The Application Of Fuzzy-Pid Controller In Automatic Dosing System

Water and steam are the working media of thermodynamic facility in power plant. As there are impurities in the working media, it will erode the thermodynamic facility and threaten boiler safety. For maintaining the system's stable working, adding hydrazine or ammonia to feed-water and phosphate to boiler water are the common methods of adjusting water quality. While adding these drugs into the system, there also result in many maters. So the amount of adding drugs must be controlled strictly, which affects the safe, economical run of power plant, especially the high parameter and large capability boilers are putted into production.Now, the main methods of dosing control are some single control arithmetic base on PID control. It's able to meet the demand of control when the water quality runs stably. Since the chemical dosing control system of fossil power plant is characterized by nonlinearity, long time lag and variation with time. While the load has severe fluctuation especially during the loading of these single control arithmetic cannot meet and demand and result in bad control quality. Therefore, fuzzy control theory is introduced in order to increase the robustness and self-adaptability of the chemical dosing control system in the power plant and fuzzy control system of dosing is designed in this paper.Firstly, this paper analyzes the main problem and system requirements of dosing system in Mawan power plant phaseⅢ. Secondly, the traditional PID control and the fundamental principles and design rules of fuzzy control are described. Idea which combines the fuzzy control with PID is proposed, and an adaptive control Fuzzy-PID control model has been designed. The dynamic performance of fuzzy and self-tuning fuzzy PID to chemical dosing system is studied by simulation. Simulation results show that the control effect by this strategy is superior to that of normal PID cascade control. It is featured by strong robustness and self-adaptability, and can readily accommodate itself to the object's parameter variation.