In this paper, we consider the problems of stabilization, estimation and robustness for a large scale system. The large scale system is composed of several low order time-delay perturbed subsystems. First, by the use of the Lyapunov stability theorem, two inequalities are derived, under which the controller gain and observer gain matrices in each nominal subsystem can be determined, such that not only the states of each nominal subsystem are asymptotically estimated, but also the whole nominal large scale system is asymptotically stable. Second, the nonlinear perturbation of each subsystem is considered, and the allowable perturbation bound is obtained, such that the whole closed-loop system remains robustly stable. This paper has two main features: 1. we need not solve any Lyapunov equation or Riccati equation in the results. 2. these results are also applicable to the system without time-delay and/or with linear perturbations.
