UNINTERRUPTIVE POWER UNIT

PROBLEM TO BE SOLVED: To provide an uninterruptive power unit of high reliability on power supply which does not affect the power supply to load, even if commercial power source goes off, at maintenance inspection of an AC switch circuit. SOLUTION: In an uninterruptive power unit composed of a CVCF1 comprising a power rectifier 11, a power inverter 12, a power rectifier-inverter 13, a selection switch 14, a switch 15, etc., a storage battery 2, a direct-sending bypass circuit 3, and an AC switch 4, the reliability on power supply is improved by enabling the inverter output of the CVCF1 to be supplied to load 7 through an AC switch maintenance to bypass the AC switch circuit 4 at maintenance and inspection of the AC switch circuit 4, by providing it with a switch circuit 5 for AC switch maintenance to bypass the AC switch circuit 4 anew.