On non-fragility of controllers for time delay systems: a numerical approach

Abstract In this paper an explicit numerical procedure is proposed to determine the non-fragility of parameters of controllers used to stabilize a class of time delay systems. The proposed procedure finds the largest possible circle inscribed in a stability subregion delimited by a simple closed curve in the plane of the controller parameters. The center of this circle is declared to be the controller’s least fragile parameters. The obtained theoretical results are applied and compared with some of the most relevant examples found in the literature. This illustrates that the proposed procedure improves previous results found in the literature so far.