Robust stabilization of time delay system against additive perturbations

A robust stabilization problem for a system with delays in control is discussed. The solvability of the problem against additive perturbations is characterized by a couple of finite-dimensional Riccati equations, and it is also shown that the required controller has a structure corresponding to both state estimation and prediction. The key point in the derivation is that the time delay system is transformed into a lumped parameter system such that both systems provide equivalent mapping from the disturbance to the regulated output. This approach makes it possible to characterize the H^∞-problem directly based on the modified algebraic Riccati equations