Research On PH Nonlinear Process Control Method Based On Lyapunov Stability Theory

PH processes are widely present in fields such as chemical engineering,pharmaceuticals,and environmental protection.Different reactions and production processes have different requirements for pH values and accuracy.With the rapid development of technology,the requirements for pH process control accuracy and effectiveness in various fields are increasingly increasing.This article applies Lyapunov stability theory and sliding mode variable structure control methods to study the control problem of pH nonlinear processes.The main work of this article is as follows:(1)A control method based on Lyapunov stability theory(Lyapunov method)was designed for the pH nonlinear process model.This method starts from the control objective and designs a Lyapunov function for the linearized system,thereby obtaining the expression of the control rate.The simulation results show that this method has better anti-interference ability,fast response ability and robustness than the fuzzy Sliding mode control(FSMC)method.(2)On the basis of Lyapunov method,a sliding mode variable structure control system based on Lyapunov stability theory(Lyapunov SMC method)is designed by combining the sliding mode variable structure control method based on LTR observer(SMC method).In the design of the control rate of the sliding mode controller,an improved exponential approach law is proposed,and the stability of the approach law is proved.The simulation results show that the improved exponential approach law effectively suppresses the chattering caused by Sliding mode control.Finally,by comparing the simulation results of Lyapunov method,SMC method,and Lyapunov SMC method,it can be concluded that compared to SMC method,Lyapunov method has smaller steady-state error and better static performance,while SMC method has faster system response speed and better dynamic performance.The Lyapunov SMC method combines the advantages of both and has the best static performance(no steady-state error),dynamic performance,anti-interference ability,and robustness among the three.