Author Topic: Direct - Drive Wind Turbines  (Read 2782 times)

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Direct - Drive Wind Turbines
« on: November 23, 2011, 09:19:56 am »
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Author : Zoran Ivanovski Msc
International Journal of Scientific & Engineering Research Volume 2, Issue 10, October-2011
ISSN
2229-5518
Download Full Paper : PDF

1. Introduction
The objective of this paper is to identify suitable generator concepts for direct-drive wind turbines by reviewing direct-drive and geared generator systems. Usually, in literature, comparison of different generator systems is discussed with the criteria based on the energy yield, cost, and weight. Because direct-drive permanent-magnet machines are more superior in terms of the energy yield, reliability and maintenance problem, different promising permanent-magnet machines proposed in literature are also discussed to find suitable generator type. Finally, suitable concepts to overcome the disadvantages of direct-drive are suggested considering both electromagnetic and mechanical structure.

During the last two decades various wind turbine concepts have been developed and built to improve the power quality, to maximize the energy harnessed and to minimize the cost. Such turbine concepts can be classified with a view to the generator system rotational speed and power regulation. When considering the construction of the generator system, the turbines can be classified into the direct-drive and the geared concepts. When focusing on the generator type, the generator system can be classified into the permanent magnet machine and the electrically excited machine. The comparisons of different generator systems for wind turbines can be summarized as the following. The direct-drive generator system, especially direct-drive permanent magnet generator system, is more superior in terms of the energy yield, reliability, and maintenance problem. The geared generator system has the advantages in terms of the cost, size, and weight. The geared drive system has been mostly used on the market of wind turbines, even though the direct-drive system is superior in performance as discussed above. In 2004 world market share of the direct-drive generator system has been around 20%, which is a sum of the share of both direct-drive electrically excited machines as 15% and direct-drive permanent magnet machines as 5%. Considering the current market status, it is expected that to make the direct-drive concept attractive compared to the geared concept will be the most important issue.

According to the review of different generator systems in literature and on the market, it can be expected that the direct-drive PM generator system with both light construction and low cost could be the most suitable system. Consequently that generator system could be defined as the most suitable generator concept with the maximum energy yield and the minimum cost.
 
2. Comparison od Direct Drive and Geared Generator Systems

Different direct-drive and geared generator systems of the wind turbines have been discussed by a number of authors.

According to the comparison of different direct-drive and geared generator systems discussed in literature, the features of the systems can be summarized as the following.

   Considering the energy yield and reliability, the direct-drive generator systems seem to be more powerful compared to geared drive systems, especially for offshore.

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