Almost-Global Trajectory Tracking Control of an UAV with Disturbances Rejection

This paper considers the trajectory tracking control of an underactuated quadrotor unmanned aerial vehicle(UAV) with disturbances rejection. There is a coupling between the position and attitude, the position tracking control is achieved by a coupled-attitude control design. An almost-globally exponential attitude tracking control law with continuous feedback is proposed. Generally, the attitude tracking control scheme needs the coupled-attitude's velocity and accelerations, which also has a complex mathematical expressions. And it is challenging to design the attitude control law when disturbances on the position channel appear. A filter is introduced to estimate the coupled-attitude's rotational velocity and acceleration, exponentially. Thus an observer-based almost-global attitude tracking control law is derived from the singular perturbation theory while the attitude control law and observer can be designed separately. Finally, the trajectory tracking control strategy is proposed, which tracks both the attitude and position of an underactuated UAV simultaneously. Simulation results complete the work.