Nonlinear and adaptive robust control of the ship course with uncertainties on the model

In this paper we present a relatively novel methodology, based on backstepping procedure, focused on solving the tracking control problem in ships whose dynamics is characterized by a nonlinear model. The sea trials of a liquefied natural gas (LNG) carrier show that the Norrbin model is capable of representing appropriately the variation of the course when a change on the rudder angle is applied. On the basis of these results, a model reference adaptive control (MRAC) algorithm based on the indirect scheme is proposed and solved as a generic control problem. The design is capable of determining the parameter values on line starting from the initial estimations. In order to reduce the number of sensors, a state observer is designed to estimate the yaw rate. In the paper it is proved that the design methodology provides a robust control system under parameter uncertainties and state variable errors.