A sliding mode controller is proposed for controlling molten steel level in a mold of continuous casting machine in this thesis. The comparisons of dynamic response, control accuracy, and reaction to perturbation between proposed controller and PID controller currently used are also presented. A perturbation estimator is embedded in the sliding mode controller in order to enhance the robustness against model uncertainty, parameter variation, and external disturbance. The perturbation considered in this thesis includes variation of casting speed, variation of area of slide gate, time delay, variation of mold area, and Dead-Band etc.. In addition, the effects of adjusting the design parameter of the proposed controller on system¡¦s dynamics are also considered.

The theoretical stability analysis of mold level control system for slab continuous casting machine is presented in this thesis. In the procedure of analyzing the stability of the mold level control system, the PLC program written for the control system is studied first in order to obtain the mathematical model of a PID controller. Then the mathematical models of servo-amplifier, servo-valve, electro hydraulic system to the output of mold level are established. A simulative control system using Matlab software is constructed in accordance with these mathematical models so that not only the results of stability analysis can be verified but also the dynamic response of controlled system can be studied. Finally, the effects of some potential disturbance on system¡¦s dynamics, stability, and control accuracy are also analyzed.