Enhanced anti-disturbance control for tethered aircraft system under input saturation and actuator faults

Airflow disturbances, input saturation and actuator faults bring great difficulties to the precise control of the tethered aircraft system. To deal with these problems, an enhanced anti-disturbance control scheme is developed. Firstly, to circumvent the nonsmooth input saturation nonlinearity, a novel auxiliary system is introduced such that not only the control input satisfies the predetermined input constraint but also the restricted control input is continuous and smooth. Meanwhile, another auxiliary system is constructed to compensate the adverse effect arising from input saturation. Subsequently, in the framework of dynamic surface control, disturbance observers are designed to ensure the anti-disturbance performance of the system by estimating the unknown lumped disturbances induced by airflow disturbances and actuator faults. Then, an acceleration function is introduced to further improve the anti-disturbance performance of the system. With the above-mentioned factors taken into consideration, an enhanced anti-disturbance controller is proposed to rapidly stabilize the tethered aircraft at the desired position. Finally, comparative simulations are carried out to prove the effectiveness of the proposed control scheme.