METHOD FOR IDENTIFYING AN EXTREME LOAD ON A WIND POWER INSTALLATION

Abstract

The invention relates to a method for identifying an asymmetrical extreme load which is caused by a gust of wind and acts on a wind power installation, wherein the wind power installation has a rotor having at least three rotor blades; the rotor blades are adjustable in terms of the blade angle thereof; and the rotor by way of the rotor blades thereof sweeps a rotor field; and the method comprises continuous detecting of a blade load for each rotor blade; ascertaining for at least one sector of the rotor field at least one temporal sector load profile from blade loads detected of different rotor blades with the same azimuth position, said sector load profile describing a temporal profile of a load on the rotor blades in the sector and containing a profile extrapolated for a future temporal period, wherein the blade loads are detected or taken into account at successive detection time points which are spaced apart by a partial period in which the rotor rotates further by one rotor blade, so that successive blade loads are detected or taken into account for the respective sector; and checking in terms of expecting an extreme load as a function of the at least one sector load profile.

Claims

1. A method comprising: identifying an asymmetrical extreme load caused by a gust of wind and acting on a wind power installation, wherein the wind power installation comprises: a rotor having at least three rotor blades; wherein the at least three rotor blades have adjustable blade angles; and wherein the rotor, by way of the at least three rotor blades, sweeps a rotor field; wherein the identifying comprises: continuously detecting blade loads for each rotor blade; ascertaining for at least one sector of the rotor field at least one temporal sector load profile from blade loads detected of different rotor blades of the at least three rotor blades with the same azimuth position, said sector load profile describing a temporal profile of a load on the respective rotor blade in the sector and containing a profile extrapolated for a future temporal period, wherein: the blade loads are detected or taken into account at successive detection time points which are spaced apart by a partial period in which the rotor rotates further by one rotor blade, so that successive blade loads are detected or taken into account for the respective sector; and checking in terms of expecting an asymmetrical extreme load as a function of the at least one sector load profile.

2. The method as claimed in claim 1, wherein: the sector load profile is configured as a temporal polynomial function of a first or a higher order; and/or the asymmetrical extreme load expected is assumed when the sector load profile for a future time point reaches or exceeds a predetermined blade load limit.

3. The method as claimed in claim 1, wherein: the sector load profile is ascertained from at least two successive blade loads of a sector and at least one associated partial period; and the method further comprising checking whether the sector load profile for a next successive detection time point, which is to occur in the future, reaches or exceeds a predetermined blade load limit, respectively.

4. The method as claimed in claim 1, comprising: ascertaining a blade load to be expected by the sector load profile for a successive detection time point to be checked; detecting the current blade load at the successive detection time point to be checked and comparing the current blade load with the blade load to be expected so as to ascertain an expectation variance; and adapting the sector load profile as a function of the ascertained expectation variance.

5. The method as claimed in claim 1, wherein the blade loads of a first rotor blade of the at least three rotor blades are detected as blade flexing or blade bending moment in a region of a blade root of the first rotor blade.

6. The method as claimed in claim 1, wherein: a plurality of sectors of the rotor field are observed for extreme loads; the blade loads for each observed sector are detected at the successive detection time points, so that successive blade loads are detected for each sector and at least one change in the blade loads of the respective sector is ascertained therefrom; and a conclusion pertaining to a change to be expected in the blade loads of a second sector is drawn from the at least one change in the blade loads of a first sector such that: the sector load profile of the second sector is adapted as a function of the sector load profile of the first sector; and/or a first sector load profile is determined for the first sector, and a second sector load profile is determined for the second sector; a first expectation variance is ascertained for the first sector load profile; and the second sector load profile is adapted as a function of the first expectation variance.

7. The method as claimed in claim 1 comprising: determining an extreme load time point at which an extreme load is expected to arise, and determining the extreme load time point from the at least one sector load profile.

8. The method as claimed in claim 1, wherein: the blade angles of the at least three rotor blades are adjustable in a mutually independent manner; and/or the respective blade angle of the respective rotor blade of the at least three rotor blades is taken into account for determining a sector load profile for each blade load detected.

