Backstepping Attitude Tracking Control Of Quadrotor UAVs Under Input Constraint

VTOL(Vertical takeoff and landing aerial vehicles)have gained wide research and application,which possess characteristics such as high adaptability and high maneuverability.The rotary-wing UAV,represented by the quadrotor UAV,has the advantages of symmetrical structure,high reliability,convenient control and wide working area,etc.Also,because the quadrotor UAV has a special control method,it has broad application prospects in recent years.The traditional control methods used by the UAV products on the market are difficult to achieve accurate control,and the presence of actuator saturation and perturbation during the UAV movement can make the UAV system unstable.At the same time,multiple UAV formations extend the range of UAVs in terms of endurance and mission load,but obstacles in the environment can have an impact on formation flight.Therefore,this thesis designs a positional controller and a formation obstacle avoidance controller for the presence of perturbations,input saturation and obstacles.The specific research work is as follows.Firstly,this thesis analyzes the general framework and motion mode of the four-rotor UAV control,and establishes the coordinate system conversion relationship based on the rotation matrix transformation.The UAV is divided into translational and rotational motions and a complete UAV dynamics model is established based on the Newton-Euler equation.Secondly,the backstepping control strategy and the working principle of the anti-saturation auxiliary system are introduced.The UAV dynamics model is decoupled into an inner-loop attitude loop subsystem and an outer-loop position loop subsystem using a series-level inner and outer-loop decoupling method,which reduces the difficulty of the UAV system in the controller design process by using the idea of turning the whole into zero with backstepping control.And the control law design is carried out for the inner and outer loops respectively.On this basis,an anti saturation auxiliary system is introduced to reduce system input and avoid actuator saturation.The simulation comparison experiment is designed to verify that the anti-saturation controller has good trajectory tracking and anti-saturation capability.Thirdly,a control strategy combining anti-saturation backstepping control and anti-interference control is proposed for the problems of external interference,input saturation and model uncertainty in quadrotor unmanned and positional control.Based on the anti-saturation backstepping control,the internal uncertainty term and external disturbance of the system are regarded as the total disturbance term of the system,and the ESO extended state observer and RBF neural network are designed for disturbance estimation and compensation.The stability of the anti-disturbance backstepping saturation controller is proved by Lyapunov stability theory,and the stability of the anti-disturbance backstepping saturation controller is verified by simulation comparison experiments.The stability and robustness of the anti-disturbance backstepping saturation controller are verified by simulations.Finally,a UAV formation controller with obstacle avoidance is designed for the problems of trajectory tracking,formation shaping and obstacle avoidance planning in UAVs formation avoidance control.Firstly,the formation controller with virtual leader is designed according to the formation requirements and consistency theory to ensure the effectiveness of formation control,and a non-exactly smooth artificial potential field function is designed for the obstacle avoidance problem,so that the UAV formation can effectively avoid obstacles and ensure the safety of flight.through simulation experiments,it is verified that the formation avoidance controller has good formation consistency and obstacle avoidance capability.