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Nonlinear models of permanent magnets for electrical machines
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.ORCID iD: 0000-0003-0173-2513
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 [en]
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: urn:nbn:se:uu:diva-527007ISBN: 978-91-513-2136-3 (print)OAI: oai:DiVA.org:uu-527007DiVA, id: diva2:1853256
Public defence
2024-06-13, Room 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2018-04617Available from: 2024-05-20 Created: 2024-04-22 Last updated: 2024-05-23
List of papers
1. An Overview of MnAl Permanent Magnets with a Study on Their Potential in Electrical Machines
Open this publication in new window or tab >>An Overview of MnAl Permanent Magnets with a Study on Their Potential in Electrical Machines
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2020 (English)In: Energies, E-ISSN 1996-1073, Vol. 13, no 21, article id 5549Article in journal (Refereed) Published
Abstract [en]

In this paper, hard magnetic materials for future use in electrical machines are discussed. Commercialized permanent magnets used today are presented and new magnets are reviewed shortly. Specifically, the magnetic MnAl compound is investigated as a potential material for future generator designs. Experimental results of synthesized MnAl, carbon-doped MnAl and calculated values for MnAl are compared regarding their energy products. The results show that the experimental energy products are far from the theoretically calculated values with ideal conditions due to microstructure-related reasons. The performance of MnAl in a future permanent magnet (PM) generator is investigated with COMSOL, assuming ideal conditions. Simplifications, such as using an ideal hysteresis loop based on measured and calculated saturation magnetization values were done for the COMSOL simulation. The results are compared to those for a ferrite magnet and an NdFeB magnet. For an ideal MnAl hysteresis loop, it would be possible to replace ferrite with MnAl, with a reduced weight compared to ferrite. In conclusion, future work for simulations with assumptions and results closer to reality is suggested.

Place, publisher, year, edition, pages
MDPI, 2020
Keywords
rare earth-free, permanent magnets, electrical machines, renewable energy, COMSOL
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-417961 (URN)10.3390/en13215549 (DOI)000588892700001 ()
Funder
StandUp
Note

Title in thesis: MnAl and other novel permanent magnets in electrical machines - a review and simulation study

Available from: 2020-08-27 Created: 2020-08-27 Last updated: 2024-04-22Bibliographically approved
2. Modelling of Permanent Magnet Synchronous Generator with Non-linear Magnets
Open this publication in new window or tab >>Modelling of Permanent Magnet Synchronous Generator with Non-linear Magnets
2021 (English)In: 2021 22nd IEEE International Conference on Industrial Technology (ICIT), IEEE Institute of Electrical and Electronics Engineers (IEEE), 2021, p. 209-214Conference paper, Published paper (Refereed)
Abstract [en]

In this paper simulation results of a spoke-type synchronous generator for a wind turbine with three different grades of Alnico magnets were presented. COMSOL Multiphysics 5.4 finite element analysis (FEA) based software was used. The proposed model was used for simulation of a synchronous generator with non-linear Alnico magnets with recoil-lines with some approximations and can be used for modelling electrical machines with other non-linear permanent magnets. The geometry of the machines was kept fixed for all scenarios. The model takes into account the irreversible loss of magnetization of non-linear permanent magnets due to the magnetic field from the stator winding during normal operation and short circuit. Modelling results show that Alnico 5 (ArKomax800) magnets have the lowest output power, but they are the least sensitive to change of the load. The generator with Alnico 8 permanent magnets have the highest output power, is good at handling the nominal load but the most sensitive to short circuits. Alnico 9 magnets could be an option if the risk for short circuits is accounted for.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE)IEEE, 2021
Series
IEEE International Conference on Industrial Technology, ISSN 2643-2978
Keywords
Alnico, COMSOL, FEM, Non-linear Permanent Magnets, PMSG, Recoil Lines
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-455447 (URN)10.1109/ICIT46573.2021.9453675 (DOI)000687856000031 ()978-1-7281-5730-6 (ISBN)
Conference
22nd IEEE International Conference on Industrial Technology (ICIT), MAR 10-12, 2021, ELECTR NETWORK
Funder
Swedish Research Council, 2018-04617
Available from: 2021-10-11 Created: 2021-10-11 Last updated: 2024-04-22Bibliographically approved
3. Measurement and Modelling of Hysteresis Curves for Nonlinear Permanent Magnets at Different Inclination Angles
Open this publication in new window or tab >>Measurement and Modelling of Hysteresis Curves for Nonlinear Permanent Magnets at Different Inclination Angles
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2023 (English)In: 2023 IEEE International Magnetic Conference (INTERMAG), Institute of Electrical and Electronics Engineers (IEEE), 2023Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the measurement results of the BH/MH curves of the Alnico 8 (LNGT40) with recoil loops and a mathematical model for the calculation of the average magnetic flux density in a cubic permanent magnet. The measurements were performed with a Vibrating Sample Magnetometer (VSM). The magnet samples have a cubic shape with 3 mm sides. BH curves in preferred (easy) and transverse directions and recoil loops were measured and compared to Alnico 9 (LNGT72) as well as to the data from the supplier. The load line of the cubic magnet in 0 A/m applied magnetic field was found. A mathematical model was developed which can approximate the MH a curve for an applied field with an arbitrarily chosen angle between the field and easy axis, given MH a curves for 0o and 90o. Also, a simplified general model of a cubic permanent magnet in the air and calculation results of stored energy and hysteresis losses were presented.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023
Series
International Conference on Magnetics, ISSN 2150-4598, E-ISSN 2150-4601
Keywords
Alnico magnets, BH curve, Demagnetization, Permanent Magnet, Recoil Line
National Category
Other Physics Topics Other Electrical Engineering, Electronic Engineering, Information Engineering Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-520985 (URN)10.1109/INTERMAG50591.2023.10265100 (DOI)001090594700054 ()979-8-3503-3246-9 (ISBN)979-8-3503-3247-6 (ISBN)
Conference
IEEE International Magnetic Conference (INTERMAG), May 15-19, 2023, Sendai, Japan
Funder
Swedish Research Council, 2018-04617StandUp
Available from: 2024-01-18 Created: 2024-01-18 Last updated: 2024-04-22Bibliographically approved
4. Dynamic Modeling of a Generator With Anisotropic Nonlinear Permanent Magnets in Finite Element Method Software
Open this publication in new window or tab >>Dynamic Modeling of a Generator With Anisotropic Nonlinear Permanent Magnets in Finite Element Method Software
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
Keywords
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:nbn:se:uu:diva-514058 (URN)10.1109/TMAG.2023.3296966 (DOI)001061030600003 ()
Funder
Swedish Research Council, 2018-04617
Available from: 2023-10-17 Created: 2023-10-17 Last updated: 2024-04-22Bibliographically approved
5. Anisotropic Model of Nonlinear Permanent Magnets in Finite Element Method Software
Open this publication in new window or tab >>Anisotropic Model of Nonlinear Permanent Magnets in Finite Element Method Software
(English)Manuscript (preprint) (Other academic)
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
Research subject
Engineering Science
Identifiers
urn:nbn:se:uu:diva-527352 (URN)
Available from: 2024-04-29 Created: 2024-04-29 Last updated: 2024-04-29

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