Research And Experiment On Discrete Time Sliding Mode Control For A Continuous Stirred Tank Reactor

The degree of automation is an important criterion for evaluating the level of industrial modernization.Continuous Stirred Tank Reactor(CSTR)is the most widely used equipment in petrochemical industry.Its performance is closely related to industrial benefits,so the research on CSTR has certain significance and economic value.Because of the high complexity of CSTR,it is necessary to design a good control algorithm for CSTR.Sliding mode control is a special kind of variable structure control.Its unique sliding mode makes the controlled system have good robustness,excellent dynamic and static characteristics.Therefore,this paper adopts sliding mode method to control the CSTR system.Firstly,the mathematical model of CSTR is obtained by the mechanism modeling.A discrete time sliding mode controller is designed for the non-linear problem of CSTR system.Aiming at the chattering problem in general discrete time sliding mode control,an equivalent control based discrete time sliding mode is designed.For the unmodeled uncertainties in the system,an adaptive control method is adopted to compensate the uncertainties,which improves the steady-state performance of the system.Secondly,considering the external disturbance of the controlled system,a disturbance observer based sliding mode control method is designed.In order to solve the convergence region problem of ordinary disturbance observer,a variable gain disturbance observer is designed,which further improves the stability of the controlled system.Followed by this,the disturbance observer and the adaptive law are combined to weaken the impact of external disturbance and modeling uncertainties.Thirdly,considering the complexity of the controlled object model in the practical application of a controller,in order to ensure the system performance,this paper linearizes the controlled object at the system working point.Followed by this,the optimal sliding surface is designed by the optimal control method,and then the optimal sliding mode motion of the controlled system is always guaranteed by designing the pre-described performance integral sliding surface.The disturbance observer is used to compensate the unknown matched and unmatched uncertainties,and the optimal performance of the system is guaranteed.The feasibility and closed-loop stability of all control methods are proved by the Lyapunov function,and the effectiveness of the proposed method is verified by simulation.Finally,the experimental platform is used to validate the designed controller,and the results show the effect of proposed method.