| 摘要 |
PROBLEM TO BE SOLVED: To prevent the output voltage of an uninterruptible power unit from becoming an overvoltage, by adding a limiting value switching circuit which switches the limiting value of a limiting operator from a first limiting value to a second limiting value which is smaller than the first limiting value, for a prescribed period of time after the power supply of a load is switched to an inverter from commercial power supply. SOLUTION: When commercial power supply is interrupted, a limiting value switching circuit 42 detects the power failure and outputs a power failure signal by means of a power failure detecting circuit, and outputs an operation signal for a prescribed period of time by starting a timer circuit 43 based on the power failure signal. While the operation signal is outputted, the circuit 42 switches the limiting value of a limiting operator 31 from a first limiting value to a second limiting value which is smaller than the first limiting value by closing a switch 44a and opening another switch 44b. Therefore, the output voltage of an uninterruptible power unit can be prevented from becoming an overvoltage by overshooting. |
