Filtered high gain observer for a class of uncertain nonlinear systems with sampled outputs

Abstract

This paper deals with the design of a Filtered High Gain Observer (FHGO) for a class of uniformly observable systems involving uncertainties. The structure of the proposed observer is very simple as it consists in two cascaded sub-systems of the same dimension as the original system. The first subsystem is nothing else than a copy of the original system with a simple correction term which (linearly) depends on the state of the second subsystem. The latter subsystem is a linear filter driven by the output observation error, namely the error between the output measurement and an output prediction provided by the first subsystem. Of fundamental interest, the FHGO design is first carried out by assuming that the output measurements are continuously available before being extended to the case of sampled outputs, leading thereby to a continuous–discrete time FHGO which inherits the main properties of the original FHGO. The performance and the main properties of the (continuous–discrete time) FHGO are highlighted and compared to those of a standard high gain observer (SHGO) through simulation results involving a single-link robot arm system.