9. The method as claimed in claim 8, wherein each blade load detected as a function of the associated blade angle is converted into an equivalent blade load which corresponds to a blade load at a predetermined reference blade angle.

10. The method as claimed in claim 1, wherein each blade load detected as a function of the associated blade angle is converted into a local wind value.

11. The method as claimed in claim 10, wherein the wind field is established from the wind values of at least some of the sectors; and/or wherein each sector load profile is converted into a wind profile in the sector so that each wind profile contains a profile extrapolated for a future temporal period, and wherein a wind field profile is established from the wind profiles of some or all sectors.

12. The method as claimed in claim 1, wherein when identifying the extreme load to be expected an installation operation in at least one sector is changed so as to reduce or delimit a load on the wind power installation, wherein the installation operation is changed in that the blade angle of at least one of the at least three rotor blades is adjusted so as to reduce or delimit a blade load on the at least one rotor blade.

13. The method as claimed in claim 12, comprising: when an extreme load time point at which the extreme load is to be expected has been identified, the installation operation is changed before the extreme load time point is reached; and/or wherein a sector in which the extreme load is expected is identified, and the blade angle of a rotor blade is changed before said rotor blade reaches the sector for which the extreme load is expected; and/or wherein the blade angles of the at least three rotor blades are adjusted.

14. The method as claimed in claim 1, wherein: from the at least one ascertained sector load profile an adjustment angle for adjusting at least one rotor blade is determined; and/or a target time point until which the adjustment angle is to be adjusted is determined, and an adjustment speed is determined and predefined from the target time point and the adjustment angle; and/or a minimum blade angle to be adjusted is determined, wherein a blade angle of at least one rotor blade is not adjusted below said minimum blade angle.

15. The method as claimed in claim 14, comprising: controlling the wind power installation as a function of the asymmetrical extreme load.

16. A wind power installation, comprising: a rotor; at least three rotor blades coupled to the rotor, the at least three rotor blades having adjustable blade angles, wherein the rotor, by way of the at least three rotor blades, sweeps a rotor field, a sensor configured to continuously sense blade loads acting on each rotor blade of the at least three rotor blades; and a processor configured to receive the sensed loads and identify an asymmetrical extreme load caused by a gust of wind from the sensed loads; and control the wind power installation as a function of the identified asymmetrical extreme load, wherein identifying the asymmetrical extreme load comprises: ascertaining for at least one sector of the rotor field at least one temporal sector load profile from blade loads detected of different rotor blades of the at least three rotor blades with the same azimuth position, said sector load profile describing a temporal profile of a load on the respective rotor blade in the sector and containing a profile extrapolated for a future temporal period; wherein the blade loads are detected or taken into account at successive detection time points which are spaced apart by a partial period in which the rotor rotates further by one rotor blade, so that successive blade loads are detected or taken into account for the respective sector; and wherein checking in terms of expecting an asymmetrical extreme load as a function of the at least one sector load profile.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0083] The invention will be explained in more detail below in an exemplary manner by means of embodiments and with reference to the appended figures in which:

[0084] FIG. 1 shows a wind power installation in a perspective illustration;

[0085] FIG. 2 shows a temporal diagram for visualizing one aspect;

[0086] FIG. 3 shows a front view of a rotor field;

[0087] FIG. 4 shows a schematic lateral view of a wind power installation and thus also of a rotor field shown in FIG. 3;

[0088] FIGS. 5 and 6 each show a front view of a rotor field at different rotor positions; and

[0089] FIG. 7 shows a temporal diagram for visualizing an improvement of the prognosis.

DETAILED DESCRIPTION

[0090] FIG. 1 shows a schematic illustration of a wind power installation according to the invention. The wind power installation 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 having three rotor blades 108 and a spinner 110 is provided on the nacelle 104. The aerodynamic rotor 106 in the operation of the wind power installation is set in a rotating motion by the wind and thus also rotates an electrodynamic rotor of a generator which is coupled directly or indirectly to the aerodynamic rotor 106. The electric generator is disposed in the nacelle 104 and generates electric power. The pitch angles of the rotor blades 108 can be changed by pitch motors at the rotor blade roots 109 of the respective rotor blades 108.

