Adaptive backstepping control for autonomous shipboard landing of a quadrotor with input saturation

This paper presents a novel autonomous shipboard landing control algorithm of a quadrotor subject to external disturbances and input saturation. A coupled six-degrees-of-freedom (6-DOF) nonlinear relative motion model is derived to facilitate the controller design. To overcome the under-actuated property of the quadrotor and avoid collision, the shipboard landing process is cooperatively completed by a relative position controller (RPC) and a relative attitude-altitude controller (RAC). The RPC is proposed for use when the quadrotor is far away from the ship, aiming to drive the quadrotor to the vicinity of the ship. The RAC is used for the situation when the quadrotor is close enough to the ship to land the quadrotor on the ship steadily. An adaptive backstepping technique is proposed for both RPC and RAC, where unknown bounds of the lump disturbances are estimated online by the adaptive laws. To satisfy the input constraint requirement, a smooth model is employed to describe the control input saturation. Stability analysis proves that all states of the closed-loop systems are uniformly ultimately bounded. A numerical example verifies the performance of the control approach.