Sensorless speed control of a permanent magnet DC motor by compensating the plant nonlinearities

Permanent magnet dc motors are popular for the simplicity of their control. Exist a few methods of sensorless speed control (SSC) of these motors. Each of these methods has its limitations that restrict its wider applicability. One of these methods uses the sensing of applied armature voltage and armature current to obtain an estimate of the motor speed, and then uses this estimate for the feedback control of the motor speed. In the microcontroller-based control of a PMDC motor, or a dc motor with separate fixed excitation, driven by a switchmode dc-dc converter, the converter may have a nonlinear input-output characteristic that reduces the tracking accuracy of this method. This paper presents a way to obtain a compensator of this characteristic automatically, and to thus improve the performance of the method.