Investigation Of Internal Model Control Based On The Relay Feedback

Time-delay is a very common phenomenon in industry. The existence of long time-delay severely influences the stability of a system, resulting in the big overshoot, long regulating time, even oscillation and divergence. The dynamic quality of the system becomes bad. Especially to some unstable systems in industry, the existence of long time-delay will make the performance of the system more worse. Under such circumstance, the ordinary PID auto-tuning method is very difficult to satisfy the demand, even can't stabilize the system.As the extension of the Smith predictor, Internal Model Control (IMC) is a very effective approach to controll the plants with long time-delay. Therefore in this thesis an improved two-degree-of-freedom IMC approach is proposed on the basis of reading a great deal of demestic and overseas correlative literatures.Firstly, the thesis introduces the research background, which includes the existing problems and further research direction of auto-tuning technology. Secondly, the paper uses an unsymmetrical relay feedback method to identify the mathematical model of a controlled process as the internal model of the system. Thirdly, the stable and unstable plants with time-delays are controlled based on the two-degree-of-freedom IMC structure proposed. There are four controllers in this structure, whose functions are discussed, and then their control algorithms are designed according to different plants. The theoretical analysis and the simulation results indicate that this method can make the system obtain good performance of setpoint tracking, disturbance rejection and robustness. Moreover, the designed controllers are characterized by simple structure, convenient adjustment of parameters, and easy practical application. Finally, on the basis of summarizing the thesis, the further prospect to the research work is made.