Research And Applications Of Dual-capacity Control System Based On Predictive PI Control Strategy

Dual-capacity systems are widely found in process industries such as chemical,petroleum,and sewage treatment.The traditional PID controllers are still used in most of dual-capacity systems.Due to the characteristics of the large inertia,nonlinearity,large delay and multi-interference in dual-capacity systems,it is difficult to obtain good control quality and ideal robustness by applying traditional control methods.Therefore,the study of the new control methods for dual-capacity systems has important practical significance.The dual-capacity water tank system is the prototype of many typical two-capacity systems in the complex process industry.In this paper,a dual-capacity water tank is taken as the research object and a cascaded control scheme based on predictive PI is proposed.Meanwhile,its parameters tuning method and principles are illustrated and the engineering implementation of the control scheme is realized in Opto22.Both the top temperature control system of depropanizer tower and the surface temperature control system of monocrystalline silicon furnace based on predictive PI are designed,and then the feasibility and practicality of the control scheme in the actual industrial process are verified..The main research contents and innovations of this paper are as follows:(1)Dual-capacity water tank system has large inertia characteristics.In this paper,the structure and working principle of single-capacity and dual-capacity water tank system are described,and then internal mechanism is analyzed.After the mathematical model is established by using mechanism modeling,the model parameters are validated through step response testing.(2)A novel control system evaluation index based on robust integral absolute error(RobustIAE)is proposed.The simulated annealing algorithm is introduced to optimize the parameters of the predictive PI algorithm so that the control effect of the predictive PI is optimal in response speed and robust performance.(3)To overcome the disadvantages of cascade control based on traditional PID controllers such as large overshoot and complicated parameter tuning,a cascaded control scheme based on predictive PI is proposed.The control effects of the two control schemes on the dual-capacity water tanks are analyzed and compared.The results show that the cascade control scheme based on predictive PI has better control quality,stronger anti-disturbance performance and good robustness.(4)Based on the Opto22 PAC Project platform,the engineering implementation of dualcapacity water tank cascade control scheme based on predictive PI is realized,and the actual control effect is verified.The control strategy is designed in Opto Control with the discretized control algorithm,and the human machine interface(HMI)is designed in the PAC Display.Through this interface,the user can observe the real-time running status of the system and adjust the parameters online.(5)The top temperature of the depropanizer tower and the surface temperature of the monocrystalline silicon furnace are both dual-capacity and delay system.Not only the predictive PI cascade control system for these two objects is designed,but also the practicality of predicting PI cascade control in the actual industrial production process is verified.