| 摘要 |
PURPOSE:To prevent an excess current from flowing through a power conversion device when a momentary power interruption time is short by delaying the start of detecting the rotating speed of an AC motor by delay means when the momentary power interruption is recovered. CONSTITUTION:A delay circuit 9 delays a recovery detection signal output from a voltage detector 6 when the momentary power interruption is recovered, and delays the start of detecting the rotating speed of a rotating speed detecting calculator 7. Since the detection of the rotating speed is not conducted during the secondary functional reduction of the rotating speed due to the influence of windage of an AC motor by the circuit 9, the calculator 7 can accurately predict the frequency at the time of power horseplay by a linear approximating calculation. Thus, an AC motor 5 can be restarted without supplying an excess power to the motor 5 and a power conversion device 1. |
