Research Of Coagulant Dosing Composite Control System Based On PLC And Fuzzy-PID

With the development of production and society, the requirement for quality of water is more and more strict. How to improve the water treatment process and insure the water quality has became the focus in the field.The paper introduced the developing situation of the auto adding control technique. Based on analyzing and studying the checking link, the control mode and control strategy on automatical adding system, in connection with some features such as long time lag, nonlinearity and modeling difficulties, the paper proposed a fuzzy control method of auto-adding process in water-treament based on PLC. This paper analyzed the advantages and disadvantages of PID controller and fuzzy controller, considering them interaction and supplementing each other's advantages. The specific methods using fuzzy self-tuning PID controller that enable controller can adjust the three parameters of KP, KI and KD according to the actual situation.The paper used MATLAB/Simulink software, the first control system for a cascade PID control and cascade fuzzy-PID control simulation of the control performance. The results showed that the control of the complex process of cascade fuzzy-PID adjustment can be achieved small overshoot, the rapid adjustment and the ability to resist a strong disturbance. So the system has excellent control precision and stability, thereby improving the dynamic quality of the entire system.The paper designed the plan of auto-adding system. The system was consisted by detection unit, control unit, inverter and metering pump. Compound control strategy was applied in the system. Coagulation effect reflected through streaming current and turbidity. The result was feedbacked by PLC. The cascade control system as primary control method. In order to further improve response speed when raw water flow change greatly, flow feed forward control was added as assistant control method. Above control output distinction function in metering pump's rotational speed and stroke.Combined with PLC, the fuzzy control could overcome the disadvantages of traditional control equipment, make full use of the advantages of PLC. Coagulant was added on line scientifically and reasonably. Meanwhile, the speed of response and the stable precision of system were raised.