Control of a wind turbine having adjustable rotor blades

Abstract

A method for controlling a wind turbine having rotor blades with an adjustable blade angle, comprising the steps operating the wind turbine in a partial load mode for wind velocities up to a nominal wind velocity, wherein in the partial load mode, a fixed partial load angle is provided for the blade angle, operating the wind turbine in a full load mode for wind velocities above the nominal wind velocity, wherein in the full load mode the blade angle is enlarged with increasing wind velocity and has values above the partial load angle, and wherein in the partial load mode, starting from a predetermined operating state, the blade angle is reduced as compared with the partial load angle.

Claims

1. A method for controlling a wind turbine having rotor blades with adjustable blade angles, the method comprising: operating the wind turbine in a partial load mode for wind velocities up to a nominal wind velocity, wherein in the partial load mode: a first partial load angle is provided for the adjustable blade angle, and starting from a predetermined operating state, the adjustable blade angle is reduced as compared with the first partial load angle, and operating the wind turbine in a full load mode for wind velocities above the nominal wind velocity, wherein in the full load mode the adjustable blade angle is enlarged with increasing wind velocity and has values above the first partial load angle, wherein in the partial load mode, a power is set as a function of the rotational speed of a rotor of the wind turbine, and, starting from at least one of a predetermined rotational speed and a predetermined power, the adjustable blade angle is adjusted as compared with the first partial load angle, and wherein the adjustable blade angle is reset to the first partial load angle before the full load mode is reached, wherein sensors are provided to detect torsion of at least one of the rotor blades about its longitudinal axis, wherein the detected torsion is used as a criterion for adjusting the adjustable blade angle, and wherein the adjustable blade angle is adjusted to have a sharper rise as a value of the detected torsion increases.

2. The method as claimed in claim 1, wherein in the partial load mode, the adjustable blade angle is adjusted as compared with the first partial load angle as a function of torsion of the rotor blades about the blade longitudinal axis, a blade loading, or both.

3. The method as claimed in claim 2, wherein the adjustable blade angle is adjusted as the rotational speed rises or as the power rises as a function of the rotational speed or the power.

4. The method as claimed in claim 1, wherein the adjustable blade angle is reduced so highly as compared with the first partial load angle that the blade angle assumes a negative value.

5. The method as claimed in claim 1, wherein, as the wind velocity increases, the adjustable blade angle in the partial load mode initially has the first partial load angle in a lower range, in the partial load mode is reduced as compared with the first partial load angle in an upper range, and in the full load mode, is increased as compared with the first partial load angle.

6. The method as claimed in claim 5, wherein in the partial load mode, following the upper range, a third range is provided, wherein the third range follows the full load mode in that the adjustable blade angle is increased at least as far as the first partial load angle.

7. The method as claimed in claim 5, wherein the upper range in the partial load mode, the adjustable blade angle is reduced as a function of: the power, the rotational speed of the rotor of the wind turbine with a predetermined gradient, or a predetermined relationship of the power or rotational speed.

8. The method as claimed in claim 1, wherein in the partial load mode, the adjustable blade angle is adjusted as compared with the first partial load angle as a function of at least one property of the air.

9. The method as claimed in claim 8, wherein in the partial load mode, the adjustable blade angle is adjusted as compared with the first partial load angle as a function of the air density or of a wind gust.

10. The method as claimed in claim 1, wherein the wind turbine has a plurality of rotor blades, and each rotor blade is configured to be adjusted individually.

11. The method as claimed in claim 10, wherein the wind turbine has three rotor blades.

12. The method as claimed in claim 10, wherein each rotor blade is configured to be adjusted cyclically in rotation such that the individual blade angle or a blade angle set point comprises a basic angle that is the same for all the rotor blades and an additional angle provided individually for each rotor blade.

13. The method as claimed in claim 1, wherein a minimum blade angle is provided, wherein the minimum blade angle is smaller than the first partial load angle, and wherein the adjustable blade angle for each rotor blade is configured to be individually adjusted to the minimum blade angle.

14. A wind turbine, configured to perform a method as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) In the following, the invention will be explained in more detail by way of example by using exemplary embodiments and with reference to the accompanying figures.

(2) FIG. 1 shows a wind turbine in a perspective view.

(3) FIG. 2 explains, schematically, possible variations in the blade angle.

(4) FIG. 3 explains, schematically, possible power curves.

(5) FIG. 4 shows, schematically, profiles of a rotor blade in order to explain possible torsion.

DETAILED DESCRIPTION

(6) FIG. 1 shows a wind turbine 100 having a tower 2 and a nacelle 104. Arranged on the nacelle 104 is a rotor 106 having three rotor blades 108 and a propeller hub 110. The rotor 106 is set moving rotationally by the wind during operation and, as a result, drives a generator in the nacelle 104.

