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Research Papers

Increased Power Capture by Rotor Speed–Dependent Yaw Control of Wind Turbines

[+] Author and Article Information
Knud A. Kragh

Department of Wind Energy,
Technical University of Denmark,
Roskilde, 4000, Denmark
e-mail: knkr@dtu.dk

Paul A. Fleming

Engineer
e-mail: Paul.fleming@nrel.gov

Andrew K. Scholbrock

Engineer National Renewable Energy Laboratory,
Golden, CO 80401

Contributed by the Solar Energy Division of ASME for publication in the Journal of Solar Energy Engineering. Manuscript received April 23, 2012; final manuscript received December 20, 2012; published online June 11, 2013. Assoc. Editor: Christian Masson.

J. Sol. Energy Eng 135(3), 031018 (Jun 11, 2013) (7 pages) Paper No: SOL-12-1107; doi: 10.1115/1.4023971 History: Received April 23, 2012; Revised December 20, 2012

When extracting energy from the wind using upwind, horizontal-axis wind turbines, a primary condition for ensuring maximum power yield is the ability to align the rotor axis with the dominating wind direction. Attempts have been made to improve the yaw alignment of wind turbines by applying advanced measurement technologies, such as light detection and ranging systems. However, application of advanced measurement equipment is associated with additional costs and increased system complexity. This study is focused on assessing the current performance of an operating turbine and exploring how the yaw alignment can be improved using measurements from the existing standard measurements system. By analyzing data from a case turbine and a corresponding meteorological mast, a correction scheme for the original yaw control system is suggested. The correction scheme is applied to the case turbine and tested. Results show that, with the correction scheme in place, the yaw alignment of the case turbine is improved and the yaw error is reduced to the vicinity of zero degrees. As a result of the improved yaw alignment, an increased power capture is observed for below-rated wind speeds.

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Figures

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Fig. 1

Wind rose for the CART3 test site. The circles indicate the probability in percent of each wind direction. The predominant wind direction is 292 degrees. The operating cone of the turbine spans from 230 degrees to 360 degrees.

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Fig. 2

CART3 turbine at the NWTC, (NREL Pix no. 18279). The met mast is located approximately 85 m upwind of the turbine in the 290 degrees direction.

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Fig. 3

Schematic of the CART3 yaw controller with rotor speed–dependent correction (---)

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Fig. 4

Observed differences between the nacelle and met mast wind direction measurements as a function of rotor speed. All measurements have been binned in rotor speed bins with a width of 0.5 rpm. x, binned observations; ---, trend line.

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Fig. 5

Amount of data available within each rotor speed bin for the uncorrected yaw controller (black) and the corrected yaw controller (white)

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Fig. 6

Amount of data available within each wind speed bin for the uncorrected yaw controller (black) and the corrected yaw controller (white)

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Fig. 7

Median turbulence intensities of the 1-minute segments, binned in bins with a width of 1 m/s for the original yaw controller (---) and the corrected yaw controller (—). The whiskers indicate the standard deviation of the turbulence intensities in each bin. Narrow whiskers are for the corrected controller; wide whiskers are for the uncorrected controller.

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Fig. 8

Medians of the binned 1-minute average yaw errors of the original yaw controller (---) and the updated yaw controller (—). Bin widths of 1 rpm. The whiskers indicate the standard deviation of the 1-min average yaw errors in each bin. The standard deviation is estimated using the median absolute deviation to decrease the influence of outliers. Narrow whiskers are for the corrected controller; wide whiskers are for the uncorrected controller. Solid squares indicate that the value of the corrected controller is significantly lower than the corresponding value of the uncorrected controller—at a level of significance of 95% using the t-distribution.

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Fig. 9

Medians of the binned 1-minute average yaw errors of the original yaw controller (---) and the updated yaw controller (—). Bin widths of 1 m/s. The whiskers indicate the standard deviation of the 1-min average yaw errors in each bin. The standard deviation is estimated using the median absolute deviation to decrease the influence of outliers. Narrow whiskers are for the corrected controller; wide whiskers are for the uncorrected controller. Solid squares indicate that the value of the corrected controller is significantly lower than the corresponding value of the uncorrected controller—at a level of significance of 95% using the t-distribution.

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Fig. 10

Theoretical median power loss of the uncorrected system compared to the corrected system in percent, assuming that the power loss caused by the yaw error is proportional to cos3(θE)

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Fig. 11

Medians of the 1-minute average power output in bins with a width of 1 m/s for the original yaw controller (---) and the updated yaw controller (—). The whiskers indicate the standard deviation of the 1-min average yaw errors in each bin. The standard deviation is estimated using the median absolute deviation to decrease the influence of outliers. Narrow whiskers are for the corrected controller; wide whiskers are for the uncorrected controller. Solid squares indicate that the value of the corrected controller is significantly higher than the corresponding value of the uncorrected controller—at a level of significance of 95% using the t-distribution.

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Fig. 12

Observed median power loss of the uncorrected system compared to the corrected system (in percent)

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Fig. 13

Median and standard deviation of the 1-Hz damage equivalent blade root bending loads (flap-wise) in bins with a width of 1 m/s for the original yaw controller (---) and the updated yaw controller (—). The whiskers indicate the standard deviation of the 1-min average yaw errors in each bin. The standard deviation is estimated using the median absolute deviation to decrease the influence of outliers. Narrow whiskers are for the corrected controller; wide whiskers are for the uncorrected controller. Solid squares indicate that the value of the corrected controller is significantly higher than the corresponding value of the uncorrected controller—at a level of significance of 95% using the t-distribution.

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