Sliding mode compensator for improving robustness of phase locked loop for encoderless servo drive

This paper presents new method for improving robustness of phase locked loop (PLL) used in encoderless control algorithm for estimating position and speed. The state based observer used as a PLL is modified by using sliding mode compensator. The sliding mode compensator is designed by using motor torque and PID compensator used in the state based observer. The proposed method is compared with the state based observer. It is verified by experiment that the proposed algorithm is robust as compared to the state based observer against the parameter variation such as load inertia.