Operation of a wind power plant during a storm

Abstract

A method of controlling a wind power plant for generating electrical power from wind is provided. The plant comprises a rotor having rotor blades with adjustable blade angles and the rotor can be operated at a variable rotational speed. The method includes controlling the plant in a partial load mode when wind speed is below a nominal speed and, controlling the plant in a storm mode when the wind speed is above a storm commencement speed. An output power of the plant in the partial load mode and storm mode is adjusted according to an operating characteristic curve that determines a relationship between the rotational speed and the output power. A partial load characteristic curve is used as the operating characteristic curve for controlling the power plant in partial load mode, and a storm mode characteristic curve is used as the operating characteristic curve for controlling the plant in storm mode.

Claims

1. A method of controlling a wind power plant for generating electrical power from wind, comprising: controlling the wind power plant in a partial load mode when wind speed is below a nominal wind speed, wherein the wind power plant includes a rotor having rotor blades with rotor blade angles that are adjustable, and wherein the rotor is operable at a variable rotational speed; controlling the wind power plant in a storm mode when the wind speed is above a storm commencement wind speed, wherein an output power to be output by the wind power plant in the partial load mode and in the storm mode is adjusted according to an operating characteristic curve that specifies a relationship between the rotational speed and the output power; using a partial load characteristic curve as the operating characteristic curve for controlling the wind power plant in the partial load mode; using a storm mode characteristic curve as the operating characteristic curve for controlling the wind power plant in the storm mode; with increasing wind speed, increasing the rotor blade angles according to the wind speed to reduce the rotational speed; and reducing the output power according to the reduction in the rotational speed, wherein the increase of the rotor blade angles to reduce the output power forms an angle/power change coefficient, and the angle/power change coefficient increases in magnitude with increasing wind speed, and the angle/power change coefficient decreases from a first reversal wind speed in the storm mode and increases again from a second reversal wind speed that is greater than the first reversal wind speed, wherein the storm mode characteristic curve and the partial load characteristic curve are different, and wherein at least one of: the storm mode characteristic curve, compared with the partial load characteristic curve, has lower rotational speeds for the same output power in at least sections of the storm mode characteristic curve, or a wind speed/rotational speed characteristic curve specifies a reduction in the rotational speed with increasing wind speed from the storm commencement wind speed, wherein a level of the reduction in the rotational speed increases with the increasing wind speed.

2. The method according to claim 1, wherein the storm mode characteristic curve, compared with the partial load characteristic curve, has lower rotational speeds for the same output power over an entire range of the storm mode characteristic curve.

3. The method according to claim 1, comprising: selecting the storm commencement wind speed according to an expected stalling of the rotor blades.

4. The method according to claim 1, comprising: selecting the storm commencement wind speed according to a power coefficient of the rotor blades.

5. The method according to claim 4, wherein the wind power plant is configured in such that the power coefficient decreases with the increasing wind speed at least from the nominal wind speed.

6. The method according to claim 4, comprising: selecting the wind speed at which the power coefficient falls below a predefined storm threshold for the power coefficient as the storm commencement wind speed.

7. The method according to claim 1, wherein the storm mode characteristic curve is a linear storm mode characteristic curve and decreases with the increasing wind speed from a storm commencement power value at a storm commencement rotational speed linearly to a final storm power value at a predefined final storm rotational speed.

8. The method according to claim 1, comprising: measuring the wind speed; and in the storm mode from the storm commencement wind speed, adjusting the rotor blade angles according to the wind speed to reach a lower rotational speed; and setting the output power according to the storm mode characteristic curve depending on the rotational speed reached.

9. The method according to claim 1, comprising: adjusting the rotor blade angles in the storm mode from the storm commencement wind speed to cause a resulting rotational speed according to the wind speed/rotational speed characteristic curve.

10. The method according to claim 1, wherein the wind speed/rotational speed characteristic curve forms a linear wind speed/rotational speed characteristic curve which decreases linearly with the increasing wind speed from a storm commencement rotational speed at the storm commencement wind speed to a final storm rotational speed at a final storm wind speed.

11. The method according to claim 1, wherein the wind speed/rotational speed characteristic curve specifies, with the increasing wind speed, a reduction of the rotational speed from the storm commencement wind speed, wherein a measure of the reduction of the rotational speed increases with the increasing wind speed.

12. The method according to claim 1, comprising: with the increasing wind speed, increasing the rotor blade angles according to the wind speed towards a feathered position such that the rotor blade angles increase in order to reduce the rotational speed.

