Performance Evaluation of Series Connected 1700V SiC MOSFET Devices

The low voltage SiC (Silicon carbide) MOSFET (1.2 kV to 1.7 kV) increases the switching frequency limits of a power electronic converter several folds compared to low voltage Si IGBTs. Significant increase in efficiency and power density of voltage source converters can be achieved. However, for medium-voltage high-power converter applications Silicon (Si) devices (4.5 kV and 6.5 kV IGBT) are still dominant. To explore the capability of low voltage SiC devices for medium or high voltage applications, series connection of 1.7 kV/300 A SiC MOSFET modules has been investigated in this paper. A simple RC snubber method has been used for dynamic voltage sharing to offset the turn-off delays due to mismatch on device's characteristics and/or gate signals. Experimental switching characterization with different values of RC snubbers have been carried out to find the optimal RC snubber which gives minimum voltage sharing difference, snubber losses and total semiconductor losses. This paper also intends to show an optimization of the RC snubber for series connection of a limited number of 1.7kV SiC MOSFETs for 6 kV dc bus and for a generalized dc bus voltage.