Research On Several Active Disturbance Rejection Control Methods For Unmanned Aerial Vehicle Systems

Due to the advantages such as low cost and low loss,unmanned aerial vehicles(UAVs)have attracted the attention of researchers around the world and are widely used in many military and civilian fields.However,in various kinds of flight tasks,the UAV is severely affected by multi-source composite disturbances,such as unmodeled dynamics,parameter perturbation and other internal uncertainties,as well as turbulence,strong airflow and other external disturbances.Therefore,researching high-performance disturbance rejection flight control methods is an important goal in the design of UAV systems.Active disturbance rejection control method has the advantages of fast,fine and non-conservative in dealing with disturbances,and can significantly improve the disturbance rejection ability and robustness of closed-loop systems.Taking small-scale UAVs as research objects and aiming at their typical flight tasks,active disturbance rejection flight control methods with high precision,strong disturbance rejection ability,and strong robustness are studied in this dissertation.The main research content of this dissertation is summarized as follows:(1)For trajectory tracking control of the disturbed small unmanned helicopter system,a feedforwardfeedback composite trajectory tracking control method based on a generalized proportional integral observer and block backstepping technology is proposed.Firstly,to solve the coupling between different channels,the small unmanned helicopter system is decoupled into three subsystems with relatively small coupling.Secondly,to improve the disturbance rejection ability and robustness of the closed-loop system,a generalized proportional integral observer is designed to estimate the multiple-source composite disturbances and their higher-order derivatives within each subsystem.Then,a feedforward-feedback composite trajectory tracking controller is designed by combining the estimated values of the disturbances and their higher-order derivatives with a block backstepping control method.The asymptotic stability of the closed-loop system is analyzed using Lyapunov theory.The results show that the proposed trajectory tracking disturbance rejection control scheme ensures that even in the presence of rapidly time-varying mismatched disturbances,the position and yaw angle of the small unmanned helicopter system can asymptotically track the desired trajectory.Finally,the effectiveness and superiorities of the designed disturbance rejection controller is verified by numerical simulation.(2)For landing control of the disturbed small unmanned helicopter system on a moving ship,a feedforward-feedback composite landing control method based on a joint state-disturbance observer/generalized proportional integral observer and state/output feedback technology is proposed.The landing control is carried out by stabilizing the error system between the small unmanned helicopter and the moving ship,and the landing process is divided into two phases.The first phase is the homing phase.A hierarchical double-loop homing control scheme based on a joint state-disturbance observer/generalized proportional integral observer is designed,allowing the small unmanned helicopter to be controlled to hover synchronously at a specific altitude above the ship.The second phase is the descent phase.A descent control scheme based on a joint state-disturbance observer is designed to keep the small unmanned helicopter synchronized with the ship’s attitude and land on the ship.The velocity and acceleration information of the ship as well as composite disturbances are estimated by joint state-disturbance observers.The asymptotic stability of the closed-loop system is analyzed by Lyapunov theory and the effectiveness of the designed disturbance rejection controller is verified by numerical simulation.(3)For the attitude and altitude tracking control of the disturbed small unmanned helicopter system,a feedforward-feedback composite attitude and altitude tracking control method based on a high-order sliding mode observer and non-singular terminal sliding mode control method is proposed.Firstly,in order to ensure a fast convergence speed,strong disturbance rejection ability,and robustness of the closed-loop system,a high-order sliding mode observer is designed to estimate the composite disturbances of the system,ensuring that the disturbance observation error converges to zero within a finite time.Secondly,a novel non-singular terminal sliding mode surface and a fast terminal sliding mode reaching law are designed to improve the convergence speed of the closed-loop system while mitigating the control chattering.Under the proposed finite-time disturbance rejection tracking controller,the closed-loop system has faster convergence speed,better disturbance rejection ability,and robustness.Finally,the effectiveness and superiorities of the designed disturbance rejection controller is verified by numerical simulation.(4)For the three-dimensional path following control of small fixed-wing UAV system affected by periodic disturbances,a feedforward-feedback composite path following control method based on a harmonic disturbance observer and finite-time control is proposed.Firstly,by parameterizing reference paths and feedback linearization technology,the path following control problem is transformed into a tracking control problem.Secondly,based on the backstepping control technique and the adding power integrator approach,a state feedback controller for the nominal system is designed.A simple fourth-order harmonic disturbance observer is designed using saturation technique to estimate mismatched wind disturbances and their derivatives.By incorporating the estimates of wind disturbances and their derivatives into the feedback control part for feedforward compensation,a feedforward-feedback composite path following controller is formed.The finite-time semi-global stability of closed-loop systems is strictly analyzed using homogeneity theory.The results indicate that for a small fixed-wing UAV system with any large initial range,the state of the closed-loop system is limited to the region of attraction related to the initial value of the system,and converges to the equilibrium point within a finite time.Finally,the effectiveness and superiorities of the designed disturbance rejection controller is verified by numerical simulation.