Safety-Critical Control of Autonomous Surface Vehicles in the Presence of Ocean Currents

Autonomous surface vehicles (ASVs) are safety-critical systems that must provide strict safety guarantees such as collision avoidance to enable fully autonomous operations. This paper presents a unified framework for safety-critical control of ASVs for maneuvering, dynamic positioning, and control allocation with safety guarantees in the presence of unknown ocean currents. The framework utilizes control Lyapunov function (CLF)- and control barrier function (CBF)-based quadratic programs (QPs), and is applicable to a general class of nonlinear affine control systems. The stabilization objective is formulated as a maneuvering problem and integral action is introduced in the CLFs to counteract the effect of unknown irrotational ocean currents. Furthermore, ocean current estimates are constructed for robust CBF design, and analytic conditions under which the estimates guarantee safety are derived. Subsequently, robust CBFs are designed to achieve collision avoidance of static obstacles. The paper concludes by verifying the framework in simulation for a double-ended passenger ferry. © 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.