Fault Tolerant Control Of Quadrotor UAV Based On Silding Mode Theory

Quadcopter UAVs are widely used in various military,agricultural and hazard operations because of their low budget,simple architecture,vertical take-off and landing,and the capabilities to work in tough conditions.During flight operations,it is inevitable that UAVs will encounter bad weather,such as strong winds;or that the UAVs themselves will suffer from the unstable flight of the fuselage,property damage and other effects due to actuator faults,which can even lead to casualties.Therefore,it is of great value to study the fault-tolerant control of quadrotor UAVs to achieve safe and stable flight of UAVs.The key points covered are the following:(1)When a quadrotor UAV actuator faults,it causes some disruption to the flight of the UAV,and the existing shortcoming for this problem is mainly the less research on multiple actuator faults and the slow conversion to a steady state after a fault occurs.Therefore,a non-singular global fast terminal sliding mode control method is proposed for a quadrotor UAV with multiple actuators in case of actuator additive errors.Firstly,a quadrotor UAV with an additive actuator fault is mathematically modelled;Next,an inner-loop attitude and outer-loop position faulttolerant controller is designed according to the proposed method,with saturation functions replacing symbolic functions to reduce the jitter of the system;Then,the stability of the designer fault-tolerant controller is then demonstrated;Finally,the simulation results show that when the quadrotor UAV has an actuator additive fault,the trajectory of the position loop tracks well and the attitude loop can converge to the steady state quickly,thus this enables to verify that the methodology is fault tolerant in some way.(2)There are many faults types of quadrotor UAV actuators,and an adaptive non-singular global fast terminal sliding model method is proposed for multiple actuators with both additive and multiplicative faults.Firstly,multiplicative faults are added to the quadrotor UAV model to obtaining a new model of the UAV with both additive and multiplicative faults;Secondly,design of an adaptive method for multiplicative fault factors to allow compensation of the impact of faults by means of adaptive reparation;Then,the stability of the designed adaptive law is justified;Finally,the simulation experimental results show that the fault tolerance performance of the adaptive non-singular global terminal sliding mode method is somewhat enhanced compared to the non-singular global fast terminal sliding mode method,and thus verifying the usefulness of the approach.(3)A fault-tolerant control method based on a sliding-mode observer is proposed for a quadrotor UAV subject to unknown disturbances.Firstly,unknown disturbances are added to the UAV with faults to obtain a new model;Secondly,a sliding-mode observer is designed for the six channels of the quadrotor UAV to compensate for the effects of external disturbances through the observed values in the observer and to stabilise the positional tracking accuracy of the UAS;Then,the stability of the designed sliding mode observer is demonstrated;Finally,by simulating and comparing trials,it is verified that the proposed error-tolerant control method based on the sliding mode observer has less steady-state error and lower jitter under the influence of timevarying disturbances compared to the adaptive non-singular terminal sliding mode method,hence the efficacy of the proposed method is proven.