METHOD FOR ADJUSTING THE OPERATING CHARACTERISTIC CURVE OF A WIND ENERGY PLANT

Description

[0001] The present invention relates to a method for adapting an operating characteristic of a wind turbine and to a method for controlling a wind turbine. Furthermore, the present invention relates to a corresponding wind turbine that uses a corresponding control method and / or uses an adapted operating characteristic.

[0002] Wind turbines are well known for generating electrical power from wind. An aerodynamic rotor is rotated by the wind, and electrical power is generated by a connected generator. The rotor speed, i.e., the rotor speed and the electrical power of the generator, can be controlled. Speed ​​and power are interdependent, and instead of power, the torque of the generator, i.e., the generator torque, can also be adjusted, or the power can be adjusted by adjusting the generator torque.

[0003] Operating curves are often used to adjust generator power or torque, at least for a partial load range where the wind speed has not yet reached the rated wind speed. However, such an operating curve can often also be present during a transition from a partial load range to the full load range, with the full load range describing a range where the wind speed has reached or exceeded the rated wind speed.

[0004] The purpose of specifying an operating characteristic curve is, in particular, to define an optimal operating point for the wind turbine for the respective wind speed. Such an optimal operating point is a characteristic at which maximum power is extracted from the wind.

[0005] However, loads on the wind turbine must also be taken into account. In particular, high rotor speeds usually place greater strain on the wind turbine than lower rotor speeds. One type of load is a so-called pivot load. A pivot load is a load resulting from the weight force on the rotor blade, particularly in the area of ​​the blade root, where the rotor blade is attached to a hub of the wind turbine. Not only the immediate attachment area can be problematic, but also a transition area that leads to the blade root or can be understood as part of the blade root. In particular, there is often a transition between a metallic connection area and an area made of another material, especially glass-fiber reinforced plastic.

[0006] In particular, the slow, constant rotor speed means that a maximum slewing load acts on the rotor blade, or particularly the blade root area, at approximately the 3 o'clock and 9 o'clock positions. In these two positions, the rotor blade is horizontal for the moment under consideration, and thus the maximum force of gravity acts on the rotor blade. This load is opposite at the 3 o'clock and 9 o'clock positions. Of course, there is also a load from gravity in the positions in between. However, it is strongest in the two positions mentioned, and these positions are also best suited to describing the problem.

[0007] With each rotation of the aerodynamic rotor, the direction of the slewing load changes twice, and this change in direction leads to the load. This total resulting load, including the load caused by the load change, can also be referred to as the slewing load.

[0008] Such slewing loads overlap with other loads that are not essential in this case and can be neglected for the purpose of explaining the problem. Therefore, there are two load cycles per rotor revolution for each rotor blade, and thus the number of load cycles is directly related to the number of revolutions. The faster the rotor rotates, the more frequent the load cycles, and the correspondingly higher the load from slewing loads.

[0009] To address this problem, a wind turbine is typically designed to withstand a certain number of load cycles over its lifetime. Essentially, the wind turbine is designed for a certain number of load cycles over its lifetime, which means it is designed for a specific number of rotor revolutions.

[0010] Thus, although a wind turbine is designed for such slewing loads, the load increases when the speed is increased because more rotations occur overall and thus more load changes occur, so that the load from slewing loads increases and can therefore potentially exceed a permissible level.

[0011] This can, in particular, lead to a speed increase being impossible, even if it could otherwise be achieved, particularly due to other loads. This has the disadvantage that an increase in power that could be achieved by increasing the speed cannot be achieved either. The additional slewing loads can therefore lead to an otherwise possible increase in power not being possible.

[0012] International Patent Application WO 2020 / 007629 A1 relates to a method for operating multiple wind turbines, in which a first wind turbine is arranged adjacent to a second wind turbine and a third wind turbine. The rotational speeds of the second and third wind turbines are adjusted to mask the tonal quality of the first wind turbine.

[0013] The European patent application EP 2463520 A2 relates to a method for operating a pitch-controlled wind turbine in which a setpoint M for the generator torque is specified depending on a speed of the generator or the rotor, wherein a transition point is provided in which a transition from partial load operation to nominal load operation takes place.

[0014] The international application with the publication number WO 2020 / 064925 A1 relates to a method for operating a wind turbine, wherein a turbulence class is determined at a location of the wind turbine and the rotor speed is set as a function of the determined turbulence class.

[0015] The present invention is therefore based on the object of addressing at least one of the aforementioned problems. In particular, a solution is to be created that enables an increase in speed, especially to increase power, without exceeding a permissible level of slewing loads. In particular, a solution is proposed that increases the total energy yield of the wind turbine, at least in terms of annual energy production, while maintaining permissible slewing loads or enables it to be increased to a high level. At the very least, an alternative solution to previously known solutions is to be proposed.

[0016] According to the invention, a method according to claim 1 is proposed. The method thus relates to the adjustment of an operating characteristic curve of a wind turbine. The wind turbine has a rotor with adjustable blade pitch. Such adjustment of the rotor blades is also referred to as pitching. The rotor, i.e., the aerodynamic rotor of the wind turbine, can be operated at a variable rotor speed. This also means, in particular, that the generator used in the wind turbine can also be operated at a variable speed.

[0017] To control the wind turbine, an operating characteristic curve is used that describes a relationship between the rotor speed and at least one other operating variable. In particular, two types of operating characteristic curves are considered: one describes a relationship between the rotor speed and the power, while another describes a relationship between the rotor speed and the generator torque.

[0018] The basic principle of such operating curves is otherwise similar or identical. Depending on a detected speed, the other operating variable, in particular the power or generator torque, is set, thus establishing the operating point. It may be that the set power or generator torque does not yet lead to a stable operating point, i.e., does not match the wind speed, so the speed changes, and then a new value for the operating variable is set until a stable operating point is reached.

[0019] It is proposed that the operating characteristic curve comprise a first characteristic curve section with a first speed range and a second characteristic curve section with a second speed range. The term "speed" is also used here as a synonym for the term "rotor speed." The first speed range has lower speeds than the second speed range.

[0020] For this purpose, it is now proposed that the operating characteristic be adjusted in such a way that values ​​of the operating variable of the first characteristic section are increased and values ​​of the operating variable of the second characteristic section are changed towards higher speeds.

[0021] It is also proposed that the operating characteristic curve be adjusted in such a way that the expected total number of rotor revolutions remains approximately the same over a given operating time of the wind turbine.

[0022] The operating variable in this respect is, of course, not the rotor speed. In particular, the operating variable can be the output power or the generator torque. The output power corresponds to the generator power; at least, in the present analysis, any differences that may be caused by power losses can be neglected. For the sake of simplicity, the term "power" is used synonymously for generator power or output power.

[0023] The purpose of the operating characteristic is to select a stable and suitable operating point for the respective wind situation. For this purpose, a power specified by the operating characteristic or a generator torque specified by the operating characteristic can be set depending on the rotor speed. For simplicity, the relationship is explained using power. Using the generator torque as the operating variable follows a similar procedure, which is well known to those skilled in the art.

