Optimization design of high-voltage-balancing circuit based on the functional model of IGCT

Integrated gate commutated thyristors (IGCTs) are commonly used for high-voltage three-level pulsewidthmodulation-controlled voltage-source inverters. IGCTs are utilized in series connection when the output voltage is greater than the maximum rated voltage. Special measure must be taken to ensure the safety and reliable operation of the inverters, and to equalize the voltages across the IGCT modules, such as the dynamic voltage-balancing circuit using an RC snubber circuit. Based on the IGCT functional model, this paper presents an optimization design procedure of a high-voltage-balancing circuit for a 6-kV/1250-kW inverter. A tradeoff is made between the voltage imbalance, maximum turn-on current, di/dt endurance, and losses. Simulation and experiments validate the feasibility of this procedure. In addition, the specific transient processes in the three-level topology with voltage-balancing circuit are simulated, and their inner mechanisms are analyzed.