13. The method according to claim 1, wherein the storm mode characteristic curve initially decreases with the increasing wind speed, from a predefined storm commencement power value at a storm commencement rotational speed to a storm auxiliary power value at a storm auxiliary rotational speed and from the storm auxiliary power value to a final storm power value at a final storm rotational speed, wherein the storm auxiliary power value at the storm auxiliary rotational speed is below a linear operating characteristic curve, and the storm mode characteristic curve is flatter from the storm auxiliary rotational speed to the final storm rotational speed than from the storm commencement rotational speed to the storm auxiliary rotational speed.

14. The method according to claim 1, wherein the wind speed/rotational speed characteristic curve decreases initially with the increasing wind speed from a storm commencement rotational speed at the storm commencement wind speed to an intermediate storm rotational speed at an intermediate storm wind speed, wherein the intermediate storm rotational speed is the same as a storm auxiliary rotational speed, wherein the wind speed/rotational speed characteristic curve decreases from the intermediate storm rotational speed at the intermediate storm wind speed to a final storm rotational speed at a final storm wind speed.

15. The method according to claim 14, wherein the storm commencement rotational speed corresponds to a higher storm commencement wind speed than the storm commencement wind speed.

16. The method according to claim 14, wherein the intermediate storm rotational speed at the intermediate storm wind speed is above the wind speed/rotational speed characteristic curve that is linear.

17. The method according to claim 14, wherein the wind speed/rotational speed characteristic curve decreases from the intermediate storm wind speed to the final storm wind speed more steeply than from the storm commencement wind speed to the intermediate storm wind speed.

18. A wind power plant for generating electrical power from wind, comprising: a rotor having rotor blades with adjustable rotor blade angles, wherein the rotor is operable at a variable rotational speed; and a controller configured to: control the wind power plant in a partial load mode when wind speed is below a nominal wind speed; and control the wind power plant in a storm mode when the wind speed is above a storm commencement wind speed; control the wind power plant such that an output power of the wind power plant in the partial load mode and in the storm mode is adjusted according to an operating characteristic curve, wherein the operating characteristic curve specifies a relationship between the rotational speed and the output power; use a partial load characteristic curve as the operating characteristic curve for controlling the wind power plant in the partial load mode; use a storm mode characteristic curve as the operating characteristic curve for controlling the wind power plant in the storm mode; with increasing wind speed, cause the rotor blade angles to be increased according to the wind speed to reduce the rotational speed; and cause the output power to be reduced according to the reduction in the rotational speed, wherein the increase of the rotor blade angles to reduce the output power forms an angle/power change coefficient, and the angle/power change coefficient increases in magnitude with the increasing wind speed, and the angle/power change coefficient decreases from a first reversal wind speed in the storm mode and increases again from a second reversal wind speed that is greater than the first reversal wind speed, wherein at least one of: the storm mode characteristic curve and the partial load characteristic curve are different, and the storm mode characteristic curve, compared with the partial load characteristic curve, has lower rotational speeds for the same output power values in at least sections of the storm mode characteristic curve; or the controller is configured to specify a wind speed/rotational speed characteristic curve which specifies a reduction in the rotational speed with the increasing wind speed from the storm commencement wind speed, wherein a level of reduction in the rotational speed increases with the increasing wind speed.

19. The wind power plant according to claim 18, comprising: a wind speed sensor configured to record the wind speed, wherein the wind power plant is configured to use the wind speed recorded by the wind speed sensor as an input variable in order to adjust a rotor blade angle in the storm mode according to the wind speed in order to reduce the rotational speed of the rotor with the increasing wind speed.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Exemplary embodiments of the invention shall now be described in greater detail with reference to the accompanying Figures, in which

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

(3) FIG. 2 shows an illustrative wind speed/rotational speed characteristic curve for the storm mode range.

(4) FIG. 3 shows a rotational speed/power characteristic curve and thus an operating characteristic curve.

(5) FIG. 4 shows an example of how the angle of attack changes in storm mode along a rotor blade from the blade root to the blade tip, as a function of the radius.

(6) FIG. 5 shows an improved wind speed/rotational speed characteristic curve.

(7) FIG. 6 shows a proposed operating characteristic curve.

(8) FIG. 7 shows another proposed operating characteristic curve.

(9) FIG. 8 compares different blade angles as a function of wind speed, for different embodiments.

