| 摘要 |
PROBLEM TO BE SOLVED: To prolong the backup time at the time of power interruption by a constitution wherein a speed control setter performs speed control of an AC motor through an inverter with the controllable speed range of the AC motor when a power interruption detection time and a DC voltage detection value drop below predetermined lower limits and minimizes the battery capacity. SOLUTION: When a commercial AC power supply is interrupted due to some causes and a battery 5 is consumed by prolonged power interruption to cause DC voltage drop below a predetermined lower limit, a DC voltage detector 17 detects the DC voltage which is then fed to a speed control setter 18. The speed control setter 18 delivers a control voltage, corresponding to preset controllable speed range of AC motors 14, 15, to inverters 10, 11 thus controlling the speed of AC motors 14, 15. Consequently, long time backup is realized upon interruption of the commercial AC power supply while minimizing the capacity of the battery 5. |
