Global robust tracking control for a class of cascaded nonlinear systems using a reduced-order extended state observer

This article considers the global robust tracking control problem via output feedback for a class of nonlinear systems subjected to dynamic uncertainties and nonvanishing disturbances. A reduced-order extended state observer is firstly designed to estimate the unmeasured states and to compensate the external disturbances. Then, we propose a deadzone-based tracking control scheme, which could make the system output track any desired reference signal with small tracking error arbitrarily, and keep all signals in the closed-loop system bounded. It is shown that the parameter drift instability may be avoided using the proposed method through a numerical example. Finally, a fan speed system is used to demonstrate the effectiveness of the control strategy.