METHOD FOR OPERATING A WIND TURBINE, WIND TURBINE AND WIND FARM

Description

[0001] The present invention relates to a method for operating a wind turbine for generating electrical power from wind, wherein the wind turbine has an aerodynamic rotor with adjustable blade angle rotor blades, and the rotor is operated at an adjustable nominal rotor speed. Furthermore, the present invention relates to a rotor blade of a rotor of a wind turbine, a wind turbine, and a wind farm.

[0002] Wind turbines are well known and, for example, as in Fig. 1 The design of wind turbines and their components is based on standardized guidelines (e.g., IEC 61400), which address the essential design requirements for ensuring the technical integrity of wind turbines. The purpose of this standard is to ensure an appropriate level of protection against damage resulting from risks during the planned service life of the wind turbine. Standard parameters are incorporated into the dimensioning of the wind turbine, which is dependent on a standardized load but not site-specific. The standard parameters include shear, the occurrence of turbulence, climatic conditions, air density, and reference speeds for wind classes and wind zones.

[0003] Depending on their location, wind turbines are subject to a wide range of environmental conditions. In particular, the characteristics of the wind field to which the turbines are exposed can vary considerably throughout the day and season. The wind field is characterized by a multitude of parameters. The most important wind field parameters are mean wind speed, turbulence, vertical and horizontal shear, wind direction change with height, oblique flow, and air density.

[0004] Turbulence describes short-term changes in wind speed around an average value at time intervals of less than 10 minutes. This is primarily caused by mechanically and thermally induced turbulence. The vertical shear of the wind field with the Earth's surface describes turbulence caused by fluid mechanics. Thermally induced turbulence, on the other hand, is caused by heat convection or dissipation. Thermally induced turbulence depends primarily on the thermal stability of the atmosphere. A dimensionless quantity called turbulence intensity is used to describe turbulence. Turbulence intensity is defined as the ratio of the standard deviation of the wind speed to the average wind speed over time intervals of, in particular, 10 minutes. Turbulence intensity is a measure of the variability of wind speed within these periods. References:

[0005] [1]J.F.Manwell, J.G.McGowan, AL.Rogers: "Wind energy explained - theory, design and application", 2nd edition, John Wiley and Sons Ltd., 2009. [2]T.Burton, D.Sharpe, N.Jenkins, E.Bossanyi: "Wind energy handbook", John Wiley and Sons Ltd., 2001. [3]F.Boettcher: "Statistical analysis of atmospheric turbulence and general stochastic processes", dissertation at the Carl von Ossietzky University of Oldenburg, 2005. [4]R.Gasch, J.Twele: "Wind turbines - fundamentals, design, planning and operation", 4th edition, Teubner Verlag, 2005.

[0006] The German Patent and Trademark Office has searched the following prior art in the priority application for the present application: US 2017 / 0328346 A1, DE 10 2008 009 585 A1, DE 10 2013 100 387 A1, US 2017 / 0218923 A1, US 2010 / 0135789 A1, EP 2518308 A1, WO 2018 / 153518 A1, US 2015 / 0159493 A1.

[0007] The European Patent Office has searched the following prior art for the present application: EP 2 518 308 A1, US 2013 / 234437 A1, US 2017 / 328346 A1, CN 207 297 229 U, and DE 10 2016 124 703 A1. Document EP 2 518 308 A1 relates to a method for controlling the operation of a wind turbine using a terrain class parameter. Document US 2013 / 234437 A1 describes storm control, i.e., the operation of wind turbines above the rated wind speed. The document US 2017 / 328346 A1 relates to a method for determining a configuration of a wind turbine of a specific type of wind turbine, wherein a plurality of combinations of physical and control parameters of the wind turbine are tabulated and a suitable combination is selected from these combinations depending on various parameters.Document CN 207 297 229 U concerns the combination of vortex generators, spoilers, and / or Gurney flaps on a rotor blade. Document DE 10 2016 124 703 A1 concerns an air density-dependent speed correction.

[0008] Against this background, it was an object of the present invention to further develop a method for operating a wind turbine which is characterized by more efficient operation, but also to provide a rotor blade of a rotor of a wind turbine, a wind turbine and a wind farm which enable more efficient operation.

[0009] The object underlying the invention is achieved by a method for operating a wind turbine having the features according to the independent claims. According to claim 1, a method for operating a wind turbine for generating electrical power from wind is provided.

