Effect of Decoupling Capacitance and $RC$ Snubber on SiC MOSFET Bidirectional Switch

Abstract

SiC MOSFET is fast switching, high voltage blocking and current carrying, and low loss device is much closer to ideal switch. Therefore, SiC MOSFETs applications are high power density matrix converter, battery charger in electric vehicles, and others. The matrix converter is built on bidirectional switches, which allow both positive and negative current and block both positive and negative voltage. The SiC MOSFET based bidirectional switches are more prone to the detrimental effect of power supply line inductance due to their very high switching speed. The very high rate of current change with time during turn OFF may damage the switch due to overvoltage across it. The conventional methods to reduce this effect are decoupling capacitance and RC snubber. The decoupling capacitance method reduces the overvoltage across the switch for small line inductances, does not slow down the switching speed, and is easier to implement compared to the RC snubber method but increases the radiated electromagnetic interference. However, these methods are not studied for SiC MOSFET based bidirectional switches. Therefore, this paper compares the two methods for SiC MOSFET based bidirectional switch with the help of time domain analysis, simulation, and experimental results. The comparison shows that sustained oscillations in switch voltage exist with decoupling capacitance and is absent with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$RC$</tex> snubber.