF. From the relationship derived, we propose a feedback compensation method in combination with a sensored BLDC motor or any sensorless drive technique to adjust commutation instant by forcing the current integrals of the two half periods in one 60° conducting period to be equal. The method is robust to variations in resistance and inductance, as well as to nonideal back-EMF, pushing the peak values of the current waveform at the front and back of each conducting period to be more identical. Simulations are presented and a digital signal processor (DSP)-based sensorless scheme contingent on a disturbance observer for back electromotive force (back-EMF) estimation in combination with the proposed control method is implemented to verify its effectiveness experimentally. The results show that proposed method is capable of running the motor at different speeds, load torque, and under the speed-varying operating condition with low levels of motor vibration and power consumption.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Flux Immunity Robust Predictive Current Control With Incremental Model and
Extended State Observer for PMSM Drive
• Authors: Ming Yang;Xiaoyu Lang;Jiang Long;Dianguo Xu;
Pages: 9267 - 9279
Abstract: A robust predictive current control algorithm for permanent magnet synchronous motor (PMSM) drives is proposed. The robust controller adopts an incremental system model, thus can operate without knowing the rotor flux, which is a pivotal parameter in conventional dead-beat control. The incremental model is easy to implement compared with relevant flux identification algorithms or observers. The robust controller adopts an extended state observer (ESO) to enhance inductance robustness to cater for the divergence caused by stator inductance mismatch. The inductance mismatch uncertainties can be estimated and compensated by ESO. Conventional dead-beat control is modified for multistep prediction to achieve high disturbance rejection. Detailed stability and disturbance rejection analysis are conducted theoretically, and rules on parameter selection are given. Comparative simulations and experimentations verify the effectiveness and superiority of proposed robust control over conventional dead-beat control.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Efficient Measurement of Thermal Coupling Effects on Multichip
Light-Emitting Diodes
• Authors: Hong-Li Lu;Yi-Jun Lu;Li-Hong Zhu;Yue Lin;Zi-Quan Guo;Tong Liu;Yu-Lin Gao;Guo-Long Chen;Zhong Chen;
Pages: 9280 - 9292
Abstract: With the emerging market for multichip module based high-power LED systems, the demand for advanced thermal management techniques has been steadily growing. This paper presents a model developed by the authors for thermal coupling matrix that can calculate temperature distribution at a given heat power of each chip. The model significantly simplifies the task of measuring thermal coupling effect on multichip light-emitting diodes with symmetrical structure, while simultaneously preserving temperature accuracy. The modeling technique was validated experimentally on three-, four-, and six-chip rectangular modules, and a ten-chip circular module, by infrared thermography and transient thermal measuring system, respectively. The modeling technique was found to be more efficient especially for large systems. The model offers a rapid way to predict thermal coupling behaviors of multichip LED systems.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Multiple String LED Driver With Flexible and High-Performance PWM Dimming
Control
Pages: 9293 - 9306
Abstract: The main objectives in driving multiple LED strings include achieving uniform current control and high-performance pulse width modulation (PWM) dimming for all strings. This study proposes a new multiple string LED driver to achieve not only current balance, but also flexible and wide range PWM dimming ratio for each string. A compact single-inductor multiple-output topology is adopted in the driver, accompanied by synchronous integrators and variable dimming frequency, to achieve both high-efficiency and high-performance dimming. By using the proposed variable dimming frequency scheme, high dimming frequency is applied to a string with high dimming ratio, which helps us to maintain the deviation of LED string current in an acceptable range, while low dimming frequency is applied to a string with low dimming ratio, which helps us to achieve rectangular LED current waveform. Meanwhile, the new time multiplexing control scheme automatically optimizes the LED strings’ bus voltages, thus minimizes each string's power loss. A three-string LED driver prototype is constructed to validate the effectiveness of the proposed control scheme, where the three strings can have different dimming ratios between 4% and 100%.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Ultrafast Reverse Recovery Time Measurement for Wide-Bandgap Diodes
• Authors: Daniel L. Mauch;Fred J. Zutavern;Jarod J. Delhotal;Michael P. King;Jason C. Neely;Isik C. Kizilyalli;Robert J. Kaplar;
Pages: 9333 - 9341