[0091] The wind power installation 100 here has an electric generator 101 which is indicated in the nacelle 104. An electric output can be generated by means of the generator 101. An infeed unit 105, which can in particular be configured as an inverter, is provided for infeeding electric output. In this way, a three-phase feed current and/or a three-phase feed voltage can be generated according to amplitude, frequency and phase, in order to be fed to a mains connection point PCC. This may take place directly or else conjointly with further wind power installations in a wind farm. An installation controller 103 is provided for controlling the wind power installation 100 and also the infeed unit 105. The installation controller 103 may also receive parameter values from outside, in particular from a central farm computer.

[0092] FIG. 2 shows a temporal diagram in which for three rotor blades an exemplary load profile of an equivalent blade load is illustrated, the latter thus being converted into a reference angle, thus standardized. These load profiles, which synonymously may also be referred to as blade load profiles, are referred to as B1, B2 and B3 in FIG. 2, thus as load profiles for a first, second and third rotor blade.

[0093] Moreover plotted is a blade angle profile 202. The blade angles can be adjusted in a mutually independent manner, this forming the basis here too, but the variances between the blades are not relevant in terms of the general explanation according to FIG. 2 so that, for the sake of simplicity, only this single blade angle profile 202 is shown in this FIG. 2.

[0094] The temporal diagram on the abscissa thus shows the time in seconds, on the left ordinate shows the load in Kilonewton meters, and on the right ordinate shows the blade angle in degrees. The temporal zero point is chosen where a load profile would have reached a limit, specifically the permissible maximum value, had the blade angle not been changed. Plotted to this end is a non-optimal blade load profile B2′ which at t=0 reaches an extreme load value 204 and reflects a profile without blade angle adjustment.

[0095] Starting approximately 5 s (seconds) ahead of this zero point, the three load profiles B1-B3 are burdened with variations but increase in terms of the amplitude. Previously, said load profiles B1-B3 were burdened with similar variations but did not increase, this not being illustrated here. The variations in the load of these three load profiles B1-B3 can also be traced back to, inter alia, the fact that the rotor blades as a result of the rotation of the rotor sweep different regions in the rotor field and, as a result, are exposed to dissimilar wind loads. The loads can be lower in particular in the lower region and higher in the upper region. To be added to this, however, are wind variations or other variations in the wind field. Moreover, the profiles are illustrated in a simplified manner, because further comparatively minor variations are not relevant here.

[0096] The temporal diagram of FIG. 2 is based on an operation of the wind power installation in which the rotor rotates at approximately 20 rpm (rotations-per-minute). In this way, the rotor rotates further by one rotor blade in approximately 1 s. Approximately every 1 s, this results in a type of load peak for respectively alternating blades. The rotor blades in the process sweep a wind range from which a high load emanates. This will also be explained in particular hereunder in FIGS. 3 and 4.

[0097] Moreover, the extreme load value 204 in the temporal diagram according to FIG. 2 is plotted as a horizontal straight line. This load illustrated should ideally not be reached, at least not exceeded.

[0098] Proceeding from the initially weak load it can be seen that this load increases. In order to now prevent that the extreme load value 204 is reached, a corresponding check can be carried out. The loads illustrated can be detected, for example, by strain gauges at the blade root, or close to the blade root, respectively, and compared with a limit such as the extreme load value 204.

[0099] However, this has the disadvantage that such a detection and such a comparison takes place at a very late stage. Alternatively, a comparison with a reduced limit could be carried out so as to trigger a countermeasure, specifically a blade adjustment, at an earlier stage. However, this could lead to undesirable triggering when the extreme load value 204 is not reached at all, but such a reduced limit is achieved only once.

[0100] Instead it is proposed that the increase to be seen in FIG. 2 is evaluated so as to anticipate that the extreme load value 204 is reached as is to be expected.

