Research On Non-linear Control Method Of Coupled-tank Water-level System

Liquid level control system is widely used in industrial production.In many sites,precise control of the liquid level is critical to increasing the service life of equipment,ensuring production safety,and improving the quality of production products.As a typical experimental device of the liquid level system,the liquid level control problem of the Coupled-Tank has always been a hot issue studied by scholars.This subject mainly takes the Coupled-Tank liquid level system produced by Canada Quanser as the research object to study the nonlinear control method of the water tank liquid level system.The research content of this paper includes:(1)Tuning method of cascade PI control parameters of Coupled-Tank based on state feedback.Feedforward plus cascade PI control is an effective control scheme for the Coupled-Tank level system.The traditional cascade PI controller parameter setting method is cumbersome,and it is difficult to select parameters by trial and error to optimize some required indicators.Starting from the mathematical model of the Coupled-Tank,this paper first obtains the correspondence between the linear Coupled-Tank state feedback control law and the cascade PI control law,and transform the PI parameter tuning problem into a state feedback controller seeking problem.Then select the Linear Matrix Inequality(LMI)tool,and optimize the gain of the state feedback controller by arranging the closed-loop poles of the system in the specified linear matrix inequality region to determine the PI controller parameters.(2)Triple-step nonlinear control method of the Coupled-Tank level system.The triple-step nonlinear control method is proposed by Jilin University and is widely used in the field of automotive electronic control.It has a clear physical meaning and a simple engineering implementation structure.In this paper,this method is successfully introduced into the field of process control,and the liquid level tracking control of the Coupled-Tank is realized.According to the unique structure of the Coupled-Tank,two control schemes are proposed.One solution is to use the idea of cascade control to decompose the system into two series-connected first-order systems,which are designed independently for each system.Another scheme designs the system as a whole second-order system.For each scheme,we deduced the steady-state control law,dynamic feedback control law and error feedback control law in detail,and conducted stability and robustness analysis.The results of simulation experiments show that both schemes can well realize the trajectory tracking control of the liquid level of the Coupled-Tank.The successful application of the triple-step method in the Coupled-Tank level system has a good reference value for the application of this method in other process control.