Wide-range speed control of industrial brushless servomotors

Considering the performance and cost, the position and wide-range speed control of a servo control system generally adopted an incremental encoder. The so-called M method, based on averaged calculation of encoder pulses, generally results in detection lag during speed estimation. It would be much worse when the interval between the pulses is wider than the sampling time at low motor speeds. As a result, the detection delay time may make the speed control system unstable. In the paper, instead of using a disturbance torque observer, a reference model via proportional-integral-derivative (PID) control is proposed to approach the instantaneous motor speed and improve the low-speed control performance. A digital signal processor (DSP)-based industrial brushless motor drive will present the experimental results, which show the improved resolution and the effectiveness of the proposed method.