Minimum-Hard-Switching-Number Modulation Method for High-Frequency SiC-Based Impedance-Source Inverters

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.