HYDRAULIC SERVO POSITION SYSTEM OF ROLLING MILL BASED ON IMPROVED EXTENDED STATE OBSERVER

The hydraulic servo position system of rolling mill is characterized by the inherent nonlinearity, parameter uncertainty, and unknown load disturbance, so the system control remains a challenge. In this paper, a composite control strategy is proposed based on an improved extended state observer and the nonsingular fast terminal sliding mode (NFTSM) control method. Firstly, the improved extended state observer is constructed with a hyperbolic tangent function to dynamically observe the states, uncertain parameters, and unknown load disturbance of the hydraulic servo position system. Secondly, the nonsingular fast terminal sliding mode controller for the hydraulic servo position system of rolling mill is designed based on the backstepping method and the double power reaching law, which effectively enhance the asymptotic tracking performance, robustness, and stability of the system. Theoretical analysis shows that the closed-loop system is globally asymptotically stable. Finally, simulation is carried out using the actual data of the hydraulic servo position system of a 650-mm reversible cold strip rolling mill. Through the simulation, the superiority of the proposed control strategy is demonstrated by comparing the results with the traditional sliding mode control method and the conventional extended state observer (ESO).