Fractional-order super-twisting sliding mode attitude control for elastic refueling boom with exogenous disturbances

During the aerial refueling alignment phase, the slender refueling boom is prone to elastic deformation under random exogenous disturbances, which deteriorates the attitude control performance. In this work, attitude tracking of the elastic refueling boom with parameters uncertainties and external disturbances is obtained by deploying fractional-order super-twisting sliding mode control. Firstly, an accurate elastodynamic model of the refueling boom is established via energy modeling and aerodynamics modeling. Then, considering that the full state variable information cannot be fed back to the control system in practical implementation, the global fast terminal sliding mode observer is designed to estimate the state variables and disturbances. Based on the estimated information, a fractional-order super-twisting sliding mode controller is developed to realize the attitude tracking and attain the elastic suppression of the refueling boom. In the presence of interference, the proposed method can ultimately and continuously ensure that the attitude tracking and elastic deformation errors converge to zero in a finite time. Finally, numerical simulation results under different cases show the superiority of the proposed control method in terms of attitude tracking and elastic suppression in comparison with the conventional sliding mode controller. In addition, the effectiveness of the method proposed is further validated by experimental test results.