Apparatus and Methods for Controlling Induction Motors

摘要

When induction motors are lightly loaded their power factors and efficiency are poor but in the present invention power factor is controlled regardless of load. An induction motor 10 is connected by way of a triac 12 to a supply 11. The voltage across the triac 12 is monitored by a comparator 21 for voltage steps which correspond to current turn-off and a signal is developed at the output of an amplifier 19 which represents error from required phase lag. A comparator 17 and trigger pulse generator 16 responsive to ramp generator 18 trigger the triac 12 in accordance with the error. A circuit 31 overrides the control system during starting. A number of further induction motors may be connected in parallel with the motor 10.