POWER SUPPLY SYSTEM OF ELECTRIC VEHICLE AND CONTROL METHOD THEREOF

A power supply system (1) for a hybrid vehicle (100) includes a main power storage device (10-1) and a plurality of sub power storage devices (10-2, 10-3) used selectively. When an SOC of one of the plurality of sub power storage devices (10-2, 10-3) decreases to a predetermined value or smaller, an ECU (22) selects this sub power storage device as a sub power storage device to be charged. The ECU (22) controls a connecting unit (18) such that the sub power storage device to be charged is connected to a second converter (12-2). Furthermore, the ECU (22) selects the HV mode as the travel mode. In the HV mode, electrical energy stored in an electric powered vehicle is maintained because of electric power generation by an engine (36).