METHOD AND APPARATUS FOR CONTROLLING INDUCTION MOTORS

摘要

The present invention provides for detecting rotor speed through the use of sense coils on the stator teeth. Voltage ripples caused by the rotor slots is detected by combining the signals of several such sense coils so that the fundamental voltage signal is cancelled or rejected and only the ripple voltages remain, a signal proportional to rotor speed. Several alternative methods for implementing that technique are discussed herein. At low induction motor speeds, the present invention filters out the voltage ripples and incident third harmonics and instead estimates rotor speed from the fundamental voltage. When the induction motor is already being driven by a prime mover, the present invention selects a proper initial frequency command for initial motor start by identifying rotor speed from the PWM inverter. Further, the present invention provides for using a generator to control voltage to the induction motor, with a PWM inverter to control frequency signals to the induction motor.