This paper contains a comparison between three topologies of a three-phase two-level inverter: a quasi-Z-Source inverter, a Voltage-Source Inverter with a Boost Converter and a Voltage-Source Inverter with an interleaved Boost Converter. Experimental results obtained from laboratory tests of equivalent 6-kW 100-kHz inverters based on SiC MOSFETs and Schottky diodes are provided. The following parameters are compared: quality of input inductor current and output phase voltage as well as total power losses in the inverters. The results for these parameters are obtained for input voltage ranging from 325 V to almost 600 V (where feasible), for two sets of equivalent modulation methods (two regular methods and two reduced-loss methods), for a couple of characteristic values of deadtime and for operation both at the maximum value of modulation index and at equal values of voltage across the inverter bridge. Results of the experiments show that the quasi-Z-Source Inverter topology may, at certain conditions, surpass the traditional two-stage inverter topologies in the areas of input inductor current quality, output voltage quality and also power losses (at high values of input voltage). What is needed to obtain that is a careful examination of operating conditions, applied modulation method and deadtime value.

Phase-Shifted Full Bridge (PSFB) topology in its four-diode variant is the choice with the lowest part count in applications that demand high power, high voltage, and galvanic isolation, such as in Electric Vehicle (EV) chargers. Even though the topology is prevalent in power electronics applications, no single, unified analytical model has been proposed for the design process of four-diode PSFB converters. As a result, engineers must rely on simulations and empirical results obtained from previously built converters when selecting components to properly match the DC source voltage level with the DC load voltage requirements. In this work, the authors provide a design-oriented analysis approach for obtaining the output voltage and semiconductor current values, ready for implementation in a spreadsheet- or MATLAB-type software to automate design optimization. The proposed formulas account for all the first-order nonlinear dependencies by considering the impact of each of the following eight design parameters: DC-link voltage, load resistance, phase-shift ratio, switching frequency, transformer turns ratio, magnetizing inductance, series inductance, and output inductance. The results are verified through experiments at the power level of 10 kW and the DC-link voltage level of 800 V by using a grid simulator and a SiC-based two-level Active Front End (AFE) with a DC–DC stage based on the PSFB topology. The accuracy of the output voltage formula is determined to be around 99.6% in experiments and 100.0% in simulations. Based on this exact model, an automated design procedure for high-power high-voltage SiC-based PSFB converters is developed. By providing the desired DC-link voltage, output voltage, output power, output current ripple factor, maximum temperatures, and semiconductor and heatsink databases, the algorithm calculates a set of feasible designs and points to the one with the lowest semiconductor losses, dimensions, or cost.

This paper discusses switching performance and power losses of silicon carbide (SiC) Metal-Oxide Semiconductor Field-Effect Transistors in a high-frequency quasi-Z-source inverter operating at unity power factor. Basic types of switching processes are distinguished and precisely analyzed. Necessity for using deadtime in impedance-source converters is explained. Shoot-through states with one, two, and three phase legs are investigated and observed processes, such as an unintentional “snubber effect” of nonswitched MOSFETs, are described for the first time. As a result of this analysis, a novel modulation method with minimum number of hard-switching transitions is developed. All discussed aspects are illustrated with experimental results of a 100-kHz/6-kW quasi-Z-source inverter built with SiC elements. The newly developed method is compared with other state-of-the-art methods, and the result is that even for high voltage boost (B = 1.9) losses are reduced by 1%, and efficiency reaches 97% at nominal conditions. At inductive power factor, the developed method also outperforms the other methods.

This work presents concept and implementation of a bidirectional coupling between direct-current circuits of significantly different voltage levels using galvanic isolation in the form of a high-frequency transformer. Standard 5-kW/100-kHz compact dual active bridge modules were used for construction of the coupling. Possibilities of modular construction of the system were presented, in which both parallel and series-parallel connections of developed modules were analyzed. The work takes into account simulation studies of the presented solution as well as studies of an experimental model equipped with an advanced control and measurement system based on DSP-type processors. Modular construction of the converter ensures simple configuring depending on the application, increased reliability and reduced design and maintenance costs.

Aside from providing voltage and current of sufficient values, a gate driver of a SiC MOSFET must also be durable enough to keep operating properly in given place of a main circuit of a converter. A high-side SiC MOSFET constitutes a challenge to being driven properly, since a high-voltage potential becomes repetitively applied at an output of the gate driver. In order to limit a resulting flow of parasitic current Cdv/dt to ground of the driver, a low-capacitance isolation must be implemented. Presented in this paper is a flyback-based gate driver, which is dedicated for driving a high-side 10-kV SiC MOSFET. Required properties of the gate driver such as high dielectric strength and low input-to-output stray capacitance were evaluated through a series of measurements. Switching voltage values and switching speeds of the driver were examined in an 800-V double pulse test with a 1.2 kV SiC MOSFET and compared with two other devices potentially capable of operating with the 10-kV SiC MOSFET.