Abstract

In this paper, modeling and control of a twin-roll strip caster are investigated. The control objectives are to achieve a constant strip thickness and to maintain a constant roll separating force. Mathematical models are derived by analyzing five critical areas: molten steel level in the pool, solidification process, roll separating force and torque, roll gap dynamics, and roll drive dynamics. A two-level control strategy is proposed. At low level, three local controllers regulate three subsystems independently. They are a variable structure controller for the molten steel level of the pool, an adaptive predictive controller for the roll gap, which is directly related to the strip thickness, and a two-degree-of-freedom robust servo controller for the roll speed. At high level, an H2 optimal controller governs the interaction dynamics among subsystems and generates a reference signal to the local roll speed controller in the fashion that a constant roll separating force is maintained. In designing the high level controller, the complex strip casting dynamics is linearized at an operating point and parameter estimation and uncertainty quantification methods are used. Simulation results are provided. r 2001 Elsevier Science Ltd. All rights reserved.

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