Operating characteristics of single-phase capacitor motors driven from variable frequency supplies

The analysis presented shows that a variable frequency power supply can be used for speed control of single-phase induction motors which are equipped with auxiliary windings and capacitors. Using the standard scalar control technique for three-phase induction motors on the capacitor motor works best at relatively high frequencies, but the torque must be derated below about 50% of base frequency to yield a sufficient margin from breakdown torque and to prevent overheating the machine. The torque performance of the capacitor motors can be enhanced by altering the voltage-frequency control law. One method that provides good results is to control the voltage such that the internal power dissipation in the motor is held constant.<>