The Study Of Robust Tracking Control For Permanent Magnet Linear AC Servo System

With the requirement of machining efficiency and accuracy becoming higher, numeric control machining technology is developed towards high speed and ultra-high speed, precision and ultra precision, the linear servo drive feed unit with high precision and high speed response ability is produced. Due to eliminating a series of adverse effects that are generated by mechanical drive linkage, the fast response ability and motion precision of the feed system are enhanced greatly, thus this becomes one representative type of the advanced technologies in the new generation numeric control machine tools. In the subject, permanent magnet linear synchronous motor (PMLSM) servo system is a researched object.Comparing with the traditional "rotating motor plus ball screw", although the linear servo system eliminates those adverse effects, this increases the difficulty on the control. The load changes and the external disturbances and so on will directly influence the servo performance of the system without attenuation. And the inner parameters perturbation of the system, the end-effects, nonlinear factors and so on will reduce the system performance and machining precision of the machine tools. The demands of the high speed, high precision and micro-feed are met difficultly. Therefore, the effective control strategy must be adopted to overcome the influences of those factors.PMLSM servo system is a dynamic complex nonlinear system with high precision and fast response characteristic, its main performances are the tracking ability to the input command and disturbances rejection ability to the disturbances. In the ideal case, the output is able to track the changes of the input command without delay and overshoot. It is difficult to meet together the requirement that is the tracking performance of the system to input signal and resistance disturbances performance to the uncertainty using conventional PID controller. For it, the zero phase two-degree of freedom (2-DOF) H_∞ robust tracking control strategy is firstly proposed to solve above-mentioned problem. Zero phase error tracking controller (ZPETC) is adopted as the feedforward controller to effectivelyimplement the fast tracking performance of the system;//?, robust controller is used as the feedback controller to eliminate the influences of the parameters perturbation, the external load disturbances and the uncertain factors, therefore the robust stability and robustness of the system are improved.ZPETC is a feedforward controller based on inverse system idea. However, it depends on the model of the system and is sensitive to the parameters changes of the system. For it, the variable gain ZPETC is presented to overcome modelled error and the influence of the parameters changes. Generally ZPETC is used as feedforward controller to compensate for the phase error, but this will also cause small gain error. To improve the tracking performance of ZPETC, the optimal design scheme of feedforward controller based on L2-norm is proposed in the paper. The optimal digital prefilter (DPF) is designed by selecting proper objective function. The scheme can ensure the phase error of the system to be zero, at the same time, the gain performance of the system is greatly improved.In the thesis, the proposed control schemes have strict theoretical basis, pass the theory verification. The simulation results show that those methods are very effective, not only enhance the fast tracking performance in the linear servo system, but also have the strong robustness to parameter variation, load disturbance and the uncertain factors.