Power supply system for electrically powered vehicle, and method for controlling the same

A power supply system for an electrically powered vehicle incorporating a motor for generating power to drive the vehicle, comprising:

• a main power storage device;
• an electric power feeding line configured to feed electric power to an inverter for driving and controlling said motor;
• a first voltage converter provided between said electric power feeding line and said main power storage device, and configured to convert voltage therebetween bidirectionally;
• a plurality of sub power storage devices provided in parallel to each other;
• a second voltage converter provided between said plurality of sub power storage devices and said electric power feeding line, and configured to convert voltage between one of said plurality of sub power storage devices and said electric power feeding line bidirectionally;
• a connection unit provided between said plurality of sub power storage devices and said second voltage converter, and configured to selectively connect a sub power storage device selected from said plurality of sub power storage devices to said second voltage converter;
• and
• a switching control device for controlling selective connection between said plurality of sub power storage devices and said second voltage converter,
• said switching control device including
• a switching determination unit configured to determine whether said selected sub power storage device should be switched based on a state of charge of each of said plurality of sub power storage devices,
• a first electric power limiter unit configured to continuously decrease upper limit values on electric power input and output to and from said selected sub power storage device to 0 when said switching determination unit determines that said selected sub power storage device should be switched,
• a switching control unit configured to switch connection between said plurality of sub power storage devices and said second voltage converter when said upper limit values on electric power input and output have reached 0, and
• a second electric power limiter unit configured to continuously increase said upper limit values on electric power input and output to values corresponding to a state of charge of a sub power storage device newly connected to said second voltage converter after said switching control unit switched connection between said plurality of sub power storage devices and said second voltage converter.