Analysis of Parasitic Capacitors' Impact on Voltage Sharing of Series-Connected SiC MOSFETs and Body-Diodes

Abstract

The voltage sharing among series-connected SiC MOSFETs is more sensitive to the surrounding parasitic capacitors than Si IGBTs due to much higher dv/dt switching speed. To this end, this paper presents a detailed study of parasitic capacitors' impact on the voltage sharing of series-connected SiC MOSFETs and body-diodes. The impact of different heatsink connection schemes and the corresponding change of the parasitic capacitors are also analyzed. The study reveals that, for series-connected SiC MOSFETs, the parasitic capacitor differences affect the gate miller plateau voltage and ultimately the dv/dt during turn-off and the voltage sharing is more sensitive to gateto-heatsink parasitic capacitor. For series-connected body-diodes, the voltage sharing is more sensitive to drain/source-to-heatsink capacitors which results in different dv/dt turn-off voltages across the body-diodes under different heatsink connections. The voltage sharing between two series-connected 10 kV SiC MOSFETs is tested in a multi-pulse test setup under different parasitic capacitors conditions.