Nonlinear output feedback control of underwater vehicle propellers using feedback form estimated axial flow velocity

Accurate propeller shaft speed controllers can be designed by using nonline ar control theory and feedback from the axial water velocity in the propell er disc. In this paper, an output feedback controller is derived, reconstru cting the axial flow velocity from vehicle speed measurements, using a thre e-state model of propeller shaft speed, forward (surge) speed of the vehicl e, and the axial flow velocity. Lyapunov stability theory is used to prove that a nonlinear observer combined with an output feedback integral control ler provide exponential stability. The output feedback controller compensat es for variations in thrust due to time variations in advance speed. This i s a major problem when applying conventional vehicle-propeller control syst ems, The proposed controller is simulated for an underwater vehicle equippe d with a single propeller. The simulations demonstrate that the axial water velocity can be estimated with good accuracy. In addition, the output feed back integral controller shows superior performance and robustness compared to a conventional shaft speed controller.