This paper considers the robust stability of singularly perturbed systems with structured state space uncertainties. By making use of Lyapunov stability criterion and combining with the Lyapunov equations, a new approach for deciding a robust stability for uncertain linear singularly perturbed systems is presented. Based on the assumption that the reduced nominal system is stable, we also derive some sufficient conditions for robust stability. Some analytical methods and the Bellman-Gronwall inequality are used to investigate such sufficient conditions.

It is worth pointing out that in this paper, we do not need to investigate both the slow system and the fast system by using the singularly perturbation method because of the proposed method is very direct. Furthermore, we only assume that the uncertainties are a norm bounded. Therefore, the robust stability condition derived here is less conservative than those reported in the control literatures. An numerical example is given to demonstrate the validity of our new results.