Attitude Control With Input Constraints For Very Flexible Aircraft

In recent years,high-altitude long-endurance aircraft has become one of the hotspots of the aviation industry.As a kind of high-altitude long-endurance aircraft with large aspect ratio flexible structure,very flexible aircraft(VFA)has good development prospects in military and civil fields.However,the VFA may undergo large deformation under normal conditions,which has a significant impact on the dynamic characteristics of the VFA and brings challenges for modeling and flight control design.In this paper,high-altitude long-endurance aircraft is set as the research background,and VFA as the research object,including the dynamic modeling,motion characteristics,input restricted control system and control optimizationFirstly,the nonlinear aeroelasticity and flight dynamics coupling model of a large flexible aircraft is established.The rigid body model is get from modified traditional model.The finite element method and the Lagrange equation are used to build the flexible wing model.The complete aircraft model is constructed by combining the rigid body model,the flexible wing model and the aerodynamic model.The dynamic model is introduced into a specific VFA.Secondly,the stability of the large flexible vehicle is analyzed according to the distribution of the eigenvalue of the model.The dynamic characteristics of the aircraft under input manipulation such as thrust and rudder are analyzed,and the dynamic characteristics under the external disturbances such as gust and atmospheric turbulence are studied.The influence of the deformation caused by the flexible module on the stability is also discussed.Thirdly,the attitude tracking control system is designed for the VFA with input constraints.Balanced singular value perturbation method is used to reduce the order of VFA model and the characteristics of the reduced-order model are compared with the original model to ensure the accuracy of the reduced-order model.The linear quadratic regulator(LQR)is designed as the basic controller,and the model reference adaptive controller is designed considering the uncertainty.Focused on the problem of input constraints,the ?-modified method is used to reduce the input beyond the saturation constraints,and the reference model is also modified.The stability of the system is proved by Lyapunov stability function and verified by simulation.Finally,the control system of VFA with input constraints is optimized.The weight matrix of the basic LQR controller is obtained by genetic algorithm instead of trial and error method.The simulation results show that the convergence rate is faster and the control effect is better by optimization.Considering that the VFA is sensitive to disturbances,the projection algorithm is applied to the adaptive law,and the results show that the projection algorithm can effectively guarantee the robustness of the system.