Development of mold level control in continuous casting by H∞ control theory

H∞ control theory is utilized to design the controller for molten steel surface level in a mold of continuous casting machine installed at Kimitsu Works of Nippon Steel. It is shown that this theory is more effective for unknown process parameter changes and disturbances. First, we show the reason why this control method is introduced. Next, we derive the mathematical model of the plant, and setup the control problem, where the generalized plant is constructed with frequency weighting functions. Finally, experimental results in the real plant is shown. Experiments were carried out in order to evaluate the performance and robustness of H∞ design compared with the adaptive control design. The results confirm the system designed by H∞ has better performance of suppressing disturbance and robustness of stable against parameter changes than the system designed by adaptive control under large disturbance.