| Unmanned aerial vehicle (UAV) has become a hotspot in the control area because of its huge potential application in civilian and military area, especially for the rotor UAV, which can vertically take off and land (VTOL). However, most VTOL UAVs have less control inputs than its degree of freedom; therefore, they are typical underactuated systems, which make it hard to find a general control design strategy. Besides, most VTOL UAVs have structural and parametric uncertainties, which make the control problem more complicated.In this thesis, two typical underactuated VTOL unmanned aerial vehicles are considered. They are quadrotor UAV and a 3 degree of freedom (DOF) helicopter which can be analyzed approximately for the helicopter vertical flight (take off, climbing, hover, descent and landing).First, a nonlinear robust control design combined with neural network is proposed for the 3-DOF helicopter test-bed which may be subjected to unknown external disturbance and has structural uncertainties. Regulation and tracking control laws are proposed for the angles of elevation, pitch and travel axes. Lyapunov based analysis is used to prove the stability of the system, and numerical simulation results are provided to illustrate that the proposed controllers achieve good performance and the closed loop systems obtain good robustness with respect to system uncertainties and disturbances.Then, a new nonlinear robust regulation controller is developed for the quadrotor UAV which is subject to unknown moment of inertia and aerodynamic parameters. Especially, an adaptive sliding mode control is proposed to stabilize its underactuated subsystem. Lyapunov based analysis is used to prove the stability of the system, and numerical simulation results are provided to illustrate that the proposed approaches are able to robustly stabilize the quadrotor UAV and move it to desired position with desired yaw angle while keeping the pitch and roll angles as zero.
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