Proceedings of 2013 ASME/IEEE International Conference on Mechatronic and Embedded Systems and Applications MESA2013 August 4-7, 2013, Portland, OR, USA DETC2013-12260 A COMBINED SPEED AND FINITE-TIME YAW CONTROLLER FOR AN UNDERACTUATED UNMANNED SURFACE VESSEL USING WAY-POINT NAVIGATION Brendan Baker Department of Electrical Engineering University of Texas at San Antonio San Antonio, Texas 78249 Email: bsbaker.ee@gmail.com Dr. Chunjiang Qian Department of Electrical Engineering University of Texas at San Antonio San Antonio, Texas 78249 Email: chunjiang.qian@utsa.edu Dr. Brent Nowak Department of Mechanical Engineering University of Texas at San Antonio San Antonio, Texas 78249 Email: brent.nowak@utsa.edu ABSTRACT This paper focuses on the speed and yaw control problem for an underactuated unmanned surface vessel (USV) with only two propellers navigating through multiple way-points using the line-of-sight (LOS) algorithm. The speed and yaw dynamics are transformed into a cascaded nonlinear system that can be re- duced to the stabilization control problem of the surge and yaw subsystems. The proposed surge speed controller uses a distance and heading error feedback control to vary its speed accordingly while the heading subsystem is stabilized via a finite-time con- troller. Comparisons of the traditional yaw rate stabilization control techniques are made with the proposed finite-time con- troller and shown to be inferior to the finite-time controller in terms of convergence rate and robustness. The stability and ef- fectiveness of the proposed control system is demonstrated and validated by simulation results of a modeled kayak. INTRODUCTION Numerous current and future marine activities require or will require dynamic positioning of an unmanned surface ves- sel (USV). The USV will have key roles in naval and military applications, merchant shipping, scientific study, environmental monitoring, and exploration of various bodies of water. All of these various tasks for the USV require that the control and sta- bilization of the surface vessel be precise and dependable. First, let a USV be defined as, in most cases, an autonomous marine vessel that operates on the surface of the water (such as a boat) that is typically powered by two propellers on opposite sides of the stern, a propeller and rudder at the stern, or a jet propul- sion system that is either steerable or uses a rudder. These thrust configurations provide the surge force and yaw moment for the vessel but lack providing a sway force. Since there are three degrees of freedom in the horizontal plane attempting to be con- trolled simultaneously with only two inputs, the control problem of an underactuated system arises. The dynamic equations of the USV then exhibit second-order nonholonomic constraints. This means there are non-integrable conditions imposed on the ac- celerations in one or more degrees of freedom because the ship does not possess the capability to command instantaneous ac- celerations in those directions of the controllable space [1]. As Brockett pointed out in his paper [2], and is reiterated in litera- ture numerous times [3, 4], these nonholonomic systems cannot be stabilized to the origin by smooth, continuous time-invariant feedback control laws. This has inspired the controls research community to look heavily into this problem over the past decade and a half [5–7]. Inspired by the work in [8, 9] and the fleet that MIT cre- ated [10] in order to have a customizable research platform that allowed for quick and inexpensive algorithm development while also contributing to environmental monitoring studies, an au- tonomous USV featuring two propellers on either side of the vessel with room for plenty of scientific observation equipment became the focus of this paper. Starting from the ground up, the 1 Copyright c  2013 by ASME