[0010] According to the invention, it is therefore proposed to dispense with a uniformly parameterized operation of wind turbines, but to use the specific turbulence class determined at a location to determine the nominal rotor speed.

[0011] According to the IEC 61400 standard, several turbulence classes are determined based on turbulence intensities. Generally, similar wind turbines, such as those in a wind farm, at locations with different turbulence classes are operated with identical parameters, which has a corresponding impact on the individual annual energy production (AEP). According to the invention, adjusting the operating parameters, in particular adjusting the rated rotor speed, therefore represents a potential improvement in the AEP.

[0012] The nominal rotor speed preferably describes the rotor speed at which a generator of the wind turbine reaches its nominal power. After this power is reached, the operation of the wind turbine preferably changes to speed control mode, in which the wind turbine is controlled to the controlled speed or target rotor speed. For reasons of system inertia and controller speed, this is preferably 0.1-0.3 rpm above the nominal rotor speed. For the purposes of this disclosure, in the case where the controlled speed deviates from the nominal rotor speed during operation at nominal power, the controlled speed is referred to synonymously with the nominal rotor speed.

[0013] Preferably, the turbulence class can be determined based on a turbulence intensity measured at the wind turbine.

[0014] The rated rotor speed can be determined depending on the specific turbulence class in such a way that the expected loads on the rotor are compensated for based on the measured turbulence intensity. Higher turbulence intensity causes an increase in the loads acting on the rotor. This can be counteracted according to the invention by reducing the rated rotor speed. To the extent that the rated rotor speed decreases, the increase in load due to the higher turbulence intensity can be partially, fully, or overcompensated.

[0015] A lower turbulence intensity, in turn, causes a decrease in the loads acting on the rotor. In this case, this can be counteracted according to the invention by increasing the rated rotor speed. Due to the reduction in loads at lower turbulence intensities, the rated rotor speed can be increased to such an extent that the load level at higher turbulence intensities is not exceeded.

[0016] According to the invention, the turbulence class is selected from the group consisting of "A," "B," and "C." The definition of these turbulence classes can be chosen, for example, based on IEC 61400.

[0017] According to the invention, the rated rotor speed is determined relative to the specific turbulence class in such a way that the rated rotor speed is lower for turbulence class "A" than for turbulence class "B" and lower for turbulence class "B" than for turbulence class "C".

[0018] Furthermore, several vortex generators can be arranged on the rotor blades between the rotor blade root and the rotor blade tip. Their number and positioning, in particular their radial extension from the rotor blade root toward the rotor blade tip, is determined depending on the specific turbulence class. The vortex generators can preferably be known arrangements with fins arranged essentially perpendicular to a rotor blade surface, for example, arranged in pairs on base plates. However, the vortex generators can also be any other passive or active means for influencing the flow, or any combination thereof.

[0019] In addition, the number and positioning of vortex generators along the rotor blade can be determined depending on the site-specific air density. A decrease in air density may require the minimum blade angle to be increased above a certain power level to prevent flow separation at the rotor blade and thus significant yield losses. This can also be counteracted by adjusting the radial extension of the vortex generator array, starting from the rotor blade root toward the rotor blade tip, to suit the air density prevailing at the site.

[0020] For this purpose, the radial extension of the vortex generators along the rotor blade can be determined depending on the air density in such a way that additional yield losses due to an increase in the blade angle required at lower air density are at least partially compensated, preferably compensated, and particularly preferably overcompensated. Arranging the vortex generators depending on the specific air density can result in a smaller increase in the blade angle due to lower air density or even eliminate it entirely. This can result in an overall increase in yield.

[0021] In one embodiment, the rated rotor speed is additionally determined as a function of a site-specific air density.

[0022] Preferably, the wind turbine can be operated according to different operating characteristics depending on the turbulence class, thus guaranteeing different power curves depending on the turbulence class. This effect can lead, particularly for wind turbines operated at locations with low average wind speeds, to the increased frequency of low wind speeds, resulting in the wind turbine delivering more yield at higher turbulence intensity than at lower turbulence intensity. In particular, at low average wind speeds, a higher yield can be generated by adjusting the operating parameters when the wind turbine is operated in the higher turbulence class "A" than in the lower turbulence class "B." Partial load operation, i.e., the range with a nearly constant tip speed ratio, is particularly relevant here.In the range close to and towards the rated power, there is no constant tip speed ratio; rather, the tip speed ratio drops in this range.

