DETERMINING A WIND SPEED VALUE

Abstract

Provided is a method of determining a value of a wind speed, the method including: measuring a first value of the wind speed using a first wind speed sensor; measuring at least one second value of the wind speed using at least one second wind speed sensor; estimating a third value of the wind speed based on at least one operational parameter of a wind turbine having a rotating rotor at which rotor blades are connected and having a generator coupled to the rotor; determining a fourth value of the wind speed by taking into account the first value and the at least one second value weighted based on the third value.

Claims

1. A method of determining a value of a wind speed, the method comprising: measuring a first value of the wind speed using a first wind speed sensor; measuring at least one second value of the wind speed using at least one second wind speed sensor; estimating a third value of the wind speed based on at least one operational parameter of a wind turbine having a rotating rotor at which rotor blades are connected and having a generator coupled to the rotor; determining a fourth value of the wind speed by taking into account the first value and the at least one second value weighted based on the third value.

2. The method according to claim 1, wherein the fourth value is determined to be between the first value.

3. The method according to claim 1, wherein the fourth value is obtained as a sum of the first value multiplied with a first weight and the second value multiplied by a second weight, further wherein the first weight and the second weight depend on a first difference between the first value and the third value and on a second difference between the second value and the third value.

4. The method according to claim 3, wherein the first weight and the second weight are different.

5. The method according to claim 3, wherein the first weight is the larger the smaller the first difference is, further wherein the second weight is the larger the smaller the second difference is.

6. The method according to claim 3, wherein the first weight is larger than the second weight, if the first difference is smaller than the second difference, wherein the second weight is larger than the first weight, if the second difference is smaller than the first difference.

7. The method according to claim 1, wherein the first value, the second value, the third value and the fourth value are determined as varying values, over time.

8. The method according to claim 1, wherein the first weight and the second weight vary over time, further wherein during a first time interval the first weight is larger than the second weight, and during a second time interval the second weight is larger than the first weight.

9. The method according to claim 1, wherein the first wind speed sensor and the at least one second wind speed sensor are installed at a nacelle of the wind turbine and are configured as anemometer.

10. The method according to claim 1, wherein, if the first difference is larger than a threshold, at least over a predetermined time interval, the first value is disregarded and/or the first wind speed sensor is recognized as faulty, further wherein, if the second difference is larger than a threshold at least over a predetermined time interval, the second value is disregarded and/or the second wind speed sensor is recognized as faulty.

11. The method according to claim 1, wherein the at least one operational parameter comprises at least one of: an output power of the wind turbine; an output voltage of the wind turbine; an output current of the wind turbine; a rotational speed of the rotor of the wind turbine; a pitch angle of a rotor blade of the wind turbine; a setting of a converter connected to a generator of the wind turbine;

12. An arrangement for determining a value of a wind speed, the arrangement comprising: a first wind speed sensor configured to measure a first value of the wind speed; at least one second wind speed sensor configured to measure at least one second value of the wind speed; a processor configured to: estimate a third value of the wind speed based on at least one operational parameter of a wind turbine having a rotating rotor at which rotor blades are connected and having a generator coupled to the rotor, and determine a fourth value of the wind speed by taking into account the first value and the at least one second value weighted based on the third value.

13. A wind turbine comprising: a rotor at which plural rotor blades are connected; a generator coupled to the rotor; the arrangement according to claim 12; and a controller configured to control the wind turbine based on the fourth value of the wind speed.

Description

BRIEF DESCRIPTION

[0048] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0049] FIG. 1 schematically illustrates a wind turbine according to an embodiment of the present invention including an arrangement for determining a value of a wind speed according to an embodiment of the present invention;

[0050] FIG. 2 illustrates a graph of wind speed measurements and an estimation employed in embodiments according to the present invention;

[0051] FIG. 3 illustrates a graph depicting a weighting for determining a wind speed employed in embodiments according to the present invention;

[0052] FIG. 4 illustrates a graph of measured and estimated free wind speed as determined according to embodiments of the present invention;

[0053] FIG. 5 illustrates a graph indicating a wind speed measurement weighting as employed in embodiments of the present invention;

[0054] FIG. 6 illustrates a graph of values of wind speed as determined according to embodiments of the present invention; and

[0055] FIG. 7 illustrates a comparison of differently determined wind speeds as considered in embodiments of the present invention.

DETAILED DESCRIPTION

[0056] The illustration in the drawings is in schematic form.

