The Gate-Turn-Off Thyristor: A Breakthrough For The Retrofit of Existing Induction Motors From Fixed To Adjustable Speed

Commutation in a current source inverter for large medium-voltage induction-motor adjustable-speed drives has been cumbersome in the past. It has required relatively complicated circuitry, sometimes including large capacitor banks and special commutating circuits. As a result, progress in converting existing fixed-speed induction motors to adjustable-speed drives for fans, pumps, compressors, and blowers to save energy has been slow. Recently a breakthrough in the design of an induction-motor drive utilizing gate-turn-off thyristors greatly simplified commutation, thus making retrofits more feasible with less complicated inverters. One of the major advantages of gate-turn-off technology is a nearly sinusoidal output waveform for the motor. Since this new product is directed for use with existing induction motors, downtime and expense for conversion on-site to adjustable speed can be greatly reduced. Less investment is needed, and payout time is shortened. The GTO technology, application considerations, and new inverter design features are presented, and an example of drive economics is provided. © 1989 IEEE