Optimal and Suboptimal MPC of Hybrid Systems for Inland Ship Maneuvering

This work develops a control method for an inland vessel with three rudder propellers for low speed maneuvers like docking, station keeping, and lock entry. The rudder propellers’ thrust, rotation, and clutch state are adjusted to control the vessel position and orientation with a focus on clutching processes beyond classical control methods. The aim is a robust, adaptive approach that simplifies operation, aids automation, and saves fuel. Two control concepts are proposed: a hybrid NMPC using a mixed integer nonlinear program to handle clutching and a second NMPC approach approximating the clutch with a sigmoid function. Simulations with the nominal ship dynamics show that the computational requirements of the mixed integer approach are too high. To meet real-time requirements, a faster, suboptimal nonlinear controller for the approximation approach is developed and its resilience to model uncertainties and disturbances is demonstrated in software-in-the-loop simulations.