[0101] Such a load increase can be identified, for example proceeding from the observation of only one blade load profile, for example of the first blade load profile B1.

[0102] To this end, an individual linear increase 206 by way of example is plotted as a solid straight line, the latter being configured fundamentally as a connection between the two maximum values of the first blade load profile B1. Such an individual linear load 206 however has the disadvantage that the latter may be inaccurate and/or requires at least one revolution of the rotor in order to be able to be recorded in the first place.

[0103] Proposed instead is a sector load profile 208 which therein is plotted as a long-dashed straight line. The sector load profile 208 here is configured as straight line and is determined from two values of the two blade load profiles B1 and B3. The two load values used to this end are plotted as the first and the second load value W1 and W2. This sector load profile 208 can be determined from these two values which in the example shown are only 1 second apart, and it can be seen that the load in the sector would very soon reach the maximum value.

[0104] This sector load profile 208 can be calculated at the moment at which the second load value W2 is reached, and it can be identified that the extreme load value 204 will soon be reached. At this time point, here thus one second prior to reaching the extreme load value 204, pitching is thus initiated. The blade angle of all blades is enlarged, the rotor blades thus being rotated out of the wind. The blade angle profile 202 shows this.

[0105] As a result of the blade angle, or the blade angles, respectively, being adjusted at an early stage, a moderate adjustment speed is possible, the latter here by way of example being 2° per second (2°/s). However, said adjustment speed may also be lower and be 1°/s, for example. In the example shown, the blade angle in the first second upon starting the adjustment has thus been changed by 2°. This already leads to the load profile B2 of the second blade no longer reaching the extreme load value 204. After two seconds, the blade angle is then adjusted by 4°, this leading to significant destressing. The blade angle can then also be, at least somewhat, reduced again. Solely for the purpose of visualization, said blade angle in the illustration of FIG. 2 as from 1 s assumes the constant value of 4°.

[0106] The following is proposed in particular. At the time point of triggering a blade adjustment, the momentary load on the blades, a pitch angle and the load to be expected are known, or can at least be estimated. On this basis, an angle can be predicted so that a resultant terminal angle is known. As a result, the pitch speed can be correspondingly predefined, and the deployment can take place slowly or rapidly, depending on the situation. The pitch speed, thus the speed at which the rotor blades are adjusted, can thus be predefined and controlled in a targeted manner.

[0107] Alternatively, this sector load profile 208 can also consider the load values of all three blade load profiles B1-B3, in that the blade load profile B2 is additionally considered as the third load value W3, for example. The sector load profile 208 in this instance would have a somewhat different profile. Said sector load profile 208 could likewise be a straight line, or else be configured as a curve of the second order, thus be described as a polynomial of the second order as a function of time.

[0108] The load values W1 to W3 can in each case be mean values of a plurality of measured values of the respective blade in the respective sector, for example. The sector load profile 208 does not have to be a tangent of the two blade load profiles B1 and B3, or of all three load profiles, respectively. However, the load values W1 to W3 are situated in the range of the maximum values of the blade load profiles, because this is where the sector with the maximum load lies. Sectors with a lower load are also examined but here do not lead to the blade adjustment being triggered. Therefore, the evaluation of said sectors with a lower load is not illustrated here.

[0109] The rotor field can be divided into 36 sectors of in each case 10°, to name one example, and in each of these 36 sectors such a sector load profile 208 is recorded, for example. In this instance, this also results in sector load profiles which may lie in the range of the lower values, for example, but then do not lead to a high load being identified.

[0110] In the example of 36 sectors, this thus results in 36 sector load profiles, and the most critical thereof is considered for minimizing the load, the most critical being the one with a tendency toward reaching the extreme load value 204. The sector load profile 208 is such a critical sector and is thus also situated approximately at the load peaks of the three blade load profiles B1-B3.

