Robust stability analysis of the hot-dip galvanising control system

Abstract

This paper presents new results to compute the robustness margin of the hot-dip galvanising control system. Compared to previous works on this issue, this paper considers a mathematical model of the plant with two inputs and one output. The inputs are used to regulate the output, which represents the Zinc mass coating of steel strip. To achieve this objective, a multivariable PI controller is used, this controller is tuned applying the well known Ziegler and Nichols method, and then the maximum parametric uncertainty is computed in order to guarantee the stability property of the closed-loop control system. The work bases its results on the value set characterisation for interval plants with uncertain time delay, along with the use of the zero exclusion principle. Both results allow to transform the original robust stability problem into a simple visual inspection of a computer aided built graph.