[0024] Thus, a power level is set as a function of the rotor speed according to the operating characteristic curve. If this power corresponds to the power extracted from the wind by the aerodynamic rotor, the stable operating point has been found, which naturally changes with changing wind speeds. However, if the wind is stronger, the rotor extracts power from the wind and accelerates, thus increasing the speed. Otherwise, the speed decreases. If the speed increases, a new power value is read from the operating characteristic curve and set. This process is repeated until this power corresponds to the power extracted from the wind at that moment.

[0025] A similar approach is used when determining generator torque as an operating variable. Here, the generator torque is adjusted according to the characteristic curve until it corresponds to the torque resulting from the effect of the wind on the aerodynamic rotor.

[0026] The operating characteristic is usually a monotonically increasing characteristic, in particular a strictly monotonically increasing characteristic.

[0027] If operating variables in the first characteristic curve section are increased at fixed speed values, this means that speed values ​​are decreased at fixed operating variable values. This is because the operating characteristic curve is rising, at least in the first characteristic curve section. Shifting it upward is like shifting it to the left, to put it more clearly. If the power or torque is increased at a certain speed, this slows down the speed, resulting in a lower speed. Increasing the operating variable therefore has the effect of decreasing the speed.

[0028] It is also proposed that the second characteristic curve section be modified toward higher speeds. To modify the operating characteristic, it is particularly proposed in this aspect that the rotor speed also exceed the previous maximum rotor speed, in particular, the previous rated rotor speed. While the second characteristic curve section previously extended up to the rated speed, it can now extend up to a value above the rated speed. This could be, for example, 5% - 10% of the previous rated speed. The rated rotor speed can be simplified and synonymously referred to as the nominal speed.

[0029] Accordingly, the proposed changes to the operating curve result in the wind turbine operating at a higher speed in the second section of the curve. Therefore, the rotor speed will be higher under the same wind conditions.

[0030] Accordingly, the situation is exactly the opposite in the first section of the characteristic curve. Increasing the values ​​of the operating variable results in these values ​​being assigned to lower rotor speeds than before. Under the same wind conditions, the wind turbine will therefore operate at a lower speed in the first section of the characteristic curve.

[0031] According to the invention, the wind turbine operates at a higher speed in the second characteristic curve section and at a lower speed in the first characteristic curve section. This also allows for higher power generation in the second characteristic curve section. The higher speed, which leads to higher slewing loads, is compensated for by operating the turbine at a lower speed in the first characteristic curve section, thus reducing the slewing loads there.

[0032] Such an adjustment of the operating characteristic curve can usually be carried out after the wind turbine has been in operation for at least one year, or even more so after several years. Sufficient measured values ​​for the wind turbine's location are then available, allowing a reliable prediction of how and for how long the wind turbine will operate in the first and second sections of the characteristic curve. This allows the operating characteristic curve to be adjusted quite precisely so that the expected total number of rotor revolutions can be accurately predicted. The operating characteristic curve can then be adjusted so that the expected total number of rotor revolutions remains approximately the same over the specified operating time of the wind turbine.

[0033] The specified operating time of the wind turbine primarily refers to the maximum service life for which the wind turbine is designed. However, it may also be possible to recalculate and thus re-specify such a specified operating time. Preferably, however, an unchanged specified operating time is assumed, i.e., the same for both the previous operating curve and the adjusted operating curve.

[0034] Here, it was particularly recognized that such an increase in speed is possible if load limits are adhered to or observed, i.e., those limits must not be exceeded. In any case, an increase in the slewing load would occur, but this can be compensated for by reducing the speed in the first speed range, i.e., in the first characteristic curve section. This can achieve a power increase that is significantly greater than the power reduction due to the compensating speed reduction in the first characteristic curve section, i.e., in the first speed range.

[0035] According to one aspect, it is proposed that the first speed range lies above a switch-on speed up to a transition speed, wherein the transition speed lies in the range of 80% - 100% of a nominal speed, and that the second speed range lies at and above the transition speed. Thus, it is particularly proposed that the second speed range, and thus the second characteristic curve section, lie at relatively high speeds.

[0036] If the transition speed is 100%, the second characteristic curve segment, at least before the change, is at 100% of the rated speed, thus forming a vertical characteristic curve segment, which can also be referred to as a vertical branch. Changing it toward higher speeds can mean a shift of this vertical branch.

[0037] It was particularly recognized that at high speeds a further, sometimes even small increase in speed can lead to a comparatively large increase in power. This is due in particular to the fact that an operating characteristic curve - in particular such an operating characteristic curve is proposed - is comparatively steep towards such higher speeds, i.e. speeds above 80% of the rated speed. A small increase in speed is therefore associated with a large increase in power. Accordingly, such an operating characteristic curve is comparatively flat at lower speeds, in particular below 80% of the rated speed, so that large reductions in speed only lead to small reductions in power. This makes it possible to compensate for the increase in speed in the second characteristic section in the first characteristic section with comparatively little loss of power, so that the operating characteristic curve as a whole is more or less neutral for all the slewing loads.

[0038] In particular, it is proposed that the second characteristic curve section be modified toward higher speeds such that, after adjusting the operating characteristic curve, the second speed range extends to a maximum speed that lies above the rated speed. In this respect, the modification of the second characteristic curve section can also be referred to as a characteristic curve extension. The second characteristic curve section is thus extended toward higher speeds.

[0039] In particular, it is proposed here that the speed be increased above the rated speed. This aspect can be used to increase the speed range in which the wind turbine operates to a maximum speed above the rated speed. To comply with the loads, in particular to comply with the slewing loads or to comply with the load limits imposed by the slewing loads, the speed in the first speed range can be reduced to compensate.

[0040] According to one aspect, it is proposed that an operating power variable be used as the operating variable, which is representative of a generator torque, a generator power, or an output power, so that the operating characteristic curve indicates a relationship between the rotor speed and the operating power variable. The generator torque can be synonymous with a generator torque.

[0041] The use of generator power or output power as an operating variable, or the use of generator torque as an operating variable, has already been explained above. This aspect clarifies that the operating characteristic curve indicates a relationship between the rotor speed and the operating power variable, which is therefore adjusted accordingly via the generator's operating characteristic curve in order to influence the power. This can then be achieved via the generator torque, the generator power, or an output power. Thus, the operating characteristic curve is modified with regard to this operating power variable in order to increase the power output.

[0042] According to one aspect, it is proposed that the first characteristic curve section lies entirely in a partial load range in which the wind speed is below a nominal wind speed and / or the rotor speed is below a nominal rotor speed. According to this aspect, it is proposed that the second characteristic curve section lies at least partially in a full load range in which the wind speed reaches the nominal wind speed and in particular is even higher, and in which the rotor speed is limited by adjusting the blade angle of the rotor blades, wherein in particular the second characteristic curve section comprises a transition range from the partial load range to the full load range, i.e. lies in this transition range.

