Study On Robust Control For PMLSM Suspension Platform

Taking the project supported by Specialized Research Foundation of Higher Doctoral Program as background, this dissertation researches on the high-precision suspension platform constituted by a single permanent-magnet linear synchronous motor (PMLSM), based on feedback linearization method, for the characteristic of suspension and the double requirements of robustness and tracking performance,the second-order sliding mode control, mixed sensitivity method of H∞are combined to solve the robust position control problem of PMLSM suspension servo system with some uncertainties such as nonlinear coupling between variables, decrease of suspension stiffness, parameters variations, end-effects and load disturbances. The main contents are as follows:For the nonlinear coupling problem between variables of PMLSM suspension platform, the nonlinear coordinates transform and nonlinear state feedback are used to decouple the more input more output (MIMO) system into two independent single input single output (SISO) subsystems. For the problem of existence of parameters and load disturbances in addition the problem that the dynamic decoupling result of feedback linearization method is affected by the parameters changes, two second-order sliding mode speed and position controllers are designed for the two linear subsystems. Firstly,the feedback linearization method is designed to accomplish the dynamic decoupling of the MIMO system, then sliding surfaces of horizontal axis controller and vertical axis second-order sliding mode controllers are independently designed. Finally, the robust control laws are designed by super twisting algorithm of second-order sliding mode control. Simulation results show that this strategy preferably achieves the dynamic decoupling between variables of PMLSM suspension system, has good robustness to load and parameters variations, and simultaneously weakens the chattering effectively.H∞speed controller based on Pseudo-differential feedforward and feedback (PDFF)and position proportional controller are designed for the problem that the decrease of suspension stiffness for the suspension platform release the freedom of vertical which result in that the length of air gap is easily affected by the triple of thrust, normal force, load disturbances and other uncertainties. The concept of H∞loop shaping design is intruded to formulate the advanced PDFF to an H∞weighted mixed sensitivity problem,then the advanced PDFF controller can be found by coprime factorization and partial pole-placement technique to achieve the maximize of the dynamic servo stiffness (the minimize of the sensitive function). Simulation results show that the proposed controllers completely accomplish the dynamic decoupling of system and meet the requirement of robustness and rapidity for high-speed high-precision PMLSM suspension system.