Nonlinear control of the HAGC by backstepping with integral action based on a circle-criterion observer

Abstract

Controlling the hydraulic automatic gauge control (HAGC) of cold reversible rolling mill is a significant engineering challenge mostly because of the complexity of the interactions between the process variables, the nonlinearities which change with the operating conditions, the time delay generated by the thickness measurement, and the long-time delays which change significantly with the mill speed. This paper describes a new control strategy by nonlinear control of the HAGC by backstepping with integral action based on a circle-criterion observer. We propose this new circle-criterion observer to estimate the unmeasured state for the nonlinear system. The main contributions of the proposed method are overcoming the interaction between tension stabilization and thickness control, considering time delay caused by measurements, and guaranteeing robustness against model uncertainties and external disturbances. The performance of the controller is also demonstrated and discussed by various simulations using MATLAB/SIMULINK software. The simulation results show clearly the effectiveness of the proposed control for improving the quality of the output web.