ELECTRIC POWER SOURCE SYSTEM FOR ELECTRICALLY DRIVEN VEHICLE AND ITS CONTROL METHOD

A power supply system includes a main power storage device (BA) and a plurality of sub power storage devices (BB1, BB2). A converters (12B) is connected to selected one of the sub power storage devices (BB1, BB2) to convert voltage between the selected sub power storage device and an electric power feeding line (PL2) bidirectionally. When a request for switching the selected sub power storage device in use is generated, upper limits on electric power input/output to/from the selected sub power storage device are continuously varied. Thus, discontinuous variation of electric power input/output to/from the power supply system during the process for switching the selected sub power storage device can be avoided. Consequently, sudden change in a behavior of an electrically powered vehicle can be avoided.