Research On Finite-Time/Fixed-Time Control Method For Quadrotor Aircraft

The quadrotor unmanned aerial vehicle(UAV)is a non-coaxial multi-rotor aircraft capable of vertical take-off and landing.The four independent motor drive systems distributed by the butterfly are used as direct power sources for flight.Due to its simple structure,strong maneuverability,flexibility and many other advantages,the quadrotor aircraft has the broad application prospects.Meanwhile,the quadrotor aircraft system is a typical underactuated system with multivariable,nonlinear and strong coupling,which is challenging in terms of control.Therefore,the research on the control method of quadrotor aircraft has not only theoretical value but also application value.In order to improve the dynamic and steady-state performance of quadrotor aircraft,many scholars at home and abroad have made in-depth research on the control method of this system.The finite-time and fixed-time control technologies are the relatively novel nonlinear control methods,which have the characteristics of fast convergence and strong anti-disturbance performance.They can effectively improve the dynamic and steady-state performance of the aircraft system.This paper first introduces the research status of quadrotor aircraft and the finite time/fixed time control theory.A simple modeling analysis is carried out for the quadrotor aircraft system.Based on this mathematical model,the trajectory tracking control problem of the quadrotor aircraft is studied based on the finite time and fixed time control techniques.Specifically,based on the backstepping method,the complete aircraft control system design process can be decomposed into the design of the aircraft position controller and attitude controller.Based on the homogeneous system theory of finite time control,the corresponding finite-time position and attitude controllers are designed.Considering the unknown parameters and external disturbances in the system,a finite-time parameter estimator and a finite-time disturbance observer are designed.Based on the designed estimators,observers and controllers,an adaptive finite-time control method for quadrotor aircraft is proposed.In order to solve the defect that the convergence time depends on the initial conditions in the finite time control method,combined with the latest fixed-time control theory,a fixed-time control scheme for the quadrotor aircraft is proposed,so that the convergence time can be independent of the initial conditions.Thus,the designer can estimate the convergence time in advance.The specific design ideas are as follows.Firstly,based on the fixed-time control theory and homogeneous system theory,this paper presents the proof idea for the homogeneous fixed-time control.Based on the proof idea,the corresponding fixed-time position and attitude controllers are designed.Considering the influence of unknown parameters and external disturbances,a fixed-time parameter estimator and a fixed-time disturbance observer are designed.Then,an adaptive fixed-time control method for quadrotor aircraft is proposed.In view of the above control method,based on Lyapunov theory,the stability of the closed-loop system is strictly proved,and the effectiveness of the controller is verified by Matlab simulation.Finally,the experimental verification results of the adaptive finite time control method for the quadrotor aircraft are given through the quadrotor aircraft position control experimental platform based on the visual positioning system.