[0023] According to a further development, a blade angle characteristic can be defined depending on the specific turbulence class. The rotor rated speed is higher in turbulence class "C" than in turbulence class "B" and higher in turbulence class "B" than in turbulence class "A." Since a lower tip speed ratio occurs at a lower rated rotor speed, the blade angle is increased according to the blade angle characteristic of the respective turbulence class to prevent stall.

[0024] According to the invention, the rated rotor speed is reduced when changing from a lower turbulence class to a higher turbulence class.

[0025] A reduction in the rated rotor speed can be associated with an increase in the blade angle at at least one operating point.

[0026] Preferably, instead of increasing the blade angle at at least one operating point, this can be counteracted by the design and positioning of vortex generators in such a way that the reduction in the rated rotor speed remains essentially yield-neutral. While there is an increase in drag caused by the extended arrangement of the vortex generators in the longitudinal direction of the rotor blade, this increase in drag is offset by the benefits of lift generation.

[0027] For example, the number of vortex generators on the rotor blades can be increased radially outwards in a turbulence class-dependent design of the wind turbine in order to essentially maintain the blade angle of a lower turbulence class when the tip speed ratio is reduced during operation due to the reduction in the rated rotor speed at a higher turbulence class.

[0028] When transitioning from a higher turbulence class to a lower turbulence class, the rated rotor speed is increased.

[0029] In this case, an increase in the rated rotor speed can be associated with a reduction in the blade angle at at least one operating point.

[0030] Preferably, instead of reducing the blade angle at at least one operating point, the design and positioning of vortex generators can also be reduced outward. All of these measures, either individually or in combination, can increase the turbine's yield.

[0031] According to a further aspect, a method for operating a wind turbine for generating electrical power from wind is described, wherein the wind turbine has an aerodynamic rotor with rotor blades whose blade angle is adjustable, and the rotor is operated at a particularly adjustable nominal rotor speed. Several vortex generators are arranged on the rotor blades between the rotor blade root and the rotor blade tip. The number and positioning of the vortex generators, in particular their radial extension from the rotor blade root toward the rotor blade tip, depends on a site-specific air density.

[0032] According to a further aspect, a method for operating a wind turbine for generating electrical power from wind is described, wherein the wind turbine has an aerodynamic rotor with rotor blades whose blade angle is adjustable and the rotor is operated at a particularly adjustable nominal rotor speed, characterized in that the speed of the wind turbine is controlled as a function of a site-specific air density.

[0033] Furthermore, a rotor blade with a suction side and a pressure side is described, wherein several vortex generators are arranged between the rotor blade root and the rotor blade tip. The number and extent of the arrangement of the vortex generators, starting from the rotor blade root toward the rotor blade tip, are determined depending on a specific turbulence class. The vortex generators are preferably arranged on the suction side and / or the pressure side.

[0034] Preferably, the extension of the arrangement of the vortex generators starting from the rotor blade root in the direction of the rotor blade tip, i.e. in the longitudinal direction of the rotor blade, can be limited by the highest turbulence class, in particular decreasing from the highest turbulence class to the lowest turbulence class.

[0035] Furthermore, the invention relates to a wind turbine comprising an aerodynamic rotor with rotor blades adjustable in their blade angle, wherein the rotor can be operated with an adjustable nominal rotor speed, and to a control system, characterized in that the control system is designed to operate the wind turbine according to a method according to at least one of claims 1 to 9.

[0036] For this purpose, the rotor can have at least one rotor blade.

[0037] Furthermore, the invention also relates to a wind farm with several wind turbines according to claim 10.

[0038] The invention will be described in more detail below using a possible embodiment with reference to the accompanying figures. Herein: Fig. 1 shows a wind turbine according to the present invention; Fig. 2 shows a schematic representation of a rotor blade; Fig. 3 shows schematic and exemplary operating characteristics for different turbulence classes; Fig. 4 shows schematic and exemplary curves of tip speed ratios for different turbulence classes; Fig. 5 shows schematic and exemplary curves of angles of attack for different turbulence classes; Fig. 6 shows schematic and exemplary curves of lift coefficients for different turbulence classes; Fig. 7 shows schematic and exemplary curves of glide ratios for different turbulence classes; Fig. 8 shows schematic and exemplary curves of power curves when operating the wind turbine in different turbulence classes; Fig. 9 shows schematic and exemplary curves of power curves at different turbulence intensities.

