Disturbance Observer-Based Saturated Control for a Quadrotor Landing on a Vessel

An autonomous vessel landing control algorithm of a quadrotor is investigated for the situation when the quadrotor hovers above the vessel with input saturation and disturbances. To facilitate the controller design, the problem of vessel landing is converted from general trajectory tracking problem of a quadrotor to a stabilization problem of relative motion. A fully actuated 4-DOF nonlinear relative altitude and attitude model with four control inputs is established. A nonlinear disturbance observer is developed to estimate the disturbances, while a compensation system is incorporated into the controller design to handle the input saturation. Then, a feedback controller is designed to synchronize the altitudes and attitudes of the quadrotor and the vessel. It is proved that the relative altitude and relative attitude converge to a small neighborhood of origin, and all states in the closed-loop system are uniformly ultimately bounded. Numerical simulation results demonstrate the effectiveness of the proposed controller.