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

Abstract

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 hydroacoustic 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 Ä 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-ofsight controller for path following. Global convergence of the cross-track error is proven by using Barbȃlat'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.

Adaptive line-of-sight path following control for underactuated autonomous underwater vehicles in the presence of ocean currents

“…Therefore, Assumption 2 is easy to meet for most AUVs. Similar assumptions for other marine vehicles can be seen in the literatures Lekkas et al 23 and Fossen et al 24 Then, the kinematics of the vehicle expressed by the relative velocities and the current velocities in vector and component forms are…”

Line-of-sight curved path following for underactuated USVs and AUVs in the horizontal plane under the influence of ocean currents

“…In [16], a LOS path following approach is used with current estimation techniques and measurements of relative velocities, allowing the USV to follow curved paths while compensating for the influence of ocean currents. The Serret-Frenet based method in [15] is extended to account for the effects of ocean current for surface and underwater vehicles in [17] and [18], respectively.…”

“…The Serret-Frenet based method in [15] is extended to account for the effects of ocean current for surface and underwater vehicles in [17] and [18], respectively. Similar to [16], this method requires estimation of the ocean current, measurements of relative velocities and a parametrization of the path as a function of arc length, which can make it challenging to find a parametrization of the desired path. Furthermore, for the underwater case, it is also required that the path torsion and curvature is known as functions of arc length.…”

Online Path Planning for Surface Vehicles Exposed to Unknown Ocean Currents Using Pseudospectral Optimal Control

“…The main contribution involves augmenting DIDO in order to incorporate online estimation and rejection of unknown ocean currents. This is achieved via the indirect adaptive integral Line-ofSight (LOS) guidance law developed by Fossen and Lekkas (2015).…”