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TECHNICAL PAPERS

A System Identification Technique Using Bias Current Perturbation for Determining the Effective Rotor Origin of Active Magnetic Bearings

[+] Author and Article Information
Robert J. Prins1

 Virginia State University, 1 Hayden Drive, Box 9212, Petersburg, VA 23806rpins@vsu.edu

Mary E. Kasarda, Samantha C. Bates Prins

 Virginia State University, 1 Hayden Drive, Box 9212, Petersburg, VA 23806

1

Corresponding author.

J. Vib. Acoust 129(3), 317-322 (Nov 08, 2006) (6 pages) doi:10.1115/1.2424976 History: Received August 11, 2005; Revised November 08, 2006

Locating the effective rotor origin of an active magnetic bearing (AMB) is an important step toward accurate characterization of the bearing air gaps for field tuning, performance analyses, and some shaft force measurement techniques. Specifically, application of current-based force measurement techniques to AMBs requires accurate modeling of air gaps in order to predict dynamic forces with accuracy. This paper discusses the application of a system identification technique that employs perturbation of the bias current and allows the user to establish the location of the effective rotor origin, an important step in characterizing the actual bearing gap. The technique analyzes the AMB system’s response to the perturbation of bias currents in conjunction with a magnetic circuit model to infer the center position. The effective rotor origin identification technique developed here does not require additional hardware and is suitable for use in the general class of AMBs in field applications. For our purposes, the effective rotor origin of an electro-magnet biased magnetic bearing is defined as the unique rotor location for which a magnetic circuit based force model of the bearing is satisfied for zero position offset of the rotor along each control axis. Note that the effective rotor origin referred to here is the radial origin.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 2

Schematic of V and W axes

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Figure 3

Laboratory rotor

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Figure 4

Position set points and associated error predictions for successive iterations (first experiment, repetition 1; V axis results)

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Figure 5

Position set points and associated error predictions for successive iterations (second experiment; V axis results)

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Figure 6

Effective rotor origin location predictions from Case I and Case II

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Figure 1

Schematic of AMB model geometry

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