[0043] The second section of the characteristic curve is therefore at comparatively high speeds and extends into the full load range. Here it was recognized that an increase in power output is still possible, particularly in the transition to this full load range. At the beginning of the full load range, the rotor blades are usually turned out of the wind so that the full available power is no longer drawn from the wind for the purpose of protecting the turbine. At the beginning of the full load range, i.e. at wind speeds that are only slightly above nominal wind speed, the load on the rotor blades is very high, but otherwise the load is not very high and an increase in speed together with an increase in power can generally be considered when the loads occurring are taken into account.If the speed is increased slightly, as suggested, the slewing loads will inevitably increase, but this can be compensated for by the lower speed in the first section of the characteristic curve. This makes it possible to convert slightly more of the available wind power into electrical power in this transitional range from the partial load to the full load range than before the operating characteristic curve was adjusted.

[0044] According to one aspect, it is proposed that the operating characteristic curve be adjusted such that the rotor speed in the second characteristic curve section is increased at least partially above the rated rotor speed, i.e., above the rated speed, to a maximum speed. The wind turbine is thus operated at a higher speed than the rated speed. As already explained, this can lead to an increase in power output.

[0045] To this end, it is proposed that the rotor speed be reduced to a rotor speed below the maximum speed, in particular to the rated rotor speed, for wind speeds above an increased wind speed, which is above a rated wind speed and characterizes a highest wind speed of the second characteristic curve section, and for wind speeds below a storm wind speed above which the rotor speed and rated rotor speed are reduced. It is therefore proposed that the rotor speed be increased above the rated rotor speed to the maximum speed, but only for the second characteristic curve section. After this second characteristic curve section, i.e. for wind speeds that are no longer assigned to this second characteristic curve section, the speed is reduced again, namely specifically to the rated speed. The rated speed is then maintained up to the storm wind speed.

[0046] This essentially ensures that the turbine operates at a higher speed at the beginning of the full-load range. This allows for an increase in power output with a comparatively small increase in load on the wind turbine. This maximum speed is particularly recommended for wind speeds from the nominal wind speed up to the increased wind speed, which represents the highest wind speed of the second characteristic curve section, thus marking the end of the second characteristic curve section in terms of wind speed.

[0047] According to one aspect, it is proposed that the wind turbine is installed at an installation location which is characterized by an altitude which indicates the altitude of the installation location, and that the adaptation of the second characteristic curve section is carried out as a function of the altitude of the installation location and / or as a function of an average air pressure at the installation location.

[0048] It was particularly recognized that installation locations at high altitudes, especially in mountains, pose a higher risk of stalls. This risk can be reduced by increasing the rotor speed. Direct wind loads are reduced due to the lower air density. However, the load from slewing loads is not reduced by the air pressure; instead, it is increased by the increased speed because the number of load cycles increases. However, it was recognized that this can be compensated for by reducing the speed in another area.

[0049] In particular, it is proposed that the values ​​of the operating variable in the second characteristic curve section be adjusted to higher speeds, the higher the altitude and / or the lower the air pressure, and, in particular, that the maximum speed be selected to be higher the higher the altitude and / or the lower the air pressure. By taking altitude and / or air pressure into account, an increase in power output can be effectively achieved by increasing the speed. An increase in load can be compensated for by increasing the swivel loads.

[0050] According to one aspect, it is proposed that a wind field and / or a temporal and / or local wind speed distribution in the area of ​​the wind turbine is recorded as the wind characteristic and that the increase in the rotor speed in the second characteristic curve section is carried out as a function of the wind characteristic, wherein the rotor speed in the second characteristic curve section is increased to the greater extent, the greater the local and / or temporal variation of the wind speed and / or the greater a detected gust is.

[0051] It was particularly recognized here that a local and / or temporal variation in wind speed and / or strong gusts can also lead to temporary high wind speeds in a temporal and / or spatial sense, which poses the risk of stall. This can be counteracted by increasing the rotor speed. In this way, it is proposed that the operating characteristic be adjusted depending on the wind characteristics. In particular, the second characteristic section is adjusted accordingly, thus increasing the rotor speed there. At the same time, however, a reduction in the rotor speed in the area of ​​the first characteristic section is proposed to compensate for this.

[0052] According to one aspect, it is proposed that at least one detection device for detecting a wind characteristic is provided on the wind turbine, in particular at least one measuring device, and by means of the detection device at least one wind property is detected, namely at least one wind shear, one wind turbulence and / or a local wind speed distribution, wherein the operating characteristic is adapted depending on the detected wind property.

[0053] This can further improve slewing load-optimized operation. It is therefore proposed to equip the turbines with suitable measuring devices that can record at least the wind speed, but preferably also shear and turbulence, in order to determine an exact wind speed distribution. The more precisely the wind speed distribution at the site is known, the more precisely the operation can be fine-tuned to maximize yield gains. Such a recording device can also easily detect wake effects, for example. If it is determined, for example, that the wind speed distribution is shifting towards lower wind speeds due to wake effects, the maximum speed can be increased further above the nominal speed.

[0054] According to one aspect, it is proposed to adapt the operating characteristic curve depending on the azimuth orientation, in particular that the increase in rotor speed in the second characteristic curve section is carried out depending on the azimuth orientation of the wind turbine. Here, it was recognized that the wind characteristics at an installation site can generally vary in different wind directions and thus depending on the azimuth orientation. For example, the wind speed can vary to different degrees depending on the wind direction and azimuth orientation. Rapidly increasing wind speeds can cause flow stalls, which are therefore particularly to be feared when the wind speed varies greatly. Such flow stalls are therefore to be feared in certain wind directions or at certain azimuth orientations, and are at least more likely there.For such azimuth orientations, increasing the engine speed can reduce the risk of stall. However, this should only be considered for such azimuth orientations.

[0055] Thus, it is specifically proposed that the rotor speed in the second characteristic curve section be increased the more turbulent the average wind pattern is for a given azimuth orientation. Here, too, the underlying idea is that a turbulent average wind pattern also contains areas of high wind speed, which can then lead to stall. This can be avoided by increasing the speed.

[0056] Additionally or alternatively, it is proposed that the increase in rotor speed in the second characteristic curve section be greater for an azimuth orientation in which the wind turbine is located in the wake of another wind turbine than for an azimuth orientation in which the wind turbine is not located in the wake of another wind turbine. Here, too, it was recognized that turbulence can occur in the wake of a wind turbine and can lead to short-term higher wind speeds, thus resulting in a stall.

[0057] In particular, it was recognized that all of this can be different for different azimuth orientations. This led to the suggestion of using different operating characteristics for different azimuth orientations. It is therefore proposed that the operating characteristic be adjusted depending on the azimuth orientation.

[0058] According to one aspect, it is proposed that the increase in rotor speed in the second characteristic curve section relative to the nominal speed is in the range of 2% - 10%, in particular in the range of approximately 3% - 8%. The idea underlying this is that, at an operating point that can be assigned to a wind speed, a rotor speed according to the characteristic curve is present or established, and this rotor speed is increased by the stated values ​​in the second characteristic curve section. In particular or alternatively, this also means that the second characteristic curve branch is changed, in particular shifted, by 2% - 10%, in particular in the range of 3% - 8%, towards a higher speed.

