Three-level converters typically feature low switching loss and small filter size. In order to realize a high-power-density design for three-level converters, SiC MOSFETs may be selected instead of using Si insulated-gate bipolar transistors. However, all-SiC-MOSFET-based converters suffer from extremely high total cost. In this paper, a SiC MOSFET and Si device hybrid active neutral-point-clamped (ANPC) converter is proposed. It consists of four Si active switches and only two SiC MOSFETs. Thus, it has lower total cost compared to the all-SiC-MOSFET-based ANPC converter. Furthermore, a dedicated modulation scheme is proposed to completely move all the switching events from Si devices to SiC MOSFETs by using redundant switching states. As a result, the switching losses are significantly reduced and extremely high efficiency is achieved. The proposed converter has fully utilized the low-switching-loss advantage of SiC MOSFETs and the low-cost advantage of Si devices, which shows significant superiority in high-end grid-connected inverter and rectifier applications.

An Extremely High Efficient Three-Level Active Neutral-Point-Clamped Converter Comprising SiC and Si Hybrid Power Stages

Hybrid switches configured by paralleling Silicon (Si) Insulated Gate Bipolar Transistors (IGBT) and Silicon Carbide (SiC) Metal-Oxide Semiconductor Field-Effect Transistors (MOSFET) have been verified to be a high-efficiency cost-effective device concept In this paper, a current-dependent switching strategy is introduced and implemented to further improve the performance of Si/SiC hybrid switches This proposed switching strategy is based on a comprehensive consideration of reducing device losses, reliable operation, and overload capability Based on the utilization of such Si/SiC hybrid switches and the proposed switching strategy, a 15-kW single-phase H-bridge inverter prototype was implemented and tested in the laboratory Simulation and experimental results are given to verify the performance of the hybrid switches and the new switching strategy

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A Current-Dependent Switching Strategy for Si/SiC Hybrid Switch-Based Power Converters

This paper presents an inverter topology named the multi-source inverter that aims to connect several independent DC sources to the same AC output using a single stage of conversion. This power converter has been developed for applications, such as electrified powertrains. Compared to the conventional hybrid powertrains that use a DC/DC converter to provide an adaptable voltage to the load, the multi-source inverter can drive a traction motor from variable DC voltages without the use of an additional power converter. Hence, the high power DC/DC converter can be dissociated from the traction mode and its use will be restricted to the engine $^{\prime }$ s start-up and regenerative braking, allowing a significant reduction of its power rating from tens of kWatts to a few kWatts. The overall efficiency of the electrified traction drive can also be improved due to the single conversion stage between the battery and the motor. In this paper, the multi-source inverter topology is introduced and its different operating modes are determined through the study of the inverter circuit. Closed-loop control simulations and experiments with a scaled-down prototype and an induction motor were performed to validate the effectiveness of the proposed topology and concept.

On the Concept of the Multi-Source Inverter for Hybrid Electric Vehicle Powertrains

This paper describes the development of a dedicated electromagnetic interference (EMI) characterization platform for the evaluation of wide bandgap-based converters in ungrounded architectures of the type likely to be employed on the future shipboard systems. This platform is designed to support the characterization of wide-bandgap-based converters operating at switching frequencies of hundreds of kilohertz; with power levels up to 100 kVA and with expected emissions up to 100 MHz. To illustrate the capabilities of this platform, the conducted emissions of a SiC-based half-bridge converter are evaluated (with a focus on common-mode (CM) behavior), and a parametric study is conducted which considers variations in the impedance between the half-bridge module base plate and a representative grounding structure. The focus of this work is not only the half-bridge converter which serves as the preliminary test subject, but also rather the custom metrological setup used for characterization, which is designed to discover sensitivities to resonant paths so that the design guidelines for peripheral structures and EMI mitigating components can be developed in the future studies. One major contribution of this work is the discovery that the symmetry of the parasitic capacitances within the converter’s multichip power module is an important factor which significantly influences the CM conducted emissions of the half-bridge structure, which serves as a building block for more complex converter topologies.

