Simulation And Application Study On Closed-loop Identification And Advanced Control Strategy For Time-delay Process

Lag is commonly found in industrial processes. This paper studies two objects, the hyperthermia instrument experimental device used for the treatment of bladder cancer and the dosing flocculation process of the water plant are both processes with large time-delay. Especially for the dosing flocculation process, the ratio of the pure delay-time and the time constant is even more than one. The existence of time-delay would have a negative impact on the control system. Especially for large time-delay process, the conventional PID controller is difficult to achieve the desired response, or even badly lead to instability. Therefore, it is necessary for the large time-delay process design of advanced control technologies. However the advanced control technologies are based on the process model as the basis for design.First, this paper presents a new closed-loop identification based on PI control method, which assumes that the process for the second-order plus time delay (SOPTD) model. It makes the closed-loop response was underdamped with the PI controller, then the PI closed-loop transfer function with SOPDT model can be approximatively obtained through the closed-loop underdamped step response. Then the open-loop transfer function of the process can be obtained by the equivalent transforming of block diagram to separate the proportional-integral controller from the closed-loop transfer function. At last, the SOPDT model of the process can be attained by coefficient of comparison. This identification method is used in the hyperthermia instrument experimental device to obtain a better identification results.Then, a PID controller based on the internal model control(IMC_PID) is designed for the dosing flocculation process. And it compares the IMC_PID controller with controller tuning by Lopez and Z-N law. Simulation results show that the IMC_PID controller has the advantages of simple structure and easily tuning on-line. And then the simulation studies of a two degrees of freedom IMC_PID show that the two degrees of freedom IMC_PID can be better able to balance the speediness and robustness.Next, it uses an improved differential evolution algorithm to optimize the PID parameter with the objective function of an anti-overshoot MITAE index. The results prove that MITAE index achieve the desired target.At last, it designs a feedforward-feedback control system based on the model free adaptive(MFA) controller of the Cybosoft. The system has been applied in the dosing flocculation process of a pilot plant in a water plant in Foshan. And it achieved a good control effect.