[0057] The wind turbine 1 schematically illustrated in FIG. 1 comprises a rotor 3 with a hub 29 at which plural rotor blades 5 are connected. The wind turbine 1 according to an embodiment of the present invention further includes a generator 7 which is coupled to the rotor 3. The generator provides (e.g. via a converter) output power 8. The wind turbine 1 further comprises an arrangement 9 for determining a value of a wind speed according to an embodiment of the present invention and further comprises a controller 11 which is adapted to control the wind turbine 1 based on the determined value 12 of the wind speed.

[0058] The arrangement 9 thereby comprises a first wind speed sensor 13 which is adapted to measure a first value of the wind speed which is supplied as a first signal 15 to a processor 17 also included in the arrangement 9. The arrangement 9 further comprises a second wind speed sensor 19 which is adapted to measure at least one second value of a wind speed which is supplied using a second signal 21 to the processor 17. Further, the arrangement 9 comprises the processor 17 which is adapted to estimate a third value of the wind speed based on at least one operational parameter of the wind speed which is represented by an operational signal 23 supplied to the processor 17.

[0059] The processor 17 is further adapted to determine a fourth value 12 of the wind speed by taking into account the first value (represented by the signal 15) and the at least one second value (represented by the signal 21) weighted based on the third value representing the estimated wind speed based on the at least one operational parameter (represented by the signal 23). The fourth value 12 is supplied to the controller 11.

[0060] The wind turbine further comprises a wind turbine tower 25 on top of which a nacelle 27 is mounted which harbours the rotor 3, the generator 7, the processor 17, and the controller 11. The first and the second wind speed sensors 13 and 19 are attached and arranged at the nacelle 27, in particular at an outer wall of the nacelle 27. The rotor blades 5 are connected to a hub 29 which in turn is coupled to the rotor 3.

[0061] The arrangement 9 for determining the value of the wind speed is adapted to carry out a method of determining a value of a wind speed according to an embodiment of the present invention.

[0062] Thereby, the free wind speed is estimated based on the operational data and the estimate is then used to assess the quality of each nacelle anemometer measurement, i.e. the measurements of the first and the second wind speed sensor 13, 19, respectively. In particular, a first value of the wind speed as measured by the first wind speed sensor 13 and a second value of a wind speed as measured by the wind speed sensor 19 are weighted based on the quality measure, i.e. based on the third value of the wind speed which is obtained by estimating the wind speed based on the at least one operational parameter. This approach may secure that the measured wind speed is based on nacelle anemometer and thus fulfilling all requirements to a valid wind speed measurement source. At the same time, the measured wind speed may be biased towards the free wind speed as estimated by the turbine operational data and thus may be more accurate and reliable.

[0063] Different embodiments of the present invention may employ different kinds of weightings. According to a particular embodiment, the following formulas are used to determine the weights w.sub.1 and w.sub.2:

[00001]$w_1=\frac{{\left(\frac{k_1+.Math.v_{\mathrm{free}}-v_2.Math.}{k_1+.Math.v_{\mathrm{free}}-v_1.Math.}\right)}^{k_2}}{{\left(\frac{k_1+.Math.v_{\mathrm{free}}-v_2.Math.}{k_1+.Math.v_{\mathrm{free}}-v_1.Math.}\right)}^{k_2}+{\left(\frac{k_1+.Math.v_{\mathrm{free}}-v_1.Math.}{k_1+.Math.v_{\mathrm{free}}-v_2.Math.}\right)}^{k_2}}$$w_2=\frac{{\left(\frac{k_1+.Math.v_{\mathrm{free}}-v_1.Math.}{k_1+.Math.v_{\mathrm{free}}-v_2.Math.}\right)}^{k_2}}{{\left(\frac{k_1+.Math.v_{\mathrm{free}}-v_2.Math.}{k_1+.Math.v_{\mathrm{free}}-v_1.Math.}\right)}^{k_2}+{\left(\frac{k_1+.Math.v_{\mathrm{free}}-v_1.Math.}{k_1+.Math.v_{\mathrm{free}}-v_2.Math.}\right)}^{k_2}}$

[0064] Thereby, v.sub.1 represents the first value of the wind speed as measured by the first wind speed sensor 13 and v.sub.2 represents the second value of the wind speed as determined by the at least one second wind speed sensor 19. v.sub.free represents the third value of the wind speed (as estimated from the operational parameters of the wind turbine). k.sub.1 and k.sub.2 represent adjustable parameters.

[0065] Applying a weighting, such as the above depicted weighting, may provide a flexible and robust weighting of the nacelle measurements which may secure a combined wind speed measurement biased towards the free wind speed estimated by the operational data. This approach may also serve as a continuous fault handling as a faulty sensor (e.g. ice on sensor) may automatically be disregarded.

