Advanced Fault-Tolerant Control Techniques For Unmanned Aero-Vehicles

In recent years,the development of related technology makes unmanned aerial vehicles(UAVs)extensively applied in anti-terrorism,surveillance,media,agriculture,fire protection and other fields.However,with the diversification of task scenarios and the complexity of the operating environment,a higher requirement is laid for the reliability of UAVs.Therefore,the fault-tolerant control(FTC)has received growing attention from researchers among fields of aerospace and electronic information.This research aims to increase the reliability of multirotor UAV systems and to maintain their benign control performance in the presence of actuator faults,sensor faults,fault estimation errors,model uncertainties,and external disturbances.First,the dynamic model of the UAV in the nonlinear Lipschitz form is built and an observer-based state-feedback controller is designed such that the tracking control performance of the UAV is improved.In addition,by combining nonlinear sliding mode control(NSMC)and state-feedback control,and adopting linear matrix inequality(LMI)to obtain optimal controller and observer gains,the adverse influence of model uncertainties and external disturbances in the tracking performance is avoided.Second,the actuator fault is considered into the nonlinear UAV model.FTC and NSMC are combined such that when there are faults or even failures in the actuators,the control inputs can be online re-allocated,the fault and failure information can be estimated,and the fault estimation errors can be addressed.A simulation on a 6-DOF(degree of freedom)UAV is carried out,which verifies that the proposed control scheme is capable of coping with the situation where main rotors(four rotors)totally fail.Finally,a robust fault-tolerant control scheme is proposed.This scheme is mainly used to solve the problem caused by actuator and sensor faults in UAV systems.An adaptive fault estimation scheme with H∞ performance is designed to estimate system states,actuator faults and sensor faults.In order to improve the tracking performance,a control scheme based on nonlinear sliding mode is proposed to modify the original control law by using the estimated information.The effectiveness of the proposed control scheme is verified on a 6-DOF UAV system.