Discrete-time sliding mode control of permanent magnet linear synchronous motor in high-performance motion with large parameter uncertainty

In order to meet the demands of high acceleration/deceleration and high-precision motion profiles, many motion control systems began to use direct-drive linear motor as the prime motion actuator. This arrangement has the advantage of providing high-performance motions with the advantage of providing high-performance motions with reduced mechanical components, but its major drawback is the effect of load variation on the overall system control. Unlike conventional ball-screw drive, a linear direct-drive system eliminates the mechanical couplings, rotary-to-linear translators, and reduction gears. Under this arrangement, any change or disturbance in the load would be directly reflected back to the motor and the control system. This would cause large deterioration in the motion profile. In this paper, a robust controller based on digital sliding mode control (DSMC) is proposed to overcome the load uncertainty problem. In the investigation, a permanent magnet linear synchronous motor (PMLSM) with large parametric uncertainty is chosen as the target study. First, the state space equations of the motor are established. Then the DSMC theory is applied to design a robust controller. The simulation results show that the system can achieve robust performance under large load variations. Thus, the proposed method is an effective mean of combating load variations and load disturbances in high-performance direct-drive systems.