Sliding Mode Control Of Linear Motor Based On Hysteresis Characteristic Function

Linear Motor is a kind of electromagnetic device used to generate linear motion directly without any intermediate transmission links. So the motor has the characteristics of simple structure, quick speed, high efficiency and easy to maintain. Especially, permanent magnet linear synchronous motor (PMLSM) has the advantages of high response, high rigidity and high accuracy, thus, it is widely applied to more and more areas gradually. PMLSM is the best choice of actuator in servo system. However, the precision control of PMLSM is seriously influenced by the linear motor’s slot effect, end effect, changes of system parameters (such as mover mass, viscous friction coefficient), non-linear changes of gliding friction and observation noise of state. Aiming at the various disturbances, PMLSM is taken as the research object and several improved sliding mode control (SMC) strategies are designed for it in the thesis. The major results achieved are as follows:(1) Analyzing the main reason of the“chattering”phenomenon in SMC, a hysteresis function is designed to replace the sign function of the exponential reaching law in order to reduce the switching frequency in the lag region, which decreases the system’s chattering frequency and restrains the system’s“chattering”phenomenon effectively. The improved control strategy is simple and it can be realized easily. The effectiveness of the proposed control strategy is demonstrated by simulation.(2) Contrasting with the reaching law based on the saturation function, a new sliding mode reaching law is proposed, in which the saturation function of the reaching law is replaced by an adaptive dead-zone saturated function. By setting the dead-zone, the system’s chattering amplitude in the lag region is decreased so as to improve the control accuracy. Meanwhile, the boundary layer gradually reduces with the convergence of the state trajectory. When the thickness of the boundary layer reduces to zero, the boundary layer coincides with the dead-zone switching plane, which enhances the system’s robustness in the dead-zone switching plane and reduces the system’s“chattering”phenomenon effectively.(3) Combining the two points above, a new sliding mode reaching law is proposed, in which a dead-zone hysteresis function is substituted for the dead-zone function of the traditional reaching law. By reducing the switching frequency in the lag region, the system’s chattering amplitude is effectively reduced. Then, the sliding mode control strategy based on the dead-zone hysteresis function is proved that can be established in theory, and its control effect and reaching effect is better than that of the sliding mode control strategy based on the dead-zone function. Thereby, the reaching law based on the hysteresis characteristic function can not only meet the basic requirements of sliding mode control, but also effectively restrain the chattering degree of the system so as to get a perfect control effect.(4) The PMLSM physical control experiments are carried on the linear motor experiment platform, including the system identification and the confirmatory experiments of the three points involved above. The merits and faults of different control strategies are compared and analyzed according to the experimental results. Experiments show that the three kinds of improved sliding mode reaching law methods, can not only work on the experiment platform of PMLSM, but also effectively mitigate the contradiction between the anti-jamming capability and the“chattering”phenomenon in SMC. Then, the system has a better robustness and a greater control effect, which means that the improved control strategies can be used in certain projects effectively.