UNINTERRUPTIBLE POWER SUPPLY

PROBLEM TO BE SOLVED: To prevent an excessive rush current from flowing to a load when switching the power supply from ON to OFF and vice versa at power failure. SOLUTION: Direct power supply is performed when a voltage of the input AC power is normal (S3), but at that time, output voltage values are measured for every n seconds to store them in a memory (S4). When there arises abnormality in an input voltage due to the instantaneous voltage drop or the like, a commercial AC power supply is cut off from the load, and electrical energy stored in an electrolytic capacitor is converted by an inverter to AC from DC so that it can be supplied to the load as compensation AC power (S6, S7), but the output voltage is controlled so as to coincide with a voltage value stored in the memory at a normal time through inverter control (S9). As a result, even if there is a variation in the voltage of the AC power supply, the voltage output to the load can be maintained nearly constant when switching the power supply from the direct power supply to the inverter power supply and vice versa the rush current caused by a potential difference can be prevented. COPYRIGHT: (C)2009,JPO&INPIT