Anti-disturbance And Fault-tolerant Control For The Quadrotor UAV

As one kind of the muliti-rotor aircraft,the quadrotor unmanned aerial vehicle(UAV)is consisted of four rotors mounted on the cross rigid body symmetrically.Compared with the fixed wing or the single wing aircraft,the quadrotor UAV has several advantages,such as simple structure,light weight,vertical take-off and landing capability,and high mobility.Owing to the outstanding properties,the quadrotor UAV has been widely used in the military,civil and commercial fields,such as battle reconnaissance,fire prevention and disaster relief,aerial photography,farmland plant protection,logistics and express delivery,etc,which has become the focus of the domestic and foreign research scholars.The flight control system is the core part of the quadrotor UAV,which is the key to realize the stable and reliable flight.In recent years,numerous control schemes have been proposed to improve the robustness and stability of control systems.However,with the continuous expansion of application fields and the continuous improvement of performance requirements,the working environment of the quadrotor UAV becomes more severe and the flight task becomes more arduous than ever before.In addition,the unknown external disturbances,parameter uncertainties and the parts failure have brought great challenges to the control design of the quadrotor UAV.The existing control schemes are not enough to solve these problems effectively.Therefore,several different anti-disturbance and fault-tolerant control schemes for the attitude and position control of quadrotor UAV based on the various nonlinear and intelligent control methods such as backstepping,adaptive and fuzzy control strategies are proposed this paper.The main contents of the paper include the following aspects:(1)The dynamics models of the rotor and the whole system of quadrotor UAV are established.The air inflow of the rotors which is the key component of the quadrotor UAV under the vertical and forward flight states are analyzed in the paper.The induced velocity of the rotor plates under the two flight conditions is deduced based on the slipstream theory,blade element theory and momentum theorem,and the aerodynamic coefficient of the rotor is formulated.Considering the whole system of the quadrotor UAV,two coordinate systems based on the ground and airframe are established,and the working principle of the quadrotor UAV is analyzed.The translational and rotational dynamics of the quadrotor UAV are established via Newton-Euler method.(2)Based on the backstepping control method,a new robust control scheme is proposed to solve the problem that the weakness of the current control method in anti-interference ability for quadrotor UAV.By redesigning the Lyapunov function and the error variables,and adding the integral of the first type of error variable and the saturation function term of the second type of error variable into the control rate,the saturation integral backstpping anti-interference control scheme is established.The tracking errors of the control system are proved to be uniformly and ultimate bounded with the stability analysis.Different kinds of external disturbances are applied to the control system in the numerical simulation,and the results show that the ability of control system to resist external uncertain interference has been improved effectively.(3)While improving the ability of the system to resist external interference,a fuzzy adaptive anti-step anti-interference control method is proposed for the quadrotor UAV system to solve the problem of variable parameters.The large changes in the parameters of quadrotor UAV system,especially the mass parameters,will greatly reduce the accuracy of the system model and introduce large errors to the flight control.Therefore,a mass parameter observer based on the adaptive control theory is designed to observe and compensate the varying mass of the quadrotor UAV system.In addition,a model-free compensation controller based on the fuzzy logic is designed to compensate the unknown external disturbances.A fuzzy adaptive backstepping control system is established by the integration of the backstepping control,the new mass observer and the compensators.The asymptotic stability of the control system is proved by the stability analysis.Numerical simulation results show that this control scheme can estimate the mass of the quadrotor system,reduce the influence from variable parameters and external disturbances,and improve the control accuracy of the system effectively.(4)An active fault-tolerant control method is proposed to solve the partial failure problem of actuator for the faulty quadrotor UAV system.By introducing the rotor efficiency and fault coefficients,the mathematical model with constant-gain actuator fault is established.The fault detection observers based on the velocity of attitudes are designed to detect the actuator faults in the roll and pitch channels.According to the law of attitude angle,a fault diagnosis algorithm is proposed to locate and isolate faults accurately.The adaptive rate of fault parameter estimation is designed by using the adaptive control method.The fault parameters are introduced into the baseline controller to reconstruct the controller,based on which the active fault-tolerant control system of the quadrotor UAV is established.The uniform and ultimate boundedness of the control system is guaranteed by the stability analysis.The control scheme is verified by numerical simulation method,and the results show that the scheme can improve the fault tolerance and security of the control system.(5)In order to further verify the proposed control scheme,the quadrotor platform is designed and built,and the hovering flight test is carried out in the outdoors environment.The overall design scheme of the platform is developed based on the modularization methodology,through which the hardware of each module is properly selected,and the design of the software program is discussed.A hover flight test of the quadrotor UAV disturbed by the wind gusts is carried out in the outdoor environment.The comparative test results show the high efficiency and enhanced robustness of the proposed control scheme for the quadrotor UAV.