Improvement Of ADRC With Applications To Quadrotor UAVs

The quadrotor unmanned aerial vehicle(UAV)is a kind of flight vehicle controlled by a radio transmitter or a self-embedded program.Quadrotor UAV has simple structure,and low cost.And it can also perform unique flight actions such as vertical take-off and landing,hovering,low-level flight and spin around.It can adapt to a wide variety of flight environments.Therefore,the quadrotor UAV has the unparalleled advantages over common UAVs in both military and civil use.However,due to the non-linearity,strong coupling,underactuation,and model uncertainty,higher demands have been put forward to the design of quadrotor UAV control systems.The design of a more efficient control system for the quadrotor UAV is of great significance.The application of Active Disturbance Rejection Control(ADRC)does not require the exact model of the controlled object.ADRC has good quality in confronting external disturbances or handling model uncertainty,and it is also effective in decoupling control.However,the extended state observer(ESO)in the traditional ADRC is just asymptotically convergent in the sense of Lyapunov,and the convergence speed still has room for improvement.This dissertation focuses on the control of quadrotor UAVs,proposes a method to improve the traditional ADRC and applies the modified ADRC to the design of quadrotor control systems.The main work is as follows:First,the structural characteristics and flight principles of the quadrotor UAV are analyzed.Based on the Newton Euler method and considering the aerodynamic interference,a quadrotor UAV mathematical model with six degrees of freedom is established.Second,the principle of ADRC is introduced with emphasis on the roles of ADRC ’s three components,i.e.,tracking differentiator(TD),extended state observer and nonlinear state error feedback(NLSEF).At the same time,the deficiency of the traditional ADRC is pointed out,and an improvement method is proposed.The modified ADRC improves the estimation speed and accuracy of the "total disturbance",thereby the control efficiency of the controller is improved.Third,considering the nonlinearity and strong coupling of the quadrotor UAV,the internal coupling and external disturbance of the UAV are regarded as the "total disturbance".A quadrotor UAV attitude controller is designed by using the modified ADRC.With the application of this controller,the quadrotor UAV’s attitude control and fixed-height flight are realized.Finally,a double-closed-loops trajectory generator is designed based on the PD controller and the modified ADRC.The position loop controller uses a simple but effective PD controller to generate the desired attitude angle,which is desired for tracking a given trajectory,through the error between the current and target positions of the UAV.The attitude loop controller is designed based on the modified ADRC to follow the expected attitude angle which is generated by the position loop.