IEEE Electrification Magazine - March 2015 - 77

r/min

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Wind Speed (m/s)

Per-Second Data for (SWT 2) 2.4-m Rotor Diameter/Battery
Connected 48 V from 31 October 2013 02:26:00 to 31 October 2013 02:28:00 Visifire Trial Edition

Time
Wind Speed (m/s)

r/min

Figure 19. The starting wind speed of the 2.4-m HP small wind turbine rotor from standstill. (Source: rurerg.net.)

OSh research and Development at the NTUa
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In addition to assessing this OSH technology, further
research and development has been carried out on the topic
of locally manufactured small wind turbines. The axial flux
generator has been modeled and simulated using finite element open-source software, such as Finite Element Method
Magnetics (FEMM), with the accuracy of the simulations
reaching 2-5% when compared with experimental results.
Higher accuracy is difficult to achieve since the generators
are manufactured with low-precision equipment and techniques resulting in nonuniformity of the construction. These
simulation models, along with different optimization techniques, have been used to perform low-cost optimizations
for axial flux generator design in battery-charging and gridconnected applications of locally manufactured small wind
turbines. The connection of the small wind turbine to the
battery bank with a power cable has also been modeled, and
the AEP of the small wind turbine has been maximized by
choosing the appropriate conductor size for the specific
application. The models described are currently being developed as online software tools to assist the OSH community
in further developing this technology and also to provide
information for constructors and installers to better configure their specific wind energy systems.
One of the main advantages of OSH designs, and of the
open design culture in general, is the adaptability of the
designs produced. OSH small wind turbine technology can
be adapted to better suit different environments such as
coastal areas with high corrosion. An alternative design
approach to the axial flux generator has been developed in
the OSH community with the use of a different magnetic
material than neodymium, specifically ferrite, which overcomes the typical problems of neodymium such as corrosion and price fluctuations. A ferrite magnet axial flux

Wind Speed (m/s)
Figure 20. The power curve of the 2.4-m HP small wind turbine up to
25 m/s. (Source: rurerg.net.)

Figure 21. The rotor disk of a ferrite magnet axial flux generator to
be driven with the 2.4-m HP rotor blades. (Source: rurerg.net.)

generator for the 2.4-m-diameter rotor has been developed
at the NTUA (Figure 21) to demonstrate the adaptability of
OSH designs. Ferrite generators are typically higher in

IEEE Electrific ation Magazine / March 2 0 1 5

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Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2015