Modeling the turn-off of IGBT's in hard- and soft-switching applications

The turn-off of IGBTs in hard- and soft-switching converters is analyzed using nonquasi-static analysis. It is shown that while the turn-off current waveform for hard-switching is governed solely by the device for a particular value of on-state current and bus voltage, turn-off current waveform for soft-switching is strongly dependent on device-circuit interactions, so that a trade-off between turn-off loss and switching time can be made using external circuit elements. Models are developed to explain IGBT turn-off for both hard- and soft-switching conditions. Hard-switching considers both inductive and resistive loads. Calculated results are validated by comparison with results of measurements and two-dimensional (2-D) numerical simulations.