Augmented Disturbance Observer-Based Appointed-Time Tracking Control of UAVs Under Exogenous Disturbance

This article investigates the tracking control issue of the nonlinear system including the unmanned aerial vehicle (UAV) subject to the disturbance that is generated by the exogenous system with uncertain structures. The mentioned uncertainty is described by a known set that consists of finite elements, where the element contains information about the structure of the exogenous system. To tackle the uncertainty, the exogenous system in augmented form is constructed that includes all the available information of elements in the known finite set. Thereafter, for estimating the above-mentioned disturbance well, the augmented disturbance observer (ADO) is designed, which makes the best use of the known information about the disturbance to make the steady-state disturbance estimation error tend to zero. To make the transient performance better, the controller is designed based on the appoint-time prescribed performance function and the disturbance estimation obtained from the ADO. Combined with the sector property of nonlinear function in the exogenous system, sufficient conditions guaranteeing the exponential stability of unconstrained error variable of the closed-loop system with the designed controller are derived. Finally, the comparative simulation shows the effectiveness of the developed control strategy with the ADO through the attitude model of the fixed-wing UAV.