The thyristor bridge of the inverter becomes eight series (one redundancy) and six arms of 6kV devices, and the ZVS commutation circuit becomes two series of 4.5kV anti-paralleled reverse-blocking self-turn-off power devices. In the ZVS commutation circuit, the same number of series as the thyristor bridge doesn’t necessary, so that only the commutation voltage of the thyristor is applied to the ZVS commutation circuit. Therefore,conduction loss of the ZVS commutation circuit is low. On the other hand, the motor loss is decreased, because its power factor is almost 1.