(10) FIG. 9 shows different angles of attack in an outer region of a rotor blade, for different embodiments.

(11) FIG. 10 illustrates the importance of the blade angle and the angle of attack.

DETAILED DESCRIPTION

(12) FIG. 1 shows a wind turbine 100 comprising a tower 102 and a nacelle 104. A rotor 106 having three rotor blades 108 and a spinner 110 is arranged on nacelle 104. Rotor 106 is made to rotate by the wind and drives a generator in nacelle 104 as a result.

(13) FIG. 1 also illustrates a control unit (e.g., controller) 130 that can control wind power plant 100. A wind speed sensor 132 (e.g., anemometer), which may be arranged on spinner 110, is provided for controlling wind power plant 100 according to the wind speed. It sends its signals to control unit 130. Control unit 130 can analyze these signals and thus control a pitch motor 134, for example, which is only shown as an illustration in FIG. 1. Only one pitch motor 134 is shown, although of course each of rotor blades 108 may have a pitch motor 134, by means of which its blade angle can be adjusted. A generator 136 is likewise indicated in FIG. 1 and can be controlled by control unit 130 to adjust the output power, if necessary.

(14) FIG. 2 shows a simple variant of wind speed/rotational speed characteristic curve 202. This curve shows the nominal speed N.sub.set at wind speeds below a minimum wind speed V.sub.min. The range up to this minimum wind speed forms the full-load range or full load mode of the wind power plant, in any case as long as the wind speed is not less than a nominal wind speed, which is not shown in FIG. 2, because the latter substantially shows only the wind speed/rotational speed characteristic curve for the storm mode. Nor are any wind speed/rotational speed characteristic curves provided for other ranges. There are known relationships between wind speed and rotational speed, but these are not normally used to control the system in full load mode and partial load mode. Only for storm mode is it proposed that the rotational speed be set as a function of the measured wind speed, in accordance with wind speed/rotational speed characteristic curve 202.

(15) In the example shown in FIG. 2, storm mode commences when the storm wind speed, referred to as V.sub.SA, is reached. From then on, the rotational speed decreases linearly in accordance with the wind speed/rotational speed characteristic curve 202 until the maximum wind speed V.sub.max is reached, at which point it equals the idle speed N.sub.t. There is also an exception where the wind power plant can be shut down at the safety wind speed V* when the wind speed exceeds the safety wind speed V* on a 10-minute average.

(16) Wind speed/rotational speed characteristic curve 202 drops linearly here and its linear drop can also be defined on the basis of a virtual starting value, which is plotted at the minimum wind speed and 1.2 times the nominal speed.

(17) FIG. 3 shows a rotational speed/power characteristic curve and thus an operating characteristic curve 302, which can also be abbreviated to BKI. This curve shows a relationship between rotational speed N and power P. At what is basically the maximum rotational speed, namely the nominal rotational speed N.sub.set, the nominal power P.sub.N is also available. At correspondingly lower rotational speeds, the power is also lower and drop to the value zero at idle speed N.sub.t. In this case, the system is operated at the idle speed without generating any power. This operating characteristic curve 302 in FIG. 3 can show or specify the relationship between rotational speed N and power P not only in partial load mode but also in storm mode. In partial load mode, however, the rotational speed would increase with increasing wind speed, whereas in storm mode the rotational speed decreases with increasing wind speed. Viewed in that way, the operating characteristic curve would apply in the reverse direction in storm mode, in relation to the wind speed.

(18) Note should also be taken of the following points. During a storm, the air flowing through the swept area of the rotor has very high kinetic energy, and only a small part of it needs to be converted by the wind power plant into rotational energy in order to generate the required power according to the operating characteristic curve.

(19) It was realized that the torque necessary to achieve that is substantially generated only in the inner region of the blade, with the result that the distribution of the angle of attack over the radius of the rotor differs fundamentally from the distribution in normal operating mode.

(20) To illustrate this, FIG. 4 shows a typical curve for the angle of attack at a wind speed in storm mode. In this regard, the angle of attack is to be understood as the angle at which air actually flows in relation to the chord of the rotor blade in the section in question. This angle of attack thus depends on the actual position of the rotor blade, the prevailing wind at that point and the rotational speed of the rotor blade at that point.

