Robust trajectory tracking control for a quadrotor subject to disturbances and model uncertainties

In this paper, a robust hierarchical controller is proposed for trajectory tracking of a quadrotor in the presence of disturbances and parametric uncertainties. The hierarchical controller has an outer-inner loop structure. The outer loop controls the position of the quadrotor and generates desired roll and pitch angles for the inner loop corresponding to desired position, velocity and heading angle. The inner loop controls the attitude of the quadrotor. A disturbance observer based backstepping controller is designed for the outer loop to compensate for disturbances and guarantee robust position tracking. An adaptive non-singular terminal sliding mode controller is designed for the inner loop to ensure the attitude angles converge to their desired values in finite time and deal with the parametric uncertainties. The stability and online estimating capability of the proposed controller are proved by using Lyapunov theory. Finally, numerical simulation results are presented to validate the effectiveness of the proposed controller.