Nonlinear Robust Adaptive Anti-disturbance Control For Unmanned Helicopter System

In recent years,with the wide application and development of unmanned helicopter,more and more scholars and research institutions have paid attention to the research of unmanned helicopter flight control.On the one hand,complex nonlinearity,uncertainty and coupling characteristics of the unmanned helicopter make great challenges to the design of flight control system.On the other hand,the complex missions and the changeable environment put forward new requirements for unmanned helicopter flight safety control.In this thesis,the robust flight control is studied for the unmanned helicopter nonlinear system.The main work is listed as follows:Firstly,the nonlinear flight dynamics model of unmanned helicopter is constructed.The rotor aerodynamic model of unmanned helicopter is established by using blade element theory,and the aerodynamic force and aerodynamic moment of tail rotor,fuselage,flat tail and vertical tail are also calculated.At the same time,in order to facilitate theoretical analysis,the effects of gust and turbulence on the flight of unmanned helicopter are fully considered in the modeling process,thus the nonlinear dynamics model of unmanned helicopter is constructed.It lays the foundation for robust adaptive disturbance rejection flight control law design of unmanned helicopter.Secondly,for meeting the mission requirement of unmanned helicopter flying envelope,the model of unmanned helicopter linear system under multiple switching modes is constructed based on the nonlinear dynamic model of unmanned helicopter.Moreover,in order to overcome the influence of aerodynamic parameter uncertainty,the robust control law with pole assignment under multiple switching modes condition is designed for unmanned helicopter in order to overcome the influence of uncertain aerodynamic parameters.Thus,the stable flight of unmanned helicopter in the large envelope range is realized under multiple switching modes.Then,considering that the working environment of unmanned helicopter rotor is more complex especially in the course of landing mission the main rotor is affected more obviously by eddy current.In order to solve the problem of modeling hysteresis caused by eddy current,a class of attitude control law for unmanned helicopter with state hysteresis is designed in this thesis.In this method,Lyapunov-Krasovskii theory is introduced,and the robust adaptive controller for unmanned helicopter with uncertainties and output constraints is designed by combining neural network and prescribed performance control method.Finally,the attitude tracking control of unmanned helicopter with output constraints under hysteresis disturbance is achieved.The simulation results verify the effectiveness of the attitude tracking control method.Next,in order to improve the fast response capability and attitude tracking control accuracy of unmanned helicopter,a prescribed performance restriction based robust adaptive finite time control law design method for unmanned helicopter attitude tracking control system is proposed in this thesis.Based on the finite time Lyapunov stability theory,a robust finite time tracking control law is designed for improve the response speed of unmanned helicopter attitude tracking systems.In order to improve the accuracy of unmanned helicopter attitude tracking system,the prescribed performance function control method is employed to further improve the transient performance of the closed loop system.The simulation results show that the robust adaptive control law can not only guarantee the stability of the attitude tracking system in finite time,but also guarantee that the tracking errors are always restricted within the prescribed performance boundary.Furthermore,due to the limitation of the structure and material of the main rotor of the unmanned helicopter,the flapping angles of the rotor usually have a range of constraints.A robust adaptive control law design method based on state constraint is proposed to solve the problem of restricted rotor dynamics of unmanned helicopter.By using hyperbolic tangent function and Barrier-Lyapunuov function,the system state constraint control problem is effectively solved.The disturbance observer is used to estimate the external disturbance and the uncertainty approximation is realized by RBF neural network.Through the coupling design of the disturbance observer and neural network,the influence of external disturbance and neural network approximation error can be reduced to some extent.Thus,the robust adaptive altitude and attitude tracking control of unmanned helicopter in the presence of restricted flapping dynamics can be achieved.The simulation results verify that there is good tracking performance for unmanned helicopter system under the designed controller.Finally,due to the physical limitations of the unmanned helicopter's actuator,there are saturated constraints on the control input signals,which cannot meet the control performance and even causes instability in the closed loop system.Therefore,considering the saturated constraints of the actuator and the bounded conditions of the output position in the nonlinear control system,a trajectory tracking control law design method based on input and output constraints is proposed by using multi-loop design structure.The disturbance observer and neural network approximator are employed into the speed control loop and attitude angle rate control loop,and the tracking control accuracy is improved through the coupling design of the disturbance observer and neural network.The position tracking error is restricted to the output performance boundary by prescribed performance function and the trajectory tracking control under the input and output constraints of unmanned helicopter is realized by robust adaptive control law design.The simulation results illustrate that the control system of the unmanned helicopter tracking control system meets the control performance requirements.