Semiconductor control of motors

Abstract

The thyristor is now well established as the power control element in many forms of static electrical energy conversion system and, in particular, is widely used for the control of speed of both d.c. and a.c. motors. In the particular case of the d.c. machine, variation of the magnitude of the voltage applied to the armature and, in some cases, the field of the motor is required. When considering the control of the speed of an a.c. motor, variation in both the magnitude and frequency of the a.c. voltage applied to the motor will generally be required. These two different requirements must always be borne in mind when considering general thyristor circuits and the particular cases of a.c./d.c. conversion (controlled rectification) and d.c./a.c. conversion (controlled inversion) are the most widely used modes of operation for the control of motor speed.