Robust Molten Steel Level Control in a Strip-casting Process

Abstract

A robust molten steel level controller is developed for a strip-casting process by using the quantitative feedback theory (QFT). The plant model for the molten steel level system is first developed as a linear time-invariant system with parametric uncertainties. The parametric uncertainties reflect the uncertain discharge coefficients of the immersion nozzle and the stopper, the uncertain transport delay of the molten steel supply system, and the various hot strip production rate of the strip-casting process. In this paper, the robust stability requirement, reference tracking capability, and disturbance rejection capability at the plant input are specified in terms of the bounds on the magnitude of the closed-loop transfer function. Then the loop shaping technique is used to design a robust QFT controller in such a way that the nominal loop transmission can meet the constraints. The simulation and experimental results show that the performance of the closed-loop system with the proposed controller is better than that with a conventional PID controller.