Research On Robust Variable Structure Control For Hydraulic Servo System Of Cold Strip Rolling Mill

Hydraulic servo system of cold strip rolling mill is a complex system which containsnonlinear characteristic, parameter uncertainty and unknown external disturbance, and itmakes the system difficult to control. In order to eliminate the uncertain disturbances anddesign the controller with strong robustness to meet the requirements of cold strip millproduction, robust variable structure control methods are researched in this paper.Firstly, a mathematical model is established for the hydraulic servo position systemaccording to its structure and working principle. Then the model of hydraulic gaugecontrol system is erected based on the time delay process of gauge detect device.Secondly, backstepping control method is introduced, and then the backsteppingposition controller is designed for the hydraulic servo position system of rolling mill.Further more, the backstepping control method and the dynamic sliding mode controlmethod is combined and the backstepping dynamic sliding mode controller is designed,which makes the position output of the system track the given signal rapidly andaccurately. The dynamic sliding mode method can obtain the continuous control law andovercome the chattering phenomenon caused by the application of the traditional slidingmode control method.Then, an adaptive backstepping sliding mode control method is proposed for thehydraulic servo position system of rolling mill, which contains nonlinear characteristics,parametric uncertainty and the control input with uncertain coefficient. By combining theadaptive backstepping and the sliding mode method, it can improve the robustness of thesystem. In the adaptive backstepping sliding mode controller design, adaptive law of theuncertain parameters is given and the stability of the system tracking is also proved.Simulation results show that the designed controller can effectively overcome theinfluence caused by the nonlinear characteristics and parametric uncertainty and achievefast and accurate tracking.Finally, an robust guaranteed-cost control method is proposed for the thicknesscontrol system , which contains parametric uncertainty, external disturbance and the detection delay. By using Lyapunov stability theory, the condition to make the closed-loopsystem asymptotically stable and robust guaranteed-cost controller exist is given in theform of LMI, and it also make sure that the system performance does not exceed a definedupper. Furthermore, the design method of robust optimal guaranteed-cost controller isgiven by solving a linear matrix inequality constrained convex optimization problem. Asimulation example is given to illustrate the efficacy of the proposed method.