IGBT behavior during desat detection and short circuit fault protection

A common fault condition in motor drive applications involves an IGBT turning on into a short-circuit. If the only impedance is the cable inductance to a shorted motor winding, the current through the device ramps up very rapidly until it saturates, forcing the IGBT voltage to rise to the DC clamp. After fault detection, depending on the point at which the fast turn-off pulse is applied, very different levels of hole current can flow under the n⁺ source region, making this an important factor in the successful containment of the fault current. We present experimental observations showing that IGBT failure under short-circuit conditions is dependent on where the turn-off pulse is applied. The physics of this behavior is explained using numerical mixed-mode simulations. A practical two step gate waveform is studied for avoidance of device failure under short-circuit conditions, and is experimentally demonstrated