| Abstract |
As power electronic engineers increase the switching speed of voltage source converters for thepurpose of higher power density, the dI/dt and dV/dt across the power semiconductors increases aswell. A well-known adverse consequence of high dV/dt is parasitic turn-on of the power device in thesame phase leg as the device being triggered. This causes a short circuit with high shoot-throughcurrent, high instantaneous power dissipation and possibly device degradation and destruction. It iscritical for converter designers to be able to accurately predict this phenomenon through diagnosticand predictive modelling. In this paper, a physics-based device and circuit model is presented togetherwith experimental results on parasitic turn-on of IGBTs in voltage source converters. Because themodel is physics based, it produces more accurate results compared with compact circuit models likeSPICE and other circuit models that use lumped parameters. The discharge of the Miller capacitance issimulated as a voltage dependent depletion capacitance and an oxide capacitance as opposed to alumped capacitor. The model presented accurately simulates IGBT tail currents, PiN diode reverserecovery and the non-linear miller capacitance all of which cannot be solved by lumped parametercompact models. This is due to the fact that the IGBT current in the model is calculated using theFourier series based re-construction of the ambipolar diffusion equation and the miller capacitancesare calculated using fundamental device physics equations. This paper presents a physics-based deviceand circuit model for parasitic turn-on in silicon IGBTs by numerically modelling the minority carrierdistribution profile in the drift region. The model is able to accurately replicate the transientwaveforms by avoiding the use of lumped parameters normally used in compact models. |
