Research On Mode-free Switching Flight Control System Of Hybrid VTOL UAV

Hybrid vertical take-off and landing(VTOL)UAV combines the advantages of multi-rotor and fixed-wing UAV.It has the characteristics of vertical takeoff and landing,hovering of multi-rotor and high-speed cruising of fixed-wing UAV.It has made rapid development in the fields of aerial mapping and logistics transportation.In order to simplify the operation difficulty of hybrid VTOL UAV and maintain its excellent flight stability when facing the increasingly c omplex external environment,it is particularly important to study the flight control system of hybrid VTOL UAV.This paper aims to study the control system of the hybrid VTOL UAV based on PX4 autopilot.The first part of this paper describes the basic composition of hybrid VTOL UAV,explains the functions of power system and control system components,clarifies the basic flight principles of quadrotor,fixed wing and hybrid VTOL UAV,and then discusses the matters needing attention in flight experiment.The second part gives a comprehensive analysis of PX4 flight control system,introduces the overall framework of the system and the mechanism of inter-process communication,analyses the overall framework,directory structure and flight control process of PX4 flight control stack,explains the attitude estimation algorithm and quadrotor attitude control algorithm of PX4 flight control stack.In the third part,through the modeling and analysis of the quadrotor part of hybrid VTOL UAV,the attitude control of the quadrotor UAV is designed by using the non-linear dynamic inversion and incremental non-linear dynamic inversion controller.The flight experiment of hybrid VTOL UAV with gust disturbance is carried out in the environment of Gazebo simulation by using software in the loop of PX4.The stability and robustness of the controller are tested by the experiment.In the last part,the concept of mode-free switching is proposed to solve the complex operation problem of hybrid VTOL UAV.Through the analysis of PX4 attitude control module of hybrid VTOL UAV,the principle of mode switching is studied,and the function of mode-free switching is designed to achieve automatic switching between multi-rotor and fixed-wing.The reliability of the mode-free switching function is verified by flight experiment.