AC UNINTERRUPTIBLE POWER SUPPLY

PURPOSE:To prevent distortion of output voltage waveform regardless of the lead or lag power factor of load by applying a DC gate signal to the thyristor in one more power supply at the variation point of current phase signal. CONSTITUTION:An inverter 2 and a commercial power supply 1 are switched through a control circuit 7 in order to feed power to a load 3. When power supply is switched from the commercial power supply 1 to the inverter 2, gate signals of both thyristors A8, B9 are turned ON at first and turned OFF instantaneously then they are held lower than the sustaining current of the thyristor B9. Upon drop of the load current below the sustaining current, the thyristor 89 is turned completely OFF and gate signals of both thyristors C10, D11 in the inverter 2 are turned ON, and power is fed from the inverter 2 to the load at this time point. By such arrangement, uninterruptible switching is realized resulting in suppression of distortion of output voltage waveform.