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Study of demagnetization risk for a 12 kW direct driven permanent magnet synchronous generator for wind power
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2013 (English)In: Energy Science & Engineering, ISSN ISSN 2050-0505, Vol. 1, no 3, 128-134 p.Article in journal (Refereed) Published
Abstract [en]

One of the main aspects when designing a permanent magnet (PM) generator is to choose suitable PMs, both in terms of achieving the required flux in the generator but also of withstanding high demagnetizing fields, that is, having sufficiently high coercivity. If the coercivity is too low, the magnets are at risk of demagnetizing, fully or partially, at the event of a short circuit and/or an increase in temperature. This study aims to determine the risk of demagnetization for a 12 kW direct driven permanent magnet synchronous generator. Furthermore, as the prices on PMs have increased drastically the last few years the possibility to use smaller and/or cheaper PMs of different grades has been investigated. A new proprietary finite element method (FEM) model has been developed, which is also presented. The study is based on simulations from this FEM model and is focused on NdFeB magnets. Results show that the reference magnet can withstand a two-phase short circuit at both the temperatures tested and in both geometries. The use of cheaper magnets, smaller air gap and in the event of a two-phase short circuit often results in partial irreversible demagnetization. However, magnets with lower coercivity are easier demagnetized.

Place, publisher, year, edition, pages
2013. Vol. 1, no 3, 128-134 p.
Keyword [en]
Demagnetization, NdFeB, permanent magnet, simulation, synchronous generator
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-212671DOI: 10.1002/ese3.16ISI: 000209695200003OAI: oai:DiVA.org:uu-212671DiVA: diva2:678837
Funder
Swedish Research Council, 2010-3950
Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2016-11-17Bibliographically approved
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. 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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