Finite-Time Hierarchical Tracking Control for a Quadrotor UAV Under Input Constraints

This paper addresses the problem of quadrotor finite-time tracking control with saturated actuation inputs and unknown disturbances. In this article, the unknown disturbances act in both the translational and rotational motions of the under-actuated quadrotor. A nonlinear finite-time disturbance observer (NFTDO) is developed to handle the unknown compound terms of the external disturbances and the nonlinear effect of the actuators saturation. A hierarchical finite-time command-filtered backstepping control is investigated for the trajectory tracking of the quadrotor with actuator saturation. The finite-time command filters, virtual control signal, and error compensation mechanism are designed for the translational and the attitude dynamics, respectively. Such techniques allows the removal of the computation complexity problem incurred by the conventional hierarchical backstepping technique. The control design inevitably guarantees that the position and attitude tracking errors reach a sufficiently small region around the origin in finite time despite the presence of unknown disturbances. The stability analysis is presented using the Lyapunov stability theory, and the effectiveness of the proposed control strategy is demonstrated through numerical simulations.