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Magnetic End LeakageFlux in a Spoke Type Rotor Permanent Magnet SynchronousGenerator
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.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wind power group)ORCID iD: 0000-0001-8598-2565
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2017 (English)Conference paper, Published paper (Other academic)
Abstract [en]

The spoke type rotor can be used to obtain magnetic flux concentration in permanent magnet machines. This allows the air gap magnetic flux density to exceed the remanent flux density of the permanent magnets but gives problems with leakage fluxes in the magnetic circuit. The end leakage flux of one spoke type permanent magnet rotor design is studied through measurements and finite element simulations. The measurements are performed in the end regions of a 12 kW prototype generator for a vertical axis wind turbine. The simulations are made using three dimensional finite elements to calculate the magnetic field distribution in the end regions of the machine. Also two dimensional finite element simulations are performed and the impact of the two dimensional approximation is studied. It is found that the magnetic leakage flux in the end regions of the machine is equal to about 20 % of the flux in the permanent magnets. The overestimation of the performance by the two dimensional approximation is quantified and a curve-fitted expression for its behavior is suggested.

Place, publisher, year, edition, pages
2017.
Keywords [en]
End effects, End leakage flux, Permanent magnet machine, Spoke type rotor
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-366658OAI: oai:DiVA.org:uu-366658DiVA, id: diva2:1265271
Conference
ICEMD 2017 : International Conference on Electrical Machines and Drives, March 26 - 27, 2017 Madrid, Spain
Funder
Swedish Research Council, 2012-4706ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 12-295Available from: 2018-11-22 Created: 2018-11-22 Last updated: 2019-03-20Bibliographically approved
In thesis
1. Design of Rare Earth Free Permanent Magnet Generators
Open this publication in new window or tab >>Design of Rare Earth Free Permanent Magnet Generators
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Low speed permanent magnet (PM) synchronous generators (SGs) are commonly used in renewable energy. Rare earth (RE) PMs such as neodymium-iron-boron are a popular choice due to their high performance. In 2011 supply and cost issues were added to the previously existing environmental concerns regarding REPM raw materials as the world's major producer China imposed export restrictions. This thesis aims to investigate and propose design solutions for PMSGs that do not use REPMs. Two approaches are used: to design generators using the cheaper and more abundant ferrite PM materials, and to investigate how properties of new PM materials influence SG design.

A ferrite PM rotor is designed to replace a REPM rotor in an experimental 12 kW wind power generator. The new design employs a flux concentrating spoke type rotor to achieve performance similar to the old REPM rotor while using ferrite PMs. The ferrite PM rotor design is built. The air gap length, magnetic flux density in the air gap, PM remanence, and voltage at both load and no load are measured. The generator has lower no load voltage than expected, which is mainly explained by lower than specified remanence of the ferrite PMs in the prototype. With the measured remanence inserted into the calculations some discrepancy remains. It is found that the discrepancy can be explained by the magnetic leakage flux in the end regions of the spoke type rotor, which is not modeled in the two dimensional simulations used for the design calculations.

To investigate the influence of PM material properties three different PM rotor topologies are optimized for torque production using PM materials described by their remanence, recoil permeability, and demagnetization resistance. Demagnetization is considered using currents determined by a novel, winding design independent short circuit model. It is found that the spoke type rotor gives the highest torque of the three rotor topologies for low remanence materials as long as the PMs have sufficient demagnetization resistance. For high remanence materials the surface mounted PM rotor can give higher torque if the demagnetization resistance is high, but otherwise a capped PM rotor gives higher torque.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 75
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1746
Keywords
permanent magnet generators, electrical machine design, ferrite permanent magnet
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-366344 (URN)978-91-513-0510-3 (ISBN)
Public defence
2019-01-18, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 12-295Carl Tryggers foundation , 15:152Swedish Research Council, 2012-4706
Available from: 2018-12-19 Created: 2018-11-22 Last updated: 2019-01-21

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Eklund, PetterSjolund, JonathanEriksson, SandraLeijon, Mats

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