An observer for a class of nonlinear systems with time varying observation delay

This paper presents a state observer for drift observable nonlinear systems when output measurements are affected by a known and bounded time varying delay. The structure of the proposed observer is very simple and it is a generalization of an existing observer for undelayed systems. The observer exhibits good performance in estimating the system state also in the presence of significant measurement delays. The technique used to prove the asymptotical convergence to zero of the observation error, based on the Lyapunov–Razumikhin approach, does not require any assumption about the dependence of the delay on the time.