Study in Low-speed Stabilization of Direct Drive Permanent Magnet Ring Torque Motor Servo System

A control scheme based on combining H_infin robust control with and sliding mode control for direct drive permanent-magnetism ring torque motor (PMRTM) in the feed driving system of NC machine rotary table is presented in this paper, which solves the conflict between tracking and robustness of the servo system. In the low-speed, the sliding mode controller is designed to ensure that the system has fast tracking characteristic. While the H_infin controller can reject suppress the disturbances within the close loop (including the load and the torque ripple), and can effectively minimize the chattering of sliding mode control which could influence the low-speed steady state performance of the system. Some simulation results show that this control scheme not only assures the low-speed steady state performance and enhance the fast characteristic, but also has strong robustness to parameter variations and resistance disturbance