A Speed and Power Factor Controller for Small Three-Phase Induction Motors

A form of controller/compensator is suggested for the speed control of small induction motors. This controller uses pairs of thyristors in each supply line, incorporated into a resistance/capacitance network. Smooth speed control may be realized over a wide speed range, and the motor current remains substantially sinusoidal. For a small laboratory type motor, the current was reduced by up to 30 percent, and high power factor was maintained over the whole speed range. The overall efficiency of the compensated system increased by about three percent over that of the uncompensated motor.