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Sensors 2013, 13(9), 12149-12165; doi:10.3390/s130912149
Article

A Self-Sensing Active Magnetic Bearing Based on a Direct Current Measurement Approach

,
 and
*
School of Electrical, Electronic and Computer Engineering, North-West University, 11 Hoffman Street, Potchefstroom 2531, South Africa
* Author to whom correspondence should be addressed.
Received: 14 July 2013 / Revised: 18 August 2013 / Accepted: 29 August 2013 / Published: 11 September 2013
(This article belongs to the Section Physical Sensors)
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Abstract

Active magnetic bearings (AMBs) have become a key technology in various industrial applications. Self-sensing AMBs provide an integrated sensorless solution for position estimation, consolidating the sensing and actuating functions into a single electromagnetic transducer. The approach aims to reduce possible hardware failure points, production costs, and system complexity. Despite these advantages, self-sensing methods must address various technical challenges to maximize the performance thereof. This paper presents the direct current measurement (DCM) approach for self-sensing AMBs, denoting the direct measurement of the current ripple component. In AMB systems, switching power amplifiers (PAs) modulate the rotor position information onto the current waveform. Demodulation self-sensing techniques then use bandpass and lowpass filters to estimate the rotor position from the voltage and current signals. However, the additional phase-shift introduced by these filters results in lower stability margins. The DCM approach utilizes a novel PA switching method that directly measures the current ripple to obtain duty-cycle invariant position estimates. Demodulation filters are largely excluded to minimize additional phase-shift in the position estimates. Basic functionality and performance of the proposed self-sensing approach are demonstrated via a transient simulation model as well as a high current (10 A) experimental system. A digital implementation of amplitude modulation self-sensing serves as a comparative estimator.
Keywords: self-sensing; active magnetic bearing (AMB); direct current measurement (DCM); position estimation; magnetic suspension; duty cycle self-sensing; active magnetic bearing (AMB); direct current measurement (DCM); position estimation; magnetic suspension; duty cycle
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Niemann, A.C.; van Schoor, G.; du Rand, C.P. A Self-Sensing Active Magnetic Bearing Based on a Direct Current Measurement Approach. Sensors 2013, 13, 12149-12165.

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