Research on an improved DC-side snubber for suppressing the turn-off overvoltage and oscillation in high speed SiC MOSFET application

摘要

Due to the high switching speed of SiC MOSFET, the parasitic parameters and the low damping in the circuit, the turn-off overvoltage and oscillation of the freewheeling diode and SiC MOSFET are very severe. Based on the terminal impedances during the turn-off transition of the freewheeling diode and SiC MOSFET, the mechanism of the turn-off overvoltage and oscillation are analyzed and the suppressing method is researched in this paper. The DC-side snubber, which is the high-frequency decoupling capacitor in parallel with the phase-leg configuration, is a simple suppressing method but will lead to the low-frequency oscillation overlaying the high-frequency oscillation on the turn-off voltage. In order to improve the suppressing effectiveness of the simple DC-side snubber to suppress the low-frequency oscillation on the turn-off voltage, this paper proposes an improved DC-side snubber, which is the high-frequency decoupling capacitor in parallel with the capacitor-damping branch. The theoretical derivation and simulation of the improved DC-side snubber are presented. Finally, the experimental verification is carried out based on the double-pulse test circuit to prove the validity and effectiveness.