METHOD AND ARRANGEMENT FOR PERFORMING A WIND DIRECTION MEASUREMENT

Abstract

Provided is a method for performing a wind direction measurement for a wind turbine, the method including: measuring plural sample pairs, each pair including a measured relative wind direction and an associated performance quantity, the measured relative wind direction representing a measurement result of measuring a difference angle between a real wind direction and an orientation of a measurement equipment, in particular a direction orthogonal to a rotor blade plane, the performance quantity indicating a performance of the wind turbine; evaluating a degree of asymmetry of the performance quantity with respect to a measured relative wind direction equal to zero; measuring a further relative wind direction; and correcting the further measured relative wind direction based on the degree of asymmetry.

Claims

1. A method for performing a wind direction measurement for a wind turbine, the method comprising: measuring a plurality of sample pairs, each sample pair of the plurality of sample pairs including a measured relative wind direction and an associated performance quantity, the measured relative wind direction representing a measurement result of measuring a difference angle between a real wind direction and an orientation of a measurement equipment, the performance quantity indicating a performance of the wind turbine; evaluating a degree of asymmetry of the performance quantity with respect to a measured relative wind direction equal to zero; measuring a further relative wind direction; and correcting the further measured relative wind direction based on the degree of asymmetry.

2. The method according to claim 1, further comprising: defining a bin vector, each component including a range of wind direction angles; defining an average performance vector, each component being an average of the performance quantity comprised in the plurality of sample pairs, for which the measured relative wind direction lies within the range of angles defined by the corresponding component of the bin vector; defining a count vector, each component comprising the plurality of sample pairs, that lie within the respective range of angles defined by the corresponding component of the bin vector; and utilizing the bin vector, the average performance vector, and the count vector for evaluating the degree of asymmetry.

3. The method according to claim 1, wherein the evaluating the degree of asymmetry further comprises: fitting a straight line on a curve defined by the plurality of sample pairs or pairs of measured relative wind direction and performance quantity as defined by the bin vector, the average performance vector, and the count vector; and determining a slope of the straight line, wherein the correcting the further measured relative wind direction based on the degree of asymmetry comprises: subtracting from the further measured relative wind direction a modification value based on the slope of the straight line.

4. The method according to claim 3, wherein the modification value is proportional to the slope of the straight line, wherein a proportionality factor is non-negative.

5. The method according to claim 1, wherein the evaluating the degree of asymmetry comprises: determining a maximum location being that measured relative wind direction or that range of angles for which the associated performance quantity or averaged performance quantity is maximal or maximized; wherein the correcting the further measured relative wind direction based on the degree of asymmetry comprises: subtracting from the further measured relative wind direction a modification value proportional to the maximum location, wherein a proportionality factor is larger than zero.

6. The method according to claim 1, wherein the evaluating the degree of asymmetry comprises: averaging the performance quantity or the averaged performance quantity for which the associated measured relative wind direction or the angle range is larger than zero, to obtain a first average performance quantity; averaging the performance quantity or the averaged performance quantity for which the associated measured relative wind direction or the angle range is smaller than zero, to obtain a second average performance quantity; and determining which of the first average performance quantity or the second average performance quantity is larger; wherein the correcting the further measured relative wind direction based on the degree of asymmetry comprises: determining a modification value that: is positive, if the first average performance quantity is larger than the second average performance quantity, and is negative, if the first average performance quantity is larger than the second average performance quantity; and subtracting the modification value from the further measured relative wind direction.

7. The method according to claim 3, further comprising: while measuring the plurality of sample pairs, determining at least one operational and/or environmental parameter; and storing the modification value in association of with the at least one operational and/or environmental parameter.

8. The method according to claim 7, further comprising: determining the operational and/or environmental parameter; and subtracting a value proportional to the modification value associated to the determined operational and/or environmental parameter to obtain the corrected measured relative wind direction.

9. The method according to claim 8, wherein a proportionality factor is selected to convert the degree of asymmetry or the modification value to an angle offset.

10. The method according to claim 1, wherein the method is continuously performed during normal operation, wherein the method is performed irrespective whether a wind direction and/or a wind speed and/or a yaw position changes or not.

11. The method according to claim 1, wherein the performance quantity is or comprises at least one of: an effective wind speed, representing a measure of the effective wind speed experienced by the wind turbine effective for energy production, the measure being a component of the effective wind speed in a direction orthogonal to a rotor blade plane, an active power, produced by the wind turbine, applied in a low wind range and a medium wind ranges; a pitch angle applied at a high wind speed; and an increase in rotor speed applied at a low wind speed.