[0059] A uniform shift means that the rotor speed is generally increased by this percentage range. Preferably, the increase can also vary within this range. In particular, it is also proposed that the second characteristic curve section be modified or extended toward higher speeds by the specified range. Assuming that the second characteristic curve section extends up to the rated speed before adjustment, after adjustment it extends to a maximum speed that is 2% - 10%, in particular 3% - 8%, above the rated speed.

[0060] According to the invention, a method for controlling a wind turbine is also proposed, wherein the wind turbine has a rotor with rotor blades whose blade angle is adjustable, the rotor can be operated at a variable rotor speed, and an adapted operating characteristic curve is used to control the wind turbine, which describes a relationship between the rotor speed and at least one further operating variable. The adapted operating characteristic curve has a first characteristic curve section with a first speed range and a second characteristic curve section with a second speed range. The first speed range has lower speeds than the second speed range, and the adapted operating characteristic curve is designed such that the operating variable of the first characteristic curve section has increased values ​​compared to an operating characteristic curve determined to be optimal.For this purpose, the operating variable in the second characteristic curve section is modified, specifically expanded, toward higher speeds compared to an operating characteristic curve determined as optimal. The first and second characteristic curve sections of the adjusted operating characteristic are coordinated such that the expected total number of rotor rotations over a given operating time of the wind turbine does not exceed the total number specified for the operating characteristic curve determined as optimal.

[0061] The wind turbine is therefore controlled using an adapted operating characteristic. In this respect, the operating characteristic is adjusted compared to an operating characteristic determined to be optimal. An operating characteristic determined to be optimal is one that is based on a maximum power coefficient. The optimal operating characteristic is therefore set or specified so that maximum power can be extracted from the wind during partial load operation, while adhering to load limits. Adhering to load limits is usually only or primarily relevant in the transition to the full load range. In particular, this means that optimal operating characteristics are based on a nominal speed of the wind turbine, i.e. a nominal rotor speed, as the maximum rotor speed.

[0062] The adjusted operating characteristic now deviates from this. In the second characteristic section, the rotor speed is increased.

[0063] To compensate, the operating variable in the first characteristic curve section is increased compared to the operating characteristic determined to be optimal. For the same rotor speed values, the operating variable therefore exhibits higher values. As explained above, this leads to lower speed values ​​in the first characteristic curve section at the same wind speeds.

[0064] A speed increase is particularly achieved in the upper range of the operating curve, i.e., at high rotor speeds, especially in the transition area to the full-load range. Here, the rotor speeds are increased more sharply toward a load limit. This is possible, in particular, by taking into account the current and individual load conditions of the specific wind turbine at the specific installation site.

[0065] To compensate, the rotor speed is reduced in the lower range of the operating characteristic curve, meaning that the wind turbine is no longer operating at its optimal operating point there. There is a loss of power, but it has been recognized that this is comparatively small because the power coefficient changes very little with the speed and thus the change in the tip speed ratio, as long as the changes in the speed and thus the changes in the tip speed ratio are not too great. It has been recognized that the power coefficient is selected to be maximum at the optimal operating characteristic curve. A characteristic curve that shows the power coefficient as a function of the tip speed ratio therefore has a maximum point at the tip speed ratio selected for the optimal operating characteristic curve. This also means, however, that it has a derivative of zero in this range, i.e., to put it simply, it has a plateau.If the tip speed ratio is changed, the corresponding point in this characteristic curve changes only slightly due to the initial gradient of zero.

[0066] This insight is exploited here. At high speeds, where the operating characteristic curve also requires consideration of load limits, increasing the speed can lead to a significant increase in power. The increased slewing loads can be compensated for by reducing the rotor speed within a range where the reduction in speed leads to only a very slight reduction in power.

[0067] According to one aspect, it is proposed that the operating characteristic determined as optimal be designed such that the wind turbine is operated in the first speed range at an optimal tip speed ratio, at which a maximum power coefficient (Cp value) is achieved, and that in the adjusted operating characteristic, the wind turbine is not operated at the optimal tip speed ratio in the first speed range. It is therefore expressly proposed that the optimal operating characteristic be based on an optimal tip speed ratio, i.e., a maximum power coefficient, and that this optimal operation is expressly deviated from in the first speed range in the adjusted operating characteristic.

[0068] It should be noted that it is a common approach for experts to design the operating characteristic curve for an optimal tip speed ratio. This means that a particular operating variable, particularly an operating power variable, is assigned to each speed, and that an optimal tip speed ratio, i.e., a tip speed ratio with the maximum power coefficient, is established at the relevant wind speed.

[0069] The maximum power coefficient, or the power coefficient in general, also depends on the blade angle of attack. In the part-load range, however, this is often set to a constant value. This blade angle can assume the same and, in particular, constant value in the operating characteristic, at least in the first section of the characteristic, i.e., in the first speed range, both for the optimal operating characteristic and for the adapted operating characteristic. In other words, when the operating characteristics are changed, the blade angle is preferably not changed in the adapted operating characteristic compared to the optimal operating characteristic. Even with the described adjustment of the operating characteristic, the blade angle is preferably not changed in the part-load range.

[0070] According to one aspect, it is proposed that at least one further operating characteristic be provided, which differs from the adjusted operating characteristic, and that the adjusted operating characteristic and the at least one further operating characteristic be used for different azimuth orientations of the wind turbine. Furthermore, or alternatively, it is proposed that wind characteristics in the region of the wind turbine be detected, and that the adjusted operating characteristic and the at least one further operating characteristic be used for different wind characteristics.

[0071] Furthermore, it is also or alternatively proposed that the rotor speed in the second characteristic curve section is higher for an azimuth orientation in which the wind energy is located in a wake area of ​​another wind turbine than for an azimuth orientation in which the wind turbine is not located in a wake of another wind turbine, wherein in particular the adapted operating characteristic curve is provided for the azimuth orientation in which the wind turbine is located in the wake of the other wind turbine.

[0072] Thus, an additional operating characteristic is provided, which is itself an adapted operating characteristic and differs from the optimal operating characteristic. The additional operating characteristic, or several additional operating characteristics, can be designed for different conditions and then used accordingly. For this purpose, it is particularly recommended to use different operating characteristics for different azimuth orientations.

[0073] From measurements taken during operation of the wind turbine or from surveying the installation site, differences for different azimuth orientations can be known. This is exploited and proposed to assign different operating characteristics to different azimuth orientations. In particular, it was also recognized that an azimuth orientation can be easily identified, since it is already a parameter in the operation of the wind turbine, and thus a corresponding operating characteristic, namely the adjusted operating characteristic or at least another operating characteristic, can be easily selected.

[0074] The importance of the different wind conditions that can occur for different azimuth orientations has already been described above in connection with adjusting the operating characteristic. These findings also apply here to the question of which rotor speed is appropriate for which wind conditions.