[0111] By using all rotor blades, thus the load values of all rotor blades of a respective sector, the sector load profile 208 can be constructed at an early stage so as to be a straight line based on two load values, thus on in each case one load value of two rotor blades, for example. However, it is also conceivable for a plurality of values, thus three values, for example, to be recorded, as has already been described above. As a result, it is still always possible for the blade load profile to be determined before the rotor has carried out a complete revolution. Nevertheless, three values are already present, the latter moreover also making it possible for the sector load profile 208 to be embodied not only as a straight line but also as a curve. When using three load values, a curve of the second order, thus able to be described by a polynomial of the second order, can be used. However, it is also conceivable for a straight line to be used nevertheless, said straight line being fundamentally overdetermined by evaluating three values, this however making it possible to compensate for inaccuracies in the values. The result can thus become more accurate.

[0112] It is also conceivable for even more values to be recorded. When four values are recorded, this then however requiring a revolution of the rotor, a straight line can continue to be used as the sector load profile 208, said straight line being even more overdetermined and inaccuracies thus being able to be better compensated for. However, it is also conceivable for a curve of the second order to be used, the latter still being overdetermined and inaccuracies thus being able to be compensated for. If required, it is of course also conceivable for a curve of an even higher order to be used.

[0113] The preferred variant is to reproduce sector load profiles by a curve of the first or the second order.

[0114] The evaluation of such a sector load profile 208 can take place in that it is checked whether the sector load profile 208 reaches the extreme load value 204 within a predetermined checking period T.sub.P. This checking period T.sub.P in FIG. 2 is approximately 2 s (seconds). However, the current value of the sector load profile, thus also the current load, has only just reached a reduced extreme load value 210. The detection is thus very early so that the measure, i.e., the adjustment of the rotor blades, leads to only the reduced extreme load value 210 being reached. This checking period T.sub.P can also be chosen as a function of the adjustment speed of the blade adjustment.

[0115] FIG. 3 shows a rotor field 320 in a front view, in which three rotor blades A-C are likewise schematically indicated. Moreover plotted is a wind event 322 which drives an extreme load, thus a gust of wind, for example. This wind event 322 is present in a specific region of the rotor field 320 and thus in a specific sector. The wind event 322 may also impact a plurality of sectors.

[0116] A rotor rotation 324 is likewise schematically indicated by a corresponding arrow. However, the position of the wind event 322 does not change as a result of the rotation of the rotor, and as a result every successive rotor blade will reach this wind event as long as the latter is present.

[0117] Illustrated in an exemplary manner in FIG. 3 are two sectors S1 and S2 which can in each case be represented by a mean angle φ.sub.x and φ.sub.y, respectively. The rotor blade B is currently situated in the sector S2. It can be detected how long one rotor blade or two rotor blades requires/require in order for this angle to be swept. A load increase speed can also be derived therefrom.

[0118] The situation in FIG. 3 is illustrated in a lateral view in FIG. 4. The wind event 322 in a simplifying manner is illustrated as a cylinder which moves in the direction toward the rotor field 320. This is indicated by the event movement 326. It can thus be seen that the wind event 322 arises only in a temporally limited manner. This is indicated by the period T.sub.E, the latter thus visualizing the timescale of the wind event driving the extreme load.

[0119] FIGS. 5 and 6 visualize how the load situation can be managed, in particular how a sector load profile can be recorded. To this end, a sector approximately in the 8 o'clock position is observed in an exemplary manner in FIG. 5. Likewise illustrated in FIG. 5 is thus a rotor field 520 which has three rotor blades A, B and C. The rotor blade C is at the 8 o'clock position. At the latter, a current load is recorded by corresponding strain gauges at the blade root, or close to the blade root, respectively, for example. Moreover recorded is a measurement angle α.sub.m; the measurement angle α.sub.m is the current blade angle of the rotor blade C. Said current blade angle can be measured, or else be read or put to further use, respectively, from the control data of the wind power installation.

[0120] A standardized load for a specific angular value thus results as a function of the rotor blade angle and the detected load. The blade angle of 0°, or a partial-load angle, can in particular be used as the reference value here. Here too, the rotor continues to rotate according to the rotor rotation 524, and one position later is visualized in FIG. 6.

