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A Complete Design of a Rare Earth Metal-Free Permanent Magnet Generator
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wind power group)ORCID iD: 0000-0003-3341-6910
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wind power group)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wind power group)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2014 (English)In: Machines, ISSN 2075-1702Article in journal (Refereed) Published
Abstract [en]

The price of rare-earth metals used in neodymium-iron-boron (NdFeB) permanent magnets (PMs) has fluctuated greatly recently. Replacing the NdFeB PMs with more abundant ferrite PMs will avoid the cost insecurity and insecurity of supply. Ferrite PMs have lower performance than NdFeB PMs and for similar performance more PM material has to be used, requiring more support structure. Flux concentration is also necessary, for example, by a spoke-type rotor. In this paper the rotor of a 12 kW NdFeB PM generator was redesigned to use ferrite PMs, reusing the existing stator and experimental setup. Finite element simulations were used to calculate both electromagnetic and mechanical properties of the design. Focus was on mechanical design and feasibility of construction. The result was a design of a ferrite PM rotor to be used with the old stator with some small changes to the generator support structure. The new generator has the same output power at a slightly lower voltage level. It was concluded that it is possible to use the same stator with either a NdFeB PM rotor or a ferrite PM rotor. A ferrite PM generator might require a larger diameter than a NdFeB generator to generate the same voltage.

Place, publisher, year, edition, pages
Basel, Switzerland: Multidisciplinary Digital Publishing Institute , 2014.
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-236639DOI: 10.3390/machines2020120OAI: oai:DiVA.org:uu-236639DiVA: diva2:764840
Available from: 2014-11-20 Created: 2014-11-20 Last updated: 2016-10-20
In thesis
1. Demagnetization Studies on Permanent Magnets: Comparing FEM Simulations with Experiments
Open this publication in new window or tab >>Demagnetization Studies on Permanent Magnets: Comparing FEM Simulations with Experiments
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In a world where money often is the main controlling factor, everything that can be tends to be more and more optimized. Regarding electrical machines, developers have always had the goal to make them better. The latest trend is to make machines as efficient as possible, which calls

for accurate simulation models where different designs can be tested and evaluated. The finite element method is probably the most popular approach since it makes it possible to, in an easy and accurate way, get numerical solutions to a variety of physics problems with complex geometries and non-linear materials.

This licentiate thesis includes two different projects in which finite element methods have had a central roll. In the first project, the goal was to develop a simulation model to be able to predict demagnetization of permanent magnets. It is of great importance to be able to predict if

a permanent magnet will be demagnetized or not in a certain situation. In the worst case, the permanent magnets will be completely destroyed and the machine will be completely useless. However, it is more probable that the permanent magnets will not be completely destroyed and that the machine still will be functional but not as good as before. In a time where money is more important than ever, the utilization has to be as high as possible. In this study the demagnetization risk for different rotor geometries in a 12 kW direct driven permanent magnet synchronous generator was studied with a proprietary finite element method simulation model. The demagnetization study of the different rotor geometries and magnet grades showed that here is no risk for the permanent magnets in the rotor as it is designed today to be demagnetized. The project also included experimental verification of the simulation model. The simulation model was compared with experiments and the results showed good agreement.