12. The method according to claim 11, wherein the effective wind speed is estimated using a wind turbine model, taking into account actual power produced, actual rotor speed, and/or actual pitch angle.

13. An arrangement for performing a wind direction measurement for a wind turbine, wherein the arrangement is adapted to receive a plurality of measured sample pairs, each sample pair of the plurality of sample pairs including a measured relative wind direction and an associated performance quantity, the measured relative wind direction representing a measurement result of measuring a difference angle between a real wind direction and an orientation of a measurement equipment, the performance quantity indicating a performance of the wind turbine to: evaluate a degree of asymmetry of the performance quantity with respect to a measured relative wind direction equal to zero; receive a further measured relative wind direction; and correct the further measured relative wind direction based on the degree of asymmetry.

14. A wind turbine, comprising: a rotor having a plurality of rotor blades connected thereto and rotatable in a rotor blade plane; an arrangement for performing a wind direction measurement for the wind turbine according to the claim 13; and a yawing system for directing the rotor blade plane based on measured relative wind directions obtained by the arrangement for performing the wind direction measurement; further comprising at least one of a wind direction measuring device: a wind vane; a sonic wind direction measuring device for measuring the plural samples of the relative wind direction.

15. The method according to claim 1, wherein the orientation of the measurement equipment is a direction orthogonal to a rotor blade plane.

16. The method according to claim 7, wherein the at least one operational and/or environmental parameter is a wind speed.

17. The arrangement according to claim 1, wherein the orientation of the measurement equipment is a direction orthogonal to a rotor blade plane.

Description

BRIEF DESCRIPTION

[0050] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0051] FIG. 1 schematically illustrates a wind turbine according to an embodiment of the present invention in a top view including an arrangement for calibrating and/or performing a wind direction measurement according to an embodiment of the present invention;

[0052] FIG. 2 illustrates in a schematic view of the effective wind vector as used as a performance parameter according to an embodiment of the present invention;

[0053] FIG. 3 illustrates a flow-chart of a method for performing a wind direction measurement according to an embodiment of the present invention; and

[0054] FIG. 4 illustrates a graph as considered according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0055] FIG. 1 illustrates, in a top view, a schematic representation of a wind turbine 1 according to an embodiment of the present invention including an arrangement 3 for calibrating and/or performing a wind direction measurement according to an embodiment of the present invention. Thereby, the arrangement 3 is adapted to perform a method for calibrating and/or performing a wind direction measurement for the wind turbine 1 according to an embodiment of the present invention.

[0056] The wind turbine 1 includes a rotor 3 including a rotor shaft 5, a rotor hub 7 and plural rotor blades 9 connected to the rotor hub 7. The rotor blades 9 rotate in a rotor blade plane 11 which is orthogonal to the rotation axis 13 of the rotor shaft 5. For measuring plural samples of the relative wind direction, the wind turbine 1 comprises an wind direction measuring device 15 which is installed at or on the nacelle 17. The nacelle 17 supports the rotor shaft 5 and further includes a not illustrated electrical generator mechanically coupled to the rotor shaft 5 and further comprises a not illustrated converter and wind turbine transformer. The nacelle direction is defined by the direction of the rotor axis 13.

[0057] The real wind direction 19 includes, in projection onto the surface of the earth at the location of the wind turbine 1, a difference angle α with the nacelle direction 13, i.e. the direction of the rotation axis 13. The angle α defines the relative wind direction, i.e. the direction of the wind 19 relative to the nacelle direction 13.

[0058] The wind direction measuring device 15 is provided for measuring the relative wind direction α. However, due to adjustment errors, measurement errors, or systematic errors of the wind direction measuring device 15, the wind direction measuring device measures an erroneous angle α′ instead of the real relative wind direction α. The arrangement 3 is provided for calibrating/correcting the erroneous measured relative wind direction α′ (and thus for performing a wind direction measurement) in order to derive a corrected measured relative wind direction α″ which should reflect to a higher accuracy the real relative wind direction α. The corrected measured relative wind direction α″ is provided to a yaw controller 21 which is adapted to control a yawing system 23 which allows to turn the rotor plane 11, in particular including the nacelle 17, around a vertical rotation axis 25, as is illustrated by the curved arrow 27, in order to direct the rotor plane 11 such as facing the wind 19, i.e. such that the rotor axis 13 aligns with the wind direction 19. In this situation, the difference angle α is 0.

[0059] According to an embodiment of the present invention, the wind direction measuring device 15 measures plural sample pairs each including a relative wind direction and a (associated) performance quantity as describe below.

