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An Overview of MnAl Permanent Magnets with a Study on Their Potential in Electrical Machines
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
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: 0000-0001-8097-0223
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.ORCID iD: 0000-0003-1027-8914
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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. Vol. 13, no 21, article id 5549
Keywords [en]
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: urn:nbn:se:uu:diva-417961DOI: 10.3390/en13215549ISI: 000588892700001OAI: oai:DiVA.org:uu-417961DiVA, id: diva2:1461821
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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
In thesis
1. Wave Power for Desalination
Open this publication in new window or tab >>Wave Power for Desalination
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This doctoral thesis presents work related to wave powered desalination. Wave power for desalination could be an interesting alternative for islands or coastal regions facing freshwater shortage, and several systems have been proposed in literature. However, desalination is a process which demands a lot of energy. Studies presented in the thesis indicate that the wave energy converter designed at Uppsala University in Sweden could be used for desalination. This wave energy converter includes a floating buoy connected via a wire to a linear generator. The linear generator has magnets mounted on its movable part (the translator). Small-scale experiments have been included, indicating that intermittent renewable energy sources, such as wave power, could be used for reverse osmosis desalination. Moreover, hybrid systems, including several different renewable energy sources, could be investigated for desalination. There may be interesting minerals in the desalination brine. The thesis also includes investigations on the magnetic material inside the linear generator, as well as on control strategies for wave energy converters. An opportunity of including different types of ferrites in the linear generator has been analyzed. The thesis also presents pedagogic development projects for the electro engineering education at Uppsala University, suggesting that including a greater variability and more student-centered learning approaches could be beneficial.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2020. p. 59
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1959
Keywords
Wave power, desalination, freshwater, engineering education, linear generator, wave energy converter
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-417998 (URN)978-91-513-0995-8 (ISBN)
Public defence
2020-10-16, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2020-09-25 Created: 2020-08-28 Last updated: 2020-10-06
2. In the Air Gap of Linear Generators for Wave Power
Open this publication in new window or tab >>In the Air Gap of Linear Generators for Wave Power
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wave power conversion is one type of renewable electricity generation. Within wave power, there are many different concepts, whereof some utilizes linear generators for converting the energy in the ocean waves into electricity. A linear generator consists of a translator, which is moving and have magnets of alternating polarity, and a stator, which have conductors sur-rounded by laminated steel. Between the translator and stator is an air gap, which is only a few millimeters wide. All linear generators for wave power, to the author’s knowledge, are permanent-magnet synchronous generators. This thesis looks into the forces and power flow in the air gap of linear generators for wave power, with the purpose of improving their future performance. The studies have focused on permanent magnet synchronous generators for wave power, but several of the results should also be applicable for other applications of linear elec-trical machines.

Depending on the design of the linear generators, the translator can move so long that it only partially overlap the stator. This is common among several different wave power concepts with linear generators. When the stator is only partially overlapped by the stator it is denoted as partial stator overlap. It is studied how partial stator overlap affects the generated electric-ity, the absorbed energy, and the tangential and normal force in the air gap. The generated electricity and absorbed energy of a linear generator are quadratically dependent on the partial stator-translator overlap is shown through Faraday’s law and simulations. Experimental data showed that the absorbed energy is both linearly and quadratic depending on partial stator over-lap, where the linear dependence is at least partially due to frictional losses. Simulated results confirm that voltage is linearly dependent on partial stator overlap, which means quadratic de-pendence between generated electric and partial stator overlap. The simulated forces showed a linear dependence.

Decades ago, the Poynting vector was used to derive an expression for the power flow in the air gap of rotating electrical machines. In this thesis the equivalent expressions for both flat and tubular linear electrical machines were derived. The analytical results were also compared with results from simulations. Both the analytical expressions and simulations showed that tubular and flat linear electrical machines have slightly different behavior.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2021. p. 96
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2084
Keywords
Linear generator, Wave Power, Poynting's theorem, Partial stator overlap, Permanent-magnet synchronous generator (PMSG), Linear electrical machines
National Category
Energy Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-456284 (URN)978-91-513-1322-1 (ISBN)
Public defence
2021-12-03, Häggsalen, 10132, Ångström, Uppsala, 09:15 (English)
Opponent
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Zoom-link: https://uu-se.zoom.us/j/63760011286

Available from: 2021-11-10 Created: 2021-10-17 Last updated: 2021-12-29
3. Models of magnetism in electrical machines
Open this publication in new window or tab >>Models of magnetism in electrical machines
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The magnetic field is a fundamental part of an electrical machine, for establishing the torque and inducing voltages and currents. Then acting as the link between mechanical power and electrical power. This thesis will give a comprehensive study of how magnetism could be modeled. Covering how the magnetic field relates to energy transfer, power flow, and the forces of electrical machines.

An electromagnetic energy transfer is usually described by Poynting’s vector, which has a different formulation than the power flow of electrical engineering. The main difference is that Poynting’s vector localizes the energy flux in the surrounding electromagnetic fields of a current-carrying conductor, instead of inside the conductor itself.

The forces in a machine can be modeled by the field lines of the magnetic flux density. The force density consists of two vector components: the magnetic tension force and the magnetic pressure gradient force. The magnetic tension force acts to straighten curved field lines, based on the curvature of the flux density. The magnetic pressure gradient force acts from areas of high flux to areas of low flux. The force density could describe the forces in a synchronous machine, both for the torque of the load and for the machine’s radial forces between the rotor and the stator.

The force density could also be used to improve the understanding of Maxwell stress tensor,as they are easier to illustrate as vectors, compared to the matrix form within the Maxwell stresstensor. It also expresses the location of the force density, which can improve the use of enclosedvolumes when calculating forces based on the divergence theorem with Maxwell stress tensor.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2023. p. 73
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2248
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-498003 (URN)978-91-513-1737-3 (ISBN)
Public defence
2023-04-19, Eva von Bahrsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Supervisors
Available from: 2023-03-28 Created: 2023-03-07 Last updated: 2023-12-11Bibliographically approved
4. 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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Kontos, SofiaIbrayeva, AnarLeijon, JenniferMörée, GustavFrost, Anna E.Schönström, LinusGunnarsson, KlasSvedlindh, PeterLeijon, MatsEriksson, Sandra

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