[0039] The explanation of the invention by way of examples with reference to the figures is essentially schematic, and the elements explained in the respective figure may be exaggerated and other elements simplified for better illustration. For example, Fig. 1 a wind turbine as such is schematic, so that an intended arrangement of vortex generators is not clearly recognizable.

[0040] 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 is arranged on the nacelle 104. During operation, the rotor 106 is set in rotation by the wind, thereby driving a generator in the nacelle 104. The rotor blades 108 are adjustable in their blade angle. The blade angles or pitch angles of the rotor blades 108 can be changed by pitch motors arranged at the rotor blade roots of the respective rotor blades 108. The rotor 106 is operated at an adjustable nominal rotor speed.

[0041] Several of these wind turbines 100 can be part of a wind farm. Depending on their location, the wind turbines 100 are subject to a wide range of environmental conditions. In particular, the properties of the wind field to which the wind turbines are exposed can vary considerably over the course of the day and season. The wind field is characterized by a multitude of parameters. The most important wind field parameters are average wind speed, turbulence, vertical and horizontal shear, wind direction change with height, oblique flow, and air density.

[0042] Turbulence, a key variable influencing the load on the rotor blades 108, describes short-term changes in wind speed around an average value at time intervals of less than 10 minutes. This is primarily caused by mechanically and thermally induced turbulence. The vertical shear of the wind field with the Earth's surface describes the turbulence caused by fluid mechanics. Thermally induced turbulence, on the other hand, is caused by heat convection or dissipation. Thermally induced turbulence depends primarily on the thermal stability of the atmosphere. A dimensionless quantity called turbulence intensity is used to describe turbulence. Turbulence intensity is defined as the ratio of the standard deviation of the wind speed to the average wind speed over time intervals of 10 minutes.Turbulence intensity is a measure of the variability of wind speed within these periods.

[0043] According to the IEC 61400 standard, locations are divided into several turbulence classes "A", "B", "C" based on turbulence intensities, as shown in the table below. Table of WEA classes: Windklasse I II III S V ave [m / s] 10 8,5 7,5 Standortspezifisch I 15 (A) 18 % I 15 (B) 16 % I 15 (C) 12 %

[0044] The table defines wind classes I, II, III, and S for different wind speeds. V ave represents the average wind speed at hub height of the wind turbine 100. I 15 denotes the percentage turbulence intensity at hub height at a wind speed of 15 m / s. "A," "B," and "C" denote different turbulence classes.

[0045] Based on the turbulence intensity I 15 , locations are classified into turbulence classes "A," "B," and "C." Turbulence class "A" has a higher turbulence intensity I 15 than turbulence class "B," and turbulence class "B" has a higher turbulence intensity I 15 than turbulence class "C." Higher turbulence results in higher loads on the rotor 106 and the rest of the wind turbine 100.

[0046] In this exemplary embodiment, the wind turbine 100 is controlled by a controller 200, which is part of a comprehensive control system for the wind turbine 100. The controller 200 will generally be implemented as part of the control system for the wind turbine 100.

[0047] Fig. 2 shows a schematic view of a single rotor blade 108 with a rotor blade leading edge 110 and a rotor blade trailing edge 112. The rotor blade 108 has a rotor blade root 114 and a rotor blade tip 116. The length between the rotor blade root 114 and the rotor blade tip 116 is referred to as the rotor blade length L. The distance between the rotor blade leading edge 110 and the rotor blade trailing edge 112 is referred to as the profile depth T. At the rotor blade root 114, or generally in the area near the rotor blade root 114, the rotor blade 108 has a large profile depth T. At the rotor blade tip 116, in contrast, the profile depth T is much smaller. The profile depth T decreases significantly, starting from the rotor blade root 114, in this example after an increase in the inner region of the blade, down to a central region. A separation point can be provided on the rotor blade, preferably in the central region (not shown here).From the middle area to the rotor blade tip 116, the profile depth T typically decreases continuously. The decrease in the profile depth T is almost constant, or the decrease in the profile depth T is significantly reduced.

