A novel reduced-order load torque observer based discrete-time sliding mode control for PMSM speed servo system

To enhance the control precision of permanent magnet synchronous motor (PMSM) under parameter variations and load torque disturbances, a minimal reduced-order load torque observer (MRLTO) based discrete-time sliding mode control (DSMC) scheme is presented. First, a DSMC controller is presented on the basis of the second-order discrete-time PMSM dynamics model to enhance the speed tracking response and robustness. Then, a self-tuning switching gain and the saturation function are introduced to suppress the chattering. Moreover, to simplify the implementation and further enhance the robustness against the disturbance of PMSM, a minimal reduced-order load torque observer is presented, which can provide accurate estimation and feed-forward compensation of the load disturbance. Stability of DSMC and MRLTO is analyzed, respectively. Simulation and experimental comparisons demonstrate the presented controller is superior.