[0075] It is also possible to additionally or alternatively record wind characteristics in the area of ​​the wind turbine. Then, depending on the recorded operating characteristics, the adjusted operating characteristic or at least one additional operating characteristic can be selected. When selecting, the wind characteristics can be specifically characterized by a value, such as a gust. For example, a gust can be characterized in a range from 0 to 1, where 0 means no gusts at all and 1 means maximum gusts. Of course, other characteristic values ​​and / or wind characteristics are also possible. The significance of different wind characteristics has already been explained above.

[0076] In particular, it is proposed that the adjusted operating characteristic and, if present, the at least one further operating characteristic be each adjusted by a method for adjusting an operating characteristic according to at least one embodiment explained above or according to an aspect explained above. The advantages described for adjusting an operating characteristic can thus be advantageously used for controlling the wind turbine. The wind turbine is then no longer controlled with the previously used optimal operating characteristic, but with the adjusted operating characteristic, possibly with a further operating characteristic depending on the situation.

[0077] According to the invention, a wind turbine is also proposed, comprising a rotor with adjustable blade angle rotor blades and a turbine controller for controlling the wind turbine, wherein the rotor is operable at a variable rotor speed, and an operating characteristic curve is used to control the wind turbine, which describes a relationship between the rotor speed and at least one operating variable. It is proposed that the operating characteristic curve be implemented in the turbine controller and have a first characteristic curve section with a first speed range and a second characteristic curve section with a second speed range.In this case, the operating characteristic curve has been adjusted compared to a previous operating characteristic curve in such a way that values ​​of the operating variable of the first characteristic curve section have been increased and values ​​of the operating variable of the second characteristic curve section have been changed towards higher speeds, and that the adjustment of the operating characteristic curve has been carried out in such a way that an expected total number of rotations of the rotor over a given operating time of the wind turbine has remained approximately the same.

[0078] In particular, it is proposed that the operating characteristic of such a wind turbine be adjusted compared to the previous operating characteristic according to a method according to one of the above-described embodiments or aspects for adjusting an operating characteristic. Thus, a wind turbine is proposed that has an adjusted and thus improved operating characteristic in order to further increase power yield.

[0079] According to one aspect, a wind turbine is also proposed that is controlled using a method according to one of the above-described embodiments or aspects relating to the control of a wind turbine. Optionally, the wind turbine is configured as described above for a wind turbine according to at least one embodiment and one aspect.

[0080] The invention is explained in more detail below using exemplary embodiments with reference to the accompanying figures. Figure 1 shows a wind turbine in a perspective view. Figure 2 shows a wind farm in a schematic representation. Figure 3 shows a diagram in which several operating characteristics are compared. Figure 4 shows a diagram in which several curves of the tip speed ratio are compared as a function of the wind speed, which correspond to the operating characteristics of the Figure 3 correspond.

[0081] Figure 1 shows a schematic representation of a wind turbine according to the invention. The wind turbine 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 with three rotor blades 108 and a spinner 110 is provided on the nacelle 104. During operation of the wind turbine, the aerodynamic rotor 106 is set in rotation by the wind and thus also rotates an electrodynamic rotor or rotor of a generator, which is directly or indirectly coupled to the aerodynamic rotor 106. The electrical generator is arranged in the nacelle 104 and generates electrical energy. 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.

[0082] The wind turbine 100 has an electrical generator 101, which is indicated in the nacelle 104. Electrical power can be generated by means of the generator 101. A feed-in unit 105, which can be designed particularly as an inverter, is provided for feeding in electrical power. This allows a three-phase feed-in current and / or a three-phase feed-in voltage to be generated according to amplitude, frequency, and phase for feeding into a grid connection point PCC. This can be done directly or jointly with other wind turbines in a wind farm. A system controller 103 is provided for controlling the wind turbine 100 and the feed-in unit 105. The system controller 103 can also receive default values ​​from external sources, in particular from a central farm computer.

[0083] Figure 2shows a wind farm 112 with, for example, three wind turbines 100, which may be identical or different. The three wind turbines 100 are thus representative of essentially any number of wind turbines in a wind farm 112. The wind turbines 100 provide their power, namely in particular the generated electricity, via an electrical farm grid 114. The currents or power generated by the individual wind turbines 100 are added together, and a transformer 116 is usually provided, which steps up the voltage in the farm and then feeds it into the supply grid 120 at the feed-in point 118, which is also generally referred to as a PCC. Fig. 2 is only a simplified representation of a wind farm 112. For example, the park network 114 can be designed differently, for example by also having a transformer at the output of each wind turbine 100, to name just one other embodiment.

[0084] Figure 3 shows a diagram with three operating characteristics that are compared here. In this example, the three operating characteristics indicate a relationship between the rotor speed n and the generator power P. The generator power P is therefore an operating variable. Instead of the generator power P, a different power or a generator torque can be used as the operating variable. All characteristics therefore indicate at which speed which generator power should be set. The diagram therefore ranges from 0 power to rated power PN . For rotor speeds, it ranges from speed 0 to slightly beyond the rated speed n N. All operating characteristics show a vertical course in the area of ​​the rated speed n N, although this can also have a slight gradient.

[0085] In Figure 3Three operating curves are shown. The current operating curve, 301, is a curve specifically designed for a new wind turbine. In particular, it represents an optimal operating curve assuming the underlying wind conditions.

[0086] In addition, an operating characteristic curve 302 adapted according to the invention is shown, which is created after adapting the previous operating characteristic curve 301.

[0087] Furthermore, an alternative operating characteristic curve 303 is shown, which serves only for the purpose of explanation and which partially corresponds to the adapted operating characteristic curve 302, namely particularly in the steep range near the nominal speed n N .

[0088] The previous operating characteristic curve 301, like all operating characteristic curves, also has a power value of 0 at a speed with the value 0. At a starting speed n A, for example, the wind turbine starts operating in such a way that some power is generated, i.e. the power value slowly increases with increasing speed. It should be emphasized that operating characteristic curves do not represent a time-dependent curve, but rather reflect stationary operating conditions. When the turbine starts up, it is usually the case that once a starting wind speed is reached, the turbine begins to rotate, the speed then increases and then once the starting speed n A is reached, the power is switched on and then increases as the wind speed continues to increase. If the wind speed does not increase any further, however, the operation of the wind turbine can continue with a low power P even at a speed only briefly above the switching-on speed n A.

[0089] In any case, an operating point of the wind turbine, characterized by speed and power, moves along the characteristic curve—in this case, initially the previous operating curve 301—as the wind speed continues to increase. Depending on the wind speed, however, any operating point on this speed-power characteristic curve can also be maintained.

[0090] At approximately rated speed n N , the previous operating characteristic curve 301 essentially reaches its maximum speed value, which corresponds to the rated speed n N , although the power can still vary depending on the wind speed. For control reasons that are not relevant here, this almost vertical branch can be slanted at the rated speed n N and does not have to be exactly vertical.

