Research On Adaptive Fault-tolerant Control For Quadrotor UAVs With Payload

Rotary-wing UAV can be widely used in military and civilian fields.Due to the diversity of work,unmanned aerial vehicles(UAVs)often need to carry certain equipment’s and supplies or other payloads to complete the specified task.Affected by the load swing,the gain matrix caused by the center of gravity and the moment of inertia of the entire UAV system become time-varying and unknown.Therefore,in actual flight,there is a large deviation between the system model with load and the classic UAV dynamic model,resulting in reduced control performance or even failure.Moreover,in actual flight,due to the limitations of the internal and external physical conditions of the drone,it is necessary to further consider the problem of actuator saturation or actuator failure,as well as state constraints,and develop a more practical fault-tolerant control method to ensure reliability and safety of UAV flight.In this paper,we take a quadrotor UAV with load as the research object,and design the adaptive fault-tolerant controllers under the practical application conditions,including actuator saturation,actuator failure and state constraints.The main research works of this paper are as follows:(1)Based on the dynamic analysis of the classic UAV,this paper considers the time-varying unknown dynamic characteristics of both of the gain matrix with the suspended load,derives and establishes a new dynamic model of quadrotor UAV with load,which can better reflect the dynamic process of the system and meet the requirement of controller design.(2)For the problem of actuator saturation and failure,this paper defines a good smoothing function without knowing the input saturation limit in advance to handle the fault of actuator input saturation with unknown asymmetry and non-smoothness.For the state-constrained problem,this paper introduces Barrier Lyapunov Function(BLF)and backstepping method to design the adaptive fault-tolerant controller with state constraints.By reasonably adjusting the design parameters,a low-cost fault-tolerant control scheme for the quadrotor UAV under the restricted system state is proposed.(3)Considering whether the swing angles of the suspended load is observable or unobservable in practical applications,this paper has designed two kinds of adaptive fault-tolerant controllers under typical working conditions,namely based on partially known(observable)and based on completely unknown(unobservable)the model parameters.The former has some known model parameters,so the design is simpler and more accurate.On the contrary,the latter is not dependent on the model parameters,so the design is more difficult but has better universality.In this paper,the stability theory is proved by Lyapunov function.The tracking error finally converges to a small finite set and good tracking control performance is achieved under the condition that all the signals in the closed-loop control system are bounded and the system state constraints are not violated.Finally,through the Matlab simulation to verify the effectiveness of the designed controller.