Low speed servo system with second-order sliding mode algorithm

Performance of a servo motor drive system may deteriorate due to the effect of load disturbances, motor torque ripple and parameters variation, etc.. Especially, during low speed operation, speed tracking performance and dynamic response further deteriorate since the speed feedback is restricted. In this paper, a speed observer based on second order sliding mode algorithm is presented, which provides the first and second derivatives of a sampled smooth signal. By using this method, a slotless permanent magnet synchronous servo motor equipped with a moderate resolution (1000 ppr) encoder can run stably over the low speed region. Experimental results verify that the proposed method has rapid dynamic performance and very strong robustness against load disturbances and simultaneously attenuates chattering effectively. The method is easy to implement in practical applications.