Research On Discrete-time Sliding Mode Control Of Linear Servo System

Direct driving linear motor servo system show its superiority performance in precision and exceed precision feed and high speed and ultra high speed move, because it can make electric energy transferred into linear motion, which doesn't need any intermediate conversion. But uncertainty of the model, inner parameters perturbation and load resistance effect directly performance of servo system, it must be take efficiency control strategy to overcome the influence of above mentioned.Permanent magnet linear synchronous motor (PMLSM) servo system is a complex nonlinear system with high thrust strength, low loss and fast response characteristic, it adopt high performance permanent magnets, so its main requests are the high tracking ability to the input command and excellent disturbances rejection ability to uncertainty.Sliding mode variable structure (SMVS) is a nonlinear control method, which is adaptive to disturbance and parameter variations. Especially, SMVS control is stable and robust against system uncertainties. However, the chattering exists in sliding mode control.Two aspects matters of PMLSM servo system have been researched in this thesis to the actuality of SMVS theory and technical requirement of servo system to control strategy.A model reference discrete-time sliding mode control (MRDSMC) is presented for high precision PMLSM servo systems with many uncertainties. The servo problems are converted to simple regulation problems in this approach. And the forgetting factor to achieve entirely robustness. Moreover, in order to restrain the chattering introduced by high frequency unmodeled dynamics, a low pass filter is added the design of MRDSMC. Theoretical analysis and simulation results demonstrate that the proposed scheme can well suppress the influence of the unmodeled dynamics, and make the system have good robust position-tracking performance.A compound position tracking control strategy based on combining discrete variable structure control (DVSC) with iterative learning control (ILC) is proposed to linear motor carrying out task repeatedly. One attractive point in ILC is the utilization of the system repetitiveness to improve the control performance. The past control input signals and tracking errors are used to construct the present control input signals. To shorten the chattering level of the input, the parameter of DVSC is regulated by adopting ILC, thus improve the static precision of the system. The simulation results show that the method not only enhances the fast tracking performance, but also has a stronger robustness against parametric variations and resistance disturbances.