Fault Tolerant Control for a Fractional Order AUV System

Fault Tolerant Control for a Fractional Order AUV System

Sneha D. Joshi (Pune University, Pune, India) and D. B. Talange (College of Engineering Pune, Pune, India)
Copyright: © 2016 |Pages: 24
DOI: 10.4018/IJEOE.2016040101
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Abstract

In the last decade Autonomous Underwater Vehicles are used in large number. The control issue of these vehicles is very challenging due to uncertain underwater environment. Conventional controllers may fail during operations especially when changes in the system occur, since it is impossible to re tune the controller in water. Hence the autonomous underwater system must have controller capability to detect, identify and tolerate fault, abort the ongoing mission and return to water surface. In this paper fault tolerant control algorithm is designed and applied to fractional order model of AUV. While designing fault tolerant controller state observer feedback technique is used. It is observed that the fractional order system is stable for fractional order greater than 1 and less than 2 under normal and under actuator failure conditions. For gain optimization of feedback controller LMI approach is used.
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2. Literature Review

A research on fault tolerant control in AUV has begun since 1990 (Phillip and Zinchuk, 1990). In later years more concentration was done on sensor and actuator faults in AUV. Fault tolerant control due to actuator or thruster faults is focused in many research papers. Fault tolerant control in AUV propulsion system is considering two vertical and two horizontal thrusters (Omerdic and Roberts, 2004). To improve the reliability of AUV new fault tolerant methods are being developed. Fault tolerant control of fractional order AUV is one of them.

From the stability analysis of fractional order systems, it is seen that using LMI approach the FOLTI systems can be explained in better way. The integer order systems and fractional order systems are equivalent at low frequencies. At high frequencies integer order system does not describe system dynamics at all. Fractional order controller show better transient response when they are applied to fractional order systems.

Fractional order controller was first time designed by Oustaloup.Infinite memory length is proved as great advantage for fractional order system, which helps in modeling and control of dynamic systems.

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