[0048] The representation in Fig. 2 shows the suction side of the rotor blade 108. Vortex generators 118, which can be designed, for example, as base plates with two fins extending therefrom, are arranged on the suction side. Alternative designs of the vortex generators 118 as active or passive elements for flow influencing are conceivable. While the vortex generators 118 are shown arranged on the suction side of the rotor blade 108 in the example, vortex generators 118 are alternatively or additionally possible on the pressure side. The vortex generators 118 are arranged in the region of the rotor blade leading edge 110. The extension of the arrangement of the vortex generators 118 begins in the region of the rotor blade root 114 and runs towards the rotor blade tip 116. Relative to the rotor 106, the vortex generators 118 extend in the radial direction over a distance D a or DB up to a position R a or RB on the rotor blade 108.Thus, the distance DB can be up to approximately 40% of the rotor blade length L, while the distance DA can be up to approximately 60% of the rotor blade length L. The distance DA or DB depends on the turbulence class "A", "B", or "C" in which the wind turbine 100 is to be operated. The relevant relationships are discussed in more detail in the description below. The values ​​of D a or DB are to be understood as examples, although values ​​significantly closer to the rotor blade tip 116, in particular up to and including the rotor blade tip 116, are also possible.

[0049] The vortex generators 118 in the hub area of ​​the rotor 106 ensure that, with the profiles of the rotor blades 108 provided there with a high relative profile thickness, the profiles can be flowed against at comparatively high effective angles of attack α eff , especially on dirty surfaces, without flow separation phenomena occurring when flowing around the profile. The profile of the rotor blade 108 equipped with the vortex generators 118 shifts the flow separation to higher angles of attack. This results in comparatively high lift values ​​compared to a profile not equipped with vortex generators. Vortex generators 118 ultimately ensure that the wind turbine 100 behaves robustly with regard to weather and environmental influences such as rain or increased contamination of the rotor blades by dirt or insects.

[0050] For efficient operation of the wind turbine 100, the turbulence class at a location of the wind turbine 100 is determined, and the nominal rotor speed is set depending on the determined turbulence class "A", "B", or "C". Uniformly parameterized operation of wind turbines 100 within a wind farm is dispensed with. Instead, the specific turbulence class "A", "B", or "C" determined at a location is used to determine the nominal rotor speed. Operating the wind turbine in a higher turbulence class "A", "B", or "C" may be more efficient, since the electrical power P that can be generated in the partial load range is greater at higher turbulence intensities I 15 than at lower turbulence intensities I 15 . The advantageous effect of the inventive solution is particularly pronounced for low-wind turbines, which already achieve nominal power at relatively low wind speeds.

[0051] Fig. 3 shows schematically and exemplary operating curves 120, 122 only for two different turbulence classes "A" and "B". The rotor speed n is plotted on the horizontal axis, and the electrical power P on the vertical axis. The operating curve 120 represents the operation of the wind turbine 100 in turbulence class "A". The operating curve 122 represents the operation of the wind turbine 100 in turbulence class "B". In turbulence class B, the wind turbine 100 is operated at a nominal rotor speed n B , and in turbulence class A at a nominal rotor speed n A , whereby the nominal rotor speed n B is greater than the nominal rotor speed n A . By reducing the nominal rotor speed n B to the nominal rotor speed n A , a load reduction is achieved. The increase in load associated with the transition to operation in the higher turbulence class due to the higher turbulence intensity I 15 can thus be partially, fully or overcompensated.The magnitude of the compensation depends on the reduction in the rated rotor speed. Alternatively, increasing the rated rotor speed n A to the rated rotor speed n B results in an increase in load. The increase in the rated rotor speed can therefore occur to the extent that the loads decrease during the transition from the higher turbulence intensity I 15 to the lower turbulence intensity and the overall load level at higher turbulence intensity and reduced rated rotor speed is not exceeded.

[0052] Fig. 4 shows schematically and exemplary curves of tip speed ratios λ for the different turbulence classes "A" and "B". The tip speed ratio λ describes the ratio of circumferential speed to the undisturbed wind flow velocity v. The exemplary curve 124 occurs during operation in turbulence class "A" and curve 126 occurs during operation in turbulence class "B". Reducing the rated rotor speed from the rated rotor speed n B to the rated rotor speed n A leads, above a certain wind speed, to lower tip speed ratios λ at which the wind turbine 100 is operated, which influences the generated power.