[0060] Therefore, the wind direction measuring device 15 measures plural samples of a relative wind direction representing a difference angle α between a real wind direction 19 and an orientation 14 of a measurement equipment, in particular a direction 13 orthogonal to a rotor blade plane 11, to obtain plural measured relative wind directions α′.

[0061] The method performed by the arrangement 3 further comprises to measure plural samples of a performance parameter indicating a performance of the wind turbine 1. The performance parameter may for example be the effective wind speed which will be explained with reference to FIG. 2. The effective wind vector 41 can be considered to be the component of the real wind direction 19 parallel to the nacelle direction 13 (corresponding to the rotor axis of the rotor shaft 5). The effective wind vector 41 may be calculated using a turbine model and taking into account actual power production, actual rotor speed and actual pitch angle.

[0062] The plural samples of the performance parameter are indicated as a signal 43 which is also supplied to the arrangement 3 (illustrated in FIG. 1) which receives the plural measured samples of the relative wind direction α′. In FIG. 1, the performance parameter 43 is estimated and output by a performance estimator 42 which receives as input not illustrated operational parameters of the wind turbine, in particular relating to electrical and/or mechanical performance of the wind turbine 1.

[0063] The arrangement 3 is adapted to evaluate a degree of asymmetry of the performance quantity with respect of a vanishing measured relative wind direction. When further plural samples of the relative wind direction are measured, the arrangement 3 outputs the corrected measured relative wind directions α″ which are corrected based on the based on the degree of asymmetry.

[0064] An example of an algorithm according to an embodiment of the present invention which is performed by the arrangement 3 is illustrated in FIG. 3 as a flow-chart 45. According to the flow-chart 45, a weather station or in particular wind direction measuring device 15 (for example the wind direction measuring device 15 illustrated in the wind turbine 1 illustrated in FIG. 1) performs plural measurements (as a function of time) of a relative wind direction and outputs the measured relative wind direction α′ and supplies it to a data processor 47.

[0065] Further, a performance estimator 42 estimates a performance quantity 51 and supplies it to the data processor 47. The measured relative wind direction α′ is also denoted x and the performance quantity 51 is also denoted y in the following. The data processor 47 forms, from plural sample pairs (x, y) a bin vector xd, each component comprising a range of angles. The data processor 47 further forms an average performance vector yd, each component being an average of the performance quantity y comprised in the sample pairs (x, y), for which the measured relative wind direction x lies within the range of angles defined by the corresponding component of the bin vector xd. The data processor 47 further constructs a count vector nd, each component comprising the number of sample pairs (x, y), that lie within the respective range of angles defined by the corresponding component of the bin vector xd.

[0066] The bin vector xd may for example comprise components each having a width of 1°. One component may for example define a range [−15°, −14°], another may define a range [−14°, 13°], . . . and a last range may be defined by [+14°, 15°]. One component may for example define a range [−15°, −14°[, another may define a range [−14°, 13°[, . . . and a last range may be defined by [+14°, 15°[. One component may for example define a range ]−15°, −14°], another may define a range ]−14°, 13°], . . . and a last range may be defined by ]+14°, 15°]. Other range widths are possible and also other limits of the overall range are possible. In other embodiments the components of the bin vector may for example define centers of ranges having a constant width.

[0067] For each bin, the accumulated average performance quantity y is stored in the average performance vector yd.

[0068] The bin vector xd, the average performance vector yd, and the count vector nd are supplied to a performance evaluator 53 which is adapted to evaluate a degree of a symmetry of the performance quantity with respect to a vanishing measured relative wind direction α′, i.e. the measured relative wind direction is zero. The evaluation performed by the performance evaluator 53 may be implemented in a number of different ways. However, in each case, the performance evaluator 53 outputs a modification value 55 which is denoted 55a, 55b, or 55c for the different ways of the evaluation.

[0069] According to a first evaluation algorithm (denoted a)), the data (xd, yd, nd) is approximated by a straight line as is illustrated in FIG. 4, the straight line being labelled with reference sign 57. Thereby, FIG. 4 illustrates a graph having an abscissa 59 indicating the relative wind direction α′ or xd and having an ordinate 61 indicating the effective wind speed as one example of a performance measure. In FIG. 4, the data points 63 are the binned raw data, i.e. the binned plural sample pairs, each comprising a measured relative wind direction and an associated performance quantity. Thereby, the measured relative wind direction is divided in bins having a width of 1° and starting e.g. from −15° and ending at 15°. Before plotting the data points 63, the effective wind speed at the measured relative wind direction of 0° has been subtracted such that the curve 65 connecting the data points 63 represents a normalized curve.

