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

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

• a main power storage device;
• an electric power feeding line supplying electric power to an inverter that controls and drives 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 selected sub power storage device selected from said plurality of sub power storage devices to said second voltage converter;
• and
• a switching control device configured to control selective connection between said plurality of sub power storage devices and said second voltage converter,
• said switching control device including:
• a first determination unit configured to detect whether a remaining capacity of the selected sub power storage device in use has become lower than a first reference value that is set in advance;
• a second determination unit configured to generate, when said remaining capacity has become lower than said first reference value, a switch request to switch said selected sub power storage device in accordance with a vehicle state of said electrically powered vehicle;
• and
• a third determination unit configured to generate, when said remaining capacity of said selected sub power storage device has become lower than a second reference value lower than said first reference value, said switch request regardless of said vehicle state.