Effects of unbalanced magnetic pull on rotordynamics of electric machines
Kim, Heesoo (2021-05-21)
Väitöskirja
21.05.2021
Lappeenranta-Lahti University of Technology LUT
Acta Universitatis Lappeenrantaensis
School of Energy Systems
School of Energy Systems, Konetekniikka
Kaikki oikeudet pidätetään.
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In reference to IEEE copyrighted material which is used with permission in this thesis, the IEEE does not endorse any of Lappeenranta-Lahti University of Technology LUT's products or services. Internal or personal use of this material is permitted. If interested in reprinting/republishing IEEE copyrighted material for advertising or promotional purposes or for creating new collective works for resale or redistribution, please go to http://www.ieee.org/publications_ standards/publications/rights/rights_link.html to learn how to obtain a License from RightsLink.
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-335-651-1
https://urn.fi/URN:ISBN:978-952-335-651-1
Tiivistelmä
The unbalanced magnetic pull (UMP) that results from air-gap eccentricity can present a potential risk to the lifetime and dynamic stability of rotating electric machines. Nevertheless, a method to identify the effects of UMP in actual industrial machines has not yet been sufficiently developed. In this dissertation, methods for the analysis and experimental verification of UMP effects on rotordynamics are developed and studied using test machines that present both permanent magnet synchronous machines and induction machines.
For accurate consideration of the eccentricity condition, mixed eccentricity, axial-varying eccentricity, and the eccentricity caused by motor frame vibration are modeled and combined. The force model is established based on a semi-analytical concept. The analytical formula is combined with a newly introduced correction factor obtained from finite element analysis results, used for the improvement of the accuracy of the model. The model of the rotor-bearing system, which includes the UMP model, is developed with two different methods. In the first method, UMP is added as a spring with negative stiffness to the rotor model, whereas in the second method, UMP is included as an external force. Based on the developed UMP and eccentricity models, rotordynamic simulation methods within the electric machine design process are proposed. Furthermore, an experimental verification process that can be applied to actual industrial machines is proposed for the case machine supported by active magnetic bearings in order to determine UMP effects on rotordynamics.
Through the case studies of three test machines, the characteristics of UMP force and stiffness are found by investigating their variation due to the change in slip, eccentricity, supply frequency, and time. Then, UMP effects on rotordynamics are found by studying forced vibration responses obtained from both time-step rotordynamics simulation and experimental measurement. The results show two main effects: reduction in the rotor’s natural frequency and additional vibration by UMP-caused harmonic excitations.
Finally, a comparison between the simulation and experiment results confirms that the proposed simulation process, based on the semi-analytical UMP model, is suitable for rotordynamics simulation and achieves a high accuracy with efficient computation.
For accurate consideration of the eccentricity condition, mixed eccentricity, axial-varying eccentricity, and the eccentricity caused by motor frame vibration are modeled and combined. The force model is established based on a semi-analytical concept. The analytical formula is combined with a newly introduced correction factor obtained from finite element analysis results, used for the improvement of the accuracy of the model. The model of the rotor-bearing system, which includes the UMP model, is developed with two different methods. In the first method, UMP is added as a spring with negative stiffness to the rotor model, whereas in the second method, UMP is included as an external force. Based on the developed UMP and eccentricity models, rotordynamic simulation methods within the electric machine design process are proposed. Furthermore, an experimental verification process that can be applied to actual industrial machines is proposed for the case machine supported by active magnetic bearings in order to determine UMP effects on rotordynamics.
Through the case studies of three test machines, the characteristics of UMP force and stiffness are found by investigating their variation due to the change in slip, eccentricity, supply frequency, and time. Then, UMP effects on rotordynamics are found by studying forced vibration responses obtained from both time-step rotordynamics simulation and experimental measurement. The results show two main effects: reduction in the rotor’s natural frequency and additional vibration by UMP-caused harmonic excitations.
Finally, a comparison between the simulation and experiment results confirms that the proposed simulation process, based on the semi-analytical UMP model, is suitable for rotordynamics simulation and achieves a high accuracy with efficient computation.
Kokoelmat
- Väitöskirjat [997]