(7) FIGS. 2 and 3 explain possible variations in the blade angle and the power P as a function of the wind velocity V.sub.W. Both FIGS. 2 and 3 show on their abscissa the wind velocity V.sub.W, and the abscissa are the same for both FIGS. 2 and 3. To this extent, the illustration of the power P in FIG. 3 should also be assigned to the corresponding blade angles in FIG. 2, this association being only schematic and not qualitative.

(8) In FIG. 2, a basic curve 2 for the blade angle is shown by the dashed line. In addition, an improved curve 4 relating to the blade angle is illustrated by a continuous line. The improved curve 4 coincides with the basic curve 2 in many sections, and these two curves are shown at a slight distance merely for reasons of improved illustration. An alternative curve 6 is illustrated by a dotted line, and this alternative curve 6 otherwise corresponds to the improved curve 4 of the blade angle .

(9) Starting from the basic curve 2, the wind turbine starts at a switch-on wind velocity V.sub.E with an initially first set partial load angle .sub.T. As the wind rises, this angle is maintained up to the nominal wind velocity V.sub.N. When the nominal wind velocity V.sub.N is reached, the blade is then rotated out of the wind, namely gradually as the wind velocity rises further, and this means that the blade angle is accordingly increased little by little. Merely by way of example, the feathered position is shown as .sub.F as the last value for the angle.

(10) This basic curve 2 thus exhibits a constant blade angle with the value of the partial load angle .sub.t in the partial load mode T and then a rising value for the full load operation V. For completeness, a sharper rise of the blade angle for the storm range S is shown, thus the blade angle is increased more sharply after a limiting wind velocity V.sub.G has been reached, until it finally reaches a feathered position, that is to say the angle .sub.F, at a shut-down wind velocity V.sub.A. It is of no consequence here that this happens exactly at the shut-down wind velocity V.sub.A and whether the feathered position is then actually reached, as FIG. 2 shows.

(11) As an improved curve 4, the curve illustrated by the continuous line is now proposed. For this purpose, for improved clarity but also as orientation for the control which has to implement the same, the partial load mode T is subdivided into three sections I, II and III. Here, the section I designates a lower range of the partial load mode, the section II designates an upper range of the partial load mode, and section III finally designates a third range of the partial load mode which, based on the wind velocity, is located above the upper range II. These sections can also be designated synonymously as ranges. At the end of the third range III, which lies at the nominal wind velocity V.sub.N, the full load mode V begins.

(12) In the lower range I, the improved curve 4 coincides with the basic curve 2. At the start of the upper range II, it is then assumed that the wind load is so high that the blade twists significantly and accordingly is counteracted by a reduction in the blade angle . The blade angle in this embodiment then decreases linearly with increasing wind velocity V.sub.W This reduction goes so far that the blade angle becomes negative. It then reaches a predefined minimum blade angle .sub.min, which here accordingly has a negative value, and thus the blade angle is then not reduced further and thus maintains this negative value as far as the end of the upper range II of the partial load mode.

(13) At the end of the upper range of the partial load mode T, the blade angle is then increased again, specifically linearly in the example as the wind rises as far as the partial load angle .sub.T, which is reached when the wind velocity V.sub.W reaches nominal wind velocity V.sub.N. Accordingly, in this embodiment, a linear rise in the blade angle up to the partial load angle is proposed in this third range III of the partial load mode.

(14) When the nominal wind velocity V.sub.N is reached, the blade angle of the improved curve 4 thus has the partial load angle .sub.T again and, at that point, the characteristic course of the basic curve 2 is again reached. The further course of the improved curve 4 can then correspond to the further course of the basic curve 2, which is accordingly illustrated in FIG. 2.

(15) As an alternative curve 6 to the improved curve 4, a deviation in the transition range from the partial load mode T to the full load mode V is proposed. Accordingly, as indicated by the dotted characteristic curve 6, the blade angle is already increased toward the end of the partial load mode, here specifically toward the end also of the third range of the partial load mode, such that it exceeds the value of the partial load angle before the nominal wind velocity V.sub.N is reached. In this way, a lower loading can be achieved in this critical transition region. In this regard, it must be noted that the loading of the blades can be the greatest at the nominal wind velocity. This is because, at the nominal wind velocity, a quite strong wind is already present, but the rotor blades are usually not yet rotated out of the wind, not even partially. The blades therefore offer the greatest angle of attack there. This can be improved by the proposed alternative curve 6. This improved curve 6 then opens into the basic curve 2 and/or into the improved curve 4 at a somewhat higher wind velocity.

(16) FIG. 3 shows, at least schematically, a possible power curve which is associated with the respective curves of the blade angles according to FIG. 2.

