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Content archived on 2024-05-07

Development of a narrow band variable speed generator



The objective of this project is to make narrow bank variable speed operation an attractive commercial prospect. The proposed system will give advantages over existing fixed speed and variable speed wind turbine systems. The result will be a reduction in the cost of wind energy, an increase in reliability and an increase in the application and penetration to weak grid areas. The target cost of energy improvement relative to a fixed speed systems at a 7 m/s site is 10%


Narrow band systems of 30% or so range provide sufficient speed variation for noise reduction and for effective power limiting, drive train compliance and power factor control by separate control of active and reactive power. In addition, because only part of the power is being electronically converted, the losses are lower than in broad band systems, the equipment is cheaper and more compact and the harmonics generated on to the grid are low enough to be negligible. These systems have worked well enough in the past in prototype form but few have yet found their way into commercial application. This is because although the systems have most of the advantages of the broad band systems, they have had up until now one major disadvantage. The over-riding problem has been the maintenance and replacement requirements of the slip rings of doubly- fed generators. This has effectively discouraged their use and the application of Pulse Width Modulated systems for partial power conversion.

PWM systems are now capable of providing reliable, wide-range frequency conversion; however it is extravagant in cost and space terms to apply this to the entire output of the wind turbine. The double-fed generator is attractive because it provides the means of electronically converting part of the power, retaining the advantages of variable speed without the disadvantages.
Weier Electromotorenwerk, well known for the development of the variable slip generators mentioned above, has now proposed a non-contact, inductive method of power transfer which will remove the need for slip-rings in a doubly-fed asynchronous generator, this will give a narrow band variable speed system with the advantages of broad full power conversion, but without the disadvantages.


This project will demonstrate the technical feasibility of narrow band variable speed operation of a wind turbine at 600 kW without the need for slip rings. Apart from demonstrating the technical merits of such a system, the project will allow the commercial benefits of such a development to be evaluated. This will be a value both to WEG, as a wind turbine manufacturer and operator, and to Weier as a manufacturer of generators. It will be valuable in pointing out the likely trend of developments at larger size.
A 10% reduction in the price of electricity from these machines is expected compared with that from a fixed speed machine. At lower windspeeds, the rotor and generator will be operated at the lower end of the speed range, which will give both a higher efficiency and a lower noise level.

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Wind Energy Group Ltd
EU contribution
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Taywood House 345 Ruislip Road
UB1 2QX Southall
United Kingdom

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