Uninterruptible power system

An uninterruptible power system capable of reducing strain in an output voltage thereof as compared with the prior art. A DC voltage control circuit of a current control system obtains an input current command value on the basis of a multiplied value between a differential voltage between a DC voltage command and a DC-side voltage of a power converter and an output of a reference voltage forming circuit. A current control circuit outputs, as a current control command, a value obtained by subtracting a value of a load current flowing to a load and a value of a current flowing from an AC side into the power converter from the input current command value. An AC current flowing through an AC switch is used as the input current command value during a period of time for which an abnormal voltage detection circuit detects momentary abnormality.