Nonlinear Control Methods,Numerical Analysis And Experiment For Attitude Of Quadrotor Unmanned Aerial Vehicle

With vertical taking off and landing,hovering,superior maneuvering,flexible operating,the quadrotor unmanned aerial vehicle(UAV)has been effectively carried out a wide range of military and civil applications,such as,search and rescue,reconnaissance,fire surveillance,traffic monitoring,and so on.Its great potential has attracted much attention and effort of researchers and communities,and it is an extensive and active researched topic.The quadrotor UAV is a typical four-input-six-output underactuated system.Although the design and manufacture of the aircraft can be achieved easily,it is a great challenge for designing the control system of quadrotor UAV.The attitude control is the basis and kernel of the quadrotor flight control system,and is the precondition for trajectory tracking control.The excellence performance of the attitude control is guaranteed for flighting control,and it is of great importance to finish the flight mission.It has been extensively attracted much effort of researchers,and various advanced control methods have been designed in recent years.However,the attitude dynamics of quadrotor UAV involves internal uncertainties including unmodeled,coupling,nonlinearity and so on,and it is also subject to external disturbances during flighting.The existed control methods can not solve all problems of the attitude control under these unfavorable factors.Therefore,high reliable,precision,robust performance control scheme is required for the attitude dynamics of the quadrotor UAV to accomplish the flight mission,improve the effectiveness and guarantee the security.In this paper,several control schemes based on nonlinear control methods are developed to address the attitude tracking problems for the quadrotor UAV under internal uncertainties and external disturbances.The main contents in this paper are follows:(1)The backstepping sliding mode attitude control of the quadrotor UAV is studied.With the small change of the attitude angle or the hover state during the flight in some applications,and according to the flight principle analysis,the attitude dynamics of quadrotor UAV based on the Euler angle-based representations is presented.The backstepping sliding mode attitude control scheme of the quadrotor UAV consists of linear extended state observer,backstepping control,sliding mode control.The proposed observer is developed for estimating the states and the extended states of the control systeme,and the states of the observer are employed in the controller design proceduce.The attitude controller of the quadrotor UAV is designed based on the backstepping control method and sliding mode control method.The stability analysis proves the control system is asymptotic stability.Numerical simulations demonstrate that the control accuracy and anti-disturbance capability of the control system are enhanced by using the proposed control scheme.(2)The active disturbance rejection attitude control of the quadrotor UAV is studied.In order to solve the differential explosion problem of the backstepping,and the contradiction between rapidity and overshoot of control,the attitude controller of the quadrotor UAV is designed based on the active disturbance rejection control method.The control scheme consists of arranging transitional process,nonlinear extended state observer,and error feedback dynamic surface controller.The discrete optimal tracking differentiator is employed for arranging transitional process.The nonlinear extended state observer is designed for estimating the states and disturbances of the attitude control system.The dynamic surface control method can avoid the differential explosion problem by using first order filter to obtain the derivative of the virtual control.By using the states of the proposed observer,the attitude controller of the quadror UAV is developed based on dynamic surface control method.The stability analysis proves the control system is asymptotic stability,all close-loop signals are uniformly ultimately bounded.Numerical simulation are performed to guarantee higher control efficiency and better robustness of the attitude control system of the quadrotor UAV.(3)The sliding mode time-delay estimation attitude control of the quadrotor UAV is studied.The rotational dynamics of the quadrotor UAV has singularity problem with Euler representation,while the quadrotor UAV flies in large angle in some applications.Therefore,the unit quaternion is employed to represent the attitude angle.The attitude dynamics of the quadrotor UAV based on the error quaternion is presented.The sliding mode time-delay estimation attitude control scheme consists of global asymptotic convergent observer,time-delay estimation,and adaptive sliding mode control.The global asymptotic convergent observer is employed to estimate the states of the control system,and the observer is better robust to reject disturbances.The disturbances of the attitude control system are estimated by using the time-delay estimation method,and the estimation is appended to the controller.The adaptive function is presented to decrease the chattering of the sliding mode control method.The stability analysis proves that control system errors are uniformly ultimately bounded.Numerical simulations illustrate that the proposed control scheme has better the effectiveness and control accuracy.(4)The dynamic surface attitude control of the quadrotor UAV is studied.For avoiding the multiple coordinate transformations in the deducting process of attitude dynamic of the quadrotor UAV based on error quaternion,the attitude tracking errors dynamics of the quadrotor UAV is presented,while a nonlinear function based on two quaternions is employed to represent error quaternion.The dynamic surface attitude control scheme consists of nonlinear augmented observer and dynamic surface control.The nonlinear augmented observer is employed to estimate the states and extended state of the control system,and it is immune to measurement noises and reject disturbances.With the states of the proposed observer,the attitude controller of the quadrotor UAV is designed based on the dynamic surface control method.The stability analysis proves the control system is asymptotic stability.Numerical simulation are performed to demonstrate that the control efficiency and the robustness of the control system are enhanced.(5)The experimental system of the attitude of the quadrotor UAV is presented.After the comparative analysis of the attitude control schemes designed in this paper,the attitude control scheme of the experimental system is determined.The designing scheme and requirements analysis of the experimental system are presented for the attitude control system of the quadrotor UAV.The hardware framework,design processs and software functions of the experimental system are introduced,which consists of the aircraft and the ground station.The experimental results show that the object of the experimental system has been achieved,and the proposed control scheme meets the attitude control requirements of the quadrotor UAV.