Tuning Of PID Controller And Its Application

With the development of industrial technology, PID tuner, which appeared in 1930s, was accepted for its better control performance than direct-action tuner. Because of simple structure and strong robustness, PID controllers and transformative PID controllers have been widely used in industrial control systems. The capability of controller directly influences the qualities of producing process and products. Therefore, parameter tuning of controllers is the most important step during system design. With the development of computer technology and artificial intelligence in automatic control field, auto-tuning PID controllers began to be used in recent years.Parameters of PID controllers can be obtained with various algorithms. Excellent control algorithms are astringent, intuitionistic and simple. Load disturbance and set-point variety also need to be considered.This thesis studies various methods of parameter auto-tuning of PID controllers. Furthermore, it focuses on the feasibility of auto-tuning methods based on relay-feedback and the least squares. The main results obtained in this thesis are as follows:To avoid the shortcoming of traditional PID controllers that they are unable to give attention to reference response and disturbance response at one time, a novel auto-tuning algorithm, which combines two-degree-of-freedom structure with parameter tuning method based on magnitude optimum criterion, is proposed in this thesis. Compared with traditional methods of controller design, it has better closed-loop response performance. Furthermore, because the coefficients of two-degree are semi-fixation, they are irrelevant to the difficulty of the controller parameters' tuning.Normal PID controllers can hardly satisfy the design requirements of unstable first-order systems with large dead time, and they cannot even ensure the stability of systems. Considering that inner-loop state feedback can improve systems' dynamic characters, this thesis adopts the double-loop control structure. Firstly, the inner loop is introduced to get better systems' dynamic performance; secondly, according to internal model control principle, the outer loop is designed to cater for systems' requirements.By setting the parameter " A." properly, this double-loop PID controller will obtain better control performance and robustness.According to the simulation results, several relay feedback control methods are adopted in the continue-time control systems; for the discrete sample data, controller parameter is obtained by identify the parameters of process model using the least squares. This thesis also presents an auto-tuning software based on the platform of Matlab/Simulink. The functions and characters of this software are mentioned, and simulation examples axe also given.The conclusion and perspective are given in the end of the thesis.