Precise Landing on Moving Platform for Quadrotor UAV via Extended Disturbance Observer

When quadrotor unmanned aerial vehicles land on moving platforms, they require not only precise landing points for safety but also high platform speeds for higher mission efficiency. However, the combined effects of wind gusts and uneven ground effects will become stronger and have faster dynamics with the increase of platform speed. These complex disturbances will deteriorate landing point precision of the quadrotor vehicles with only traditional control methods. In order to suppress the complex disturbances and improve landing point precision, an extended disturbance observer based block backstepping control scheme is proposed for a quadrotor unmanned aerial vehicle landing on a moving platform. Firstly, two observers are designed to accurately estimate the complex disturbances for the translational and rotational subsystems respectively after the disturbances are modelled as high-order time polynomials. Secondly, the position and attitude controllers are designed recursively between the subsystems with the outputs of the observers as feedforward compensation following the idea of block backstepping. Asymptotic boundedness of the whole closed-loop system is proved by Lyapunov stability theory. Finally, landing experiments on a moving platform of 20 km/h demonstrate the superiority of the proposed scheme over other ones in improving both platform speeds and landing point precision.