[0070] As can be appreciated from FIG. 2, the curve 65 (connecting the data points 63) is asymmetric with respect to the measured relative wind direction of 0°. It is obvious from the graph 65 that the effective wind speed (as one example of a performance quantity) is generally higher for a measured relative wind direction larger than 0° than for measured relative wind direction smaller than 0°.

[0071] The degree of asymmetry may be evaluated in a number of different ways by the performance evaluator 53 illustrated in FIG. 3.

[0072] According to the evaluation algorithm a), the data (xd, yd, nd) is approximated by the straight line 57, as illustrated in FIG. 4. The slope of the line 57 (positive or negative) indicates where the performance is superior. For a negative slope, the performance is superior for relative wind directions less than 0°. For a positive slope, the performance is superior for relative wind directions larger than 0°. Based on the sign of the slope of the straight line 57, the performance evaluator 53 outputs the modification value 55a associated to this evaluation algorithm. The modification value is supplied to the wind direction modifier 67 which outputs a wind direction offset which is either increased or decreased by the modification value 55a. The modification can be applied with a fixed step side or may be based on a change that is a function of the slope of the straight line 57 (for example a steeper slope may indicate a higher certainty).

[0073] According to an evaluation algorithm b), the relative wind direction sample with highest performance is considered. Thereby, the data (xd, yd) may directly indicate which relative measured wind direction maximizes the performance quantity. In the example data set illustrated in FIG. 4 it is obvious that yd is maximized for xd=5°, being the maximum location 58. Hence, it is expected that the performance is improved for a relative wind direction of 5° (which is relative to the current reading of the wind turbine, which may already be compensated by a wind direction offset). For this evaluation algorithm, the performance evaluator 53 outputs the modification value 55b and supplies it to the wind direction modifier 67 which, based thereon, determines a wind direction offset 69. The wind direction offset may be added to the measured relative wind direction or may be subtracted from the relative wind direction as originally measured by the wind direction measuring device 15.

[0074] According to an evaluation algorithm c), the relative wind direction modification direction is considered. This algorithm is somehow similar to the evaluation algorithm a) (“slope”). Herein, the binned performance quantity, yd, is averaged for binned relative measured wind directions smaller than 0° (xd<0°) and averaged for binned relative measured wind directions larger than 0° (xd>0°), respectively. The higher average value indicates the direction which the wind direction should change to maximize the performance quantity. A positive output is provided, if the average of yd at (xd>0°) is superior. A negative output is provided, if the average of yd at (xd<0°) is superior. Accordingly, the performance evaluator 53 outputs a modification value 55c and provides it to the wind direction modifier 67 which uses this value 55c to derive a wind direction offset 69.

[0075] The values 55a, 55b, 55c may be considered as a modification value as used herein. Alternatively, the wind direction offset 69 may be identified as the modification value used herein.

[0076] It should be noted that the performance evaluator may only output one of the different modification values, i.e. either 55a, 55b or 55c. In other embodiments, two or more of the different modification values 55a, 55b, 55c may be combined, for example averaged and the average may be provided to the wind direction modifier 67.

[0077] The wind direction offset 69 may, in particular embodiments, be binned according to some sorting parameter, for example the wind speed. Thereby, a wind direction measurement calibration/correction that takes the wind speed into account can be achieved.

[0078] Embodiments of the present invention may thereby provide reliable wind direction measurement equipment which may allow to remove yaw errors, increase turbine power production significantly, decrease turbine load, and align turbines.

[0079] According to embodiments of the present invention, the change in the wind direction and the change of some performance parameter are continuously expressed. Further, the correlation, or any other value related to the correlation, between changes in the wind direction and changes in the performance parameter are continuously estimated. Further, continuously, a small gain directly proportional the estimated correlation is subtracted from the wind direction as measured by the wind direction measuring device. Further, the wind direction measurement is modified with the wind direction modification derived from the correlation value. Embodiments of the present invention may increase the turbine power production significantly and/or may decrease turbine loads.

[0080] As has been mentioned earlier, the performance parameter could comprise or be many different quantities. It is suggested to use the effective wind speed, but other quantities like produced power, rotor speed, pitch angle, or some quantity expression the turbine loads could also be used. In fact, any parameter related to the nacelle yaw position (relative to the wind direction) could potentially be used.

[0081] As has also be mentioned above, the wind direction modification may be a single number applied under all (wind) conditions at all time, but in other embodiments it could also be any kind of transfer function expression how the wind direction should be modified depending on one or more parameters, for example the wind speed.

[0082] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0083] For the sake of clarity, it is to be understood that the use of ‘a’ or ‘an’ throughout this application does not exclude a plurality, and ‘comprising’ does not exclude other steps or elements.