[0053] Fig. 5 shows schematically and exemplary curves 128, 130, 132 of effective angles of attack α eff for different turbulence classes "A", "B". The effective angle of attack α eff is plotted on the vertical axis. The length L of the rotor blade 108 is plotted on the horizontal axis. The curve 128 shown occurs when the wind turbine 100 is operated in turbulence class "B". Several of the vortex generators 118 are arranged starting from the rotor blade root 114 in the direction of the rotor blade tip 116. The number and positioning of the vortex generators 118, in particular their radial extension over the distance DB up to the position RB, is determined depending on the turbulence class "B" determined at the location of the wind turbine 100.

[0054] The curve 130 for the effective angle of attack α eff is established during a change in the operation of the wind turbine 100 from turbulence class "B" to turbulence class "A", wherein the radial extent of the arrangement of vortex generators 118 remains unchanged up to a maximum of the position RB, which is determined by the turbulence class "B".

[0055] The curve 132 finally occurs when the operation of the wind turbine 100 changes from turbulence class "B" to turbulence class "A", whereby the radial extent of the arrangement of the vortex generators 118 has been adapted to the turbulence class "A" and now extends to a maximum of the position RA.

[0056] Fig. 6 shows schematically and exemplary curves 134, 136, 138 of lift coefficients cl for the two different turbulence classes "A" and "B." The lift coefficient cl is plotted on the vertical axis. The length L of the rotor blade 108 is plotted on the horizontal axis. The curve 134 occurs when the wind turbine 100 is operated in turbulence class "B" with a radial expansion of the vortex generators 118 up to position RB on the rotor blade 108. The curve 136 occurs when the wind turbine 100 changes operation from turbulence class "B" to turbulence class "A," with the radial expansion of the vortex generators 118 remaining unchanged up to a maximum of position RB.The curve 138 is established when the operation of the wind turbine 100 changes from turbulence class "B" to turbulence class "A", whereby the radial extent of the vortex generators 118 has been adapted to the turbulence class "A" and now extends to a maximum of the position RA.

[0057] Fig. 7 shows schematically and exemplarily curves 140, 142, 144 of glide ratios c1 / c1, i.e. a quotient of a lift coefficient c1 to a drag coefficient c1 for different turbulence classes "A" and "B". The glide ratio c1 / c1 is plotted on the vertical axis. The length L of the rotor blade 108 is plotted on the horizontal axis. The curves 140, 142, 144 correspond to the Figur 5 und 6 operating conditions already described.

[0058] Accordingly, a reduction in the tip speed ratio λ, which results from the reduction of the nominal rotor speed, results in an increase in the angle of attack α eff, which is shown by the curve 130 in Fig. 5 The increase in the angle of attack α eff is greater the closer a profile section of the rotor blade 108 is shifted from the blade tip 116 towards the blade root 114. In a generally usual design of a rotor blade, the reduction of the tip speed ratio leads to a corresponding increase in the angle of attack α eff , as the curve 130 in Fig. 5 so that the maximum permissible angle of attack would be exceeded. Flow separation is accompanied by a drop in the lift coefficient ci , as shown in curve 136 according to the Fig. 6 shows, as well as the increase of the drag coefficient cd to a drop in the glide ratio cl / cd , which is the course 142 according to the Fig. 7 Both circumstances result in significant power losses, which the invention aims to avoid. In contrast, increasing the tip speed ratio leads to a reduction in the angle of attack α eff , thus reducing the risk of flow separation from the rotor blade root 114. The radial expansion of vortex generators can be reduced, which can lead to an increase in power.

[0059] The reduction in the rated rotor speed and the associated increase in the angle of attack α eff can be responded to by simultaneously increasing the blade angle or pitch angle. Increasing the pitch angle prevents flow separation and the associated power loss. However, increasing the pitch angle also leads to an undesirable, albeit smaller, power loss. Alternatively, the increase in the rated rotor speed and the associated reduction in the angle of attack α eff can be responded to by simultaneously lowering the blade angle or pitch angle. Lowering the pitch angle can lead to an increase in the turbine yield.

[0060] A further objective of the invention is to achieve the reduction of the rated rotor speed for load reduction during a transition from the lower turbulence class to the higher turbulence class with as little impact on the yield as possible. For this purpose, the rotor blades 108 are configured to determine the number and positioning of the vortex generators 118, in particular their radial extension starting from the rotor blade root 114 toward the rotor blade tip 116, depending on the specific turbulence class "A", "B", or "C".

