Improved indirect adaptive line-of-sight guidance law for path following of under-actuated AUV subject to big ocean currents

Abstract

This paper presents a novel indirect adaptive disturbance observer (IADO)-based line-of-sight (LOS) guidance law for path following of under-actuated AUV in the presence of time-varying big ocean currents. The influences of ocean currents on AUV are expressed in the kinematic model. An indirect adaptive disturbance observer is designed and utilized to estimate and compensate for the ocean currents-induced uncertainties when following a curved path. In addition, an adaptive look-ahead distance is proposed for better following the curved path with sharp turnings. Then, an improved LOS guidance law is designed to follow the desired path accurately by introducing an auxiliary variable to the conventional LOS and utilizing the indirect adaptive disturbance observer to estimate the ocean current-induced disturbances in the kinematic model. Furthermore, the closed-loop cascade IADO-LOS guidance system, composed of a tracking error subsystem and estimation error system, is proven to be globally uniformly asymptotically stable according to the Lyapunov stability theory. The proposed guidance law is intended for maneuvering AUVs in the horizontal plane to follow a predefined curved path with sharp turning under time-varying big ocean currents. Extensive simulation studies demonstrate that the proposed approach has good tracking accuracy, low chattering, and anti-jamming ability.