Patent ID: 8217618

Claim:
A controller for a three-phase induction motor, comprising: an exampling circuit configured to check a zero passing point of three-phase source voltages and output a first signal; a sensing circuit configured to sense variation in a motor load and output a second signal and a third signal; an acquiring circuit configured to check the zero-passing point of motor current and output a forth signal; a processing unit configured to receive the first signal from the exampling circuit and compute a firing angle based on the first signal to generate a fifth signal, and to determine whether the three-phase induction motor is operating normally based on the second signal and the third signal from the sensing circuit, and the forth signal from the acquiring circuit; a firing circuit configured to receive the fifth signal from the processing unit and output a sixth signal based on the fifth signal; and an AC to AC converter configured to drive the three-phase induction motor based on the sixth signal.