Realization Of Fuzzy-smith Control On PLC And Its Application

Time-delay process, as an important part of complex control system, widely exists in modem industrial process. At the same time, time-delay process is also an important field for the application of the control theory. The Smith control method for time-delay process was studied in this paper, and it was applied to the level control of tanks.The mathematical model of the generalized object which consisted of a liquid level sensor, an electric control value, and the tanks was established with the method of mechanism modeling and experimental modeling. To improve the robustness of Smith predictor, the structure of Fuzzy-Smith controller was adopted according to the characteristics of the level control system. To eliminate steady state error caused by fuzzy control, a Fuzzy-Smith predictor controller with Integral (I-Fuzzy-Smith) was proposed. The Matlab simulation research was done for I-Fuzzy-Smith controller. The simulation results showed that I-Fuzzy-Smith controller has better robustness, gives good performance in the overshoot, settling time, steady state error, etc.The Adaptive-Smith controllers based on the theory of local optimal parameters and Lyapunov stability were designed. They have the advantages of Adaptive controller and Smith controller. The simulation results showed that the Adaptive-Smith controllers have a better perfonnance in transient response, anti-interference and robustness, etc.Through the above theoretical and simulation studies, the I-Fuzzy-Smith was applied to the level control of the tanks on the THJ-1 process control equipment. The system's controller is Siemens S7-300 PLC. The fuzzy inquiry table was calculated off-line, and Smith predictor was discretized. Through programming with ladder diagram in STEP7, I-Fuzzy-Smith control algorithm was developed on Siemens S7-300 PLC. The monitoring software was designed in the HMI software WinCC to achieve real-time monitoring of the experiments. The experiments proved that I-Fuzzy-Smith control algorithm does not need the precise mathematical model, and can effectively overcome the time-delay. It has good control quality, and better robustness than PID-Smith.