(21) To illustrate the blade angle γ and the angle of attack α, these are shown in FIG. 10 for a profile section 1000. This profile section 1000 thus stands for a rotor blade section. Turning the rotor blade in rotor plane R at rotational speed ω results in a blade section velocity V.sub.BA for profile section 1000 under consideration, said velocity thus being parallel to the rotor plane. The true wind speed V.sub.W results in an apparent or relative wind speed U.sub.rel when the blade section velocity V.sub.BA is taken into account. This is shown as a schematic vector diagram inserted into FIG. 10. Only the relative wind direction U.sub.rel is indicated on profile section 1000. The angle between this relative wind direction U.sub.rel and chord c is the angle of attack α. It also depends directly on the set blade angle γ in relation to rotor plane R. A small blade angle γ corresponds to a setting in partial load mode.

(22) In FIG. 4, it can be seen that positive angles of attack are found only in the inner part of the blade and that the value of the angle of attack decreases sharply towards the outside and becomes clearly negative towards the blade tip. It should be mentioned that the abscissa in FIG. 4 shows the respective position on the rotor blade in relation to the total length of the blade. At the blade tip, the position is therefore equal to the length of the rotor blade, so the value there is 1. The position is treated as a radius r of the rotor in relation to the total radius R of the rotor. The abscissa does not quite go to the value zero, because the value zero is located at the axis of rotation and therefore in the spinner or hub.

(23) FIG. 4 shows only one example, but it was realized that the higher the wind speed and the less power the wind power plant feeds into the grid at these higher wind speeds in storm mode, the more pronounced this trend or phenomenon becomes. It was realized that this can be problematic, as at high negative angles of attack there is a risk that negative stall, i.e., stalling on the pressure side of the profile, can occur at the profiles where these high negative angles of attack arise. Depending on the profile and the structural design of the rotor blade, there may therefore be a risk of undesirable aeroelastic phenomena on the rotor blade due to operation in sections of the rotor blade with negative stall. This means that feedback may occur between the forces exerted by the flow of air around the rotor blade and the elastic deformations that arise as a result. Such deformations, in turn, can cause changes in the flow of air and changing forces due to aerodynamic factors.

(24) It was also realized in this regard that such feedback can be manifested in a way that leads to oscillating motion about the longitudinal axis of the rotor blade. In that case, the rotor blade would therefore be subject to torsion with a high frequency and amplitude. Such rotor blade vibrations could even acquire amplitudes that can cause damage to the rotor blade. Preventive measures are therefore proposed. It was realized here, in particular, that such stalling can occur when a wind power plant is in storm mode and negative angles of attack occur at the rotor blade. It is proposed, accordingly, that this phenomenon in particular, i.e., such negative angles of attack, be counteracted and prevented as far as possible.

(25) FIG. 4 thus shows the angle of attack α over the length of a rotor blade having a total length R, wherein the maximum radius of the rotor in which the rotor blade is operated is actually used as the total length R, so the maximum radius R indicates the value from the rotational axis of the rotor to the tip of the blade. The radius r under consideration is normalized to this maximum radius R, so the abscissa extends to the value of 1.

(26) It can be seen that this angle of attack curve 402 takes negative values from about half way along the rotor blade, i.e., from about the value 0.5 for the radial position on the rotor blade, and that the magnitude of those negative values becomes even greater towards the blade tip, i.e., are even further below zero. This is an example of a rotor blade whose blade angle has been adjusted too much in storm mode in order to reduce the rotational speed too strongly as a result. If the blade angle were adjusted less, with the rotational speed being reduced less or later, the angle of attack would not turn negative so strongly, or indeed not at all.

(27) Based on this finding, the object to be achieved for the storm mode of a wind power plant is to prevent the occurrence of stalling when the rotor blade has negative angles of attack.

(28) To achieve this, it is therefore proposed that operation during a storm be adjusted accordingly. It is proposed, in particular, that the operating characteristic curve or the wind speed/rotational speed characteristic curve, or both characteristic curves simultaneously, be modified in comparison with the variants used hitherto. The proposed improvements or options for improvement are illustrated in the following FIGS. 5 to 7, in particular.

