Path Following Control of Autonomous Underwater Vehicles

Abstract

In the recent years a lot of interest is seen on research on Autonomous Underwater Vehicles. This control is to the fact that AUVs find application in several areas such as oceanographic observations, mine counter measure, defence, risky missions, military, pipeline inspections, ocean floor investigation and return of lost man-made objects. Research on AUVs is motivating and challenging. The motion control of AUV involves a number of complex problems including to path following, navigation and co-operative motion control problems. Many complexities arise for motion control of AUV. In case of path following control it is necessary to develop efficient control algorithms such that a desired path mcan be tracked accurately.
Ocean current and hydrodynamic effects appear external disturbances in the dynamics of AUV. In this thesis, firstly kinematics and dynamics of AUV are reviewed. Subsequently, open loop response of the AUV has been studied.
AUV is an under actuated system i.e. the number of control inputs are fewer than the number of degrees of freedom to be controlled. Hence control of AUV is a difficult task. The control law should be generated such that AUV follows the predefined desired path.The control laws are generated using Serret Frenet frame for designing path following control of AUV. Lyapunov and backstepping technique is employed for developing path following control laws. Serret frame is basically a virtual frame which considered to be attached with a path. The kinematics of AUV is represented in serret frame and the appropriate thrust force and rudder orientation are to be maintained which enable AUV to track the desired path. In order to accomplish this task, appropriate thruster and torque will be generated by using propeller and rudder through generation of control signals. In many of the past work although error backstepping approach has been employed in a number of past works for example control of path following but in there surge motion dynamics was not considered. Therefore, in this thesis the surge motion dynamics is considered in the design of controller for path following task.
It is well known that fuzzy logic technology is very suitable for developing control systems in handling situations where uncertainties are encountered in the dynamics. In the view of this fuzzy logic controller is designed for achieving path following task of AUV.