[0066] FIG. 2 and FIG. 3 illustrate an example of a utilization of the method for determining a value of the wind speed according to an embodiment of the present invention. On the abscissas 31, the time is indicated and on the ordinate 33 of the coordinate system of FIG. 2, the wind speed is indicated, while on the ordinate 35 of the coordinate system of FIG. 3, the respective sensor weight is indicated. The first value of the wind speed (obtained by the first wind speed sensor 13) is indicated by a curve 37, the second value of the wind speed (as measured by the second wind speed sensor 19) is indicated by the curve 39 and the third value of the wind speed (as estimated by the processor 17 based on operational wind turbine data) is indicated as a curve 41.

[0067] The third value 41 of the wind speed (as estimated from operational parameters of the wind turbine) may be estimated in many different ways. For example, an available power estimator (APE) as used in some conventional wind turbines may be employed. However, other embodiments also support many other methods, for example simple comparison between produced power and power curve or data from a meteorological mass. An idea of embodiments of the invention may be that some sources other than the nacelle anemometer are used to estimate the free wind speed. For example, the processor may access the internet and from there meteorological data regarding pressure distribution, wind speed, precipitation and the like to estimate the wind speed at the location of the wind turbine. How to assess the quality of each nacelle anemometer measurement and to translate that quality measure into a weighting may be done in many different ways. The embodiments are not bound to a specific implementation or formula but rather that some weighting depending on an estimated free wind speed is used.

[0068] It should be noticed that the first anemometer measurement in FIG. 2 is closest to the estimated free wind speed at lower wind speeds in a time interval 32, while the second anemometer measurement is closest to the estimated free wind speed at higher wind speeds in time interval 34.

[0069] The curve 43 in FIG. 3 indicates the first weight with which the first value of the wind speed is weighted and the curve 45 indicates the second weight, i.e. the weight with which the second value of the wind speed is weighted. It should be noticed that in the time period 32, where the first value of the wind speed is closest to the estimated wind speed, the first weight (curve 43) is higher than the second weight (curve 45), while in a time period 34 in which the second value of the wind speed is closest to the estimated wind speed, the second weight is greater than the first weight.

[0070] FIGS. 4 and 5 illustrate a portion of the plots illustrated in FIGS. 2 and 3, respectively, wherein again the abscissas 31 denote the time, while the ordinate 33 denotes the wind speed and the ordinate 35 denotes the respective sensor weight. As can be appreciated from FIG. 5, the first weight 43 and the second weight 45 vary with time. The fourth value of the wind speed is then calculated by determining a weighted mean of the first value 37 and the second value 39 weighted with the first weight 43 and the second weight 45, respectively.

[0071] FIG. 6 thereby shows in a coordinate system having an abscissa 31 indicating time and having an ordinate 35 indicating the wind speed as a curve 47 a simple mean, as a curve 49 the third value of the wind speed (as estimated from the operational parameters) and as a curve 51 a fourth value of the wind speed as is determined according to embodiments of the present invention as a weighted mean of the first value 37 and the second value 39 of the wind speed weighted by the first weight 43 and second weight 45. The combined measurement is closer to the estimated free wind speed if embodiments of the invention are used than if a simple mean is used.

[0072] FIG. 7 shows a graph having an ordinate 53 indicating the estimated free wind speed and having an ordinate 55 indicating the measured wind speed. The linear curve 57 represents a simple mean of the measurements of the first and the second wind speed sensors 13, 19 the data points 59 indicate the weighted mean as determined according to embodiments of the present invention. The dots 59 are the data points, e.g. 1-second value, 10-second value, or something similar, to which a line is fitted. In particular, FIG. 7 shows that the anemometer measurements are not consistent with the estimated free wind speed. However, using embodiments of the present invention some of that error may be compensated.

[0073] According to an embodiment of the present invention, the free wind speed estimation which is obtained from turbine operational is used to assess the quality of each nacelle anemometer measurement. The assessed quality is then used to discriminate the weighting of the nacelle anemometer measurements. Thereby, a number of advantages may be achieved: [0074] A more correct determination of the wind speed for the turbine shutdown in high-speed may be achieved. [0075] A more robust and accurate wind speed measurement may be determined in general. [0076] A continuous compensation of badly calibrated nacelle anemometers may be achieved and a continuous fault handling of faulty nacelle anemometers may be achieved.

[0077] 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 intention.

[0078] 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. The mention of a unit or a module does not preclude the use of more than one unit or module.