Niall McMahon

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DCU Computing Talk - Wind Turbine Models

2011-07-08

Niall McMahon

Notes to accompany a lecture delivered to the School of Computing in Dublin City University on July 7th, 2011.

Summary

There is a more about my current research here. The Centre for Renewable Energy at DkIT was founded by Larry Staudt in June 2002. Its mission is to assist with Ireland's coming transition to a renewable energy-based economy. Paul MacArtain and Ray Byrne have worked with the centre for more than five years.

A good place to start reading about wind turbines is at the Danish Wind Industry Association's Guided Tour. The Danes were pioneers of modern wind. Vestas, a Danish firm, is one of the world's largest manufacturers of wind turbines. For the past year, I worked with Ampair, the UK's oldest extant wind turbine manufacturer.

As well as online sources, many textbooks give very useful introductions to the technology of wind turbines. These include the Wind Energy Handbook, Wind Energy Explained and Renewable Energy in Power Systems. Slimmer, more practical texts include Windpower Workshop. More journalistic and readable texts include Wind Energy Basics. Each constituent technology can be investigated as deeply as necessary. For example, achieving a thorough understanding of wind turbine aerodynamics involves a similar amount of effort to understanding aircraft aerodynamics. Wind turbine electrical theory is similarly rich.

Detailed standards for small wind turbine design exist so that machines are built to meet minimum safety and quality performance criteria. The International Electrotechnical Commission oversees the development and maintenance of these documents. Ireland is not an IEC member. Nevertheless, Ray Byrne of the Centre for Renewable Energy currently represents Ireland as an observer, unofficially and by the kind invitation of the chairman, to the current committee responsible for the third edition of the small wind design standards.

Speed control is critical for meeting a minimum standard of safety. Over-speed events, though rare, are often catastrophic.

One dramatic and very rare example, caught on camera, is the February 2008 failure of a Vestas 600 kW machine in Halling, Denmark. You can find the final report into this incident here (written by National Laboratory for Sustainable Energy - Risø DTU). The explosive collapse was in large part due to the simultaneous failure of all the turbine's brake systems.

Robust control is technically hard to achieve. Additionally, small- and medium-sized machines occupy an economically difficult position: too small to support the cost of advanced mechanisms yet too big to do without performance and emergency controls. Sound understanding must underpin the development of such control systems.

Mathematical and computational models help a lot with this; if a system can be coded, and the model output validated against reality, then the real system is probably on the way to being understood. Such codes already exist, published by NREL, among others, but there is value in doing it from scratch and using basic building blocks.

Well known mathematics, together with airfoil data, from experiment or codes, can be used to describe the aerodynamic forces (e.g. Glauert's blade element momentum technique) and the resulting rotor torques, while electrical theory can describe generator behaviour. Newton's laws can then be used to calculate the net rotational acceleration of the system, i.e. how quickly it speeds up and slows down. The model can be made as complicated as the system it describes.

Languages that we have used for implementation include Python and VB, with Gnuplot for visualisation. Assuming that no computational fluid dynamics is used, such codes can execute in seconds.

Such models can be used to examine system behaviour in extreme circumstances, to conduct forensic analyses and as real-time diagnostic tools.

Additional Notes

You can read about the Vestas V52 machine at DkIT here.

There were some nice questions at the end of the talk. Thanks to all who attended and took part.

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