Sensorless speed control of high speed brushed DC motor by model identification and validation

Abstract

The paper describes an accurate method for speed control medium torque (92.17 mN·m), high speed (9778 RPM) Brushed DC motor without using a physical speed sensor. The back EMF is a representative value for the rotational speed of the motor which has been further used for correlation with speed. Several experiments have been carried out to relate back EMF with speed of the motor rotating a fixed load, no load and variable load. The speed so calculated will generate the error data after comparison with set point. The error is corrected by a discrete PID controller with sampling time of 50 ms, developed in an embedded system. A model of DC motor is identified and validated to determine optimum P, I, D constants and transfer function for accurate speed control. The closed loop system gives an accurate control of DC motor with settling time of 2.45 seconds, peak overshoot of less than 5% and accuracy of speed control less than +/- 1% of full scale.