Robust control synthesis for dynamic vessel positioning

This article considers key theoretical and practical issues that arise in the robust control synthesis for dynamic positioning. A dynamically positioned vessel maintains its position (fixed location or predetermined track) by means of active thrusters and propellers. The concise kinematics and vessel dynamics are presented using three degrees of freedom model for describing the horizontal motions. Then, the mixed H and mu-synthesis framework has been employed to deal with perturbed model under external disturbances as well as measurement noises. To avoid excessive control energy for dynamic positioning system, the high frequency waves have been filtered using simple weighting functions. Using optimal Hankel-norm model approximation, the resulting full-order controller has been significantly reduced to make it easy to implement the practical works. Next, the simulation results in both frequency and time domains are presented to demonstrate the effectiveness of the robust control algorithms using the appropriate weighting functions. Finally, it is found that the proposed dynamic positioning system provides good maneuverability and robustness over a wide range of operating conditions, even under parametric variations and sea disturbances with sensor noises.