Nonlinear Sliding Mode Berthing Control of Underactuated Surface Ships

A novel output feedback strategy is presented for the berthing control of underactuated surface ships with nonintegrable acceleration constraint. Saturations on actuators, systemic uncertainties and drift caused by current or wind are considered. The problems of trajectory planning and tracking are circumvented by means of iterative nonlinear sliding mode control (INSMC) method. The sliding modes are decentralized and recursively designed on phase planes in the augmented states space. Increment feedback control law is developed based on the INSMC to (locally) stabilize the ship´s motion without estimation of uncertainties and disturbances. Numerical simulation results on a full nonlinear hydrodynamic model of a training ship are presented to validate the invariability and excellent performance of the proposed algorithm.