Power supply system for vehicle

The invention relates to an A.C. generator (1) with a rotor that is equipped with a permanent magnet and a field coil. The output of the A.C. generator (1) charges the high-voltage battery (12). Voltage of the high-voltage battery (12) is stepped-down by a DC/DC converter (6) and supplied to the low-voltage battery (11). When the motor controller (9) detects that the field coil has not been energized, the higher-rank controller (40) switches so as to generate power by means of the permanent magnet of the A.C. generator (1) and charge the low-voltage battery (11). This mechanism enables power to be generated when a circuit malfunctions. Thereby, a power supply system for vehicle can generate power when a circuit malfunctions so that the driver on the vehicle can drive the vehicle to a repair shop.