Delay-dependent robust unknown input observer for nonlinear time-delay systems

In this paper we address the problem of robust unknown input observer design for continuous nonlinear time-delay systems. To investigate the robustness of the studied system, we compare between two approaches both dependent on the delay, the first one is based on a standard ℋ_∞ method and the second on Sobolev norms. New sufficient synthesis conditions are given in Linear Matrix Inequality (LMI) form.