IFAC PapersOnLine 51-13 (2018) 161–166 ScienceDirect ScienceDirect Available online at www.sciencedirect.com 2405-8963 © 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Peer review under responsibility of International Federation of Automatic Control. 10.1016/j.ifacol.2018.07.272 © 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. 1. INTRODUCTION Nowadays, 95 % of the ocean remains unexplored based on data from the National Oceanic and Atmospheric Admin- istration (NOAA). In recent years, the Unmanned Under- water Vehicles (UUV’s) are used in different missions such as maritime inspection, maintenance of structures, marine archeology, monitoring of dissolved oxygen, and so on. In general, the UUV’s are classified into two main types: Re- motely Operated Vehicle (ROV) which are controlled by a remote human operator and the Autonomous Underwater Vehicle (AUV) which refers to the vehicle that performs particular tasks without human intervention. It is essential to analyze the type of mission that will be carried out since it will define the kind of structure and the embedded system (Moreno Avalos et al. (2014)). In order to provide autonomy to the underwater robot to perform a mission, the vehicle must have a certain level of autonomy. For this reason, different control techniques have been developed to stabilize the submarine even with unknown perturbations and modeling uncertainties. The most important actions to provide autonomy to a sub- marine are stabilization to a point, path following and trajectory tracking (Encarna¸ c˜ao and Pascoal (2001)). In the literature, in stabilization problem of an underwater vehicle. For example, in Cui et al. (2016), Li and Lee (2005) and Manzanilla et al. (2017) different control tech- niques with adaptive properties are presented to stabilize an underwater vehicle in the presence of external distur- bances. On the path following problem, different authors propose several controllers. In Lapierre et al. (2003), the authors design a controller based on the Lyapunov theory and Backstepping technique. In Elmokadem et al. (2016) a robust controller based on sliding modes technique is presented, the designed controller can ensure finite time convergence of the AUV to the desired path even in the presence of bounded perturbations. However, both papers demonstrate the efficiency of the proposed controller only through simulations. Finally, a broad class of controls for the trajectory tracking problem have been proposed. In Sahu and Subudhi (2014) an adaptable controller capable of estimating parametric perturbations and uncertainties is shown. Also, in Li et al. (2015) an adaptive fuzzy PID controller is designed to follow straight lines that are commonly used in underwater reconnaissance missions. The main contribution of this work is to present a ro- bust algorithm based on the second order sliding mode technique with a self-adjusting gain proposed by Gonzalez et al. (2011) which is applied to a Linear Time Invariant (LTI) system. In this work, we design a trajectory track- ing controller based on the Generalized Super-Twisting Algorithm (GSTA) with self-adjusting gains for a MIMO system. Moreover, we demonstrate the robustness of the controller to external disturbances and parametric uncer- tainties through real-time experiments. The paper is organized as follows: In section 2, the AUV model considered in this work is shown. A control law Keywords: AUV, Sliding-mode control, Robust Control,Tracking Control, MIMO. Abstract: This paper deals with the design and implementation of a nonlinear control strategy to solve the path tracking problem for an Autonomous Underwater Vehicle (AUV) under model uncertainties and external disturbances. First, the AUV model is transformed into the so-called regular form by an appropriate selection of state variables. The method is based on the second-order sliding mode technique known as Generalized Super-Twisting Algorithm (GSTA) introducing the design of an auto-adjustable gain controller which offers a way to ensure robustness to modeling errors and bounded external disturbances. The control law is designed to maintain a minimum margin of error in the trajectory tracking of the AUV even in the presence of damping and buoyancy disturbances. Finally, experimental results are also provided to illustrate the performances of the closed-loop system using the proposed controller. * Department of Automatic Control, Center of Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV), Mexico City, Mexico, (e-mail: jguerrero,jtorres,eantonio@ ctrl.cinvestav.mx) ** UMI-LAFMIA CNRS 3175, Center of Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV), Mexico City, Mexico, (e-mail: amanzanilla@cinvestav.mx,rogelio.lozano@hds.utc.fr) J. Guerrero * E. Antonio * A. Manzanilla ** J. Torres * R. Lozano ** Autonomous Underwater Vehicle Robust Path Tracking: Auto-Adjustable Gain High Order Sliding Mode Controller