The HOLI 300 small wind turbine comprises a Ginlong GL-PMG-500A brushless permanent magnet generator. In this section we explain how this generator was selected.

Important Note

Preliminary content from design report

The content of this article is taken from the December 2013 preliminary design report. It represents intention of design at that stage but does not necessarily show the final version of the HOLI 300 turbine design.

Generator

An electric generator is a device that converts mechanical energy to electrical energy. A generator in a wind turbine is used to convert the aerodynamic mechanical power of the blades to electrical power. Electrical power can be produced in two forms alternating (Alternating Current AC) or direct (Direct Current DC). For this design contest the desired output of the electrical system is DC for 24 V Voltage DC battery charging. Generators have two main subcategories, AC and DC. For each subcategory, there are several options. AC generators have subcategories of Synchronous and Asynchronous, and DC generators just have the subcategory brushed. Brushed DC generators have a lot of maintenance need with the brushes and was quickly eliminated as an option for the wind turbine. Asynchronous and synchronous AC generators have several options, however permanent magnet was chosen because they are often produced with a high number of poles, which allows for a low RPM (revolutions per minute) range, and turbine production without a gearbox. the figure below shows the available options for generators.

Overview of generator types
Overview of generator types

Permanent Magnet Synchronous Generator (PMSG)

In the majority of PMSG designs, the rotor contains the magnet(s) and the stator contains the windings, which are electrically connected to the load. Permanent Magnet synchronous generators are very often produced with 3 phases for higher efficiency power production. The figure below displays the general construction of a PMSG.

Illustration of a PMSG [<a class=1]” width=”420″ height=”330″ />
Illustration of a PMSG [1]

Synchronous generators are known as synchronous, because the frequency f of the induced voltage in the stator is directly proportional to RPM, the rotational speed of the rotor. This relationship can be expressed with the formula:

 f=\frac{RPM\cdot p}{120}

where p is the number of magnetic rotor pole pairs. For this equation with a constant frequency, if the number of pole pairs is increased, the RPM decreases.

Design Generator Power Range

The desired design power of the generator was chosen by the examination of generator power size and percentage energy capture. The wind regime provided with Weibull parameters of A=4.5\,\frac{\textrm{m}}{\textrm{s}}, k=2, and V_{\textrm{ave}}=4.0\,\frac{\textrm{m}}{\textrm{s}} was examined and the potential annual potential energy production was calculated. The effects of decreasing generator size were examined versus potential energy capture for a very efficient small wind turbine blade with a power coefficient c_{\textrm{P}} of 0.4. From the analysis it was determined that a 250-500 Watt generator could capture 89-99 % of aerodynamic power available and would be a good range for acceptable generator power ratings which can be seen in the table below.

Generator Size and Energy Capture
Generator Size in WEnergy in kWhEnergy Capture in %
Infinite489100
800488100
50048299
40047397
35046796
30045593
25043389
20041685
10032065

Matching of Power Curves

A major problem in designing small direct drive wind turbines is the matching between the power curves of turbine and generator. The maximum power is extracted out from wind and fed into the load only if it is a match between the power curves of turbine rotor and generator [2]. Three blades with high coefficients of power were designed with tip speed ratios of 4.5, 5 and 6 used as a comparison with generators found on the Internet with power in the range of 250–500 Watt and high efficiency. Graphs of RPM versus Power and RPM versus Torque were created for determining which generator would match up the best for maximum power extraction. It was determined that the Ginlong GL-PMG-500A would work best for the following reasons:

  •  availability of technical data
  • operation below rated power allows the use of the generator as a electromagnetic brake
  • operation in the field weakening range is avoided by not controlling the generator around rated power which is supposed to be beneficial for the MPPT control

Ginlong GL-PMG-500A

The Ginlong GL-PMG-500A is the generator we have chosen for a permanent magnet generator, with rated power of 510 W, rated rotational speed of 450 RPM, and rated torque of 14.8 Nm. The generator has 16 poles, or 8 pole pairs, which make for a low RPM range, ideal for direct drive. A picture of the inside of the Ginlong generator is shown in the figure below, and the specification sheet can be found here.

Inside view of generator GL-PMG-500A
Inside view of generator GL-PMG-500A
[1] P. D. F. W. Fuchs, “Power electronic generator systems for wind turbines,” , 2011.
[Bibtex]
@ELECTRONIC{Fuchs2011,
author = {Prof. Dr.-Ing. Friedrich W. Fuchs},
year = {2011},
title = {Power Electronic Generator Systems for Wind Turbines},
language = {English},
organization = {Christian-Albrechts-University of Kiel},
owner = {helgehamann},
timestamp = {2013.12.15}
}
[2] M. Predescu, A. Bejinariu, A. Nedelcu, O. Mitroi, C. Nae, M. V. Pricop, and A. Craciunescu, Wind tunnel assessment of small direct drive wind turbines with permanent magnets synchronous generatorsProceedings of the International Conference on Renewable Energies and Power Quality, 2008.
[Bibtex]
@PROCEEDINGS{Predescu2008,
title = {Wind Tunnel Assessment of Small Direct Drive Wind Turbines with Permanent
Magnets Synchronous Generators},
year = {2008},
publisher = {Proceedings of the International Conference on Renewable Energies
and Power Quality},
organization = {ICREPQ08},
abstract = {Most of the small wind turbines for battery charging application are
direct drive type with permanent magnets synchronous generators.
A major problem in designing small direct drive wind turbines is
the matching between the power curves of turbine and generator. The
maximum power is extracted out from wind and fed into the load only
if it is a match between the power curves of turbine rotor and generator.
The assessment of the main components performances which contribute
to the conversion process, namely turbine and generator, is made
in wind tunnel. The experiments described below were carried out
on wind turbines with carefully studied blade profile and permanent
magnets synchronous generator, designed using a dedicated procedure.
The paper describes the experimental layout and the results of the
wind tunnel tests of two wind turbines, 250W and 1kW, designed for
battery charging. The work has two objectives: measurement of the
power curve of the turbine and the performances of the turbine-generator
assembly with the load and the verification of the design method
for maximum power delivered to the load.},
author = {M. Predescu and A. Bejinariu and A. Nedelcu and O. Mitroi and C.
Nae and M.V. Pricop and A. Craciunescu},
owner = {helgehamann},
timestamp = {2013.12.15},
url = {http://www.icrepq.com/icrepq-08/287-predescu.pdf}
}

David SmithAbout the author:
David Smith
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2 replies
  1. Ahmed fouaad says:

    How are yuo ?
    I want to know your circuit after generator how you control your volt
    i know you must convert Ac to Dc by using rectifier , did you use voltage regulator after rectifier to get fixed volt or what ?
    thanks in advance

    Reply
    • Florian Roscheck
      Florian Roscheck says:

      Hi Ahmed!
      We used a load controller with a 75 Ω dump load and a car battery behind the generator. We went for the “WindMax500″ controller (see http://www.schams-solar.de/windmppt.html ).

      The battery charging application was a set constraint in the contest that we participated in. Depending on your application it might make sense to pick a different controller.

      In any case, I feel it makes sense to pick a controller that is specifically designed for small wind turbines. In this way, you can effectively limit your losses.
      I hope this information is helpful!

      Florian

      Reply

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