POWER SUPPLY SYSTEM OF ELECTRICALLY DRIVEN VEHICLE AND CONTROL METHOD THEREOF

At the time of external charging, an external charging relay (RL1, RL2) is turned on, and a system main relay (SMR1, SMR2) is turned off. Therefore, a main battery (10) can be charged by electric power from an external power source (400), without applying an output voltage of the main battery (10) to a PCU (20). At the time of external charging, basically, a power supply voltage (Vs) for an auxiliary system (low voltage system) is generated by a sub DC/DC converter (115) of a small capacity, while a main DC/DC converter (60) of a large capacity used when vehicle is running is stopped. Only when the output of sub DC/DC converter (115) is insufficient to cover the power consumption by the auxiliary system, an ECU (80) operates the main DC/DC converter (60). Therefore, ECU (80) and auxiliary load group (90, 95) can be operated reliably while efficiency of external charging is improved.