JPS5612877A - Method of equalizing and controlling synchronous motor - Google Patents

Abstract

PURPOSE:To rapidly synchronize a synchronous motor by using an output signal corresponding to the potential of both voltage of bus power supply and the voltage of the motor as a speed correction signal when the frequency difference between the bus power supply and the motor becomes zero. CONSTITUTION:When the speed of a synchronous motor 6 becomes equal to the frequency of an AC bus power supply 1 to reach a synchronous speed, a signal SY representing that the motor 6 reaches synchronous speed is supplied to a phase difference detecting circuit 14 from an eqaul speed signal circuit 13. The circuit 14 detects the phases of the induced voltage of the motor 6 and of the power supply 1 and is operated to produce a correction signal proportional to the phase difference to equalize both the phases. A phase difference correcting circuit 16 applies a phase difference correction amount Stheta for generating an acceleration amount corresponding to the phase difference signal from the circuit 14 to an AC variable speed drive unit 3. On the other hand, the signal SY is also applied to a synchronous speed reference circuit 15, which thereupon retains the speed reference value thereat, and accordingly corrects the motor 6 only the phase difference at the time when reaching the synchronous speed to zero. Accordingly, it can rapidly synchronize the motor.