Distributed Control Of Anti-disturbance In Chemical Polymerization Process Based On Disturbance Observer

With the rapid economic development,the demand for various chemical products has increased significantly.As an important component of the chemical industry,polymer materials have received more and more attention on how to achieve high-efficiency polymerization.Besides,the molecular weight distribution,as an important parameter of high molecular polymers,determines the properties of the product and is also a key factor in process control.At the same time,high molecular polymerization is a very complex chemical industry production process,which includes the characteristics of non-Gaussian,nonlinear and multiple coupling.It is very susceptible to all kinds of disturbances in different factors,resulting in the change of molecular weight distribution,and then affects the polymer properties.Therefore,the research on anti-disturbance control technique of non-gaussian polymerization process has always been a difficult point in the chemical production industry and is also a hot spot in the field of control engineering.The thesis takes the polymerization process of styrene body as the research object,and considers the influence of exogenous disturbances and saturation nonlinearities.By using disturbance observer(DO),convex hull representation and convex optimization algorithm,an effective composite anti-disturbance control algorithm is proposed to guarantee the stable of the styrene bulk polymerization process and the desired styrene molecular weight distribution.The main contents are listed as follows:(1)Under the typical styrene polymerization process,the research background,significance and economic value of molecular weight distribution control are elaborated on successively.Furthermore,the development of stochastic distribution control theory and the DO-based anti-disturbance control algorithm are introduced.(2)By using the parameterized model derived from the principle of styrene polymerization reaction,its molecular weight distribution can be obtained;The B-spline function is introduced to approximate the output molecular weight distribution function,and the corresponding dynamic weight vector can be calculated;Furthermore,based on the input and output data pairs,and by using the recursive least square algorithm,the parameter matrix of the system can be obtained and the state space model between the weight vector and the control input can also be constructed.(3)Based on the state space model of styrene polymerization reaction,the design of anti-disturbance control algorithm under the influence of unknown disturbances is studied.By combining the polymerization system model and the extended disturbance model,the disturbance observer is constructed to estimate the dynamics of unknown disturbances.Then,based on the PI feedback control and the disturbance estimation information,a composite controller is designed to ensure the stability of the closed-loop controlled system.The weight vector can track the desired weight and then the ideal molecular weight distribution can be obtained.(4)Based on the state-space model of the styrene polymerization reaction,under the influence of unknown disturbance and actuator saturation,the anti-disturbance control problem of the polymerization system is studied in known states and unknown states respectively.When the system state is known,the single DO is constructed to estimate unknown disturbances in real time,and the convex hull representation is used to deal with the saturation constraint.When the system state is unknown,a composite hierarchical observer is constructed to dynamically estimate the unknown states and unknown disturbances,and the sector boundary condition is used to decouple the phenomenon of actuator saturation.Furthermore,based on convex optimization theory,the stability and dynamic tracking performance of the system can be guaranteed,and the ideal molecular weight distribution is also obtained.(5)The above algorithms are all realized by Matlab/Simulink simulation.By considering the influences of harmonic disturbance and actuator saturation,the anti-disturbance control algorithm of the styrene bulk polymerization process is realized,which verifies the effectiveness of the algorithm and obtains a satisfactory control effect.