Study on High-Speed-to-Hovering Back-Transition Control of Ducted Fan UAV

The ducted fan unmanned aerial vehicle (UAV) can transit from hovering to high-speed flight by continuously pitching down, reaching a high-speed and high-efficiency status. However, during the back-transition process from high speed to hovering, unstable environmental airflow and improper velocity planning could lead to serious oscillation, or even divergence of the aircraft states. In this paper, we address this control problem of a ducted fan UAV by utilizing an expected velocity planning method and a robust controller. The expected velocity curve is planned to ensure the dynamic effect of the deceleration process and decrease the computational complexity in solving the numerical optimization problem. The robust controller aims to reduce the tracking error of velocity and angular velocity considering modeling uncertainty and disturbance. Furthermore, the unit quaternion is selected to represent the attitude to avoid the singularity problem. Theoretical analysis verifies the stability of the proposed controller based on unit quaternion. Moreover, the simulation and experimental results collectively indicate the effectiveness of our methods.