Nested extended state observer design for uncertain nonlinear systems under time‐varying disturbance

Abstract

AbstractWith rising demands on system performance and reliability in engineering practice, researchers are increasingly interested in disturbance rejection control, of which state and disturbance observation is the essential element. The extended state observer (ESO, or extended high‐gain observer) is extensively utilized to compensate disturbance, nevertheless, the neglect of lumped disturbance's first derivative and peak phenomenon in classical ESO design impose obstacles to further promotion. In this article, nested ESO (NestedESO) is proposed to estimate states and disturbance simultaneously for general uncertain nonlinear systems under time‐varying disturbance. In NestedESO framework, low‐gain generalized ESO is implemented to obtain a rough estimation of lumped disturbance in the first stage. Then, a novel proportion‐filter‐derivative disturbance estimation refinement mechanism is introduced to provide accurate disturbance estimation. With refined disturbance estimation, modified Luenburger observer is put forward to reconstruct state. Besides, extension to sampled‐data systems is investigated to adapt the networked signal transmission scenario. Numerical examples are given to illustrate the validity and effectiveness of the proposed method.