Stability analysis of time-delay systems in the parametric space

This paper presents a novel method for stability analysis of a wide class of linear, time-delay systems (TDS), including retarded non-neutral ones, as well as those incorporating incommensurate and distributed delays. The proposed method is based on frequency domain analysis and the application of Rouche's theorem. Given a parametrized TDS, and some parametric point for which the number of unstable poles is known, the proposed method is capable of identifying the maximum surrounding region in the parametric space for which the number of unstable poles remains invariant. First, a procedure for investigating stability along a line is developed. Then, the results are extended by the application of Holder's inequality to investigating stability within a region. Contrary to existing approaches, the proposed method is uniformly applicable to parameters of different types (delays, distributed delay limits, time constants, etc.). Efficacy of the proposed method is demonstrated using illustrative examples.Comment: 11 pages, 5 figures, submitted to Automatic

Adaptive Parameter Estimation in LTI Systems

An adaptive algorithm solving the on-line parameter estimation problem for a broad class of linear systems is proposed. The approach can be applied to systems with delay, distributedparameter systems, fractional-order systems, and others that are stable or stabilized by linear feedback. The proposed scheme can be applied to simultaneously track sufficiently slow changes in process gains, delays, time constants, diffusivity, and other parameters. The proposed method is gradient-based, and it yields a relatively efficient numerical implementation. Convergence and robustness of the algorithm are investigated through Lyapunov analysis, yielding explicit convergence conditions that generalize the well-known “persistence of excitation” and identifiability requirements arising in conventional adaptive estimation. The method is illustrated by several examples