Advances in brushless motor control

Brushless DC servomotors have been replacing brush type motors in machine tool and robotics applications over the last number of years. The well known advantages of brushless over brush motors include improved reliability, higher power to weight ratios, and an overall better dynamic performance. This paper briefly describes the evolution in the control of brushless drive systems which has been driven by higher levels of integration and reductions in cost of the control electronics. The first electronically controlled DC brush motor systems used analog control circuits and thyristor power switches. The present day brushless drives use high power transistor switches and a high speed microcontroller or a digital signal processor which implements digital control loops for the motor position, velocity and current. This paper describes in some detail the hardware and software elements in some typical drive systems.