Patent ID: 7019989

Claim:
An uninterruptible power supply system comprising: a circuit cutoff unit, inserted between an input end to which alternating-current power is supplied and an output end connectable to a load, for isolating the alternating-current power supplying side; a parallel power converting unit connected between the cutoff unit and the output end in parallel to the input end; a series power converting unit connected in series between a parallel connected point of the parallel power converting unit and the output end; an electricity storing unit permitting electric power to be interchanged between the parallel power converting unit and series power converting unit; and a power failure detecting unit that detects a power failure, wherein when the supply of the alternating-current power is within a normal predetermined range, the series power converting unit compensates the supply of the alternating-current power with the electricity storing unit taken as an electric power source so that a value of an alternating-current power output at the output end becomes a specified value of output, and the parallel power converting unit charges and discharges the electricity storing unit so that an amount of stored electricity in the electricity storing unit becomes a specified amount, and wherein when the power failure detecting unit detects a power failure, the cutoff unit isolates the alternating-current power supplying side, and the series power converting unit operates with the electricity storing unit taken as a power source so that the value of the alternating-current power at the output end becomes the specified value of output.