THREE-PHASE POWER FACTOR CONTROLLER WITH INDUCED EMF SENSING

摘要

A power factor controller for an A.C. induction motor (10) is provided which is of the type comprising thryistor switches (110), (111) and (112) connected in series with the motor, phase detectors (122), (124) and (126) for sensing the motor current and voltage and providing an output proportional to the phase difference between the motor voltage and current, and a control circuit, responsive to the output of the phase detector and to a power factor command signal, for controlling switching of the thyristor. The invention involves sensing the induced emf produced by the motor during the time interval when the thryistor is "off" and for producing a corresponding feedback signal for controlling switching of the thyristor. The sensed emf is also used to enhance "soft" starting of the motor.