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Title:
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Extreme Turbulence Control for Wind Turbines
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Author(s):
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Published by:
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Publication date:
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ECN
Wind Energy
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27-2-2017
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ECN report number:
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Document type:
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ECN-E--16-062
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ECN publication
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Number of pages:
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Full text:
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30
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Download PDF
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Abstract:
The components of a wind turbine are designed to ensure that they can withstand the (fague and extreme) loads during their lifeme. To this end, the loads are analyzed using simulations under a large set of design conditions. These design conditions include normal operation, but also operation under extreme conditions such as extreme wind gusts and direction changes as well as internal and external failures. The wind turbine control system has e?ect on the loads for many of these design conditions, and speci?c control algorithms have been developed in the past to actively reduce fague and ultimate loads, o?ering bene?ts in terms of lighter designs (material cost savings), applications to higher wind turbine classes (larger market), increase of rotor size, etc. Currently, control algorithms exist for reduction of fague loads during normal operation, and extreme loads during extreme wind gusts and some failures (loss of electric
network, blade failures).
One of the most demanding design condition, however, is operation under extreme turbulence conditions. For many turbines’ this is a design driving load case, as is the case with the InnWind 10MW RTW wind turbine. To present, reduction of loads during extreme turbulence using the wind turbine controller has not been considered explicitly. In this report, an extreme turbulence control algorithm is developed to actively reduce the ultimate loads during operation in extreme turbulence conditions.
The bene?ts of the algorithm are demonstrated in two test cases: with the InnWind 10MW and InnWind 20MW reference wind turbines. Besides the di?erent sizes, these turbine models also di?er in the wind turbine class for which they are designed (class 1A for the 10MW model vs 1C for the 20MW model). This allows to get a better understanding of the potential bene?ts from ECT. To improve the ultimate load reduction capabilities, some small power production loss during normal operation (around 0.5%) is considered acceptable in the ETC design. Then ETC is optimized to minimize the ultimate loads on tower and blades in the range of wind speeds where these are highest. For the InnWind 10MW model, the highest loads occur at high wind conditions (above 19 m/s), so that by increasing the ETC sensitivity at these winds has relatively small effect on the power production. Due to this fact, a substantial reduction of ultimate loads on tower and shaft were achieved of well above 20%. These bene?ts are, however, less pronounced for the InnWind 20MW model. Due to the much lower turbulence class, extreme turbulence conditions are, in an absolute sense, more di?cult to di?erentiate from normal turbulence conditions. Moreover, the highest ultimate loads on the tower and blades no longer occur around cutout wind speeds, but rather at, and just above, rated wind speeds. This signi?cantly complicates the ETC design because power dips there have higher contribution to the power loss on yearly basis than for higher wind speeds. This fact is re?ected in the ?nal results achieved with ETC on the InnWind 20MW model, which show a reduction of ulmate loads on tower and blades by just a few percent. However, the shaft loads are well reduced with ETC and because these are highest at cutout wind speeds, even further reduction should be possible by optimizing the ETC for higher winds speeds.
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