Autonomous underwater vehicle (AUV) are underwater robotic devices intended to explore hostiles territories in underwater domain. AUVs research gaining popularity among underwater research community because of its extensive applications and challenges to overcome unpredictable ocean behavior. The aim of this paper is to design discrete time terminal sliding mode control (DTSMC) reaching law-based employed to NPS AUV II purposely to improve the dynamic response of the closed loop system. This is accomplished by introducing a nonlinear component to sliding surface design in which the system state accelerated, and chattering effect is suppressed. The nonlinear component consist of fractional power is to ensure steeper slope of the sliding surface in the vicinity of the equilibrium point which lead to quicker convergence speed. Thus, the chattering effect in the control action suppressed as the convergence of the system state accelerated. The stability of the control system is proven by using Sarpturk analysis and the performance of the DTSMC is demonstrated through simulation study. The performance of DTSMC is benchmarked with DSMC and PID controller

<p>In this study, mechanism for reducing chattering in discrete conventional Sliding Mode Controller (DSMC) for Autonomous Underwater Vehicle (AUV) was designed in discrete time domain. The combination of reaching law approach and discrete Terminal Sliding Mode Control (DTSMC) scheme was employed to alleviate chattering effect caused by Quasi Sliding Mode (QSM). First, 6 DOF NPS AUV II equation of motion is linearized to diving mode subsystem. Second, linear sliding surface in discrete time domain is designed and Reaching Law Based (RLB) is employed to the control law. Thirdly, discrete nonlinear sliding surface, specifically DTSMC is designed to reduce chattering phenomena and improved precision control simultaneously. Finally, comparative experimental results are presented to illustrate the effectiveness and advantages of the nonlinear sliding surface. (9 pt).</p>

This study presents a Discrete Time Sliding Mode Controller (DSMC) application on depth plane of Autonomous Underwater Vehicle (AUV). The main contribution on this work is an implementation of DSMC on NSP AUV II. Sliding Mode Control (SMC) is a robust type of controller and certainly suitable for controlling AUV in the presence of environmental disturbances and uncertainties. DSMC preserves the properties of standard SMC. Linearized dynamic model of NSP AUV II is used in the numerical simulations. Discrete Proportional Integral Derivative (PID) controllers are used for performance comparative analysis. The design of discrete PID and DSMC for NSP AUV II depth is described. Comparative study between the control laws is presented. The simulated results illustrate strong robustness, improve performance and satisfactory stability of DSMC as compared to discrete-time PID controller.

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