Disturbance-observer-based output feedback control of non-linear cascaded systems with external disturbance

The output feedback robust controller is proposed for a class of non-linear systems with integral input-to-state stable inverse dynamics and external disturbance. The investigated systems represent more general classes of non-linear uncertain systems. An extended state observer (ESO) is designed to estimate both the system states and the external disturbance by use of the disturbance as a generalised state. Based on the given reduced-order ESO, a new error dynamic system is constructed. The global asymptotic regulation is guaranteed under the presented anti-disturbance controller by the combined approach of backstepping and linear matrix inequality. The simulation result demonstrates the effectiveness of the given algorithm.