Subspace model identification and H∞ servo control of tandem cold mill

This paper studies the development of a mathematical model and the design of H^∞ servo controller to produce precisely mill product of tandem cold mill (TCM). To improve the performance of the automatic gauge control system based on the Taylor linearized model of TCM, a new mathematical model which can complement Taylor linearized model is constructed by using the MIMO output-error state-space model identification algorithm based on the subspace method. The H^∞ servo controller is designed for robust stability on the variation of system parameters, restrain disturbances and tracking the setup value of the strip thickness. The H^∞ servo problem is modified as a usual H^∞ control problem, and this modified problem can be solve by using linear matrix inequality techniques. Consequently, the effectiveness of the proposed H^∞ servo controller is shown in comparison with the existing PD feedforward controller