Research On Flight Control Of Four-rotor UAV Based On Active Disturbance Rejection Control

In recent years,four-rotor unmanned aerial vehicle(UAV)have been widely used in military,civil,and scientific research fields due to their flexibility,compact size,low cost,high reliability and good service.More and more people begin assemble quadrotors to study UAV flight control system.At present,the four-rotor UAV attitude controllers commonly used in the market are mostly based on cascade PID controllers.This control method is simple and easy to implement,but the quadrotor UAV is a strong coupling and nonlinear system.There are interferences from internal uncertainties and external environments during flight,and it is difficult for cascade PID controllers to resist these disturbances.In the actual hover flight,the attitude angle will fluctuate,and when the quadrotor is subjected to external interference,the fluctuation is greater and the hovering effect is worse.Therefore,the attitude controler that can effectively resist internal and external interference should be designed.The control algorithm commonly used for quadrotor,like the classic sliding mode control algorithm,has strong anti-interference ability,but the high frequency jitter is prone to occur in practical applications.The backstepping control algorithm is not sensitive to external disturbances,but control effect of this control algorithm depends on the accuracy of the controlled object model.However,the actual quadrotor parameters in the flight may change due to load changes,and the precise control model is difficult to establish.The fuzzy control algorithm has strong anti-interference ability and has good control effect on nonlinear systems.However,it is necessary to select appropriate fuzzy rules for the control object.Active disturbance rejection control(ADRC)algorithm is almost independent of the mathematical model of quadrotor.It has natural decoupling performance and anti-interference ability,and can estimate the uncertainty inside the UAV and the external environment interference in real time,compensate in the control quantity,which it is very easy to implemented on the processor and it is ideal for the control of quadrotor drones.However,most of the existing four-rotor UAV attitude controllers based on the ADRC design do not consider the influence of the power system on the control effect.After a complete analysis of the attitude control process of the quadrotor UAV,the powertrain model is introduced based on ADRC theory to design the attitude controller,and the flight effect is verified by the Pixhawk flight control board.In the use of Pixhawk flight control board,it is found that software code PX4 firmware of this flight control board multi-waypoint trajectory generation adopts the way of connecting the waypoints in a straight line.However,when the trajectory generated in this way is traced,the desired position signal input to the position controller at the waypoint will jump,which has a great influence on the continuity of the drone speed and acceleration.Based on the dynamic characteristics of the four-rotor UAV,the Mini Snap constraint is used to optimize the path trajectory generation.The main work of this paper is as follows: Firstly,the flight principle of the quadrotor UAV is analyzed.Then the coordinate system commonly used to describe the attitude and position of the quadrotor UAV is introduced.The conversion relationship between the two is studied and the nonlinear mathematical model of quadrotor is derived based on the kinematics and dynamics equations.For each hardware component of the four-rotor UAV,the appropriate components were selected,and the flight platform was assembled and debugged.Then considering the dynamic characteristics of the power system,the attitude controller based on ADRC is designed.The controller is divided into two parts: the angle part adopts proportional control,and the angular speed part adopts auto disturbance rejection control to offset internal and external interference.The MATLAB/Simulink simulation model is established to verify the effectiveness of the control scheme and some control parameters were set by the seeker optimization algorithm.The comparison flight control experiment and anti-interference flight experiment with the cascade PID controller were carried out to verify the anti-interference performance of the designed control scheme.In the flight test,the experiment shows that controller scheme design here has stronger anti-interference ability.Finally,in the case of trajectory generation for multi-waypoint,based on the dynamic characteristics of the quadrotor and the differential flatteness theory,horizontal path trajectory of quadrotor was generated by Mini Snap.Aiming at the frequent acceleration and deceleration problems in the trajectory tracking experiment,the trajectory tracker is designed and the trajectory tracking effect of the design scheme is verified by simulation.