Robust Repetitive Control For Permanent-magnet Linear Synchronous Motor

Taking the project supported by National Science Foundation of China and by Education Office Foundation of Liaoning Province as background, this thesis researches on the Permanent Magnet Linear Synchronous Motor(PMLSM) servo feeding system used in NC machine of high speed and high precision. For the characteristic of direct drive and the double requirements of tracking performance and robustness for servo system in NC machine tool, it is very difficult to obtain the requirements of high velocity and high precision using traditional control scheme, therefore in the thesis the proposed scheme is to combine repetitive control, structure singular value and variable structure control against periodic disturbances caused by end-effects and friction, parameter variation and load disturbances to track periodic signals for PMLSM servo system.The thesis studies permanent-magnet linear synchronous motor servo system used in NC machine tool based on theoretical analysis and computer simulation. The mathematical model of PMLSM are analyzed, the vector control scheme (id=0) is confirmed, and Pseudo Derivative Feedback with Feed-forward(PDFF) speed controller is designed to increase servo stiffness and response speed of the system. To meet the high precision of tracking displacement, displacement controllers are designed respectively against end-effects, load disturbances and some uncertainties.Firstly, the essential repetitive control is developed to decrease the periodic disturbances of PMLSM and increase the tracking precision. The developed repetitive controller is composed of the phase exceeding compensator and the essential repetitive controller to counteract the response delay of speed controller and motor. The system is stable based on small gain theorem; therefore the servo system reduces the influence of the periodic disturbance of PMLSM servo system, and makes the system have good displacement-tracking performance for the periodic input signals.Secondly, the structure singular value repetitive controller was designed, which associated structure singular value theory(μtheory) with the discrete-time repetitive control theory in the existence of periodic disturbances, load disturbances and parameters variations uncertainties. The problem of structure singular value repetitive control was transformed into one of H∞optimal control using Linear Fractional Transformation(LFT). The Structure Singular Value Repetitive Controller(SSVRC) was achieved using D-K iteration procedure and made the servo system have stability, robustness and tracking performance.Finally, the discrete-time variable structure repetitive controller(DVSRC) was designed to increase the action of the repetitive control in the first period, to decrease the tracking error and develop the robustness of system, which associated variable structure control with repetitive control and included the quasi-sliding mode surface design and repetitive reaching control law design. The quasi-sliding mode surface decreased periodically and was defined in the boundary. DVSRC decreases the chatter, ensures the robustness to the exogenous disturbances periodically and improves the tracking precision of the servo system.