Research On PH Adaptive Control Based On Multiple Model Switching Approach

pH control is recognized as a classic and difficult control problem due to its severe nonlinearity, as reflected in the titration curve of the process stream. On the other hand, pH control has found many applications in different industries. It is well established in the literature that the conventional proportional integral derivative (PID) controller has a poor performance in controlling pH processes. Many papers on modeling and control of pH have appeared in the literature and it is still a problem many scholars pay attention to.Based on multiple model theory and adaptive theory, according to the problems existed in Continuous Stirred Tank Reaction of Beijing ATOFINA stabilizing project, combined with the principle of titration reaction, an multiple adaptive control scheme is presented. This paper makes a deep research on the pH process control of CSTR and the good control results have been demonstrated.As for the characteristics of high nonlinearity, the concept of Strong Acid Equivalent is introduced. An approximate equivalent linear control model is attained through the strict derivation of dynamic model and static model of pH process, which can be seen as a linear model when the process flow rate is much greater than titration flow rate.According to the susceptibility of pH, this paper adopts multiple models to adapt to the changes of titration curves. A fixed multiple models plus adaptive models was designed in which the fixed models can accelerate the transient performance and the adaptive model eliminate the stable error. In addition, the switching method among multiple models was given and different controllers were designed to meet different sub models. In the end the stability analysis is made. Simulation results show that this scheme has high identification precision, excellent control performance, strong tracking ability, and can solve the time variant and nonlinear problems remarkably.