[0091] To adapt the operating characteristic, i.e. to change the previous operating characteristic 301 into the adapted operating characteristic 302, a first speed range A1 and a second speed range A2 are considered. The first speed range A1 ranges from a starting speed n A to a transition speed n U , and the second speed range A2 ranges from the transition speed n U to the maximum speed n M or at least to the nominal speed n N . The part of the respective operating characteristic that lies in the first speed range A1 is thus a first characteristic section, and the part of the respective characteristic that lies in the second speed range is thus a second characteristic section.

[0092] In order to adapt the operating characteristic, it is now proposed that values ​​of the operating variable, in this case power values ​​P of the second characteristic section, be changed towards higher speeds, i.e. that the second characteristic section is extended to higher speeds. Basically, the second characteristic section is shifted to the right according to Figure 3, i.e. towards higher speeds. This is indicated by speed increase arrows 306. The second speed range A2 of the previous operating characteristic 301 essentially only ranged from a speed just below the nominal speed n N up to the nominal speed n N . This second speed range A2 has now been extended to such an extent that it is now extended up to a maximum speed n M . The speed can therefore now reach up to this higher value of the maximum speed n M.

[0093] It should be noted that, for the sake of clarity, the second speed range for both the previous operating characteristic 301 and the adapted operating characteristic 302 (and later also the alternative operating characteristic 303) is always referred to as the second speed range A2, although the second speed range of the adapted operating characteristic 302 is extended and covers a larger speed range than for the previous operating characteristic 301.

[0094] Of course, it should also be noted here that although the second speed range A2 is quite small, a large power range exists in the second characteristic curve section of the adjusted operating characteristic 302 in the second speed range A2. Depending on the wind speed, the power can vary, and different power values ​​can be provided with only a slight variation in the speed.

[0095] It should also be taken into account that the operating characteristics, i.e. all three operating characteristics 301 to 303, can in practice also be implemented partly with the help of a control system, in particular a speed control. In particular in the very steep branch of the second characteristic section, especially when it is vertical, implementation by means of a speed control can be provided. Such a speed control regulates the speed, i.e. the rotor speed, of the wind turbine to the value shown, with the power P being the manipulated variable. The higher the wind speed, the higher the power drawn must be in order to maintain the speed. The generator power that results when the speed is regulated thus corresponds to the power assigned to the current wind speed, without the wind speed needing to be recorded. This results in a point on the relevant operating characteristic curve.If such a controller has an integral component, even a vertical branch of the operating characteristic can be realized. In a pure P-control, the branch should not be completely vertical, but rather have a steep slope.

[0096] The adjusted operating characteristic curve 302 thus leads to an increased rotor speed in the second speed range A2. This would increase the total number of revolutions for the operating time of the wind turbine. To compensate for this, it is proposed to reduce the speed in the first speed range A1, which can be the same for all three operating characteristic curves shown. This is achieved by increasing the values ​​of the operating variable, i.e. the values ​​of the generator power P. This is indicated by power increase arrows 308. By increasing the power values ​​according to the power increase arrows 308, the previous operating characteristic curve 301 is changed and thus adapted to the adjusted operating characteristic curve 302. This increase in the power values ​​corresponds to a reduction in the speed.This first characteristic curve section of the previous operating characteristic curve 301 in the first speed range A1 has the same effect as a change of this first characteristic curve section to the left, i.e. towards lower rotor speed values.

[0097] In any case, this creates an adapted operating characteristic curve 302, which achieves an increase in the speed in the second speed range A2 and results in a reduction in the rotor speed in the first speed range A1. This rotor speed increase in the second rotor speed range A2 and the rotor speed reduction in the first speed range A1 are coordinated in such a way that, as a result, the expected total number of rotor rotations remains approximately the same over the specified operating time of the wind turbine, i.e., the same as in the previous operating characteristic curve 301.

[0098] Essentially, the procedure can be such that a speed increase is carried out to improve the power output, in particular to avoid flow stalls in the second speed range A2. Theoretically, it is also possible to perform only this speed adjustment, and this is precisely what the alternative operating characteristic curve 303 demonstrates. With the alternative operating characteristic curve 303, the rotor speed is essentially only increased compared to the previous operating characteristic curve 301. However, this leads to a higher total number of rotor rotations over the specified operating time of the wind turbine and therefore leads to excessive loading of the wind turbine or is inadmissible due to such an increased load.

[0099] Essentially, the proposed remedy is to additionally adjust the existing operating characteristic 301 by reducing the speed in the first speed range A1, in addition to changing the alternative operating characteristic 303. This can be achieved by increasing the values ​​of the operating variables in the range, as indicated by the power increase arrows 308.

[0100] Figure 4 shows three characteristic curves, each showing the progression of a tip speed factor λ as a function of the wind speed VW. Figure 3 shows the Figure 4 thus a previous λ characteristic curve 401, an adapted λ characteristic curve 402 and an alternative λ characteristic curve 403.

[0101] Figure 4is for illustrative purposes only, and therefore no values ​​are shown for either the tip speed factor λ or the wind speed VW. However, the values ​​for the wind speed VW increase to the right and for the tip speed factor λ increase upward.

[0102] The previous λ characteristic curve 401 is essentially selected to result in an optimal power coefficient, at least in the first wind speed range B1. As a precaution, it should be noted that the tip speed is defined as the quotient of a blade tip speed divided by the wind speed. The tip speed is therefore the speed of the blade tip of a rotor blade of the wind turbine rotor and can also be referred to as the orbital speed. The tip speed ratio λ is also an important parameter for the aerodynamic behavior of the rotor because this quotient of blade tip speed to wind speed influences the actual angle of attack of the rotor blade. This, in turn, influences whether stalls are to be feared.

[0103] Therefore, a high rotor speed and thus a high tip speed ratio may be desirable, especially at high wind speeds. Accordingly, an increase in the tip speed ratio is proposed, particularly in the second wind speed range B2, which Figure 4 as a tip speed ratio increase 406. This increase is proposed for both the adjusted λ characteristic 402 and the alternative 403.

[0104] To compensate, however, a λ reduction 408 is proposed for the adjusted λ characteristic curve 402. A reduction in the rotor speed and thus the tip speed ratio in the first wind speed range B1, i.e., at low wind speeds, is less likely to lead to a stall risk, so this compensation can be easily implemented. Furthermore, this reduction in the rotor speed or the tip speed ratio in the first wind speed range B1 also leads to only a slight reduction in the power coefficient, so that only a slight power loss occurs, which is acceptable in view of the significant power gain in the second wind speed range B2.

[0105] Essentially, the first wind speed range B1 can be assigned to the first speed range A1, and the second wind speed range B2 to the second speed range A2. This also clearly shows that both wind speed ranges B1 and B2 can be similar in size. Upon reaching the second wind speed range B2, a comparatively high rotor speed is already present, which does not increase any further, or not significantly, as the wind continues to increase in the second wind speed range B2. However, as explained, the generator power P continues to increase with increasing wind speed, even in the second wind speed range B2.

