Switching LOS guidance with speed allocation and vertical course control for path-following of unmanned underwater vehicles under ocean current disturbances

Abstract

This paper presents an application and stability result of a modified line-of-sight (LOS) guidance law for 3-D path-following (PF) of an unmanned underactuated underwater vehicle subject to environmental disturbances. The PF problem is solved using a revised relative system model with an improved FLOW frame and a complete model of ocean current/wave disturbances. The PF approach uses course control and speed allocation, which is the problem of allocating the desired inertial total speed into desired BODY velocities including current/wave velocities. The definitions of track-errors in the general PF problem have been accurately illustrated in the inertial frame. The course control strategy, defined by incorporating the slip angles into the desired heading angles, has been extended to vertical plane with the new definition of vertical-slip. Stability results include local exponential stability (LES) of the enclosure-based LOS (ELOS) and semi-global exponential stability (SGES) of the modified LOS guidance laws. The 3-D LOS vector is tracked simultaneously in both planes using a planar speed assignment strategy in 4-DOF for a coupled 3-D tracking. Simulation results show robust PF performance of a sway-underactuated AUV in course control in the presence of significant ocean current disturbances and measurement noises. The effectiveness of simple course control and speed allocation in disturbance rejection has also been illustrated.