Asymptotic tracking control of an underactuated tilt trirotor unmanned aerial vehicle

Abstract

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 disturbances. 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.