PURPOSE: To eliminate the application of an overvoltage to an inverter at abrupt load reducing time by interrupting a thyristor which forms a part of a rectifier when the output voltage of the rectifier arrives at a reference voltage.

CONSTITUTION: The high frequency wave 3-phase output of a high frequency generator 12 connected directly with a gas turbine engine 10 is converted by a full-wave rectifier 14 including a thyristor into a DC power. The output of the rectifier 14 is supplied through a smoothing capacitor 15 and an inverter 16 to a load. An overvoltage preventing circuit 18 interrupts thyristors 14a∼14c when the output voltage of the rectifier arrives at the value of the reference voltage. Thus, it prevents an inverter from damaging due to the overvoltage of the output of the rectifier.