| Summary: | In this paper, we discuss the problem of motion synchronization for a formation of marine vessels with the unknown, external disturbance. A novel distributed control algorithm is proposed, which comprises a disturbance observer and a synchronization controller. The disturbance observer is constructed for estimating the unknown time-variant disturbance from the external environment, such as wind, wave, and ocean current. The synchronization controller is designed to compensate for the synchronization error between the vessels and the tracking error of the desired trajectory. By distributed, we mean that each vessel can execute the algorithm with only the knowledge of the local information broadcast by its neighbors within the communication network of the formation, though reasonably, certain bounds determined by limited centralized information are known. By modeling the network topology of the formation as a directed graph, we show that global synchronization of the vessel formation can be achieved if the gains in both disturbance observer and synchronization controller satisfy certain lower bounds. We further introduce a constant time delay to the communication process to validate the robustness of our proposed algorithm. The simulations of a four-vessel formation are provided to verify the effectiveness of our proposed algorithm.
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