Research On Direct Drive Control Algorithms For Linear Permanent Magnet Synchronous Motors

Linear permanent magnet synchronous motor (LPMSM for short) servo control system has been investigated.Compared with the traditional "rotating motor plus ball screw", the linear motor servo system has eliminated a series of adverse effects that are generated by mechanical drive linkage. Therefore, the factors, such as load varieties and the external disturbances, would directly influence the performance of the servo system without attenuation. End-effects, slot effects and the parameter changes of the linear motor system would also reduce the system performance and machining precision of the machine tools, which increases the difficulty in the control. Therefore, some new effective control strategies must be adopted to overcome the influence of these factors.For LPMSM servo system as such a fast dynamic complex nonlinear system with high precision, the stabilization and robustness are the important performance indexes. Many kinds of methods were presented to optimize the performance of the system. With the advantage of simple structure and good steady-state behavior, the traditional PID controller was used in common servo system. But its robustness was not ideal in the presence of parametric variation and external perturbation.Firstly, considering the demand of speed in servo system, the fuzzy sliding mode speed controller based on the model reference adaptive control has been presented. Through compared the real model with reference model, the sliding mode control strategy takes the parameter variations as disturbance rather than identifying them, which can decide the current of stator through the uninterrupted switching that satisfies the sliding mode condition. So, the servo system has the good robustness to the parameter variations and external disturbances. Meanwhile the cumbersome procedure of system identification is abbreviated. Because the chattering problem is the main obstacle for the abroad application of sliding mode control method, the fuzzy arithmetic is added to solve the inherent chattering problem. The rules of the fuzzy control is that adding the controllable variable to the former ones in the controller in terms of the position, the velocity and the direction of moving point of the trajectory in a phase plane Then, the system not only can achieve the robustness, but also can decrease the chattering.Secondly, a tracking controller based on iterative learning feedforward control has been proposed to improve the tracking precision and to eliminate the influence of the model uncertainties and disturbances of permanent magnet linear synchronous motors for the repetitive trajectory tracking task. Based on the stability guaranteed by IP feedback controller, an iterative learning control scheme has been designed as the feedforward controller to improve the trajectory tracking precision and to minimize the tracking error by obtaining the experience from the repeated execution of the same operations.Finally, the results of the simulation show the validity of the proposed methods.