PURPOSE:To obtain an auxiliary power device generating a less noise in operation and requiring less cost for output by driving a cage type 3-phase induction machine as a generator with an internal combustion engine for travel, or supplying a 3-phase electric current from a commercial power supply or a battery loaded in a vehicle to a 3-phase electric motor. CONSTITUTION:In the first mode, a cage type 3-phase induction machine 2 connected to an internal combustion engine 1 is operated as a generator for generating a 3-phase AC current. The 3-phase AC current so generated is converted to a DC current via the first inverter circuit 4 connected via a selector circuit 10. This DC current is supplied to the second inverter circuit 8 and again converted to an AC current for supply to a 3-phase electric motor 7. The power so obtained is fed to a load 6. In the second mode, the selector circuit 10 is connected to a 3-phase power receptacle 9 and the inverter circuit 4 is operated as a rectifying bridge for a commercial power supply, thereby feeding power from the commercial supply to the 3-phase electric motor 7. Furthermore, in the third mode, a current is supplied from a battery 5 to the DC side of the second inverter circuit 8, and this 3-phase current is supplied to the 3-phase electric motor 7 for giving power to the load 6.
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