Development Of PID Autotuning Software Package Based On Relay Feedback And Related Algorithms Study

PID controller has a simple structure with excellent adaptability and robustness to parameter change without dependence on accurate process model. So it has widely application in the process control field especially when it is difficult or impossible to get the accurate process model. The performance of the PID controller has great influence on the quantity and quality of the product. So the researches on the PID controller design and its tuning algorithms have not only much value in theory but also significant meaning in practice.But in practice, most tuning processes of the PID controller depend on the engineers' reckoning with his own practical experience or even by error and try tests which are both time consuming and not very satisfactory. The surveys over industrial practices in Japan, Canada and UK indicate that more than 90% of the control loops are of the PID typed where about 30% of the controllers are operated in manual model and 20% of the loops use factory tuning. The conclusion is that only a small proportion of the control loops work on well tuned condition. The PID controller parameters are always not well tuned in time especially when the process is time variant and nonlinear or has large and frequent load disturbance. In one word, we can get the conclusion that PID controllers are most widely applied but poorly tuned in the industrial practice.As a step in the direction of solving the above problem, some researches on the PID autotuning algorithms were done and a PID autotuning software package was developed. In this thesis, the main contributions are summarized as follows. Firstly, the problem of PID controller design and different autotuning algorithms were introduced and analyzed. Then the problem of relay feedback autotuning approach was mainly discussed. Secondly, the problem of the improved relay feedback method was in-depth analyzed. The key idea of using the saturation relay feedback is to enhance the information getting from the relay feedback experiment by using the "shaped" relays. The reason of the failing of relay feedback tests and methods to prevent it were analyzed through the...