UNINTERRUPTIBLE POWER SUPPLY

PURPOSE:To increase the operating frequency of an inverter transformer or an output transformer and to realize reduction in size and weight of an uninterruptible power supply by directly converting a commercial power supply frequency into a high frequency and operating the inverter in a high frequency region. CONSTITUTION:Power is normally fed from an AC power supply 1 through a first switch 2, a first power converter 4, a high frequency transformer 10 and a third power converter 20 to an output terminal 29. The first power converter 4 converts a commercial power supply frequency into a high frequency and a high frequency voltage corresponding to the waveform applied on the primary winding is induced in the secondary winding 18 of a high frequency transformer 10. An inverter is operated in the high frequency region and a high frequency transformer is employed as an output transformer communicating the primary and the secondary. Secondary output of the high frequency transformer is then converted into an AC commercial frequency waveform subjected to high frequency modulation from which high frequency components are eliminated to produce a commercial frequency sine wave which is fed to a load.