| In recent years,with a series of advantages such as vertical take-off,free landing,side-flight and upside down flight,the small-rotor unmanned aerial vehicle(UAV)can complete various tasks in narrow terrain,dangerous and complex environment.Therefore,the small-rotor UAV has been used more extensive in military and civil.However,the small-rotor UAV is often affected by external disturbances during the flight,and the model characteristics are changed due to the influence of altitude or other factors.These uncertainties will affect the attitude control performance of the small-rotor UAV.The three degree of freedom(3-DOF)helicopter studied in this paper can well simulate the key dynamic characteristics of the small-rotor UAV and has been an important auxiliary tool to study the attitude control problems of the small-rotor UAV.Therefore,this paper will research the model uncertainties and external disturbances in the3-DOF helicopter.The main contents of this paper are as follows:(1)Based on the disturbance observers design approach,this paper researches the attitude tracking control problem for a 3-DOF helicopter with external disturbances.Firstly,the disturbance observers are used to estimate the external disturbances of the 3-DOF helicopter.Then,with the aid of the estimations and Backstepping design method,the new nonlinear tracking controllers with disturbance compensations are proposed.And,it is verified that the resulting closed-loop 3-DOF helicopter system is asymptotically stable by employing Lyapunov stability theory.Finally,simulation results demonstrate the effectiveness of the proposed design approach.(2)In this paper,the attitude tracking control problems of the 3-DOF helicopter with external disturbances are studied,and the model uncertainty problems of the 3-DOF helicopter are further considered.Therefore,this paper proposes the attitude tracking controller design scheme for the 3-DOF helicopter with unknown model uncertainties and external disturbances by combining command filter with neural network techniques.On the basis of Backstepping design method,the unknown model uncertainties and external disturbances are firstly reconstructed by adopting command filter.Then neural network technique is used to approximate the reconstructed model uncertainties and external disturbances to realize the high precision attitude tracking control of the 3-DOF helicopter.Finally,the stability of the closed-loop tracking control system of the 3-DOF helicopter is verified by Lyapunov stability theory.Simulation results verify the effectiveness of the proposed method. |
