ELECTRIC POWER SUPPLY SYSTEM

An electric power supply system includes an alternating current electric power supply circuit that converts direct current electric power of a first direct current sweep unit including a battery string into alternating current electric power using a first inverter and outputs it, and an alternating current sweep unit that includes a U-phase battery string, a V-phase battery string, and a W-phase battery string that are Y-connected. Output densities of batteries of the battery string are higher than output densities of batteries of the alternating current sweep unit. Alternating current electric power is output from the alternating current sweep unit and the alternating current electric power supply circuit, and after a predetermined period elapses, the output of the alternating current electric power from the alternating current electric power supply circuit is stopped.