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This paper proposes and develops a new analytic bearingless machine model that incorporates multiple airgap harmonic field interactions and has several advantages. The model can be used to address levitation performance requirements by developing force/torque regulation methods to precisely calculate commands to current regulators. This allows relaxing constraints during the design stage and has the potential to enable consideration of higher performance bearingless machines. Furthermore, analogous to torque enhancement in conventional electric machines, the proposed model can be used to identify options for suspension force enhancement in bearingless motors by controlling multiple magnetic field harmonics. This paper provides a detailed derivation of the model and shows how it can be used to improve force regulation accuracy and enhance force capacity. The paper finds that by controlling four airgap harmonic fields, instead of the typical two harmonics, force capacity can be increased by approximately 40%. Hardware measurements using a 10-phase bearingless induction machine validate the proposed model and force capacity increase.
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Analysis of Force Capacity in Magnetic Bearings and Bearingless Motors from the Perspective of Airgap Space Harmonic Fields
This paper studies the force creation capabilities of active magnetic bearings (AMBs) and bearingless motors from the perspective of multiple airgap space harmonics/pole-pairs. This approach is analytic-based and is useful in explaining the underlying physics of the machine and conducting force capacity analysis for different numbers of phases/poles. The presented per unit (p.u.) model makes the force capacity results applicable to any motor dimensions and peak airgap field value. An explanation of the force capacity in bearingless motors is provided when only two harmonics are controlled (which is the typical approach in bearingless motor literature) and the relationship between torque, force, and magnetizing field values is identified. Using this relationship, optimal magnetizing field values for maximum torque-force capability are identified, which is useful to consider when designing a bearingless motor. This paper extends the force capacity analysis to bearingless motors with multiple (more than two) controllable space harmonics and proposes that force enhancement can be achieved through the control of the magnitudes and angles of these harmonics. Results show that potential force enhancement of over 40% in bearingless machines can be achieved when controlling four airgap harmonics as opposed to two harmonics. These results suggest that being able to control multiple harmonics can yield high performance designs.
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- Award ID(s):
- 1942099
- PAR ID:
- 10488285
- Publisher / Repository:
- magneticbearings.org
- Date Published:
- Journal Name:
- 18th International Symposium on Magnetic Bearings
- Subject(s) / Keyword(s):
- Active magnetic bearing, bearingless motor, self-bearing motor, current sequences, force enhancement
- Format(s):
- Medium: X
- Location:
- Lyon, France
- Sponsoring Org:
- National Science Foundation
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