Abstract: A system is presented that is capable of measuring subnanosecond reverse recovery times of diodes in wide-bandgap materials over a wide range of forward biases (0 – 1 A) and reverse voltages (0 – 10 kV). The system utilizes the step recovery technique and comprises a cable pulser based on a silicon (Si) Photoconductive Semiconductor Switch (PCSS) triggered with an Ultrashort Pulse Laser, a pulse charging circuit, a diode biasing circuit, and resistive and capacitive voltage monitors. The PCSS-based cable pulser transmits a 130 ps rise time pulse down a transmission line to a capacitively coupled diode, which acts as the terminating element of the transmission line. The temporal nature of the pulse reflected by the diode provides the reverse recovery characteristics of the diode, measured with a high bandwidth capacitive probe integrated into the cable pulser. This system was used to measure the reverse recovery times (including the creation and charging of the depletion region) for two Avogy gallium nitride diodes; the initial reverse recovery time was found to be 4 ns and varied minimally over reverse biases of 50–100 V and forward current of 1–100 mA.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Short-Circuit Degradation of 10-kV 10-A SiC MOSFET
• Authors: Emanuel-Petre Eni;Szymon Bęczkowski;Stig Munk-Nielsen;Tamas Kerekes;Remus Teodorescu;Raghavendra Rao Juluri;Brian Julsgaard;Edward VanBrunt;Brett Hull;Shadi Sabri;David Grider;Christian Uhrenfeldt;
Pages: 9342 - 9354
Abstract: The short-circuit behavior of power devices is highly relevant for converter design and fault protection. In this paper, the degradation during short circuit of a 10-kV 10-A 4H-SiC MOSFET is investigated at 6 kV dc-link voltage. The study aims to present the behavior of the device during short-circuit transients as it sustains increasing short-circuit pulses during its lifetime. As the short-circuit pulse length increases, degradation of the device can be observed in periodically performed characterizations. The initial degradation seems to be associated with the channel region, and continuous stressing leads to an overall increase in device on-state resistance at the end of the degradation study. Thermal simulation shows that the surface aluminum metalization reached its melting temperature and the top part of the device reaches temperatures above the rated junction temperature. Scanning electron microscope investigation shows aluminum reconstruction and cavities at the contact interface between the aluminum surface metalization and source contacts.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Online Parameter Identification for Supercapacitor State-of-Health
Diagnosis for Vehicular Applications
• Authors: Asmae El Mejdoubi;Hicham Chaoui;Hamid Gualous;Jalal Sabor;
Pages: 9355 - 9363
Abstract: In power electronic applications, aging of the electric double layer capacitors (EDLCs) is considered as a serious issue since it may lead to failure. Their degradation is usually evaluated by an increase of the internal resistance or a decrease of the equivalent capacitance. These aging indicators have a good correlation with the supercapacitor's state-of-health (SoH). Generally, SoH is measured by electrochemical impedance spectroscopy (EIS). However, this technique must be performed offline and requires interruption of the system's operation. In this paper, a sliding mode observer is designed to estimate online the EDLC's aging indicators. Unlike several online estimators, the supercapacitor's parameters are considered as a nonlinear random distribution with external noises which yields accurate estimation. In addition, the relationship between the capacitance and the bias voltage is considered to be nonlinear. Lyapunov stability analysis is also provided. The proposed approach is validated experimentally using a standardized dynamic current profile. Furthermore, comparison against EIS is carried out for different aging phases and under different environmental temperature conditions.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• An Adaptive Power-Split Strategy for Battery–Supercapacitor
Powertrain—Design, Simulation, and Experiment
• Authors: Li Sun;Kaiwu Feng;Chris Chapman;Nong Zhang;
Pages: 9364 - 9375
Abstract: Electric vehicles (EVs) adopting both batteries and supercapacitors have attracted a significant amount of attention in research communities due to their unique power-sharing capabilities. A hybrid energy storage system (HESS) can effectively reduce power stress that would, otherwise, be applied to batteries alone, and whose weight and size is still a common concern when competing against conventional internal-combustion-engine-powered cars. In this paper, a high-level algorithm is developed to adaptively split the load between two sources for an EV adopting HESS under real-life load fluctuations. A converter—supercapacitor pack (SP) coupled HESS upon which such an algorithm is deployed on, is proposed to divert excess power into the SP via a smart power converter, which is located in between in order to regulate both behaviors. A power-split strategy is designed to track real-time load profiles and determine one important variable: the cutoff frequency. As a consequence, relatively higher frequency portion of the load power gets channeled to the SP, and the remaining less-varying power demand is sent to the BP based on the fundamental energy-balancing equation. A simplified HESS model is developed in MATLAB, and the real-time power-split algorithm is coded using Labview and verified on a test rig. Both simulation and experimental results prove its effectiveness in coping with even the harshest driving scenarios in real life.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Thermal Stresses Relief Carrier-Based PWM Strategy for Single-Phase
Multilevel Inverters
• Authors: Mokhtar Aly;Emad M. Ahmed;Masahito Shoyama;
Pages: 9376 - 9388
