Patent ID: 7872888

Claim:
An electric power conversion system comprising: a direct current power supply; a plurality of main circuit switching devices bridge-connected to convert direct current of the direct current power supply to alternating current, each respectively including a free wheeling diode connected in reverse parallel thereto; and a reverse voltage applying means for applying a reverse voltage smaller than a voltage of the direct current power supply to the free wheeling diode, upon a cutoff of back-flow current of the free wheeling diode, the reverse voltage applying means comprising a series connection of a low-voltage direct current power supply having a lower voltage than the direct current power supply, a reverse voltage application switching device having a lower withstand voltage than the main circuit switching device and adapted to turn on upon a reverse recovery of the free wheeling diode, and an auxiliary diode having a shorter reverse recovery time than the free wheeling diode, the reverse voltage application switching device being a device having holes as a majority carrier.