Abstract

In this work axial flux permanent magnet generators are studied as parts of small wind turbines in off-grid systems. The majority of these generators are manufactured today with neodymium magnets (NdFeB), which although extremely powerful magnets, have been associated with various problems of economic, social, environmental and functional nature. For these reasons, the change of the magnetic material of the generator and, in particular, the possibility of replacing neodymium magnets with ceramic magnets (hard ferrites) is investigated.

At the beginning of the work, an introduction to the concepts of open knowledge and intermediate technology is made, as well as to the role that small wind turbines can have in meeting human needs in electricity while preserving the environment.

The operation of axial flux permanent magnet generators is analyzed in theory and the subject of the material of these generators is investigated. The results of a questionnaire on locally manufactured small wind turbines are presented, which was created as part of this work and, based on these results and literature research, the decision to study generators with ferrites is made.

Ferrite generators and neodymium generators are designed and simulated for four sizes of blade rotor radius and the magnet dimensions for each one of them are optimized according to certain criteria.

Having found the optimal magnets for each generator, the optimal universal magnet is sought (one for each magnetic material) that can be satisfactorily used for generators throughout the range of radii that are studied. For each material, the universal magnet is compared with the optimal magnets per rotor radius and with the most common commercial magnet in the market.

Finally, an 850W ferrite generator – designed to operate with a 2.4m diameter rotor – is manufactured, and its performance is compared in the lab with the performance of an equivalent power typical generator with neodymium magnets.

Keywords: small wind turbines, permanent magnets, ferrites, axial flux, off-grid systems, efficiency-cost optimization, universal magnet, questionnaire, open source, intermediate technology

Author: Katerina Troullaki

Responsible PhD: Kostas Latoufis / latoufis@power.ece.ntua.gr

Supervising Professor: Nikos Hatziargyriou / nh@power.ece.ntua.gr

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