Adaptive filters for rotational speed estimation of a sensorless DC motor with brushes

Brush-commutated small DC motors are widely used because they are cheap and easy to run. In controlling speed of such motors, estimation of rotational speed without sensors are required. In this study, a method to estimate the rotational speed is proposed, based on the fact that rotational speed of this motor is proportional to the fundamental frequency of the ripple component on the supply current of the DC motor. In the proposed method, an adaptive line enhancer (ALE) is used, and is modified to obtain the fundamental frequency of the ripple current. In the modified ALE, a solution using a lowpass filter is proposed and it is confirmed that the variance of the parameters of ALE can be reduced and rotational speed of the DC motor can be estimated.