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Applying Standard Industrial Components for Active Magnetic Bearings
Open AccessFeature PaperArticle

Transpermeance Amplifier Applied to Magnetic Bearings

School of Science and Technology, Federal University of Rio Grande do Norte, Natal-RN 59000-000, Brazil
Department of Integrated Science and Technology, James Madison University, Harrisonburg, VA 22807-1003, USA
Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA 22904-4246, USA
Author to whom correspondence should be addressed.
Academic Editor: Delbert Tesar
Actuators 2017, 6(1), 9;
Received: 30 November 2016 / Revised: 24 January 2017 / Accepted: 7 February 2017 / Published: 15 February 2017
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
PDF [2119 KB, uploaded 15 February 2017]


The most conventional approach of controlling magnetic forces in active magnetic bearings (AMBs) is through current feedback amplifiers: transconductance. This enables the operation of the AMB to be understood in terms of a relatively simple current-based model as has been widely reported on in the literature. The alternative notion of using transpermeance amplifiers, which approximate the feedback of gap flux rather than current, has been in commercial use in some form for at least thirty years, however is only recently seeing more widespread acceptance as a commercial standard. This study explores how such alternative amplifiers should be modeled and then examines the differences in behavior between AMBs equipped with transconductance and transpermeance amplifiers. The focus of this study is on two aspects. The first is the influence of rotor displacement on AMB force, commonly modeled as a constant negative equivalent mechanical stiffness, and it is shown that either scheme actually leads to a finite bandwidth effect, but that this bandwidth is much lower when transpermeance is employed. The second aspect is the influence of eddy currents. Using a very simple model of eddy currents (a secondary short-circuited coil), it is demonstrated that transpermeance amplifiers can recover significant actuator bandwidth compared with transconductance, but at the cost of needing increased peak current headroom. View Full-Text
Keywords: transpermeance; flux feedback; flux estimation; AMB bandwidth; actuators; amplifiers; eddy current transpermeance; flux feedback; flux estimation; AMB bandwidth; actuators; amplifiers; eddy current

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Ferreira, J.; Maslen, E.; Fittro, R. Transpermeance Amplifier Applied to Magnetic Bearings. Actuators 2017, 6, 9.

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