Wide bandgap (WBG) device-based power electronics converters are more efficient and lightweight than silicon-based converters. WBG devices are an enabling technology for many motor drive applications and new classes of compact and efficient motors. This paper reviews the potential applications and advances enabled by WBG devices in ac motor drives. Industrial motor drive products using WBG devices are reviewed, and the benefits are highlighted. This paper also discusses the technical challenges, converter design considerations, and design tradeoffs in realizing the full potential of WBG devices in motor drives. There is a tradeoff between high switching frequency and other issues such as high dv/dt and electromagnetic interference. The problems of high common mode currents and bearing and insulation damage, which are caused by high dv/dt , and the reliability of WBG devices are discussed.

Wide Bandgap Devices in AC Electric Drives: Opportunities and Challenges

Wide-bandgap (WBG) power semiconductor devices have become increasingly popular due to their superior characteristics compared to their Si counterparts. However, their fast switching speed and the ability to operate at high frequencies brought new challenges, among which the electromagnetic interference (EMI) is one of the major concerns. Many works investigated the structures of WBG power devices and their switching performance. In some cases, the conductive or radiated EMI was measured. However, the EMI-related topics, including their influence on noise sources, noise propagation paths, EMI reduction techniques, and EMC reliability issues, have not yet been systematically summarized for WBG devices. In this article, the literature on EMI research in power electronics systems with WBG devices is reviewed. Characteristics of WBG devices as EMI noise sources are reviewed. EMI propagation paths, near-field coupling, and radiated EMI are surveyed. EMI reduction techniques are categorized and reviewed. Specifically, the EMI-related reliability issues are discussed, and solutions and guidelines are presented.

A Survey of EMI Research in Power Electronics Systems With Wide-Bandgap Semiconductor Devices

Today, conventional power systems are evolving to smart grids, which encompass clusters of AC/DC microgrids, interfaced through power electronics converters. In such systems, increasing penetration of the power electronics-based distributed generations, energy storages, and modern loads provide a great opportunity for power quality control. In this paper, an overview of the power quality control of smart hybrid AC/DC microgrids is presented. Different types of power quality issues are studied first, with consideration of real-world hybrid microgrid examples, including data centers, electric railway systems, and electric vehicles charging stations. It shows that compared to traditional centralized power quality compensations, smart interfacing power converters from distributed generations, energy storages, and loads, and the AC and DC subgrids interfacing converters are promising candidates for power quality control. To realize the smart interfacing converters' power quality control, both primary converters control and secondary system coordination are required. In this paper, a thorough review of the primary control of interfacing converters to integrate the power quality compensation are presented, with a focus on the hybrid AC/DC microgrid harmonics compensation and unbalance compensation. For multiple interfacing converters, the secondary control with system-level coordination and optimization for harmonics and unbalance compensation (considering both unbalance and harmonics in single-phase and three-phase systems) are also presented. Challenges like low switching frequency of interfacing converters, parallel interfacing converters operation, and interfacing converters communications are discussed, and typical solutions for primary and secondary controls to deal with them are presented. The paper also includes rich case study results.

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Power Quality Control of Smart Hybrid AC/DC Microgrids: An Overview

LCL -filtered grid-connected converters are widely used for distributed generation systems. However, the current regulation of such converters is susceptible to weak grid conditions, e.g., grid impedance variation and background harmonics. Paralleling multiple harmonic compensators (HCs) is a commonly used method to suppress the current distortion caused by grid background harmonics, but the control bandwidth should be wide enough to ensure system stability. In order to enhance the adaptability of LCL -filtered grid-connected converters under weak grid operation, this paper proposes an improved capacitor-voltage-feedforward control with full delay compensation. When used with converter-side current feedback, the proposed control can keep system low-frequency characteristic independent of grid impedance and provide a high-harmonic rejection capability without using additional HCs. Moreover, it completely avoids the design constraints of an LCL filter, i.e., $\omega _{r} is required for single-loop converter-side current control. Therefore, a higher resonant frequency can be designed to achieve a wider control bandwidth and to lower the current distortion caused by the paralleled filter capacitor branch. Experimental results are finally presented to verify the proposed control, which are also in good agreement with theoretical analysis.

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Capacitor-Voltage Feedforward With Full Delay Compensation to Improve Weak Grids Adaptability of LCL-Filtered Grid-Connected Converters for Distributed Generation Systems

The performance of the grid-connected inverter was affected by the uncertainty of the grid conditions including the background distortion and the grid impedance. Typically, the feedforward of the grid voltage at the point of common coupling (PCC) highly suppressed the grid current harmonics caused by the grid voltage distortion; however, the PCC grid usually had a nonnegligible grid impedance, and the PCC voltage feedforward aroused serious grid current harmonics or instability. This study proposes a novel adaptive algorithm for the PCC voltage feedforward to work well with the varied grid impedance. In the proposal, the band-pass filters at the harmonic frequencies are used to detect the variation of the grid impedance as well as to facilitate the adaptive PCC voltage feedforward. It is not necessary to inject an additional harmonic to estimate the grid impedance. The basic principles as well as the realization and logic of the proposed algorithm are detailed, and some selected waveforms are provided to verify the superior performance. Compared with the typical robust design or adaptive control, the proposed algorithm does not have to sacrifice the dynamic or the harmonics rejection performance, or to use the on or offline grid impedance estimation.

