Robust Energy-Optimal Control for 3-D Path-Following of Autonomous Underwater Vehicles Under Ocean Currents
Niankai Yang · Chao Shen · Ziyou Song · Matthew Johnson-Roberson · Jing Sun
TL;DR
An underwater vehicle controller picks forward speeds that cut energy use on a planned path while staying robust to errors in ocean current estimates.
BRIEF
Underwater vehicles carry limited battery, so how they move along a planned route matters. Line-of-sight guidance keeps a vehicle on its path in ocean currents, but it does not consider energy use. This work keeps that guidance for heading and chooses the forward speed that minimizes energy per unit distance in the expected current. It then adjusts that speed to limit the worst-case energy loss if the current estimate is wrong. In simulation, the controller saves considerable energy while still following the path well.
Abstract
Energy efficiency is crucial for autonomous underwater vehicles (AUVs) with limited on-board energy resources. In this paper, we study the energy-optimal control problem for an AUV to follow a planned reference in ocean currents. The objective of reference following in ocean currents can be effectively achieved by the line-of-sight (LOS) guidance-based path following control, which yet does not explicitly address the problem of energy minimization. We propose a method of LOS guidance-based control that incorporates energy minimization while achieving robust path following in the presence of uncertainty in ocean current information. First, the desired heading of a vehicle is obtained based on a LOS guidance law and the optimal surge speed is computed by minimizing the energy consumed for traveling unit distance towards the desired heading in the nominal current. Then, to deal with uncertainty, we analyze the sensitivity of the resulting optimal surge speed to bounded uncertainty around the nominal current and robustify the optimal surge speed by minimizing the maximum potential energy loss due to the uncertainty. The proposed controller tracks the desired heading and the optimal surge speed in a model predictive control framework. The simulation results show that the proposed method can save considerable energy while maintaining a satisfactory path following performance under bounded uncertainty in the nominal current.