The second project treated the redesign of the rotor in the generator previously mentioned. The goal was to redesign the surface mounted NdFeB rotor to use a field concentrating design with ferrite permanent magnets instead. The motivation was that the price on NdFeB magnets has fluctuated a lot the last few years as well as to see if it was physically possible to fit a ferrite rotor in the same space as the NdFeB rotor. A new rotor design with ferrite permanent magnets was presented together with an electromagnetic and a mechanical design.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 43 p.
Series
UURIE / Uppsala University, Department of Engineering Sciences, ISSN 0349-8352 ; 338-14L
Keyword
Permanent magnet, demagnetization, simulation, FEM, Comsol Multiphysics, VAWT
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-236301 (URN)
Presentation
2014-06-05, Å4101, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2010-3950
Available from: 2014-11-25 Created: 2014-11-17 Last updated: 2014-11-25Bibliographically approved
2. Rare Earth Metal–Free Permanent Magnet Generators
Open this publication in new window or tab >>Rare Earth Metal–Free Permanent Magnet Generators
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Permanent magnet (PM) synchronous generators (SGs) are used in renewable energy production. The preferred PM material is neodymium-iron-boron (NdFeB), which has very high performance and, until recently, low cost. In recent years there has emerged a cost and supply insecurity in NdFeB PMs due to export restrictions imposed by China, where the majority of the raw materials are produced. In this thesis various methods of avoiding the use of PM materials based on NdFeB, or other rare earth metals, are investigated.

One approach is the use of the cheap and abundant ferrite PM. A ferrite PM rotor intended to be interchangeable with an NdFeB PM rotor is designed and built. Some initial investigation of the performance of the new rotor, and how this relates to manufacturing tolerances, is also made.

Another approach is to make parameter studies in anticipation of new PM materials. A study of how three different rotor topologies perform with different PM materials, described by their remanence and recoil permeability, is made. The rotor topologies are: a spoke type PM rotor, a surface mounted PM rotor and a capped PM rotor.

It is concluded that a viable replacement rotor can be designed using ferrite PMs. The new rotor will be heavier and mechanically more complex, and give slightly lower output voltage. Losses in the machine will increase slightly. A study is made on the impact of manufacturing tolerances on the performance of the resulting rotor.

The different rotor topologies work best with different PM material properties. The surface mounted PM and capped PM rotors require higher remanence for good performance; the spoke type PM rotor works well with larger amounts of low remanence material. The recoil permeability should be low for the surface mounted and high for the capped PM rotor.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, Institutionen för teknikvetenskaper, 2016. 51 p.
Series
UURIE / Uppsala University, Department of Engineering Sciences, ISSN 0349-8352 ; UURIE 348-16L
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-292963 (URN)
Presentation
2016-06-13, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2012-4706ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 12-295
Available from: 2016-07-07 Created: 2016-05-11 Last updated: 2016-07-07Bibliographically approved
3. Demagnetization and Fault Simulations of Permanent Magnet Generators
Open this publication in new window or tab >>Demagnetization and Fault Simulations of Permanent Magnet Generators
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Permanent magnets are today widely used in electrical machines of all sorts. With their increase in popularity, the amount of research has increased as well. In the wind power project at Uppsala University permanent magnet synchronous generators have been studied for over a decade. However, a tool for studying demagnetization has not been available. This Ph.D. thesis covers the development of a simulation model in a commercial finite element method software capable of studying demagnetization. Further, the model is also capable of simulating the connected electrical circuit of the generator. The simulation model has continuously been developed throughout the project. The simulation model showed good agreement compared to experiment, see paper IV, and has in paper III and V successfully been utilized in case studies. The main focus of these case studies has been different types of short-circuit faults in the electrical system of the generator, at normal or at an elevated temperature. Paper I includes a case study with the latest version of the model capable of handling multiple short-circuits events, which was not possible in earlier versions of the simulation model. The influence of the electrical system on the working point ripple of the permanent magnets was evaluated in paper II. In paper III and VI, an evaluation study of the possibility of creating a generator with an interchangeable rotor is presented.  A Neodymium-Iron-Boron (Nd-Fe-B) rotor was exchanged for a ferrite rotor with the electrical properties almost maintained.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1444
Keyword
Demagnetization, Permanent magnet, Finite Element Method, Synchronous generators, Wind power
National Category
Engineering and Technology Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-303517 (URN)978-91-554-9733-0 (ISBN)
Public defence
2016-12-09, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2016-11-16 Created: 2016-09-20 Last updated: 2016-11-28

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Eklund, PetterEriksson, SandraMats, Leijon

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