Digital power factor controller for induction motor

摘要

The power factor for an AC induction motor is automatically corrected by a digital control circuit which senses the supply voltage and current. It compares the power factor with a demanded value to allow the motor to work at optimum efficiency whatever the loading. An amplifier produces a square wave signal from the supply voltage and a second amplifier in the motor circuit produces pulses corresponding to motor current. A multivibrator produces pulses each time the current passes through zero and its output is applied to a microprocessor which determines the phase angle for comparison with a demand value held in the memory. An output via a switching circuit causes a triac to switch the motor on or off to correct the power factor.