Dynamic voltage balancing of series connected IGBTs using slope regulating and voltage clamping

Series connection of IGBTs is applied to increase the voltage rating of converters. The critical issue is to balance the dynamic voltage of each device in the series string. This paper investigates an auxiliary circuit as a solution involving slope regulating and voltage clamping. It adjusts the Miller capacitance and gate current with additional capacitors and feedback current from collector to gate, by which the gate voltage and then the collector-emitter voltage are controlled. Consequently, the differences between block voltages of IGBTs are restrained. A 15 kV test rig is established and experiments are carried out successfully based on up to sixteen 1.7 kV/800 A IGBTs in series connection. It is proved that the proposed circuit has no limitation to the number of series connected devices and is simple, reliable and low-cost.