[0061] The radial extension of the arrangement of the vortex generators 118 beyond the position RB up to the position RA causes the profile sections with vortex generators 118 to have a worse glide ratio cl / cd due to an increase in the drag in the area between the positions RB and RA, as can be seen from the comparison of the curve 140 during operation in turbulence class "B" with the curve 144 during operation in turbulence class "A" in Fig. 7 However, in the range between positions RB and RA, the curve 144 lies significantly above the curve 142 for operation in turbulence class "A" without an adjustment of the radial extension of the vortex generators 118. Thus, in an exemplary wind turbine 100, the measure of adapting the radial extension of the arrangement of the vortex generators 118 to turbulence class "A" is preferable from a yield perspective to the measure of maintaining the rotor blade 108 with vortex generators 118 and increasing the pitch angle.

[0062] Fig. 8 shows schematically and exemplary courses of power curves 146, 148, 150 during operation of the wind turbine 100 in different turbulence classes "A" and "B", plotted against the wind speed v. The course 146 shows the power curve that occurs when the wind turbine 100 is operated in turbulence class "B". The vortex generators 118 extend in the radial direction up to a maximum of the position RB . The course 148 shows the power curve that occurs when the wind turbine 100 is operated in turbulence class "A". The vortex generators 118 extend unchanged in the radial direction up to a maximum of the position RB . The curve 150 shows the power curve that occurs when the wind turbine 100 is operated in turbulence class "A", wherein, depending on the specific turbulence class "A", the radial extent of the vortex generators 118 has been extended to the position RA.The latter course of the power curve 150 is based on an operation which differs from an operation in turbulence class "B" by a reduced pitch angle.

[0063] Fig. 9shows schematically and by way of example, courses 152, 154, 155 of certain power curves at different turbulence intensities I 15 . The course 152 of a power curve shown as a dotted line depends on a low turbulence intensity I 15 , for example 8%. The course 154 of a power curve shown as a solid line depends on an average turbulence intensity I 15 , for example 12%. The course 156 of a power curve shown as a dashed line depends on a high turbulence intensity I 15 , for example 16%. The exemplary courses 152, 154, 156 of the power curves depend on the turbulence intensity I 15 of the wind field, so that in the part-load range at higher turbulence intensities I 15 more power is generated and in the range towards the nominal load P nominal less power P el is generated. As described, the wind field is characterized by a multitude of parameters.The most important wind field parameters are mean wind speed, turbulence, vertical and horizontal shear, wind direction change with height, oblique flow, and air density. Rated load is, in particular, the load acting on the wind turbine at which the wind turbine generates rated electrical power.

[0064] This effect can lead, particularly in the case of wind turbines 100 which are operated at low average wind speeds v, to the fact that, due to the increased frequency of low wind speeds v, the wind turbine 100 delivers more yield at increased turbulence intensities I 15 than at lower turbulence intensities I 15 .

[0065] Thus, by creating turbulence-dependent power curves 152, 154, 156, it is possible to take into account the fact that, at low average wind speeds, operating the wind turbine 100 in the higher turbulence class "A" generates a higher yield than operating it in the lower turbulence class "B." Thus, the yield loss caused by the nominal speed reduction can be further reduced and, if necessary, completely compensated for using the inventive method.

[0066] The implementation takes place on variable-speed, pitch-angle-controlled wind turbines 100, which are operated in different turbulence classes "A", "B", and "C" and, by means of a controller 200, are capable of taking the rated rotor speed or the torque and / or the pitch angle into account when controlling or regulating the wind turbine 100. The invention enables a virtually or completely yield-neutral reduction or compensation of turbine loads of a pitch-angle-controlled, variable-speed wind turbine 100 during a transition from turbulence classes with lower to higher turbulence intensity, from turbulence class "C" to turbulence class "B" or from turbulence class "B" to turbulence class "A", by reducing the rated rotor speed.In addition, the use of a site-dependent vortex generator configuration can be provided, whereby the radial extent of the vortex generators 118 is determined depending on the turbulence class "A," "B," or "C" determined at the site. Alternatively, when transitioning from a higher to a lower turbulence class, the turbine's yield can be increased by increasing the rated rotor speed and simultaneously reducing the blade angle and / or the radial extent of existing vortex generators.

