A separation principle for dynamic positioning of ships: Theoretical and experimental results

This paper presents a globally asymptotically stabilizing (GAS) controller for regulation and dynamic positioning of ships, using only position measur ements. It is assumed that these are corrupted with white noise hence a pas sive observer which reconstructs the rest of the states is applied. The obs erver produces noise-free estimates of the position, the slowly varying env ironmental disturbances and the velocity which are used in a proportional-d erivative (PD)-type control law. The stability proof is based on a separati on principle which holds for the nonlinear ship model in this paper. This s eparation principle is theoretically supported by recent results on cascade d nonlinear systems and standard Lyapunov theory, and it is validated in pr actice by experimentation with a model ship scale 1:70.