Optimisation of overvoltage limiters for IGBT inverters

The short circuit clearance in IGBT based power must be done with gate control such that the current and voltage ratings are not exceeded. Conventional drives, using conventional off-commutation circuit, usually react quickly to the fault with current commutation time optimised for the normal working conditions of the converter. For inverters in the power range of several tens of kVA the physical arrangement of the semiconductors does not allow to continuously reduce the leakage inductance. So this fast commutation time diverts almost all the short circuit current to the limiter capacitor causing its overdimensioning, derating the commutation frequency. If the short circuit current is shared between the limiter and the power semiconductor the overvoltage may be reduced enabling the use of a smaller capacitor that benefits the duties and working frequency. This paper presents the design and operation characteristics of a drive circuit ruling these characteristics