Stability of current-sensorless control of permanent magnet synchronous motors

Abstract

This study applies Lyapunov's direct method to verify the stability of permanent magnet synchronous motors under singular perturbation control designs. The position and velocity controller designed herein does not require the current information of the motor for feedback purposes (current-sensorless), but the steady-state d-axis current can still be controlled to zero to minimize power dissipation. Combining Lyapunov's linearization stability analysis, the relation between overall closed-loop stability and control gains of this controller is also revealed. Experimental results demonstrate the effectiveness of this current-sensorless controller. In addition, the performance of this current-sensorless controller is compared with that of a full-state feedback controller. Clearly, the proposed current-sensorless controller can achieve zero positioning error within the resolution of an optical encoder. However, the same result is less easy to achieve using a full-state feedback controller due to the noise effect on the current measurements.