US5300841A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Inductive air gap estimation method for active magnetic bearings
Assignee: General Electric Co
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Filing: 1992-11-02
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Granted: 1994-04-05
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Expires: 2012-11-02
Abstract
Abstract In an active magnetic bearing system employing radial or thrust bearings, rotor shaft position is determined without requiring air gap position sensors, resulting in a high reliability system. The flux paths for each respective electromagnetic force actuator of the active magnetic bearing are isolated in order to minimize the magnetic coupling therebetween. In this way, the current (or magnetomotive force, mmf) in each respective actuator is functionally related to the flux therethrough, independent of the currents (or mmf's) in adjacent actuators. Application of a digital PWM pole voltage waveform during normal bearing operation results in a ripple current waveform at the PWM switching frequency. The resulting change in stator pole current and pole voltage are measured, and the average differential inductance is determined therefrom. Then, with knowledge of the differential inductance and the average pole current, the effective air gap length, air gap velocity, and magnetic flux are determined according to the inherent magnetization characteristic of the magnetic bearing.
Inventors
- 👤 Mark A. Preston
- 👤 James P. Lyons
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 18:33
CPC Classifications
F; F16; F16C; F16C32/00; F16C32/04; F16C32/0406; F16C32/044; F16C32/0474; F16C32/048; F16C32/0482; F16C32/0442; F16C32/0444; F16C32/0446; F16C32/0448; G; G01; G01B; G01B7/00; G01B7/14; G01B7/144; F16C32/0459
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
118 words
A method for sensing air gap length in an active magnetic bearing having a rotor and a stator including a plurality of electromagnetic force actuators, comprising: magnetically separating said force actuators such that each has a substantially isolated flux path; measuring a voltage applied to at least one of said force actuators; measuring a change in current in said force actuator resulting from application of said voltage thereto; determining an average differential inductance of said force actuator from said voltage and said change in current; and determining the effective air gap length, air gap velocity, and magnetic flux from said change in current and said differential inductance according to predetermined flux versus current characteristics of said magnetic bearing.
Claim 2
Independent Claim
118 words
A method for sensing air gap length in an active magnetic bearing having a rotor and a stator including a plurality of electromagnetic force actuators, comprising: magnetically separating said force actuators such that each has a substantially isolated flux path; measuring a voltage applied to at least one of said force actuators; measuring a change in current in said force actuator resulting from application of said voltage thereto; determining an average differential inductance of said force actuator from said voltage and said change in current; and determining the effective air gap length, air gap velocity, and magnetic flux from said change in current and said differential inductance according to predetermined flux versus current characteristics of said magnetic bearing.
Claim 3
Dependent Claim
67 words
The method of claim 1 wherein said average differential inductance L avg is determined according to: ##EQU16## where V 1 represents said voltage over a time Δt 1 and ΔI 1 represents the change in current over the time Δt 1 ; and V 2 represents said voltage over a time Δt 1 and ΔI 2 represents the change in current over the time Δt 2 .
Claim 4
Dependent Claim
41 words
The method of claim 1 wherein the steps of determining the average differential inductance of said force actuator and determining the effective air gap length are performed by a microprocessor, said predetermined flux versus current characteristics being stored in microprocessor memory.
Claim 5
Dependent Claim
92 words
The method of claim 1 wherein the step of magnetically separating said force actuators such that each has a substantially isolated flux path involves configuring said stator to have at least six adjacent magnetic actuators configured such that each magnetic actuator is situated opposite from a corresponding magnetic actuator, adjacent magnetic actuators being separated by non-magnetic flux barriers, opposite pole pairs functioning as a magnetically isolated control axis, such that there are at least three control axes, only two of said control axes being required to maintain operation of said magnetic bearing.
Claim 6
Dependent Claim
14 words
The active magnetic bearing of claim 4 wherein said stator has three control axes.
Claim 7
Dependent Claim
16 words
The method of claim 1 wherein said active magnetic bearing is an actively biased magnetic bearing.
Claim 8
Dependent Claim
145 words
Apparatus for estimating air gap length in an active magnetic bearing having a rotor mounted for rotation within a stator and for coupling to a shaft, said stator including a plurality of electromagnetic force actuators, comprising: non-magnetic flux barriers for magnetically separating adjacent force actuators such that each has a substantially isolated flux path; voltage sensing means for measuring a voltage applied to at least one of said force actuators; current sensing means for measuring a change in current in said force actuator resulting from application of said voltage thereto; computer means for determining an average differential inductance of said force actuator from said voltage and said change in current, said computer means determining the effective air gap length, air gap velocity, and magnetic flux from said change in current and said differential inductance according to predetermined flux versus current characteristics of said magnetic bearing.
Claim 9
Dependent Claim
145 words
Apparatus for estimating air gap length in an active magnetic bearing having a rotor mounted for rotation within a stator and for coupling to a shaft, said stator including a plurality of electromagnetic force actuators, comprising: non-magnetic flux barriers for magnetically separating adjacent force actuators such that each has a substantially isolated flux path; voltage sensing means for measuring a voltage applied to at least one of said force actuators; current sensing means for measuring a change in current in said force actuator resulting from application of said voltage thereto; computer means for determining an average differential inductance of said force actuator from said voltage and said change in current, said computer means determining the effective air gap length, air gap velocity, and magnetic flux from said change in current and said differential inductance according to predetermined flux versus current characteristics of said magnetic bearing.
Claim 10
Dependent Claim
69 words
The apparatus of claim 7 wherein said computer means determines said average differential inductance L avg according to: ##EQU17## where V 1 represents said voltage over a time Δt 1 and ΔI 1 represents the change in current over the time Δt 1 ; and V 2 represents said voltage over a time Δt 2 and ΔI 2 represents the change in current over the time Δt 2 .
Claim 11
Dependent Claim
23 words
The apparatus of claim 7 wherein said computer means comprises a microprocessor, said predetermined flux versus current characteristics being stored in microprocessor memory.
Claim 12
Dependent Claim
46 words
The apparatus of claim 7 wherein said electromagnetic force actuators comprise stator pole-pairs, opposing stator pole-pairs comprising a magnetically isolated control axis, such that there are at least three control axes, only two of said control axes being required to maintain operation of said magnetic bearing.
Claim 13
Dependent Claim
12 words
The apparatus of claim 10 wherein said stator has three control axes.
Claim 14
Dependent Claim
16 words
The apparatus of claim 7 wherein said active magnetic bearing is an actively biased magnetic bearing.
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| 3.5 Years (Year 4) | 1997-04-04 | 1997-10-04 | 1998-04-05 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2001-04-04 | 2001-10-04 | 2002-04-05 | $3760.00 | Window Closed / Lapsed |
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