Research On Robust Disturbance Rejection Method Of Quadrotors

Quadrotor is a kind of rotor aircraft with power device.Compared with fixed-wing aircraft,quadrotor has the advantages of small weight,simple mechanical structure,vertical take-off and landing,strong maneuverability and high flexibility.It can be used in aerial reconnaissance,forest fire monitoring,water transportation,agricultural spraying,ground mapping,aerial photography and other fields,and has wide application prospects.With the expansion of the application field of quadrotor,higher and higher requirement is put forward for its stability and control performance,thus the flight control methods of quadrotor become a hot research.This paper mainly investigates the robust disturbance rejection control problem under the influence of external disturbance,model uncertainty,input saturation and unmeasurable state.This main researches of this paper are as following:(1)This paper analyzes the flight principle of the quadrotor with six degrees of freedom.According to Newton's law and Euler equation,a nonlinear dynamic mathematical model is structured.(2)For the attitude system,the external disturbances,coupling terms and modeling uncertainties are regarded as the total disturbances of attitude system.The nonlinear extended state observer is designed to estimate the total disturbances of attitude system,and further compensate them in the controller.In addition,in order to avoid the impact of large control variables on the system caused by the sudden change of expectations,we design the tracking differentiator to provide a transition process for the reference signals.Then,a nonsingular fast terminal sliding mode controller is designed based on the nonlinear extended state observer and tracking differentiator.Finally,the simulation and experiment results all verify the feasibility and effectiveness of the proposed control method.(3)A novel double closed-loop integral sliding mode control for the robust trajectory tracking of a quadrotor is designed.Firstly,the globally asymptotically stable position controller is designed based on hyperbolic function.Application of hyperbolic function provides bounded control inputs and smooth control process,improving the tracking performance.Then,a robust double closed-loop integral sliding mode attitude controller is proposed based on linear extended state observer.The linear extended state observer is designed to estimate the total disturbances and further compensate them in the controller,enhancing disturbance rejection ability of the attitude system.The designed controller can simultaneously track the attitude angle changes and angular velocity changes to improve the accuracy and stability of the proposed control laws.Further,the integral term is incorporated into the sliding mode surface design,which can effectively reduce the static error,resulting in a better system stability.Simulation and experiment results all verify the feasibility and effectiveness of the designed control method.(4)The adaptive robust disturbance rejection control of quadrotor with input saturation,external disturbance,model uncertainties,parameter uncertainties and unmeasurable state is studied.First,an adaptive radial basis function neural network is designed to approximate the model uncertainty terms of quadrotor system.Further,for the unmeasured state,the state observer is designed by the output state to provide real-time state observation feedback.After that,for the input saturation problem,an auxiliary system is designed to compensate the saturation.Then,the actuator disturbance and neural network approximation error caused by external disturbance and parameter uncertainty are compensated by designing a nonlinear disturbance observer.Finally,a robust disturbance rejection control of quadrotor based on adaptive neural network and nonlinear disturbance observer is proposed,and the stability of the closed-loop system is proved via Lyapunov analysis method.The simulation results show that the designed controller guarantees satisfactory tracking performance,robustness and disturbance rejection ability.