The Research On Safety Landing Control Technology Of High-speed Unmanned Aerial Vehicle

The landing of UAVs is a complex and high-risk process,and the safety and reusability of UAVs are determined by the quality of flight control at this stage.Therefore,it is one of the key technologies of flight control to design an autonomous landing control scheme with sufficient robustness,which can improve the control accuracy and landing safety.In this paper,a high-speed UAV with small aspect ratio is taken as the research object,according to the existing problems,the landing control is optimized and reconstructed based on the original control scheme.Firstly,the nonlinear kinematics model of UAV is established under the conditions of considering aerodynamic force and torque,engine model and steering gear dynamics,etc.,and the variable wind field model based on discrete gust,ground boundary layer wind shear and micro-downdraft is improved.On this basis,the basic aerodynamic performance,static operation stability and dynamic operation stability characteristics of different flight state points are analyzed.The original landing control scheme is introduced in this paper,and five shortcomings of the scheme,including the fluctuation of the throttle in the pull-up section,the poor ability of wind interference resistance,the complex parameters of the guidance loop,the poor robustness of attitude control and the lack of emergency landing scheme,are analyzed and pointed out.In this paper,the original control algorithm and guidance algorithm are improved one by one.Firstly,the all-envelopment attitude controller of UAV is designed based on cascade active disturbance rejection control(ADRC).The time-delay ignoring method and input estimation method are adopted to eliminate the influence of actuator dynamics on the performance of the control system and improve the robustness of the system.Secondly,based on the exponential pull-up scheme,Gaussian pseudo spectral method is used to re-plan the trajectory,so that the throttle trajectory remains monotonically reduced in the pull-up period.At the same time,the control scheme of the lifting speed is designed based on the ADRC,which solves the problems of throttle fluctuation and weak resistance to wind interference in the pull-up period.Thirdly,overturning the original total energy control scheme,and the multiple input multiple output and single input single output ADRC landing guidance scheme are designed,which can solve the problem of complex guidance loop parameters.In the simulation platform,the comparative simulation verification of landing under parameter uncertainty and wind disturbance is completed.The results demonstrate that optimized scheme has better control performance,which can accurately control the touch-down sinking rate and landing point position,meanwhile,it has higher robustness and stronger ability to suppress wind disturbance.Finally,the emergency landing program is designed supplementarily.By analyzing the performance of UAV in different states after one-engine-out,the emergency landing is divided into four stages:heading adjustment stage,return course stage,energy management stage and landing stage,and the trajectory,guidance and control strategy are designed respectively.In the simulation platform,the designed emergency landing scheme is verified,the scheme can ensure the safe landing of the UAV after one-engine-out in a certain range,and has good control performance and robustness.