[0121] In FIG. 6, the rotor blade B is thus at the 8 o'clock position, and the load on the blade and the blade angle, visualized by the measurement angle α.sub.m, is recorded again at this position. Here, the load standardized for a reference angle can be calculated, and this then results in two values from which a sector load profile can already be determined. As a result of the standardization, different blade positions can be calculated, as it is possible that a blade adjustment has been carried out during the rotation of the rotor blade B from the 4 o'clock position to the 8 o'clock position. It is also possible for the rotor blades B and C to have different blade angles. However, in order to be able to make a statement pertaining to the respectively observed sector, in particular pertaining to the load profile, based on values of different rotor blades, this standardization preferably takes place so as to relate to a reference angle.

[0122] The procedure explained in an exemplary manner in the context of the 8 o'clock position takes place in a similar manner and also substantially simultaneously for all sectors into which the rotor and thus the rotor field 520 have been divided. Of course, a load value cannot be recorded exactly simultaneously for all sectors, because the rotor blades can of course only always be present in one sector at the same time. The corresponding values can thus be recorded simultaneously for three sectors.

[0123] FIG. 7 shows a temporal diagram in which load measurements for two sectors are illustrated. The abscissa here shows a time axis and the ordinate shows a load which could, at least fundamentally, correspond to the left ordinate in FIG. 2. The improvement of prognosis is to be explained in principle in FIG. 7, so that specific load values are not plotted. FIG. 2 is very schematic also in other aspects. It is assumed here that, for just under one rotation, load values are in each case considered in two sectors.

[0124] Measurements in the sector S.sub.1 are illustrated by +, and measurements in the sector S.sub.2 by x. Accordingly, the first measurement for the first sector takes place at the time point t.sub.1, the next measurement for the second sector takes place at the time point t.sub.2. Another measurement in the first sector, specifically for the next blade, takes place at the time point t.sub.3, and for the second sector, likewise for this next blade, takes place at the time point t.sub.4. These measured values are identified as measured values M.sub.1-M.sub.4. In this way, a sector load profile, for example as a straight line, can be determined from the measured values M.sub.1 and M.sub.3 for the first sector. A load value for the time point t.sub.5 can be predicted therefrom, said load value being plotted as P.sub.5 in the diagram. A circle has been chosen as the symbol so as to highlight that this is not a measurement but a prognosis. A prognosis value P.sub.6 for the second sector has likewise been determined for the time point t.sub.6, specifically from the measured values M.sub.2 and M.sub.4.

[0125] Now, a further measurement M.sub.5 is carried out at the time point t.sub.5, and it is established for said further measurement M.sub.5 that the latter lies above the prognosis value P.sub.5. It can thus be derived that the wind speed increases, as opposed to the prognosis. This information can also be used for the second sector S.sub.2. It can be derived therefrom that the prognosis P.sub.6 is potentially too low. Accordingly, it can be derived for the more intense increase of the wind speed derived from the development of the first sector that this is also to be expected for the sector S.sub.2. Accordingly, the prognosis P.sub.6 can be escalated to the corrected prognosis K.sub.6.

[0126] The invention thus describes a solution by way of which a sector load profile can be identified at an early stage. A load profile is thus identified by sectors, specifically based on values of each rotor blade which is situated in the sector at a measurement time point.

[0127] FIG. 2 in particular visualizes a so-called load control event which, while indeed being schematically illustrated therein, corresponds to an actual load recording. The illustration here is also intended to relate in principle that it can be seen that the loads on all blades already continuously increase and an early intervention by means of the blade angle is therefore possible.

[0128] The following assumptions have been made in particular here. It has been assumed that the loads increase over a characteristic time scale, the latter typically being a plurality of seconds long. It is furthermore assumed that a local asymmetrical wind speed increase which does not act across the entire rotor field prevails. This is to be visualized in particular by FIGS. 3 and 4. Therefore, the event illustrated may also be considered to be a shear event. A magnitude of the timescale is assumed in which each blade sweeps multiple times across the wind event, or the wind condition, driving the extreme load, respectively. Each blade thus sweeps multiple times across the corresponding sector or the corresponding sectors in which a wind event driving such an extreme load arises.

