a charging facility collects dc power supplied from a plurality of power supply devices in a dc bus , and then uses the dc power to charge an on - board rechargeable battery for an electric vehicle . in an energy management method for a charging facility , each power supply device operates under independent automatic control according to a change in voltage in the dc bus . an upper - level control unit which collectively controls a plurality of power supply sources is not required , and a plurality of power supply devices can be combined with a simple configuration achieved by merely connecting respective output terminals to the dc bus . in addition , the entire charging facility can be operated flexibly . thus , it is possible to achieve a simple configuration and to allow flexible operation while a plurality of power converters are combined with a system power supply .