[0106] The alternative λ characteristic curve 403 essentially shows a desirable curve, in which the λ characteristic curve reaches high values ​​in the first wind speed range B1, where a high power coefficient exists. The alternative λ characteristic curve 403 is therefore optimal in the first wind speed range B1. In the second wind speed range B2, it is also increased and can achieve the advantages already explained for the increase in speed or the increase in the tip speed ratio. However, the slewing loads increase, which can lead to an excessively high overall load, in particular to an impermissibly high load due to the slewing loads, so that this otherwise perhaps desirable alternative λ characteristic curve 403 is not possible. In order to nevertheless exploit the described advantages to the greatest extent possible, the adapted λ characteristic curve 402 is proposed, which is lowered in the first speed range B1.However, it was recognized that the disadvantages of this reduction are comparatively small.

[0107] According to the invention, the following was particularly recognized.

[0108] Increasing the rated speed is a proven way to increase the yield of a wind turbine. The turbine typically achieves better aerodynamic performance coefficients because higher rated speeds allow the turbine to operate at the optimal tip speed ratio for longer, and even after the optimal tip speed ratio has been exceeded, the turbine continues to operate at higher tip speed ratios than when operating at reduced rated speeds.

[0109] However, increasing rated speeds is subject to limitations. One important limitation is compliance with maximum sound power levels. If such a requirement exists and the turbine already reaches these maximum permissible sound power levels when operating at a non-increased rated speed, increasing the rated speed to increase yield is usually not feasible. At many locations, such regulatory requirements are either temporarily or completely absent.

[0110] Another very important limitation in many practical cases is the load balance of the turbine, especially the slewing loads and, in particular, the operating slewing loads. For the sake of simplicity, the slewing loads are equated with the operating slewing loads. The operating slewing loads are, to a good approximation, generated primarily by the number of revolutions during the turbine's operating life. Increasing the rated speed would inevitably lead to a higher number of revolutions and possibly to exceeding the certified loads. A yield gain could then not be realized, as the planned measure of increasing the rated speed is not feasible due to load constraints.

[0111] Increasing the rated speed, i.e. increasing the speed or maximum speed above a previous rated speed, is particularly advantageous and desirable if the turbine has a rotor blade that is subject to flow separation phenomena during operation. Flow separation can also be synonymously referred to as flow stall. This phenomenon can occur, for example, in locations where the air density is lower than the air density for which the rotor blade was designed. This is especially the case for mountainous locations. At such locations, it can regularly occur that flow separation on the rotor blade occurs at wind speeds before the turbine's rated power is reached.

[0112] In such a case, increasing the speed, or rather the rated speed, is a particularly effective measure, since the associated increase in the tip speed ratio and the resulting reduction in blade angle of attack counteract flow separation and avoid the associated power losses.

[0113] In summary, it can be stated that increasing rated speeds has aerodynamically beneficial effects, leading to more efficient power conversion at the rotor blade, and thus to increased yield. This applies both to rotor blades that are aerodynamically clean, i.e., without the occurrence of flow separation, and to rotor blades that are operated in critical conditions, i.e., in operating conditions with temporary or permanent flow separation.

[0114] However, increasing the rated speed, i.e., increasing the speed above the previous rated speed, is limited by increased operating slewing loads, meaning the full potential for increased yield cannot be realized. The task is therefore to establish a procedure that enables increasing the rated speed, i.e., increasing the speed above the previous rated speed, without exceeding the system loads, especially the operating slewing loads. In other words, the task is to find a slewing load-optimized operating management system.

[0115] The basic approach to slewing load-optimized operation is to keep the number of revolutions constant throughout the system's lifetime. If the rated speed is increased, as described in the previous section as advantageous, the speeds in another operating range of the system must be reduced to keep the number of revolutions constant.

[0116] According to the invention, this is achieved in the partial load range by lowering the partial load tip speed ratio. Naturally, performance drops must be expected in the partial load range, since it can be assumed that the system has been operating at an optimal partial load tip speed ratio up to this point. Overall, an increase in yield can then be expected if the performance increase from increasing the rated speed is greater than the performance drop in the partial load range.

[0117] If the nominal speed and part-load tip speed ratio parameters are carefully selected, for example, with the aid of numerical optimization tools, the desired yield increase can be achieved overall. This is especially true at locations where flow separation occurs before reaching nominal power, e.g., at locations with lower air density, where the yield increase by avoiding flow separation can be particularly significant.

[0118] Slewing load-optimized operation control must be implemented according to the wind speed distribution at the site and is therefore site-specific. The better the wind speed distribution at the site is known, the better the operation control can be optimized and thus ultimately the yield gain. However, the wind speed distributions are often insufficiently known, especially in large wind farms for turbines that are often located in the wake of upstream turbines.

[0119] To further improve slewing load-optimized operation, it is therefore proposed to equip the turbines with suitable measuring devices that can measure at least the wind speed, but preferably also shear and turbulence, in order to determine an exact wind speed distribution. The more precisely the wind speed distribution at the site is known, the more precisely the operation can be fine-tuned to maximize yield gains. If, for example, it is determined that the wind speed distribution is shifting toward lower wind speeds due to wake effects, a further increase in the rated speed could be considered.

Claims

1. A method for adapting an operating characteristic (302) of a wind power installation (100), wherein - the wind power installation (100) has a rotor (106) with rotor blades (108), the blade angle of which is adjustable, - the rotor (106) is operable with a variable rotor rotational speed (n), - in order to control the wind power installation (100), use is made of an operating characteristic (302) which describes a relationship between the rotor rotational speed (n) and at least one operating variable (P), wherein - the operating characteristic (302) has - a first characteristic portion with a first rotational speed range (A1), and - a second characteristic portion with a second rotational speed range (A2), wherein - the first rotational speed range (A1) has lower rotational speeds (n) than the second rotational speed range (A2), and - the operating characteristic (302) is adapted in such a manner that - values of the operating variable (P) of the first characteristic portion are increased, and - values of the operating variable (P) of the second characteristic portion are changed toward higher rotational speeds, and characterized in that - the operating characteristic (302) is adapted in such a manner that the wind power installation operates at a higher rotational speed in the second characteristic portion and at a lower rotational speed in the first characteristic portion, such that an expected total number of revolutions of the rotor (106) over a predetermined lifetime of the wind power installation (100) remains approximately the same.

2. The method as claimed in claim 1, characterized in that - the first rotational speed range (A1) lies above a switching-on rotational speed (nA) up to a transition rotational speed (nU), wherein the transition rotational speed lies in the range of 80% to 100% of a nominal rotational speed, and - the second rotational speed range (A2) lies at and above the transition rotational speed (nU), wherein in particular - the second characteristic portion is changed toward higher rotational speeds such that, after adaptation of the operating characteristic (302), the second rotational speed range (A2) extends up to a maximum rotational speed (nM) which lies above a nominal rotational speed (nN).

3. The method as claimed in claim 1 or 2, characterized in that - the operating variable (P) used is an operating power variable (P) which is representative of a generator torque, a generator power (P) or a power output, so that the operating characteristic (302) specifies a relationship between the rotor rotational speed (n) and the operating power variable (P).

