Robust observer design for time-delay systems: a Riccati equation approach

This problem has been solved by Watanabe et al. [14], [13] by introducing a distributed time-delay in the observer dynamic system. Also, Pearson et al. [10] and Ramos et al. [12] have built observers for delayed-state systems by computing the unstable eigenvalues of the system under consideration which, in some case, may be a very difficult numerical problem [7]. In those papers the robustness issues have not been considered. Yao et al. [15] have used a factorization approach in order to parameterize some observers for time-delay systems, however, no explicit procedure is given to obtain the observer.