Nonlinear Feedback Control Of Underactuated Surface Ships

In order to solve the motion control problems of underactuated surface ships with second order nonholonomic constraint, systemic uncertainties, and saturations on actuators, nonlinear feedback control designing is focused in this dissertation.From conventional feedback control, a recursive sliding mode designing procedure is derived and proposed, by which the control objectives can be transformed into stabilization of a series of nested scalar zero-order-systems. Integrated with increment feedback, a novel feedback control method is developed. Problems of the chattering in variable structure control and the overshoot or static error are circumvented.The proposed control method is extended to underactuated and nonholonomic systems. Stabilization control laws are presented with simulation results for chained-form-system, nonholonomic integrator and wheeled mobile robot(WMR).For a class of planar nonholonomic systems, like WMR and surface ships, a novel virtual guide control method is presented, by which the nonholo- nomic stabilization can be transformed into control problems of holonomic subsystems.For the challenging problems of tracking and stabilization control of underactuated surface ships, nonlinear feedback control laws are presented for straight/curved path following, trajectory tracking, underactuated positioning, and typical automatic berthing control utilizing ships' characteristic kinematics. The systemic uncertainties, high nonlinearity, lateral drift caused by current or wind, and saturations and mechanism characteristics on/of actuators were well considered. Numerical simulations were carried out on a full nonlinear hydrodynamic model of a training ship "YULONG". High reliable results are presented to validate the robustness and excellent performance of the proposed algorithms.By theoretical analysis and control examples, the effectiveness and constructive -ness of the proposed control method are demonstrated in dealing with motion control of underactuated ships and nonholonomic control problems.