Effects of stray inductance on switching transients of an IGBT propulsion inverter and resulting gate control strategies

A 720 kVA transistor-based inverter unit for local transportation systems is described. The discussion is focused on the stray inductance of the commutation circuit (L/spl sigma/), the switching transients and a novel gate control strategy which limits transient overvoltages due to L/spl sigma/. A simple measurement of L/spl sigma/ is introduced. Based on switching transients, L/spl sigma/ can be calculated with a standard deviation of 4%. A closed loop control of the IGBT gates uses the collector emitter voltage as a feedback signal and adjusts the turn-off speed according to the inverter's point of operation. This guarantees an energy optimal turn-off transient without danger of transient overvoltage. Even under short circuit condition remains below a preset value.