Nonlinear Model Predictive Control for Trajectory Tracking of Underactuated Ships with Maneuvering Motion

This study addresses the control problem of an underactuated ship while taking its maneuvering motion into account. Underactuated ships are characterized by having fewer control inputs than degrees of freedom, which makes their control particularly challenging. To tackle this issue, a nonlinear model predictive control (NMPC) method is considered to be useful. Model predictive control is an advanced optimal feedback control technique that optimizes the control input over a finite prediction horizon using a performance index with moving initial and terminal times. One of the key advantages of MPC is its ability to incorporate constraints on both the system states and control inputs in a systematic manner. In this study, the NMPC method is designed for trajectory tracking of underactuated ships by introducing appropriate system model that considers the maneuvering motion and the fluid forces generated by rudder and propeller operation. The effectiveness of the proposed control method is demonstrated through numerical simulations, showing that the ship can accurately follow the desired path.