Research On Nonlinear Control Method Of Strip Rolling Mill Gauge

The demand of high precision strip is increasing rapidly with the development of world economy,so strip rolling mill has been widely concerned and developed in recent years.Design of controller for strip rolling mill is a difficult and challenging research topic in dealing with system with significant nonlinearity,uncertainty and multi-disturbance.In order to design a stable tracking controller,the thesis is extended progressively from system nonlinearity,uncertainty and multi-disturbance.The research issues include additive state decomposition(ASD),dynamic inversion,quasi-continuous high order sliding mode control method and finite-time stability theory in the gauge tracking control for the strip.In this thesis,aiming at the problems of the inner-loop hydraulic servo position control system and the outer-loop automatic gauge control(AGC)system,and the controllers are analyzed and designed by ASD and quasi-continuous high-order sliding mode control methods.Firstly,the models of the electro-hydraulic servo valve,hydraulic cylinder,roll system are established,based on which the strip rolling mill control system simulation platform is established.Then the strip rolling mill gauge control strategy is divided into hydraulic servo position control and AGC,and specific control objectives and control strategies are analyzed respectively.Secondly,considering the uncertainty and nonlinearity of hydraulic servo position control system,a position controller based on additive decomposition and dynamic inverse method is designed.The problem of hydraulic servo position control is decomposed into two sub problems by ASD method,which are the tracking problem of linear time-invariant primary system and the stabilization of secondary system.Then,the controller of the system is designed by dynamic inversion.The stability of the controller is proved.Simulation results show that the controller can deal with uncertainties and nonlinearities much better and ensure the accuracy of the system position tracking and smooth control output.Finally,the robust stability problem of external disturbance for AGC are investigated.According to integral sliding mode and high-order sliding mode theory,a gauge controller based on quasi-continuous high-order sliding mode control method is designed.Based on Lyapunov stability theory,the stability of the controller is proved.Simulation results show that the controller has a strong robustness,can track the desired gauge in finite time and effectively decrease the chattering problem of the sliding mode control.