Performance Improvement of Medium Voltage Modular Multilevel Converter based Motor Drive using SiC MOSFETs

Modular Multilevel Converters have been proposed to be a viable topology for medium voltage and high power motor drives due to the stackable structure of the topology. This allows for a transformer-less drive, better output current THD and reduces input and output filter sizes compared to traditional topologies. Replacing the traditional Si IGBT based submodules with SiC MOSFETs has been shown to improve the overall efficiency of the MMC. However, the lower switching losses of SiC MOSFETs have not been fully utilized to realize further system level improvements in the MMC. In this paper, the impact of the SiC MOSFETs on the efficiency, power density and output current THD of the drive is compared against Si IGBTs using analytical and simulation. A 7 kV dc bus, 4.16 kV ac, 1 MVA, 0-1,000 Hz medium voltage variable speed drive based on 1.7 kV devices based is used for the comparison.