Saturated output feedback control for quadrotor trajectory tracking via fixed-time observers

In this paper, a saturated output feedback trajectory tracking scheme for a quadrotor is developed by using the fixed-time observer (FxTO) technique. The translational controller is examined based on a saturated nonlinear control law, where the unmeasurable velocity states are estimated by the FxTO. The proposed FxTO theoretically guarantees the convergence of the estimation errors in a fixed time, and the stability of the closed-loop system is proved. Next, a cascaded attitude controller is explored, and a feedforward compensation is introduced via the differential flatness approach. Additionally, a fixed-time disturbance observer (FxTDO) is incorporated to improve robustness against disturbances. Finally, the tracking accuracy and robustness of the proposed method are verified through simulations and experiments.