Robust Speed Control For Permanent-magnet Linear Synchronous Motor Based On Sliding Mode

Taking the project supported by National Natural Science Foundation of China and by Education Office Foundation of Liaoning Province as background, this dissertation researches on the permanent-magnet linear synchronous motor(PMLSM) servo feeding system used in modern advanced NC machine tool. And based on sliding mode control, for the characteristic of direct drive and the double requirements of robustness and tracking performance, several theories and methods, such as feedback linearization, high-order sliding mode and singularly perturbation, are combined to solve the robust speed control problem of PMLSM servo system with some uncertainties such as nonlinear coupling between variables, parameters variations, end-effects and load disturbances. The main contents are as follows:For the electromechanical coupling problem of PMLSM, the nonlinear coordinates transform and nonlinear state feedback are employed to decouple the servo system into two independent subsystems, that is, linear current and speed subsystems. Then, a speed tracking controller is designed for the linear speed subsystem. The mover acceleration and load disturbance signals needed by feedback linearization are observed robustly through an extended sliding mode observer. The stability of nonlinear closed-loop system composed of feedback linearization, speed tracking controller and sliding mode extended observer is analyzed by Lyapunov stability theory.The second-order sliding mode control is employed to realize the dynamic robust decoupling between speed and currents, and between direct and quadrature axis currents of PMLSM servo system in the existence of parameters and load disturbances uncertainties. The sliding surfaces of speed controller and direct axis current controller are independently designed. The robust control laws are designed by twisting algorithm of second-order sliding mode control. And a robust differentiator is designed to observing the acceleration signal robustly based on the super twisting algorithm. This strategy preferably achieves the dynamic decoupling between variables of PMLSM servo system, has good robustness to load and parameters variations, and simultaneously weakens the chattering effectively.For the high-order nonlinear coupling model of PMLSM servo system, the block-diagonalization method of singularly perturbation theory is used to decouple PMLSM servo system into fast and slow subsystems with two different time scales. The controllers of fast and slow subsystem are designed by sup-twisting algorithm of second-order sliding mode control respectively. Then the time scales are uniformed and the control signals are synthesized to obtain the composited control, to implement the high response robust speed control for PMLSM servo system.The PMLSM experiment system is established using TMS320 LF2407A. A dual-linear motor system added load experiment scheme is employed, in which one of the two linear motor control system adopts speed open-loop and current closed-loop to simulate the suddenly added load. Vector control based on PI control, second-order sliding mode control and second-order sliding mode control based on singularly perturbation are experimentally compared and studied with no-load, load and mover quality variations respectively, which verify the feasibility of the theory studies and simulation results of the proposed control methods.