| 摘要 |
PURPOSE:To prevent a synchronous motor or a load from being damaged due to transient current and switch a variable frequency power source to another AC power source, by correcting the deviation of an internal phase difference angle due to the scale of motor armature current, and by executing synchronous detection. CONSTITUTION:By a phase arithmetic unit 12, the load inducedvoltage E of a synchronous motor 1 and armature current Ia fed from a variable frequency power source 5, including phase between them are detected, and arithmetic is performed on an internal phase difference angle. As this result, a phase difference taken into another consideration, for example, an element due to the natural deceleration of the motor is added to, and a detection phase difference is suggested to a synchronous detector 10. Accordingly, a phase difference between the voltage of an AC power bus line 1 at the time point when the making of a system switch 2 is completed, and the voltage of a motor bus line 7 is made less because a difference between non-load induced-voltage and load induced-voltage is corrected, and great transient current is not to flow, and so the motor or the load can be prevented from being damaged. |
