Finite-time disturbance observer-based modified super-twisting algorithm for systems with mismatched disturbances: Application to fixed-wing UAVs under wind disturbances

This article proposes a finite-time disturbance observer-based modified super-twisting algorithm (FDO-STA) for disturbed high-order integrator-chain systems under matched and mismatched disturbances. We first design a finite-time observer for disturbance estimation, in which we show the finite-time convergence of disturbance estimation errors to zero. Second, by employing the estimates of disturbances and their derivatives, a new dynamic sliding surface is derived, which ensures the finite-time convergence of the controlled output to zero in the sliding phase. Then, based on the estimates of disturbances and their derivatives, the designed sliding surface, and a modified super-twisting algorithm, we develop the FDO-STA, which guarantees the finite-time convergence of the sliding variable to zero in the reaching phase. Rigorous analysis is provided to show the finite-time stability of the overall closed-loop system under the proposed control scheme. We finally apply the proposed FDO-STA framework to the path following control for fixed-wing UAVs under wind disturbances. Various simulation results are provided to show the effectiveness of the proposed controller, compared with the existing control approaches.