Methodology for Characterization of Common-Mode Conducted Electromagnetic Emissions in Wide-Bandgap Converters for Ungrounded Shipboard Applications

In this paper, a new type of hybrid switching device with parallel connection of SiC and Si active switches, such as “SiC JFET + Si IGBTs” or “SiC MOSFET + Si IGBTs”, is introduced and applied to a 250kW back-to-back Voltage Source Converter (VSC). Considering the different switching speeds and output characteristics of SiC and Si devices in such hybrid structure, a novel optimal switching pattern is proposed to enable the Zero Voltage Switching (ZVS) for Si IGBTs. This proposed switching pattern optimally utilizes the better conduction characteristics and lower switching loss of SiC devices based on the instantaneous load current values, therefore significantly reduces the semiconductor losses in comparison to conventional all-Si VSCs. Simulations of back-to-back converters with different hybrid devices namely, “SiC JFET + Si IGBTs” and “SiC MOSFET + Si IGBTs”, are carried out in PLECS environment. Simulation results illustrate that the overall efficiency of back-to-back VSC can be improved by up to 4.8% if conventional Si devices are replaced with “SiC+Si” hybrid devices with the proposed switching pattern.

An optimal switching pattern for “SiC+Si” hybrid device based Voltage Source Converters

The rapid development of renewable energy systems (RES), especially photovoltaic (PV) energy and wind energy, poses increasing requirements for highpower, low-loss, fast-switching, and reliable semiconductor devices to improve system power capacity, efficiency, power density and reliability. The recent commercialization of wide bandgap (WBG) devices, specifically Silicon Carbide (SiC) and Gallium Nitride (GaN) devices, provides very promising opportunities for meeting such requirements with their attractive features of high voltage blocking capability, ultra-low switching losses, fast switching speed, and high allowable operating temperatures. This paper analyzed the performance benefits and application challenges of using SiC or GaN devices in both PV and wind energy conversion systems. Solutions to these challenges of using WBG devices in various RES were reviewed and proposed, and the benefits of using such emerging devices were confirmed in simulation based on a 250 kW commercial-scale PV inverter and a 250 kW doubly fed induction generator wind turbine system.

Application of wide bandgap devices in renewable energy systems — Benefits and challenges

This paper presents a novel loss balancing modulation method for more evenly distributing semiconductor losses in multilevel active neutral-point-clamped (ANPC) converters. The presented method is achieved by optimally utilizing the redundant switching states of space vector pulse width modulation (SVPWM) in ANPC converters. A comparison of the effect of losses distribution between the proposed loss balancing SVPWM (LB-SVPWM) method and the conventional phase-shifted PWM (PS-PWM) methods is carried out in simulation. The effectiveness of the presented LB-SVPWM method is also verified in ANPC converters based on all-SiC MOSFETs. The results show that the proposed method can distribute the device losses more evenly, especially for all-SiC based ANPC converters, which can in turn improve the output power capacity and switching frequency. In addition, with utilization of the introduced loss balancing SVPWM method in ANPC converters, 15% higher output voltage and lower harmonic distortion can be achieved compared to PS-PWM modulated ANPC converters.

Loss balancing SVPWM for active NPC converters

This paper presents the application and losses analysis of three-level active neutral-point-clamped (ANPC) back-to-back converters in a doubly-fed induction generator (DFIG) wind energy conversion system (WECS). A phase-shifted sinusoidal PWM strategy with the advantages of doubling the apparent switching frequency and better balancing loss distribution among switches is employed for the ANPC back-to-back converters. Comparative losses analysis between three-level ANPC and traditional NPC converters is conducted based on the applications in a 1.5 MW DFIG WECS. Moreover, dynamic modeling and control strategies for the DFIG WECS are introduced. Finally, simulation analysis of the three-level ANPC converters excited 1.5 MW DFIG WECS is carried out. The simulation results verified the advantages of ANPC converters and the corresponding modulation strategy on improving loss distribution and doubling apparent switching frequency in this WECS application.

Xin Jing

Papers

Application of wide bandgap devices in renewable energy systems — Benefits and challenges

Loss balancing SVPWM for active NPC converters

Application and losses analysis of ANPC converters in doubly-fed induction generator wind energy conversion system