PURPOSE: To supply power to a load even upon interruption of a system power supply and to interrupt short circuit current upon occurrence of failures by detecting the current of an induction generator exceeding a predetermined level and interrupting a power converter.

CONSTITUTION: An inverter 2 is subjected to PWM control by a control circuit 3 such that a set phase lead reactive current is equal to an inverter output current I2 detected through a current detector CT2 and a phase lead reactive power of required capacity is outputted. When the output current I1 from an induction generator IG exceeding a predetermined level is detected, the PWM control is interrupted by a control interruption circuit thus interrupting the output from the inverter. If a fault occurs in a system power supply ES during operation excited with the power supply ES, a short circuit current flows from the induction generator IG and a self-excited operation unit 1 to the power supply ES side. The control circuit 3 detects the short circuit current and interrupts the PWM control signal thus interrupting the output from the inverter 2. Consequently, power can be fed to the load even upon interruption of the system power supply and short circuit current can be interrupted upon occurrence of failures.