(17) In FIG. 3, the basic curve 32 is also illustrated dashed, and an improved curve 34 is plotted with a continuous line. In addition, an alternative curve 36 is shown as a dotted characteristic curve in FIG. 3. These three curves 32, 34 and 36 thus correspond to the curves 2, 4 and 6 of the blade angle according to FIG. 2, with the difference that the power is illustrated here. Differing from FIG. 2, in relation to the basic curve 32 and the improved curve 34, the basic curve 32 is shown only if it differs from the improved curve 34.

(18) It can thus in principle be seen for the basic curve 32 and the improved curve 34 that the power is connected at the start-up wind velocity V.sub.E and has a low value. The power then rises continuously but always more sharply until, at the end of the partial load mode T, it has reached its nominal value P.sub.N at the nominal wind velocity V.sub.N. This nominal value is then maintained for the full load mode V and, starting at the limiting wind velocity V.sub.G, is reduced and, toward the end of the storm range S, reaches a low value, which can also be zero, at the shut-down wind velocity V.sub.A.

(19) FIG. 3 now shows that the basic curve 32 deviates at the start of the upper range II of the partial load mode T, specifically has a somewhat lower power. Initially, however, it can be seen that this deviation begins at a power value P.sub.1. This power value P.sub.1 can thus serve as a predetermined power, starting from which the reduction in the blade angle, which is shown in relation to the improved curve 4 in FIG. 2, begins.

(20) Once the power curve of the improved curve 34 reaches the second predetermined power value P.sub.2, this can be evaluated as information or used as a basis that the end of the upper range II of the partial load mode has been reached and the blade angle should be increased again, as illustrated in FIG. 2. Accordingly, in the third range III of the partial load mode T, the blade angle is increased again and reaches the partial load angle .sub.T at nominal wind velocity. Accordingly, the basic curve 32 and the improved curve 34 then also coincide with regard to the power P produced.

(21) It can be seen from this FIG. 3 that, as a result of the proposed reduction in the blade angle, the power yield can sometimes also be increased. However, it can also be seen that advantages in the course of the power can also additionally result here. In particular toward the end of the partial load mode T, the rise in the power is very sharp. This means that small changes in the wind velocity can lead to large changes in the power. In the practical implementation, this can mean that small changes in the rotational speed can lead to sharp changes in the power. This can throw up control problems, and the proposed reduction and then increase again in the blade angle can lead to a not quite so steep rise in the power P in this range, even according to practically chosen values.

(22) The alternative curve 36 for the power P shows in FIG. 3 that, in the transition range from partial load mode T to full load mode V, the power can be reduced somewhat as compared with the improved curve 34 and also as compared with the basic curve 32. For this purpose, however, in this specific range the loading of the blades is reduced, and also the rise of the power P can be reduced again in this range, which may be advantageous for the implementation of the control.

(23) FIG. 4 now basically shows two profiles 42 and 44 of a rotor blade 40. The first profile 42 is in the vicinity of the blade root, and the second profile 44 is in the vicinity of the blade tip. Here, too, the profiles are also illustrated only schematically in their size. In relation to the second profile 44, a rest profile 44 is also shown dotted. The second profile 44 and the rest profile 44 are identical, with the difference that the second profile 44 is rotated as compared with the rest profile 44 because of torsion in the rotor blade 40. This is shown as torsion angle . As a reference alignment, for each of the profiles a skeleton line 46, 46 and 46* has approximately been used as a basis here.

(24) In any case, it can be gathered from FIG. 4 that in its rest position, that is to say when it is already finished in the factory, the rotor blade 40 has a rotational angle between the first 42 in the root region and the second profile 44 at the blade tip. To this extent, FIG. 4 shows an operating point at which the rotor blade 40 is in use and the wind has led to torsion, accordingly the second profile 44 is rotated by the torsion angle as compared with the rest profile 44, that is to say the second profile 44 in the rest position. The blade 40 is thus twisted and leads to this angular deviation according to . This situation can, for example, correspond to the stage at the end of the upper range II or at the start of the third range III of the partial load mode T, based on FIG. 2.

(25) FIG. 4 also illustrates to this extent that this torsion of the rotor blade by the wind loading leads to the rotor blade 40 being rotated somewhat more in the direction of the feathered position .sub.F, particularly in the region of its rotor blade tip. The rotation into the feathered position is an increase in the blade angle, and it is thus proposed to reduce the blade angle in order to counteract this. This reduction direction is shown as .sub.v in FIG. 4 with a corresponding arrow for illustration. The length of this arrow .sub.v is not important here.

(26) By means of the proposed method, effects as a result of the blade torsion during operation, which is illustrated in FIG. 4, can thus be counteracted. This counteraction is illustrated in particular by the improved curve 4 of the blade angle according to FIG. 2, and the power curves in principle resulting therefrom can in this respect be gathered from FIG. 3.