Nonlinear Positioning Control for Underactuated Unmanned Surface Vehicles in the Presence of Environmental Disturbances

This article presents a nonlinear positioning control method for underactuated marine surface vehicles via the adaptive heading assignment to resist unknown environmental disturbances. A coordinate system rotated about the desired position is established and three control objectives are presented, namely, the along-track error minimization, the yaw-track error minimization, and the rotated adaption of this coordinate system. The last control objective is to minimize the cross-track error by properly making use of the sway disturbance force. The cross-track stability analysis shows that the proposed adaptive law to adjust the rotated coordinate system can make the cross-track system globally bounded and locally exponentially stable when the control gain of the proposed adaptive law is appropriately set. Both simulated and experimental validations demonstrate that the vehicle can keep the preset desired position when the sway disturbance force added to the vehicle hull is close to zero and the vehicle orientation toward the opposite mean disturbance force is maintained at the same time.