Direct and indirect adaptive integral line‐of‐sight path‐following controllers for marine craft exposed to ocean currents

Summary We present a direct and an indirect nonlinear adaptive path‐following controller for marine craft based on a line‐of‐sight guidance principle used by ancient navigators. The control laws are implemented using hydro‐acoustic relative velocity measurements as opposed to absolute velocity measurements. For this purpose, a kinematic model for relative velocity in amplitude‐phase form is derived. The first contribution is an adaptive indirect controller based on a disturbance observer designed for estimation and compensation of ocean currents. The equilibrium points of the cross‐track and parameter estimation errors are proven to be globally κ exponentially stable. This guarantees that the estimated drift term converges to its true value exponentially. The observer is used in conjuncture with a control law to obtain asymptotic tracking and path following in the presence of ocean currents. The second contribution is a direct adaptive integral line‐of‐sight controller for path following. Global convergence of the cross‐track error is proven by using Barbălat's lemma, which ensures that the parameter estimation error is bounded. Both methods can be applied to the horizontal‐plane motion of surface vessels and autonomous underwater vehicles. An autonomous underwater vehicle case study is included to verify the results. Copyright © 2015 John Wiley & Sons, Ltd.