Abstract: Enhancing power cycling capability of power semiconductor devices is highly demanded in order to increase the long-term reliability of multilevel inverters. Ageing of power switches and their cooling systems leads to their accelerated damage due to excess power losses and junction temperatures. Therefore, thermal stresses relief (TSR) is the most effective solution for lifetime extension of power semiconductor devices. This paper presents a new TSR carrier-based pulse width modulation (TSRPWM) strategy for extending the lifetime of semiconductor switches in single-phase multilevel inverters. The proposed strategy benefits the inherent redundancy among switching states in multilevel inverters to optimally relieve the thermally stressed device. The proposed algorithm maintains the inverter operation without increased stresses on healthy switches and without reduction of the output power ratings. In addition, the proposed algorithm preserves voltage balance of the dc-link capacitors. The proposed strategy is validated on a single-phase five-level T-type inverter system with considering different locations of thermal stresses detection. Experimental prototype of the selected case study is built to verify the results. Moreover, comparisons with the most featured strategies in literature are given in detail.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Supercapacitor-Based Energy Recovery System With Improved Power Control
and Energy Management for Elevator Applications
Pages: 9389 - 9399
Abstract: This paper proposes a supercapacitor-based energy recovery system (ERS) with improved power control and energy management (PC&EM) capability for elevator applications. The ERS is connected to the dc link of the elevator motor drive through a bidirectional dc–dc converter for storing and then recovering the braking energy. The proposed PC&EM technique provides improved cost effectiveness and exploitation of the ERS capability, by adjusting the elevator power requirements with the ERS power capability through cabin speed regulation within predefined limits. The proposed control system can be easily installed without requiring modifications in the elevator motor drive, and thus, it can be easily applied to any existing elevator applications. Also, an experimental procedure is proposed in order to online determine and periodically fine-tune the parameters of the suggested PC&EM controller. In this paper, the proposed control technique has been applied in an ERS with a nonisolated dc–dc converter; however, it can as well be used in the isolated counterpart. Selective experimental results are presented in order to verify the effectiveness of the proposed control technique and demonstrate the resulting operational improvements.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• A Concise Discrete Adaptive Filter for Frequency Estimation Under
Distorted Three-Phase Voltage
• Authors: Xiangjun Quan;Xiaobo Dou;Zaijun Wu;Minqiang Hu;Feng Chen;
Pages: 9400 - 9412
Abstract: To improve the control performance for grid-tied power converters, the fundamental frequency and harmonics of the grid voltage should be quickly and accurately estimated even under distorted voltage condition. This paper introduces a straightforward discrete adaptive filter to observe fundamental and harmonic sequence components of the grid voltage. The proposed filter possesses a simple and straightforward implementation. Based on the newly developed filter, frequency error transmission was analyzed when the frequency of the input voltage was unequal to the center frequency of the filter. Consequently, a frequency estimation loop was designed to adapt to the frequency variation for the filter. Compared to previous algorithms, the proposed algorithm has a better dynamic performance rating for frequency estimation, robust stability, and a simpler implementation. The effectiveness of the algorithm is verified by simulations and laboratory experiments.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Power Control With Z-Source Converter Based Unified Power Flow Controller
• Authors: R. Thirumalaivasan;Yunjian Xu;M. Janaki;
Pages: 9413 - 9423
Abstract: In this paper, we propose a Z-source converter (ZSC)-based unified power flow controller (ZSC-UPFC) to enhance power control for long transmission lines. As a multifunctional controller, the UPFC has been adopted to regulate both the active and reactive power flows in transmission lines and to control the AC bus voltage. A recently proposed converter topology, ZSC, uses a Z-network on its DC side to support the desired AC output voltage. The proposed ZSC-UPFC configuration places a Z-network between the dc-link capacitor and the series converter to boost the series converter DC voltage. The integration of Z-network provides the desired converter voltage even with reduced dc-link capacitor voltage setting. We develop a detailed three-phase model for the proposed ZSC-UPFC by modeling the converter operation with switching functions, which are generated by the space vector pulse width modulation (SVPWM) technique. We conduct linear analysis on the D-Q model as well as extensive transient simulation (based on a detailed nonlinear three-phase model) to evaluate the performance of the overall system with the proposed ZSC-UPFC configuration. Our simulation results demonstrate the effectiveness of ZSC-UPFC: 1) The series converter provides the series compensation in a long transmission line with Z-network, and 2) the shunt converter maintains a constant dc-link capacitor voltage and provides reactive power support for the AC bus.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Bifurcation Phenomena and Stabilization With Compensation Ramp in
