In this dissertation, we investigated the problems of the estimation, H-infinity filtering and the controller based-observer design for standard large scale systems and for algebro-differentials ones called also singular large scale systems. So, we began to propose methods for decentralized observer design with unknown interconnections for standard and singular systems. We search here to decouple the unknown interconnections and the dynamics of the observation error. The method is based on LMIs approach to find the gain matrix implemented in the observer matrices. The LMI formulation is based on Lyapunov approach and deduced from various bounded lemmas. We propose then, filters that permits to ensure, in addition to the stability, an H-infinity performance criteria; we search to attenuate the perturbations effect, supposed unknown but of bounded energy, on the dynamics of the estimation error. We discussed after the study of inter- connected observers for large systems, we have proposed a new method to design a new form of interconnected observers connectively stable. We are interested in the ability of observer to be robustly stable towards uncertainties in the interconnections between sub-observers. Finally, we are interested to the application of the proposed estimation methods to the control purpose. Indeed, in a first step, we propose a decentralized control based on a filter H-infinity for a class of large scale standard systems with nonlinear interconnections. Then, we focus our attention on the observer based control for singular systems to search for a control law which ensures an H-infinity performance criteria. The approach is an extension of recent works of Kalsi and al. to the case of disturbed large scale systems. One of the main contributions of our work was to propose a new method of control design based on a filter H-infinity which generated by using less restrictive conditions than those introduced in the work of Kalsi and al. Thus, we have relaxed the constraint on the distance between the pair of matrices formed by the state matrix and input matrix and the set of pairs of matrices uncontrollable. In addition, we consider the maximization of the bound of the interconnection, which is very important in practice. Our approach is obtained into two steps. The first one consists on calculating the gain state feedback that meets the specifications of the closed loop system. The second one, then we reconstruct this control law using our previous results on the H-infinity filtering. The approach has been validated on an example of a system composed of three interconnected electrical machines.
