Method for controlling a wind turbine and wind turbine

Abstract

A method for controlling a wind turbine and an associated wind turbine. The wind turbine is operated according to an operating point, wherein the operating point is determined at least by a pitch angle and a tip speed ratio, wherein one of the operating points corresponds to a maximum power coefficient, wherein, in a partial load range, the wind turbine is operated at an operating point which differs from the operating point with the maximum power coefficient. The distance of the operating point from the operating point with the maximum power coefficient is set in accordance with a measured turbulence measure.

Claims

1. A method for controlling a wind turbine, comprising: operating the wind turbine according to a first operating point, wherein the first operating point is determined at least by a pitch angle and a tip speed ratio, wherein the first operating point corresponds to a maximum power coefficient, and in a partial load range, operating the wind turbine at a second operating point which differs from the first operating point with the maximum power coefficient, wherein a distance of the second operating point from the first operating point with the maximum power coefficient is set in accordance with a measured turbulence measure and with a degree of rotor blade soiling.

2. The method as claimed in claim 1, wherein the measured turbulence measure comprises a turbulence intensity.

3. The method as claimed in claim 1, wherein a higher measured turbulence measure corresponds to a higher distance of the second operating point from the first operating point with the maximum power coefficient.

4. The method as claimed in claim 1, wherein at least one of a pitch angle or a tip speed ratio of the second operating point is increased with respect to the first operating point with the maximum power coefficient.

5. The method as claimed in claim 4, wherein the tip speed ratio of the second operating point is controlled by controlling rotational speed, torque, or both.

6. The method as claimed in claim 1, wherein the maximum power coefficient improves when a gust of wind occurs.

7. The method as claimed in claim 1, wherein the turbulence measure is measured in real time.

8. The method as claimed in claim 7, wherein 15-second mean values of the turbulence measure are made available in real time.

9. The method according to claim 1, further comprising controlling the wind turbine in accordance with a measured wind shear.

10. The method as claimed in claim 9, wherein the wind turbine is controlled in accordance with the measured wind shear and the measured turbulence measure taking into account a time of day.

11. The method as claimed in claim 1, wherein the turbulence measure is measured with spatial resolution over a rotor of the wind turbine.

12. The method as claimed in claim 1, wherein the second operating point is set taking into account acoustic boundary conditions.

13. A wind turbine, wherein the wind turbine is a pitch-controlled wind turbine with a variable rotational speed, the wind turbine comprising: a turbulence sensor configured to measure a turbulence measure; and a controller configured to control the wind turbine, wherein the controller is configured to operate the wind turbine according to an operating point, wherein the operating point is determined at least by a pitch angle and a tip speed ratio, wherein a first operating point corresponds to a maximum power coefficient, wherein, in a partial load range, the controller is configured to operate the wind turbine at a second operating point which differs from the first operating point with the maximum power coefficient, wherein the controller is configured to set a distance of the second operating point from the first operating point with the maximum power coefficient in accordance with the turbulence measure which is measured by the turbulence sensor, and wherein the controller is further configured to set the distance of the second operating point from the first operating point with the maximum power coefficient is set in accordance with a degree of rotor blade soiling.

14. The wind turbine as claimed in claim 13, wherein the turbulence sensor is configured to measure a turbulence intensity.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention will be explained in more detail below on the basis of embodiments by way of example with reference to the accompanying figures.

(2) FIG. 1 shows a wind turbine in a schematic illustration.

(3) FIG. 2a shows a schematic view of the profile between the tip speed ratio λ and wind speed v.

(4) FIG. 2b shows a schematic view of the profile between the pitch angle γ and the wind speed v.

(5) FIG. 3 shows a schematic view of the profile between the power coefficient c.sub.p and tip speed ratio λ at a constant pitch angle γ.

(6) FIG. 4 shows a schematic view of various power coefficient profiles as a function of a turbulence measure.

(7) FIG. 5a shows a schematic view of the profile between the tip speed ratio λ and wind speed v in the case of a rising turbulence measure.

(8) FIG. 5b shows a schematic view of the profile between the pitch angle γ and the wind speed v in the case of a rising turbulence measure.

(9) FIG. 6a shows a schematic view of the influence of blade soiling in the case of low incoming flow turbulence.

(10) FIG. 6b shows a schematic view of the influence of blade soiling in the case of relatively high inflowing turbulence.

DETAILED DESCRIPTION

(11) FIG. 1 shows a wind turbine 100 with a tower 102 and a nacelle 104. A rotor 106 with three rotor blades 108 and a spinner 110 is arranged on the nacelle 104. During operation, the rotor 106 is set in a rotational motion by the wind and, as a result, drives a generator in the nacelle 104.