Converter With Power Semiconductor Filter
• Authors: John Wing-to Fan;Henry Shu-hung Chung;
Pages: 9424 - 9434
Abstract: A concept, named as power semiconductor filter, has been demonstrated to be an alternative to perform input harmonic filtering in switched-mode power converters. It utilizes a series pass device (SPD) to profile the wave shape of the supply current, while the voltage across the SPD is regulated at a threshold voltage between the linear and saturation regions of the SPD to minimize its power dissipation. Bulky passive components for input harmonic filtering can then be eliminated or shrunk with such active supply current control. For the sake of circuit elegancy, regulation of the SPD voltage is realized by a bang-bang (peak-voltage) controller to vary the input characteristics of the power conversion stage through adjusting some control parameters, such as duty cycle and switching frequency. Experiments reveal that the entire system might exhibit bifurcation phenomena under some supply and load conditions. This paper will derive a sampled-data model to characterize such system behaviors and to identify the onset of bifurcation and chaos. A compensation ramp will be proposed to introduce into the bang-bang controller to stabilize the system operation. Moreover, the slow-scale dynamics will be studied with small-signal models. The investigations will be exemplified on a 48 W, 40–140 V/24 V buck dc–dc converter prototype.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Power Routing for Cascaded H-Bridge Converters
• Authors: Youngjong Ko;Markus Andresen;Giampaolo Buticchi;Marco Liserre;
Pages: 9435 - 9446
Abstract: Modular power converters are expected to play a major role in medium- and high-voltage/power applications. Normally, each module processes the same amount of power; however, this does not take into consideration that different modules can have a different remaining useful lifetime. This paper proposes the concept of power routing for cascaded H-bridge (CHB) converters, with the purpose of delaying the failure of the system. A third-harmonic injection into the duty cycles allows extending the imbalance capability of the structure, keeping the CHB operational even if some power paths are completely unloaded. Analytic investigation in conjunction with simulation and experimental measurements demonstrate the power routing by means of the proposed method.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Reactive Power Compensation Capabilities of V2G-Enabled Electric Vehicles
• Authors: Giuseppe Buja;Manuele Bertoluzzo;Christian Fontana;
Pages: 9447 - 9459
Abstract: Vehicle-to-grid (V2G) paradigm is a way of executing services in favor of the grid by electric vehicles (EVs) with bidirectional battery chargers (BBC). The V2G service that has attracted the major interest is the exchange of active power for load leveling purposes. Less attention has received the so-called ancillary V2G services, such as the reactive power compensation. This service is much attractive since it does not involve any exchange of active power and, therefore, leaves the EV batteries charged and does not expose them to additional discharging–charging cycles. The purpose of this paper is to investigate the capabilities of V2G-enabled EVs in executing the reactive power compensation, whether done alone or simultaneously with either battery charging or battery power delivery to the grid. Two topologies of BBC are examined, namely the topologies with the dc side of the charger either directly connected to the battery or through a bidirectional dc–dc converter of buck type. This paper closes by reporting experimental results that corroborate the theoretical findings.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

• Fast Commutation Instant Shift Correction Method for Sensorless Coreless
BLDC Motor Based on Terminal Voltage Information
• Authors: Xinxiu Zhou;Xi Chen;Fanquan Zeng;Jiqiang Tang;
Pages: 9460 - 9472
Abstract: Due to the phase delay caused by low-pass filter, device retarding, and software retarding, the extracted sensorless motor commutation signal deviation occurs. Unfortunately, the relationship between the phase shift and inactive phase freewheeling has been scarcely referred to through the published papers, and most of the commutation instant shift compensation methods present slow convergence rate. Therefore, a fast commutation instant shift correction method based on analyzing the back-electromotive force (EMF) harmonic information is proposed in this paper. The method is effective both in the steady-speed control and in variable-speed control. Considering that commutation instant shift may induce inactive phase freewheeling and negative torque in motor windings, the freewheeling condition and motor electric operation condition are analyzed as well. Furthermore, to exactly delay the zero-crossing points (ZCPs) of EMF by 30° and compensate the commutation instant shift, the speed detection accuracy and feedback frequency are enhanced by measuring and summing up the 2 × P consecutive half-period of the ZCPs signal. Finally, the validity of the proposed commutation instant shift correction method is verified through experimental results.
PubDate: Dec. 2017
Issue No: Vol. 32, No. 12 (2017)

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