Gate drive power recovery and regenerative snubber scheme for series-connected GTOs in high voltage inverters

Pulsewidth modulated (PWM) inverters for power levels above 10 MW are presently the target of ongoing research. The implementation implies the series-connection of semiconductor devices, like GTOs or IGCTs, even if multilevel topologies are considered. Areas of application are flexible AC transmission systems (FACTS), transformerless reactive series compensators, HVDC transmission, static VAr compensators, and high-power AC drives. Existing problems are dynamic voltage balancing between the series-connected devices, snubber energy recovery and the transfer of gate drive power across potential barriers of more than 10 kV. The paper proposes an integrated solution for these problems. Experimental results from an inverter half-bridge composed of four IGCTs are presented. The respective device ratings are 4.5 kV and 4 kA. The DC-link voltage is 10 kV