Hybrid Multi-level Clamp for Series-connected IGBT Voltage Balancing

Series-connected of medium voltage IGBT can achieve better trade-off between turn-off loss and saturated voltage drop, total costs of devices could be lower with most advanced chip technology and largest scale of mass production. In this paper, three voltage imbalance modes of series-connected IGBTs are analyzed to get detailed insight and guide equalization circuit development. Then, a hybrid multi-level clamp circuit which integrated static resistor, multi-level active clamp and tail current passive clamp is proposed. Modified active clamp function are added to maximize the clamp current influence on switch trajectory control. The proposed multi-level clamp circuit can be adapted to busbar voltage fluctuation and load current variation, experiment results verified that the circuit can even the voltage imbalance in different stages of switching with much lower losses and volume.