Analysis of SiC MOSFETs under hard and soft-switching

Analytical models for hard-switching and soft-switching SiC MOSFETs and their experimental validation are described in this paper. The models include the high frequency parasitic components in the circuit and enable very fast, accurate simulation of the switching behaviour of SiC MOSFET using only datasheet parameters. The much higher switching speed of SiC devices over Si counterparts necessitates a clear detailed analysis. Each switching transient was divided into four distinct sub-periods and their respective equivalent circuits were solved to approximate the circuit state variables. Nonlinearities in the junction capacitances of SiC devices were considered in the model. Analytical modelling results were close to the LTspice simulation results with a threefold reduction in the simulation time. The effect of snubber capacitors on the soft-switching waveforms is also explained analytically and validated experimentally, which enables the analytical model to be used to evaluate future soft-switching solutions. It was found that the snubber branch can significantly reduce the turn off ringing of the SiC MOSFET in addition to the reduction of switching losses.