Uninterruptible power supply apparatus and power failure compensating system

The present invention discloses an uninterruptible power supply apparatus, there is provided a certain incident detection period detecting the instantaneous voltage drop of the commercial power accident and the accident detection means blackout, a high-speed current limiting means and standby power interruption means, an accident of the commercial power supply occurred, until the above-described accident detecting means detects the accident, the high-speed current limiting means interrupts until the interrupt power supplied to the load circuit from the commercial power source, power is supplied from the DC power supply to a load immediately and the accident point continuously detected in the accident detecting means when the accident to a commercial power source, stops the PQ control, the high-speed current limiting circuit interrupting means interrupts the power when the load is supplied only from the direct current power source to supply electric power to the load from the commercial power source; and the response time of the PQ control is set to be more than accident detection period of the commercial power source detecting means accident length; also discloses a power compensation system, wherein: there is provided an uninterruptible power supply apparatus, an emergency generator, and a switch.