Study On Nonlinear Control For The Cold Rolling Mill’s Hydraulic Servo System

With the advancement of science and technology and the development of nationaleconomy, the requirements for plate strip quality are improving. Electro-hydraulic servocontrol system is the core part of the cold rolling AGC system. To design simple andefficient control strategies for the electro-hydraulic servo system is an important means toimprove the quality of the cold rolled products, which has attracted many researchers’attention. In this paper, a roll mill hydraulic servo control system was studied, the maincontent as follows:A fuzzy adaptive backstepping sliding mode control method is presented for thehydraulic gap nonlinear system with uncertain parameters and load disturbances. Fuzzyadaptive systems are employed to approximate the uncertain parameters and loaddisturbances, which eliminates the impacts of uncertain parameters and load disturbances.According to the characteristics of the hydraulic gap nonlinear system, the appropriateLyapunov functions are selected to reduce the steps of the backstepping design and aneffective solution is given to the problem of “explosion of calculation” among thebackstepping design process of high-order systems. The sliding mode control method isintroduced in the final step of backstepping design to further improve the robustness of thesystem. In the controller design, the adaptive laws of uncertain parameters are given andthe convergence of the system tracking error is proved. The simulation results show thatthe controller can achieve fast, accurate and stable tracking of the specified location.Considering that to measure the speed and acceleration of electro-hydraulic servosystem is very difficult. Thus, in this paper, an output feedback finite time control methodis presented based on the extended state observer for the cold rolling mill under pressureelectro-hydraulic servo nonlinear system with uncertain parameters and load disturbances.The extended state observer is employed to observe the state variables of the system, so asto solve the problem that the speed and acceleration of electro-hydraulic servo system isdifficult to measure, and make the system has robustness for unknown function anddisturbance. According to the finite time control theory, the finite time controller is designed by backstepping method, and the global stability of the controller is proved. Thesimulation results show that the extended state observer can estimate the system statevariables quickly and accurately; the finite time controller based on extended stateobserver can make the system track the specified location quickly and accurately, and hasstrong robustness.