Research On Robust Disturbance Rejection Control Technology Of Quadrotor Unmanned Aircraft Vehicle

The quadrotor unmanned aerial vehicle(UAV)which is capable of vertical take-off and landing,hovering in the air,sideward flight and inverted flight can be categorized to the unmanned rotorcraft family.Compared with the fixed wing UAV,the quadrotor has better maneuverability and greater flexibility in the process of the flight mission.The quadrotor can be used in air reconnaissance,forest fire monitoring,water transportation,agricultural spraying and ground mapping and so on,so it has widely prospect in application.Accordingly,the flight control of the quadrotor has become one of the hot issues in the field of flight control.In this dissertation,the mathematical model of the quadrotor is established,and the robust disturbance rejection flight control methods of the quadrotor under the influences of modeling errors,input constraints and external disturbances are studied.The main research contents are as follows:Firstly,the flight principle of the quadrotor is introduced,and the nonlinear dynamic models of the quadrotor are established based on mechanism modeling method.The allocation relationship between the desired rotor speed and the force and torque is analyzed,and the overall control scheme based on the inner and outer loops is designed based on the characteristics of underactuativity of the quadrotor.Then,the influences of different winds on the attitude and position of the quadrotor are analyzed,and the common mathematical models of wind fields are discussed.A robust flight control method based on sliding mode control for the quadrotor under wind disturbance is designed,and the stability of the closed-loop control system composed of position loop and attitude loop is proved by Lyapunov method.And the simulation results show that the whole closed-loop system has good tracking performance and strong robustness to external wind disturbances.Next,the robust disturbance rejection control of the quadrotor with modeling error,coupling between attitude angles and unknown disturbances is studied.Taking into account that the load equipped with body of the quadrotor will change when performing different flight tasks,the total mass of the quadrotor and the load will become uncertain in different flight tasks.At the same time,this will also have an impact on the inertia of the quadrotor.Considering the system modeling error,the coupling relationship between attitude angles and unknown external disturbances,a dynamic model of the quadrotor is established.In the position subsystem,an adaptive estimation of the total mass of the body and the load and the external slowly varying disturbances is performed.In the attitude subsystem,the method of sliding mode control is designed with inaccurate inertia matrix model.The stability of the whole closed-loop system is proved by Lyapunov method,and the control method is verified on the MATLAB simulation platform.The simulation results show that the closed-loop system has good tracking performance and strong robustness when the load quality changes and the external disturbances change slowly.Following,a disturbance observer based robust disturbance rejection control method of the quadrotor is studied.For the position subsystem,a nonlinear disturbance observer is designed to estimate unmeasured disturbance,the position controller is designed based on Backstepping method,and the estimation of disturbance is introduced into position control law.For the attitude subsystem,a nonlinear disturbance observer is designed to estimate unmeasured disturbance,the attitude controller is designed based on linear filtering order reduction method,and the estimation of disturbance is introduced into attitude control law.The Lyapunov method is used to prove the stability of the whole closed-loop system,and MATLAB simulation is performed for the whole closed-loop system.The simulation results show that the designed disturbance observer has good estimation performance,which effectively reduce the effect of disturbance on the quadrotor,and the whole system has good tracking performance and strong robustness.Finally,the robust disturbance rejection control method of the quadrotor with input saturation,modeling error and external disturbance is studied.Considering the input saturation,the modeling error and unknown external disturbance,a modified dynamic model of the quadrotor is established.The neural network disturbance observers are designed to deal with the actuator saturation and model uncertainty in the position subsystem and attitude subsystem.In order to deal with the influence of neural network approximation error and external disturbance,nonlinear disturbance observers are introduced to estimate the complex disturbances.The position controller is designed based on Backstepping method,and the attitude controller is designed based on linear filtering order reduction method.The output of the neural network disturbance observers and the output of the nonlinear disturbance observers are introduced into the control laws of the position loop and the attitude loop,and the stability of the whole closed-loop system is proved by Lyapunov method.MATLAB simulation results show that the proposed controllers make the quadrotor with input saturation,modeling error and external disturbance has good tracking performance and strong robustness.