A Comparative Survey in Determining the Imaginary Characteristic Roots of LTI Time Delayed Systems

Authors:	Sipahi Rifat, University of Connecticut, United States Olgac Nejat, University of Connecticut, United States
Topic:	2.2 Linear Control Systems
Session:	Frequency-domain Analysis and Design of Time-Delay Systems
Keywords:	linear time invariant, time-delay systems, stability, stability tests

Abstract

The aim of this study is to offer a comparison of the numerical procedures for an important problem, the determination of purely imaginary characteristic roots of LTI-Time Delayed Systems (LTI-TDS). This problem, in fact, has a crucial role in assessing the stability of the general class of vector LTI-TDS, x'=Ax+Bx(t-tau). There are many procedures discussed in the literature for this purpose. Those, which are exact, first determine the complete set of imaginary characteristic roots of the dynamics, as they constitute the only points where stability switching can take place. These approaches are, in fact, some variations of the five main methods, which may demand numerical procedures of different complexity and they may result in different precisions in finding the roots. This paper offers a unique comparative survey to demonstrate the strengths and weaknesses of these methods.