Speed Control For Asynchronous Motors

EE 29 February 1989 DESIGN IDEAS The contents of this column are based solely on information supplied by the author and do not imply practical experience by Elektor Electronics. SPEED CONTROL FOR ASYNCHRONOUS MOTORS The possible design is discussed of a remarkably simple frequency converter that ensures good torque over a wide speed range for mains-powered motors of up to 100 W Applications of the speed controller include ventilators and pumps. Induction motors with a squirrel-cage rotor are popular because of their simplicity and low cost. Compared with other types of AC-powered motors, speed control for the squirrel-cage in- duction motor, is, however, a relatively complex matter. Simply reducing the motor voltage generally gives poor speed control, and results in inacceptable loss of torque at low speeds. Frequency con- trol of the motor supply voltage is a bet- ter method, since it exploits the fact that speed of the squirrel-cage motor is directly related to frequency. The ba...