Guidance and Control Based on Adaptive Sliding Mode Strategy for a USV Subject to Uncertainties

This article addresses a guidance and control strategy for an unmanned surface vehicle subject to uncertainties. The controller uses a dynamic three-degree-of-freedom model with identified parameters of an experimental platform. A strategy based on adaptive sliding-mode control is designed for the motion control of surge speed and heading variables, whereas a line-of-sight guidance law, with time-varying look-ahead distance, is applied to achieve path following. The adaptive controller is robust against bounded uncertainties/disturbances, and it does not overestimate the control gain. Outdoor experimental results validate the performance and advantages of the proposed control scheme in three different scenarios: 1) set-point regulation; 2) tracking of time-varying references; and 3) path following. To further demonstrate the characteristics of the proposed controller, a comparison against a standard controller while carrying an extra payload of 20% of the mass of the vessel is included.