A Lyapunov-based approach to stability of descriptor systems with delay

The Lyapunov second method is developed for linear coupled systems of delay differential and functional equations. By means of conventional approaches, such equations may be reduced to neutral systems, and the known results for the latter may be exploited. In this paper, we introduce a new approach by constructing a Lyapunov-Krasovskii functional that corresponds directly to the descriptor form of the system. Moreover, by representing a neutral system in the descriptor form, we obtain new stability criteria for neutral systems which lead to results that are less conservative than the existing results. Sufficient conditions for delay-dependent stability are given in terms of linear matrix inequalities. Illustrative examples show the effectiveness of the method.