(12) The wind turbine 100 has a measuring system which is suitable for determining a measure of the inflowing turbulence in real time and for correspondingly adjusting the wind turbine 100 in real time according to the measured values.

(13) The wind turbine 100 is configured to adapt the operating point in the partial load range 200, that is to say to select the tip speed ratio and the pitch angle in the partial load range 200, as a function of the turbulence intensity of the incoming flow. In the following, the turbulence intensity Ti defined above is described by way of example as a turbulence measure, wherein, of course, this constitutes only an example and other variables which permit definitive information to be obtained about the extent of the turbulence of the incoming flow are likewise also conceivable.

(14) In FIG. 4, profiles of the power coefficient c.sub.p plotted against the tip speed ratio λ are shown for three different turbulence intensities Ti.sub.1, Ti.sub.2 and Ti.sub.3, said profiles each corresponding to a different value of the pitch angle γ.sub.1, γ.sub.2 and γ.sub.3. However, it is essential that different tip speed ratios λ with a maximum power coefficient c.sub.p 411, 412 and 413 are obtained for each of the profiles with different turbulence intensities. The operating point at which the wind turbine 100 is operated at the different turbulence intensities Ti.sub.1, Ti.sub.2 and Ti.sub.3 is the operating point 421, 422 and 423 which are each operated a tip speed ratio λ which is higher, by a difference Δλ.sub.1, Δλ.sub.2, Δλ.sub.3, than the tip speed ratio which is associated with the maximum power coefficient.

(15) The selection of the distance or of the difference from the operating point with the maximum power coefficient, in this example Δλ.sub.1, Δλ.sub.2, Δλ.sub.3 is in accordance with the measured turbulence measure and not constant. In this example, Ti.sub.1<Ti.sub.2<Ti.sub.3 and correspondingly Δλ.sub.1<Δλ.sub.2<Δλ.sub.3. In other words, the difference from the operating point with the maximum power coefficient is greater, the greater the measured turbulence measure.

(16) Three effects which play a significant role in the selection of the adapted operating point are described below with reference to FIG. 4.

(17) Firstly, the distance of the operating point from the optimum of the power coefficient Δλ will therefore already be a function of the turbulence intensity, since, if no inflowing turbulence were present at all, the operating point could be positioned directly at the optimum, that is to say Δλ=0, since then there would be no variation in the tip speed ratio λ.

(18) Secondly, it is to be borne in mind that the optimum of the power coefficient of the rotor blade basically shifts toward relatively high tip speed ratios and pitch angles under the influence of the inflowing turbulence. This is expressed in FIG. 4 by the fact that the points with the maximum power coefficient c.sub.p 411, 412 and 413 shift to the right as the turbulence intensity Ti increases.

(19) Thirdly, when the turbulence intensities Ti are very high, it may be the case that flow separation can also occur in the partial load range 200, since the effective attitude angles increase as a result of the reduction of the tip speed ratios λ. This flow separation gives rise to a considerable decrease in performance, which therefore has to be avoided. This is in turn achieved by raising the pitch angle and/or the tip speed ratio.

(20) All of the described effects lead to a situation in which adaptation of the tip speed ratio and of the pitch angle in the partial load range is performed in accordance with the turbulence intensity, determined in real time, of the incoming flow, preferably in such a way that, in the case of partial load with increasing turbulence intensity, the tip speed ratio λ and/or the pitch angle γ adapted, in particular rises as can be seen particularly well in FIGS. 5a and 5b. This is indicated in FIGS. 5a and 5b by the upwardly directed arrow in the partial load range 200, while in the full load range 210 there is no adaptation dependent on the determined turbulence measure.

(21) FIGS. 6a and 6b show the profiles of the power coefficient plotted against the tip speed ratio schematically and by way of example for various respective pitch angles, wherein the values of a clean rotor blade are illustrated by unbroken lines and those of a soiled rotor blade by dashed lines. FIG. 6a shows the profiles for low turbulence intensity, while, in contrast with this, the profiles for relatively high turbulence intensity are shown in FIG. 6b.

(22) It can be seen that, of course, the maximum power coefficients for soiled blades lie clearly below the values for non-soiled rotor blades irrespective of the turbulence intensity.

(23) However, it has been shown that the distance between the tip speed ratios at which the power optimum is reached for a clean rotor blade and for a soiled rotor blade depends on the turbulence intensity. While this distance tends to be large in the case of low turbulence intensity, cf., FIG. 6a, it is significantly lower in the case of relatively high turbulence intensity, cf., FIG. 6b. It has also been shown that the power optimum migrates toward relatively high tip speed ratios and pitch angles as the inflowing turbulence increases. All of these realizations, in particular including the rotor blade soiling, are preferably used by the wind turbine 100 for the purpose of adjustment, in order to achieve optimum operation of the system.