Optimisation of IGBT switching by adaptive gate voltage control

The short circuit clearance in switching of PWM 3-phase inverters in a few industrial applications must be done in such a way that the maximum current and voltage ratings are not exceeded. The probability of frequent load short circuit, due to the load conditions, justifies the use of a special gate turn off scheme. As conventional RCD topologies should be avoided, in power inverters, due to additional stresses in the IGBT, owing to the interaction between the complementary snubber capacitors of an arm, this justifies the choice for a commutation aid and protection circuit based on a voltage limiter. Conventional drives, which have current commutation time optimised for the normal conditions of the converter, react quickly to the fault. This fast commutation diverts almost all the short circuit current to the limiter capacitor causing its overdimensioning, for the short circuit condition. If the short circuit current could be shared between the limiter and the power semiconductor the overvoltage may be reduced enabling the use of a capacitor with almost the same rating necessary for normal operation. This benefits the duties and working frequency. This paper presents the design and operation characteristics of a drive protection circuit ruling these characteristics.