Adaptive Feedforward Algorithm Without Grid Impedance Estimation for Inverters to Suppress Grid Current Instabilities and Harmonics Due to Grid Impedance and Grid Voltage Distortion

In this paper, the inverter output impedance is passivized for solving the harmonic and the stability problems in the multiparallel inverters The harmonics are easily aroused because of the disturbances, and the system stability is challenged by the grid impedance Based on the simplified equivalent impedance model, the two problems are analyzed in the low-frequency (LF) band and the high-frequency (HF) band, respectively Aiming at improving the LF performance, the weighted-proportional grid voltage feedforward and the harmonic quasi-resonant controller with phase compensation are proposed The dynamic performance is enhanced with an additional current reference generation scheme In order to improve the HF performance, a novel digital phase lead filter which brings the system back to a minimum-phase case is proposed By the proposed control method, the high modulus of each inverter output impedance $Z_{o}$ is guaranteed, while the phase angles of $Z_{o}$ over the entire frequency band are avoided to be lower than −90° The experiments based on four-parallel inverters have been conducted to validate the effectiveness of the proposed control method

Harmonic Suppression and Stability Enhancement for Parallel Multiple Grid-Connected Inverters Based on Passive Inverter Output Impedance

In the distributed power generation systems (DPGSs) based on the renewable energies, the stability and harmonics of the grid-connected inverter are seriously affected by the uncertainties of the grid at the point of common coupling (PCC). More importantly, as several inverters are usually tied at the PCC together, the interactions among the inverters and the grid impedance can cause more serious harmonics and instabilities at the low frequencies. Hence, the phase-locked loop (PLL) affecting the low-frequency behaviors must be considered. This study aims to provide a comprehensive study of the stability and harmonics of single-phase inverters in the weak grid. Modelings of single-inverter and multiple-inverter systems considering the PLL are established. The impacts of different PLLs on the low-order current harmonics and stability are then studied. It has been proved that the maximum ability of inverters in suppressing the low-order grid current harmonics closely relates to the PLL, even if a harmonic resonant controller and/or PCC voltage feedforward is used. Thus, using different PLLs yields quite different performances. Simulation and experimental results will be given to demonstrate the analysis, which is helpful for the readers to design a proper PLL for DPGSs.

Harmonics and Stability Analysis of Single-Phase Grid-Connected Inverters in Distributed Power Generation Systems Considering Phase-Locked Loop Impact

Silicon carbide (SiC) devices have attracted widespread attention because of their superior characteristics. However, not only the higher slew rate of drain–source voltage but also the higher slew rate of reverse recovery current can result in a more serious crosstalk problem than Si-based devices in a half-bridge application. Crosstalk suppression should be integrated into the gate driver to ensure the safe operation of SiC devices. Therefore, a specific mathematical analysis is done in this paper to figure out the crosstalk phenomenon. The limitations of the existing suppression methods are illustrated. Thus, a gate driver based on the magnetic coupling is proposed to ensure the gate–source voltage within the safe range, even when the positive and negative spurious pulse voltages appear. The proposed gate driver uses three ring transformers to insulate the control signal and driver power supply. So, it is feasible to drive a half-bridge circuit in the medium or high power applications. By saving optical couplers and isolated drive power supplies, the gate driver can realize fully galvanic isolation and generate the positive and negative gate–source driving voltage simply. The results derived from the proposed mathematical analysis and the effectiveness of the proposed driver in suppressing the spurious pulse voltage are verified by the experiments.

A Magnetic Coupling Based Gate Driver for Crosstalk Suppression of SiC MOSFETs

For the grid-connected LCL -filtered inverter, the grid current feedback active damping (AD) can assure a desirable bandwidth and a good robustness against certain parameter variations by using a minimal number of sensors. However, the inverter performance was seriously endangered by nonideal conditions at the point of common coupling (PCC), including background voltage distortions and grid impedance variation. The grid current AD could not work well for wide grid impedance variation. Hence, in this study, the robustness with such control is discussed and its relations with system parameters are derived through mathematic derivations. It is proved that, for the typical grid current AD control, a contradiction between high bandwidth and high robustness exists. On the basis of analyzing the reasons for the limitations of the typical control, a systematic approach for enhancing the robustness under complex grid conditions has been proposed. The proposed fundamental PCC voltage feedforward enhances the robustness, while the proposed phase shaping compensator assures a higher robustness with a desired bandwidth. Comparative waveforms with the typical grid current AD control have been provided to verify the correctness of the analysis and the improvement of the proposed approach.

Binfeng Zhang

Papers

Adaptive Feedforward Algorithm Without Grid Impedance Estimation for Inverters to Suppress Grid Current Instabilities and Harmonics Due to Grid Impedance and Grid Voltage Distortion

Harmonic Suppression and Stability Enhancement for Parallel Multiple Grid-Connected Inverters Based on Passive Inverter Output Impedance

Harmonics and Stability Analysis of Single-Phase Grid-Connected Inverters in Distributed Power Generation Systems Considering Phase-Locked Loop Impact

A Magnetic Coupling Based Gate Driver for Crosstalk Suppression of SiC MOSFETs

Robust Grid Current Control With Impedance-Phase Shaping for LCL -Filtered Inverters in Weak and Distorted Grid