Asymptotic tracking control of an underactuated tilt trirotor unmanned aerial vehicle

In this paper, a novel nonlinear tracking control strategy is developed for an underactuated tilt trirotor unmanned aerial vehicle (UAV) which is subject to unknown external distur-bances. The control scheme is developed based on the inner-loop-outer-loop methodology. Both effects of the unknown external disturbances on the inner-loop and outer-loop are compensated through the proposed control law. The unknown external disturbances which affect the outer-loop (or position loop) are compensated via a nonlinear observer that is designed based on the super-twisting method. The unknown external disturbances that affect the inner-loop (or attitude loop) are rejected via a sliding-mode based nonlinear robust control component. The stability of the closed-loop system for the tilt trirotor UAV, together with the convergence of the UAV's position and heading tracking errors, are proved via a Lyapunov based stability analysis. Hardware-in-loop (HIL) flight experiments are performed to validate the control performance of the proposed nonlinear robust control strategy. (c) 2021 Elsevier Ltd. All rights reserved.