Output tracking for nonlinear systems subject to unmodeled sluggish actuator dynamics via model-based extended state observer

Abstract

We propose an output tracking control approach for a class of uncertain, nonlinear systems with unmodeled, sluggish actuator dynamics. The normal extended state observer (ESO) is modified with a nominal model of the largely unknown actuator dynamics. The total disturbance is redefined to include the uncertainties of the actuator dynamics. The feedback law is correspondingly designed to cancel the estimated total disturbance. The closed-loop system is guaranteed with bounded stability through theoretical analysis. The proposed controller is extensively validated and compared to normal active disturbance rejection control (ADRC), nonlinear dynamic inversion control (NDIC), and L1 adaptive control by a numerical example, and a practical application to both the attitude control and velocity control of a hypersonic vehicle, where the deflection of the elevator and the thrust variation of the scramjet engine are considered.