Abstract
VSS observers are considered for continuous-time systems, in which the nominal plant model is linear, but there exist bounded plant and output uncertainties. We first present a design method of a VSS observer based on use of some extensions of a conventional approach that uses an algebraic Lyapunov equation. It is then shown that such a method cannot be successfully applied to the system with any linear part, if we desire to use a unique solution to the algebraic Lyapunov equation. Namely, this method is only applicable to a restricted class of systems. In order to develop a VSS observer applicable to a wider class of systems, we next propose a design method based on use of an algebraic Riccati equation, associated with a linear filtering problem. A relationship between the two design methods is also discussed. Simulation results show that the proposed method is effective for designing a VSS observer for a second-order nonlinear system with band limited output noise, as the output uncertainty.
