H∞ robust control of permanent magnet linear synchronous motor in high-performance motion system with large parametric 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 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 will be directly reflected back to the motor and the control system. This will cause large deterioration in the motion profile. In this paper, the authors proposed to use an H_∞ robust-controller 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 H_∞ control theory is applied to design a robust controller which allows mass variation of the moving part ranging from 0 to 100 percent of nominal load. To minimize the error between the actual response and the reference, the controller parameters are optimized using genetic algorithms (GA). The simulation and experimental results both 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.