[0129] The following measures which are also to be explained in the figures are proposed in particular. A temporal profile of the blade bending moments of all blades is recorded. For example, strain gauges which are continually evaluated can thus be present.

[0130] The determination of a difference between two blade bending moments of two successive blades can take place, for example from blade C to blade B, as is explained in FIGS. 5 and 6. The load can be recorded as a function of the rotor position and a difference can be formed. In this case, two load values are thus recorded.

[0131] The influence of the blade angle is additionally taken into account when determining the blade flexing or blade load, and thus also when determining the difference between two blade bending moments. For this purpose, the blade angle of the leading blade can be taken into account, for example, or a general reference angle can be used as the basis. In any case, the influence of the blade angle is taken into account, and this can take place in that the blade angle difference between the two measuring time points, thus between the two rotor blades, is determined. This blade angle difference can be additionally taken into account in the difference between the two blade load values, thus between the two blade bending moments, because said blade angle difference causes a relative change in the blade bending moment, the latter being taken into account as a result.

[0132] An increase by means of which an extreme load to be expected at specific discrete temporal intervals is estimated is determined by means of these differences in terms of the blade angle as well as time.

[0133] The increase can be determined by a linear straight line, or else by a polynomial of a higher order. To this end, more than two values may optionally be recorded.

[0134] When a limit criterion is exceeded, a control action for enlarging the blade angle of one or all blades so as to minimize the extreme load to be expected is then triggered. The limit criterion can be formed from a combination of an extreme load limit, such as the extreme load value 204 of FIG. 2, and a temporal spacing from the current time point until a corresponding extreme load arises, thus until the extreme load limit is reached. In other words, the straight line, should the latter ascend in the first place, can indeed reach the limit criterion, thus the extreme load value 204, but should this be far in the future no measure must yet to be taken.

[0135] The resolution of the rotor field in terms of sectors can be chosen, for example so as to be 36 sectors of in each case 10°.

[0136] In this way it can be achieved that the blade angles can be adjusted by observing such a gradient at an early stage, as a result of which a low pitch speed can be chosen. Accordingly, besides reducing an extreme load on the blades, a gentler operation management can also be made possible. It can be achieved in particular as a result that peak loads in pitch motors are avoided, and the tower deflection in extreme scenarios is minimized.

[0137] The load for a third of a rotor revolution can in particular be extrapolated. Following a third of the rotor revolution, two values can be recorded, specifically for one blade and a following blade, and an extrapolation can be performed therefrom. The quality of the prognosis for each observed sector is thus known after 1/X rotor revolutions. It is currently assumed that X=3. The focus here is in particular on identifying the quality of the prognosis, or improving the prognosis, as is explained in FIG. 7.

[0138] While a third of the rotation is indeed required in order to rotate the rotor from one rotor blade to the next in one sector, an estimation of the quality of the prognosis is indeed possible before a further third of a rotor revolution takes place, whereby it would also be possible to wait for a third of a rotor revolution. It can already be identified when the rotor has moved somewhat onward whether a stronger or weaker increase in the wind is generally present. This finding can be applied to the prognoses already established, and the quality can be estimated in this way. Should the wind increase thus accelerate during this time, it can then be seen that a prognosis will be exceeded. This information can now be utilized for the following sectors in order for the prognosis to be corrected, as is explained in FIG. 7.

[0139] An improvement has in particular been achieved by the solution proposed. In a previous variant, which is now being improved, the pitch system reacts when an extreme load arises in a single blade and attempts to avoid any further increase of the load by very rapidly pitching out of position. As a result of such a brief reduction of the thrust absorbed by the rotor, the tower is heavily accelerated toward the front, this likewise leading to undesired extreme loads on the tower. The proposed solution however enables slower pitching, thus a slower adjustment of the rotor blades, this not resulting in a rapid decrease in thrust, and the tower thus not being heavily accelerated toward the front. Previously, the tower, proceeding from a heavy thrust previously received, would swing toward the front, so to speak. This is now avoided.

[0140] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.