(29) FIG. 5 shows, inter alia, the wind speed/rotational speed characteristic curve 202 of FIG. 2. It is now proposed, specifically, to deviate from this wind speed/rotational speed characteristic curve 202, and to that end an improved wind speed/rotational speed characteristic curve 502 is proposed. This improved wind speed/rotational speed characteristic curve 502 does not start to reduce the rotational speed until a higher storm commencement wind speed V.sub.SA2 is reached. From there, the rotational speed decreases with a smaller initial speed gradient until the second minimum wind speed V.sub.min2, where it reaches the first minimum rotational speed N.sub.min1. From there, the improved wind speed/rotational speed characteristic curve 502 drops with a gradient of increased magnitude to idle speed N.sub.t at maximum wind speed V.sub.max. In this way, it is possible for this improved wind speed/rotational speed characteristic curve 502 to lie above wind speed/rotational speed characteristic curve 202. The first minimum rotational speed N.sub.min1 may also constitute an intermediate storm rotational speed or a storm auxiliary rotational speed, which may also be equal in value to a storm auxiliary rotational speed that is used in an operating characteristic curve described further below. This improved wind speed/rotational speed characteristic curve 502 thus reduces the rotational speed comparatively late and also reduces it comparatively little, at lest initially. It is not until later, namely from the second minimum wind speed V.sub.min2 or when the first minimum rotational speed N.sub.min1 is reached, that the rotational speed then drops steeply.

(30) Shutdown of the wind power plant when the 10-minute average wind speed is above the safety wind speed V* can also be carried out at a higher rotational speed, namely the second minimum rotational speed N.sub.min2.

(31) The aim of the proposal according to the improved wind speed/rotational speed characteristic curve 502 is to raise the rotational speed in storm mode, compared to previous approaches. In other words, the rotational speeds are to be reduced later and/or less with increasing wind speed, at least at the beginning of storm mode. The cut-out wind speed, which can also be referred to as the maximum wind speed V.sub.max, remains the same, and a linear relationship between the wind speed and the rotational speed can also be used, according to one embodiment at least. However, it is proposed that the relationships be specified linearly here in sections, in particular in two sections, of which the first, i.e., the one for lower wind speeds, is flatter, and the second, later one, i.e., the one used at higher wind speeds, is steeper.

(32) Such first and second sections 504, 506 are shown in FIG. 5. It is therefore proposed as an improvement that the commencement of the storm mode is postponed from the storm commencement wind speed to a higher storm commencement wind speed V.sub.SA2. A characteristic curve with linear sections of different gradients is also proposed with the aim of increasing the rotational speeds throughout the entire storm mode in comparison with the variant shown in FIG. 2.

(33) To that end, preferably adapted operating characteristic curves as shown in FIGS. 6 and 7 are also proposed. The aim of these modifications of the operating characteristic curves is to increase the power at a given rotational speed. One way of achieving this is to shift an operating characteristic curve as shown by way of illustration in FIG. 6. By way of comparison, and as indicated by an arrow, a first operating characteristic curve, which can also be referred to as a normal operating characteristic curve 602, is shown there which can basically be moved to the left to the improved operating characteristic curve 604. This shift means in effect that the power P has the same gradients as before, only at a lower rotational speed in each case. The power output for a given rotational speed is thus increased. Due to the shift, however, the nominal power P.sub.N is also maintained even when the rotational speed is slightly lower.

(34) As far as the specific gradients of the operating characteristic curve are concerned, the improved operating characteristic curve 604, which forms a storm mode characteristic curve here, decreases initially, with increasing wind speed V.sub.W, from the predefined storm commencement power value P.sub.N at the predefined storm commencement rotational speed N.sub.set to a storm auxiliary power value P.sub.H at a predefined storm auxiliary rotational speed N.sub.H, and from there to the final storm power value, namely zero, at the predefined final storm rotational speed N.sub.t.

(35) In another embodiment, a linear relationship between power and rotational speed may be provided from the nominal speed N.sub.set to the idle speed N.sub.t. This is illustrated in FIG. 7, which also shows by way of comparison a normal operating characteristic curve 702 which is not a straight line, i.e., which does not define a linear relationship between power and rotational speed. As indicated by the arrow, this normal operating characteristic curve 702 is modified to obtain the improved linear operating characteristic curve 704. It was also realized here, in particular, that such a linear relationship for an operating characteristic curve is suitable for the storm mode, but is less suitable for the partial load mode.

(36) It partial load mode, it makes particular sense for aerodynamic reasons to initially increase the rotational speeds as quickly as possible with increasing wind, because at low wind speeds this can result in aerodynamically favorable tip speed ratios. However, it was realized that it may make sense in storm mode not to reduce the power too much when the wind is increasing and the rotational speed is reduced. In storm mode, potential aspects of the wind power plant stalling do not play a role, either, so the power can be kept relatively high there on the operating characteristic curve. That is precisely what can be achieved by the improved linear operating characteristic curve 704 being proposed. In addition, a relative high power output can nevertheless be generated despite reducing the rotational speed and power in storm mode in order to protect the wind power plant. The improved linear operating characteristic curve 704 being proposed can provide such an advantage.

