Gate driver, snubber and circuit design considerations for fast-switching series-connected SiC MOSFETs

Abstract

Series connection of Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) is an interesting solution to design switches for voltages that are not yet commercially available or limited for single-die devices. However, inherent static and dynamic voltage balancing must be achieved. Voltage imbalance is caused by the device parameters spread, whose impact is pronounced in low-inductive circuit layouts. This study investigates the optimal design and tuning limits of resistor-capacitor (RC)-snubber circuits and non-adaptive, standard, voltage-source gate drivers for achieving the best balancing in transient and steady-state voltage distributions among series-connected discrete SiC MOSFETs operating at speeds up to $90kV/\mu s$. It has been shown that a larger parameter mismatch will lead to uneven switching energy losses and larger voltage imbalances. It was also experimentally shown that increasing the gate resistor to slow down the devices will not always improve balancing when their parameter spread is large. Thus, tuning recommendations for the RC-snubber circuit and gate driver were developed based on these findings.