Predicting SiC MOSFET behaviour under hard-switching, soft switching and false turn-on conditions.

Circuit level analytical models for hard-switching, soft-switching and dv/dt-induced false turn on of SiC MOSFETs and their experimental validation are described. The models include the high frequency parasitic components in the circuit and enable fast, accurate simulation of the switching behaviour using only datasheet parameters. To increase the accuracy of models, nonlinearities in the junction capacitances of the devices are incorporated by fitting their nonlinear curves to a simple equation. The numerical solutions of the analytical models provide more accurate prediction than a LTspice simulation with a threefold reduction in the simulation time. The analytical models are evaluated at 25°C and 125°C. The effect of snubber capacitors on the soft-switching waveforms is explained analytically and validated experimentally, which enables the techniques to be used to evaluate future soft-switching solutions. Finally, the dv/dt- induced false turn on conditions are predicted analytically and validated experimentally. It was observed that consideration of nonlinearities in the junction capacitances ensures accurate prediction of false turn on, and that the small shoot through current due to false turn on can increase the switching loss by 8% for an off state gate bias of -2V.