(37) It was realized at the same time that when characteristics of the generator being used are taken into account, in particular its maximum, speed-dependent power output, it is nevertheless possible to generate a relative high power output.

(38) Achievable effects are shown in FIGS. 8 and 9. FIG. 8 illustrates for three different cases how the blade angle γ changes as a function of wind speed V.sub.w in storm mode. FIG. 8 thus shows three different blade angle curves 802, 804 and 806. The first blade angle curve 802 can also be referred to as a normal blade angle curve and basically belongs to the wind speed/rotational speed characteristic curve 202 in FIG. 2. At the same time, an operating characteristic curve according to the normal operating characteristic curve 602 or 702 of FIG. 6 or 7, respectively, is used as a basis.

(39) A second and thus improved blade angle curve 804, likewise based on the wind speed/rotational speed characteristic curve 202 in FIG. 2, is also shown, but for which an improved operating characteristic curve was used. An improved operating characteristic curve 604 or 704, or similar, may have been used in this regard. The third, further improved blade angle curve 806, is also based, in comparison with the second improved blade angle curve 804, on the improved wind speed/rotational speed characteristic curve 502, rather than wind speed/rotational speed characteristic curve 202.

(40) In FIG. 8, it can be seen in particular that blade angles are smaller due to an improved operating characteristic curve being used and in addition due an improved wind speed/rotational speed characteristic curve being used. At the beginning of the storm mode, i.e., at storm commencement wind speed V.sub.SA, the blade angles are also the same and then increase to different extents as the wind speed increases. As a result of the proposed measures, individually and also in combination, it is possible to reduce the blade angle in storm mode compared to variants in which such an improved operating characteristic curve and/or an improved wind speed/rotational speed characteristic curve is not used.

(41) One particular reason for this is that the proposed measures basically lead to an increase in power compared to variants in which these measures are not performed, i.e., to generation of an increased output power that is also fed into the electrical supply grid. More power is thus extracted from the wind, and the wind power plant is curtailed to a lesser extent as a result. This is expressed in reduced blade angles, which can also be referred to as pitch angles or rotor blade angles. Smaller rotor blade angles also result directly in bigger angles of attack. This was realized, and it was also realized that this is an advantageous effect for preventing very small angles of attack and the risk of flow separation.

(42) This is shown in FIG. 9. FIG. 9 shows, for the three blade angle curves 802, 804 and 806 and one wind speed, how the angle of attack changes in the outer region of the rotor blade, namely at a radius r of 70% to 100% in relation to the maximum radius R. FIG. 9 shows the angle of attack curves 902, 904 and 906 corresponding to blade angle curves 802, 804 and 806, respectively. Thus, FIG. 9 also shows the distribution of the angle of attack at the blade tip region that results from the types of operational management mentioned in connection with FIG. 8.

(43) For example, if the rotor blade design used profiles for the 0.96<r/R<1 region, where there is a tendency to stall at angles of attack less than −11°, thus triggering the aeroelastic problems mentioned above, it would also be possible with the proposed measures to prevent wind power plants from being operated in this angle of attack range with values less than −11° and thus to prevent potential vibration and associated damage to the rotor blades. FIG. 9 shows, namely, that only angle of attack curve 902, which results when operational management is unchanged, achieves a significantly lower angle of attack than angle of attack curves 904 and 906 according to the improved operational management.

(44) Provided is increasing the angle of attack, especially in the blade tip region. In storm mode, negative angles of attack may arise in the blade tip region, i.e., the flow stagnation point then lies on the suction side of the profile. At high negative angles of attack, flow separation typically occurs on the pressure side. In certain circumstances, when operating the system with flow separation on the pressure side, also known by those skilled in the art as negative stall, the rotor blade may start to vibrate due to aeroelastic factors, which in turn can cause damage to the rotor blade. By modifying the operational management, the proposed invention aims to prevent critical negative angles of attack being reached in storm mode and thus to safeguard or at least improve the integrity of the rotor blade.

(45) By means of the proposed measures, it is thus possible to reduce the load on the rotor blades when in storm mode, while simultaneously allowing a higher power yield.