A Study Of Fuzzy PID Control And Its Application In Tank Process Control System

Conventional PID controller has simple structure, good robustness and high reliability etc. It is widely used in process control system. But with the development of science and technology, there is large time delay, nonlinear and complicated process in industrial control system. It is difficult to tune the PID parameters in such a system, so it is not easy to achieve the desired performance. Fuzzy control strategy does not rely on mathematical models, and has a strong adaptability. It opens up a new way for the complex control system.The mathematical model of the two-tank plant was established with the method of mechanism modeling and experimental modeling. A level-level cascade control scheme was adopted. The main regulator respectively used traditional PID and fuzzy PID algorithm, the deputy regulator used proportional control algorithm. A suitable fuzzy ruler was designed according to the characteristics of the level control system, and the corresponding fuzzy PID query table was calculated. The parameters of PID was adapted according to the query table .The Matlab simulation research was done for the conventional PID control and the fuzzy PID control on this cascade system. The simulation results showed that the fuzzy PID control had a better performance in transient response, anti-interference and robustness.On the basis of these simulations, the fuzzy PID algorithm was applied to the actual level control of two-tank process. This experimental plant was THJ-1 Fieldbus process control equipment. The conventional PID algorithm and the fuzzy PID algorithm were designed with the Siemens S7-300 PLC and its configuration software STEP7. The PID algorithm and fuzzy PID algorithm were applied to the level control of two-tank. The fuzzy PID control algorithm was achieved with two methods. In the first method, the off-line parameters were calculated by Matlab and the online parameter query tables were built in STEP7. Thus, the fuzzy control algorithm was implemented in the PLC controller. The second method used the Global Script of WinCC. The fuzzy control algorithm was embedded in WinCC. The fuzzy control strategy was realized by the communication between WinCC and the PLC.The monitoring software was designed in the HMI software WinCC to real-time monitor the experiment. The experimental results showed that the fuzzy PID control had a better control quality of the overshoot, response speed and etc.