POWER SUPPLY SYSTEM FOR ELECTRIC VEHICLE AND CONTROL METHOD THEREOF

A power supply system includes a main power storage devices (BA) and a Plurality of sub power storage devices (BB1, BB2). A converter (12B) is connected to a selected one of the sub power storage devices (BB1, BB2) to convert voltage between the selected sub power storage devices and an electric power feeding line (PL2) bidirectionally. Connection of the sub power storage devices is switched and, when the last sub powder storage is used, a request to disconnect the sub power storage devices is generated based on the SOC of the sub power storage device and the vehicle state. Specifically, where the SOC is included in a disconnection forced region in which the SOC is smaller than a reference lower limit, the sub power storage devices is forced to be disconnected regardless of the vehicle state. Where the SOC is included in a disconnection permitted region in which the SOC is higher than that in the disconnection forced region, the disconnection request is generated on condition that the vehicles is in such a state that will not affect vehicle's drivability.