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Dynamic Modeling of a Generator With Anisotropic Nonlinear Permanent Magnets in Finite Element Method Software
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.ORCID iD: 0000-0001-8598-2565
2023 (English)In: IEEE Transactions on Magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 59, no 9, article id 7401308Article in journal (Refereed) Published
Abstract [en]

In this article, a method of dynamic modeling of nonlinear permanent magnets (PMs) with recoil lines in 2-D finite element analysis (FEA) software was presented. COMSOL Multiphysics 6.0 FEA software was used in this study. The method is implemented through the variable utilities. The simulation results of a spoke-type synchronous generator for a wind turbine with anisotropic aluminum-nickel-cobalt (Alnico) 5, 8B, and 9 grades were used to exemplify the model and compared. The proposed methodology can be used for the simulation of nonlinear PMs with recoil lines and includes reversible and irreversible losses of magnetization of nonlinear PMs. The effect of the magnetic field from the stator winding on nonlinear PMs during normal operation and short circuits was studied. The modeling results were compared to the model without any demagnetization and a previous study with recoil lines and averaged minimum magnetic flux points. The no-load (NL) voltages were compared before and after a demagnetization. The dynamic model showed considerable demagnetization of Alnico magnets during normal operational and three-phase short circuits. Alnico 5 and 9 showed higher sensitivity to short-circuit currents and the short-circuit currents caused remagnetization of the upper part of the magnet in the opposite direction. The anisotropy of the PM implemented in the model improved the magnetic field simulation inside the magnet and partially protected the magnet from demagnetization by inclined fields. At last, the method was experimentally verified by tests on an iron core.

Place, publisher, year, edition, pages
IEEE, 2023. Vol. 59, no 9, article id 7401308
Keywords [en]
Aluminum-nickel-cobalt (Alnico), COMSOL, demagnetization, finite element method (FEM), nonlinear permanent magnets (PM), PM synchronous generator (PMSG), recoil line
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-514058DOI: 10.1109/TMAG.2023.3296966ISI: 001061030600003OAI: oai:DiVA.org:uu-514058DiVA, id: diva2:1805362
Funder
Swedish Research Council, 2018-04617Available from: 2023-10-17 Created: 2023-10-17 Last updated: 2024-04-22Bibliographically approved
In thesis
1. Nonlinear models of permanent magnets for electrical machines
Open this publication in new window or tab >>Nonlinear models of permanent magnets for electrical machines
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increased demand for electricity, environmental problems related to mining of rare earth metals and to usage of fossil fuels, national security issues, and monopolization of the rare earth metals market forcing society to explore alternative options for conventional rare earth permanent magnets. Generally, the relationship between magnetic flux density and the magnetic field of permanent magnets has a nonlinear shape, but the operating region of conventional permanent magnets is linear. There is no convenient model of permanent magnets in existing commercial finite element method software that models partial demagnetization and remagnetization of nonlinear permanent magnets correctly. This thesis presents a model that is able to model an electrical machine with nonlinear permanent magnets and does not require a large computational power. A gradual improvement of the model resulted in four versions of it. It started with a simple linear model and ended with a model that is able to simulate partial demagnetization and remagnetization of the magnet and includes all four quadrants of the BH loop. Also, the last version limits the maximum magnetization depending on the angle of normalized magnetization. The magnetic characteristics of Alnico 8 LNGT40 and Alnico 9 LNGT72 magnets were measured in a vibrating sample magnetometer in order to obtain the material data required for this research work. A mathematical model of the MH loops of Alnico 8 LNGT40 in different directions was developed. The models of a synchronous permanent magnet generator with a spoke type topology with Alnico 5, 8 and 9 magnets were tested under normal and three phase short circuit conditions. The results were compared and discussed. It is found Alnico 5 is more sensitive to short circuit than Alnico 8 and 9. Electric steel clamps holding the permanent magnets and airgap above the magnets protect them from demagnetization.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. p. 62
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2404
Keywords
Aluminum-nickel-cobalt (Alnico), COMSOL, demagnetization, finite element method (FEM), nonlinear permanent magnets, permanent magnet synchronous generator (PMSG), recoil line
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-527007 (URN)978-91-513-2136-3 (ISBN)
Public defence
2024-06-13, Room 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2018-04617
Available from: 2024-05-20 Created: 2024-04-22 Last updated: 2024-05-23

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Ibrayeva, AnarEriksson, Sandra

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