A power factor control system for an A.C. induction motor determines the difference in phase between the voltage applied to the motor and the current drawn by the motor. Based upon this difference in phase, an integrator generates an error signal. The error signal is compared with a ramp wave to derive...http://www.google.de/patents/US5389869?utm_source=gb-gplus-sharePatent US5389869 - Power control system for an A.C. induction motor