[0067] The site-dependent design of the radial extension of the vortex generators 118 is also expedient in another context. A reduction in air density has the same physical effects as a reduction in the rated rotor speed. When a reduction in air density occurs, the pitch angle is also increased above a certain power level in order to prevent flow separation at the rotor blade 108 and thus significant yield losses. As already explained above, the less severe yield losses from pitching out can possibly be further minimized if the vortex generators are configured to match the air density prevailing at the location of the wind turbine 100.By adjusting the radial expansion of the vortex generators depending on the air density at the location, the increase in the pitch angle is less pronounced or can even be eliminated entirely, which ultimately results in higher yield. For a site-specific yield increase, an air density-dependent arrangement of vortex generators can be provided.

Claims

1. A method for operating a wind power installation (100) for the purpose of generating electrical power from wind, wherein the wind power installation (100) has an aerodynamic rotor (106) having rotor blades (108) that can be adjusted in their blade angle, and the rotor (106) is operated at a settable rated rotor speed (nA, nB), wherein a turbulence class at a site of the wind power installation (100) is determined, and the rated rotor speed (nA, nB) is defined in dependence on the determined turbulence class, and in the case of a transition from a lower turbulence class to a higher turbulence class, the rated rotor speed (nA, nB) is lowered, characterized in that the turbulence class is selected from the group that includes "A", "B" and "C", wherein the rated rotor speed (nA, nB) is defined, with respect to the determined turbulence class, in such a manner that the rated rotor speed (nA, nB) is lower for turbulence class "A" than for turbulence class "B", and lower for turbulence class "B" than for turbulence class "C".

2. The method as claimed in claim 1, characterized in that the turbulence class is determined on the basis of a turbulence intensity (I15) measured at the wind power installation (100) and preferably the definition of the rated rotor speed (nA, nB) in dependence on the determined turbulence class is effected in such a manner that the loads to be expected on the rotor (106) due to the measured turbulence intensity (I15) are compensated.

3. The method as claimed in any one of the preceding claims, characterized in that a plurality of vortex generators (118) are arranged on the rotor blades (108), between the rotor-blade root (114) and the rotor-blade tip (116), the number and positioning of which, in particular their radial extent (DA, DB) starting from the rotor-blade root (114) in the direction of the rotor-blade tip (116), is determined in dependence on the determined turbulence class and preferably the number and positioning of the vortex generators (118) along the rotor blade (108) is determined in dependence on a site-specific air density and further preferably the radial extent of the vortex generators (118) along the rotor blade (108) is determined in dependence on the air density in such a manner that additional yield losses due to an increase in the blade angle necessary at lower air density are at least partially compensated.

4. The method as claimed in any one of the preceding claims, wherein the rated rotor speed (nA, nB) is determined in dependence on a site-specific air density.

5. The method as claimed in any one of the preceding claims, characterized in that the wind power installation (100) is operated, in dependence on the turbulence class, according to differing operating characteristics, such that differing power curves (152, 154, 156) are guaranteed in dependence on the turbulence class.

6. The method as claimed in any one of the preceding claims, characterized in that a blade angle characteristic is defined in dependence on the determined turbulence class.

7. The method as claimed in any one of the preceding claims, characterized in that, a lowering of the rated rotor speed (nA, nB) is associated with an increase in the blade angle at at least one operating point and further preferably the increase in the blade angle at at least one operating point is counteracted by the design and positioning of vortex generators (118) in such a manner that the lowering of the rated rotor speed (nA, nB) remains substantially neutral in respect of yield.

8. The method as claimed in claim 7, characterized in that, in the case of the wind power installation (100) designed in dependence on a turbulence class, the assignment of vortex generators (118) to the rotor blades (108) is increased in a radially outward direction in order, in the case of a lowering in the tip-speed ratio (A) caused by the lowering of the rated rotor speed (nA, nB) in the case of a higher turbulence class, to substantially maintain during operation the blade angle of a lower turbulence class.

9. The method as claimed in claim 7 or 8, wherein the air density is taken into account in the design and positioning of vortex generators (118).

10. A wind power installation (100), comprising an aerodynamic rotor (106) having rotor blades (108) that can be adjusted in their blade angle, wherein the rotor (106) can be operated at a settable rated rotor speed (nA, nB), and comprising a closed-loop control system (200), characterized in that the closed-loop control system (200) is configured to operate the wind power installation according to a method as per at least one of claims 1 to 9.

11. A wind farm having a plurality of wind power installations (100) as claimed in claim 10.