Wind turbine efficiency breakthrough by Dr Markus Mueller and Dr Alasdair McDonald

A wind turbine efficiency breakthrough by Dr Markus Mueller and Dr Alasdair McDonald of the University of Edinburgh’s Institute for Energy Systems has the potential to revolutionize the wind energy industry by making large turbines more failure-proof by cutting their weight in half.

Edinburgh’s Institute for Energy Systems does extensive engineering research on generators and electrical machines for a variety of renewable energy systems and wind power, including wind turbines, wave energy converters and tidal current systems.

Till now; the blades of wind turbines have been connected to a generator via a gearbox. Their technology substituted a C shaped core generator (initially in a 20 kW prototype) to test to see if by changing the mechanical structure of the generator they could still maintain rigidity and structural integrity while cutting the weight by more than half.

The researchers have formed NGenTec; a spin-off company, with the help of Derek Douglas, an entrepreneur familiar with raising money for start-ups. The University will retain a minority stake in the new business.

The technology would reduce costs for both land-based and off-shore wind farms, while having a more marked effect on repair costs of hard to-get-to locations.

The novelty in the concept lies in the arrangement of electromagnetically active components –magnets, steel and copper – such that the structural mass can be reduced. It has also been designed such that during the assembly of large diameter permanent magnet machines there are no magnetic forces to worry about.

As wind turbine unit rating increases there has been an increasing number of gearbox failures. Hence there is more interest in direct-drive systems amongst manufacturers, but the mass of such generators is a significant issue.

Work presented at EWEC 2007 by the authors showed that the structural mass of a direct-drive generator can be in excess of 80% of the total mass. This structural mass is required to overcome the magnetic attraction force between the stationary and moving parts of the generator.

This attraction force is a result of the normal component of Maxwell stress. It can be 10 times the torque producing shear stress. The airgap clearance between the rotor and stator must be maintained; otherwise the generator can be damaged.

A successful directly-driven generator will be able to produce a moderate to high shear stress while elegantly negating the effect of the magnetic attraction. The authors present a new topology which has the potential to meet that challenge, without having to resort to exotic structural or magnetic materials such as superconductors.

The innovative step in this new concept has been to take the active materials in the machine – copper, magnets and steel – and change their relative positions to minimise the effects of the normal force. The result is a machine in which the structure only has to support the mass of the active components, leading to a reduction in total mass in the region of 55% compared to conventional permanent magnet (PM) machines.

A novel PM generator topology has been introduced in which the relative positions of the active materials (copper, magnets and iron) have been chosen to counter the magnetic attraction forces inherent in all iron-cored machines. As a result the structural support only has to bear the mass of the machine.

A comparison with a conventional PM rotary machine topology shows that the new topology rotary machine mass is reduced by over 55% for a 100 kW machine. In comparison to other air-cored PM machine topologies the PM material in the new topology will be minimised, which will have a positive impact on cost. A modular construction is employed in both the rotor and the stator, so that large scale production is possible.

A major benefit of this topology is that assembly is made simple and straightforward because the attractive force between rotor and stator has been removed.

NGenTec Limited is a spinout company from Institute for Energy Systems, in the School of Engineering at the University of Edinburgh. Dr Markus Mueller and Dr Alasdair Mc Donald developed our proprietary C-GEN technology and are both founders and directors. C-GEN technology was developed with funding from Scottish Enterprise under the Proof of Concept programme.

The key to the C-GEN technology is the elimination of undesirable magnetic forces, which brings with it benefits in ease of manufacture, ease of assembly, and a significant savings in cost and mass.

We presently have a 20kW prototype working in the laboratory at the University of Edinburgh and a 15kW prototype running on a wind turbine in the TUV NEL test site in the West of Scotland.

Derek Shepherd is the Founder, Chairman and acting CEO. Until he retired from Aggreko Plc he was Managing Director of Aggreko International and a main board Director of Aggreko plc for 11 years, where he built a $1bn business. The other founder and director is Dr Derek Douglas CBE who is a serial entrepreneur.

The Company is presently raising its first round of funding of £4 million. This will enable us to develop, manufacture and build a 1 MW modular unit over the next 12 months. This 1MW modular unit will be specifically designed to form part of a 6MW generator we plan to manufacture and test the following year.

Discover the Benefits of our Innovative Multi-MW Generator Technology – C-GEN

Welcome to NGenTec: we are developers of multi-MW direct drive permanent magnet generators and providers of specialist electro-mechanical engineering services for the power engineering sector. We pride ourselves in providing our clients with generator solutions that are customised and optimised for their specific needs.

C-GEN generator technology provides the following advantages over existing direct drive permanent magnet machines:

* Up to 50% Lighter
* More Scalable at Multi-MW Ratings
* Modular, leading to a robust and fault tolerant design
* Easier to Manufacture
* High efficiency over a broad range of wind speeds

Reduced costs associated with:
* Installation
* Transportation
* Turbine Structure
* Operation and Maintenance

We are developing our technology for use in multi-MW wind energy markets, in particular for the growing offshore wind market. C-GEN also has promising future application in both wave and tidal energy.