Robust tracking control of ocean surface vessels using disturbance observer

In this paper, robust adaptive tracking control scheme is developed for ocean surface vessels with unknown time-varying external disturbances and system uncertainties. Radial basis function neural networks (RBFNNs) are adopted to approximate the system uncertainties and the disturbance observer is introduced to estimate the unknown external disturbance. Using backstepping and disturbance observer based techniques, robust tracking control is presented to track the desired system output of ocean surface vessels in the presence of unknown system uncertainties and external time-varying disturbance. Rigorous stability analysis shows that semiglobal uniform boundedness of all signals is guaranteed by appropriately choosing design parameters. Finally, simulation study is given to illustrate the effectiveness of the proposed tracking control.