4. The method as claimed in one of the preceding claims, characterized in that - the first characteristic portion lies completely in a partial load region in which the wind speed lies below a nominal wind speed, and / or the rotor rotational speed (n) lies below a rotor nominal rotational speed (nN), and - the second characteristic portion lies at least partially in a full load region in which the wind speed reaches the nominal wind speed and in particular also lies above same, and the rotor rotational speed (n) is limited by adjustment of the rotor blades (108) in their blade angle, wherein in particular - the second characteristic portion comprises a transition region from the partial load region to the full load region.

5. The method as claimed in one of the preceding claims, characterized in that - the operating characteristic (302) is adapted in such a manner that the rotor rotational speed (n) in the second characteristic portion is increased at least partially via a or the rotor nominal rotational speed (nN) to a or the maximum rotational speed (nM), and that - for wind speeds (VW) above an increased wind speed which lies above a nominal wind speed and characterizes a highest wind speed of the second characteristic portion, and below a storm wind speed, from which the rotor rotational speed (n) is reduced below the rotor nominal rotational speed (nN), the rotor rotational speed (n) is reduced to a rotor rotational speed (n) below the maximum rotational speed (nM), in particular to a rotor nominal rotation speed (nN).

6. The method as claimed in one of the preceding claims, characterized in that - the wind power installation (100) is erected at an erection site which is characterized by an elevation which specifies the height of the erection site, and - the adaptation of the second characteristic portion is undertaken depending on the elevation of the erection site and / or on a mean air pressure at the erection site, wherein in particular - values of the operating variable (P) of the second characteristic portion are changed more powerfully to higher rotational speeds, the higher the elevation and / or the lower the air pressure are / is, and in particular - a or the maximum rotational speed (nM) is selected to be greater - the higher the elevation and / or the lower the air pressure are / is.

7. The method as claimed in one of the preceding claims, characterized in that - a wind field and / or a temporal and / or local wind speed distribution in the region of the wind power installation (100) is recorded as the wind characteristic, and - the operating characteristic is adapted depending on the wind characteristic, in particular that - the increase in the rotor rotational speed (n) in the second characteristic portion is undertaken depending on the wind characteristic, wherein - the rotor rotational speed (n) in the second characteristic portion is increased more powerfully, the greater a local and / or temporal variation in the wind speed and / or the greater a detected gustiness is.

8. The method as claimed in one of the preceding claims, characterized in that - at least one detection device, for detecting a wind characteristic, in particular at least one measuring instrument, is provided on the wind power installation (100), and the detection device is used to detect at least one wind property from the list comprising - wind shear, - wind turbulence, and - a local wind speed distribution, wherein - the operating characteristic (302) is adapted depending on the detected wind property.

9. The method as claimed in one of the preceding claims, characterized in that - the operating characteristic (302) is adapted depending on azimuthal orientation, in particular that - the increase in the rotor rotational speed (n) in the second characteristic portion is carried out depending on an azimuthal orientation of the wind power installation (100), in particular such that - the rotor rotational speed (n) in the second characteristic portion is increased more powerfully, the more turbulent an average wind characteristic for a respective azimuthal orientation is, and / or - the increase in the rotor rotational speed (n) in the second characteristic portion is greater for an azimuthal orientation in which the wind power installation is located in a wake region of a further wind power installation than for an azimuthal orientation in which the wind power installation is not located in a wake of a further wind power installation.

10. The method as claimed in one of the preceding claims, characterized in that - the increase in the rotor rotational speed (n) in the second characteristic portion lies in the range of 2 to 10%, in particular in the range of approximately 3 to 8%, with respect to a or the nominal rotational speed (nN).

11. A method for controlling a wind power installation (100), wherein - the wind power installation (100) has a rotor (106) with rotor blades (108), the blade angle of which is adjustable, - the rotor (106) is operable with a variable rotor rotational speed (n), - in order to control the wind power installation (100), use is made of an adapted operating characteristic (302) which describes a relationship between the rotor rotational speed (n) and at least one further operating variable (P), wherein - the adapted operating characteristic (302) has - a first characteristic portion with a first rotational speed range (A1), and - a second characteristic portion with a second rotational speed range (A2), wherein - the first rotational speed range (A1) has lower rotational speeds than the second rotational speed range (A2), and - the adapted operating characteristic (302) is designed in such a manner that - the operating variable (P) of the first characteristic portion has increased values in relation to an operating characteristic (301) identified as optimum, and - the operating variable (P) of the second characteristic portion is changed toward higher rotational speeds in relation to an operating characteristic (301) identified as optimum, characterized in that - the first and second characteristic portion of the adapted operating characteristic (302) are coordinated with each other in such a manner that - the wind power installation operates at a higher rotational speed in the second characteristic portion and at a lower rotational speed in the first characteristic portion, such that an expected total number of rotations of the rotor over a predetermined lifetime of the wind power installation (100) does not exceed a total number predetermined for the operating characteristic (301) identified as optimum.

12. The method as claimed in claim 11, characterized in that - the operating characteristic (301) identified as optimum is designed in such a manner that the wind power installation (100) is operated in the first rotational speed range (A1) with an optimum tip-speed ratio at which a maximum power coefficient (Cp value) is reached, and that - when the operating characteristic (302) is adapted, the wind power installation (100) is not operated in the first rotational speed range (A1) with the optimum tip-speed ratio.

13. The method as claimed in claim 11 or 12, characterized in that - at least one further operating characteristic is provided which differs from the adapted operating characteristic (302), and - the adapted operating characteristic (302) and the at least one further operating characteristic are used for different azimuthal orientations of the wind power installation (100), and / or - wind characteristics in the region of the wind power installation (100) are detected, and the adapted operating characteristic (302) and the at least one further operating characteristic are used for different wind characteristics, and / or - the rotor rotational speed (n) in the second characteristic portion is greater for an azimuthal orientation in which the wind power is located in a wake region of a further wind power installation than for an azimuthal orientation in which the wind power installation is not located in a wake of a further wind power installation, wherein in particular the adapted operating characteristic (302) is provided for the azimuthal orientation in which the wind power installation is located in the wake of the further wind power installation.

14. The method as claimed in one of claims 11 to 13, characterized in that - the adapted operating characteristic (302), and optionally the at least one further operating characteristic, have each been adapted by a method as claimed in one of claims 1 to 10, and / or that - at least one detection device, for detecting a wind characteristic, in particular at least one measuring instrument, is provided on the wind power installation, and the detection device is used to detect at least one wind property from the list comprising - wind shear, - wind turbulence, and - a local wind speed distribution, wherein - the operating characteristic is adapted depending on the detected wind property.

15. A wind power installation (100) having a rotor (106) with rotor blades (108), the blade angle of which is adjustable, and an installation controller (103) for controlling the wind power installation (100), wherein - the rotor (106) is operable with a variable rotor rotational speed (n), and - in order to control the wind power installation (100), use is made of an operating characteristic (302) which describes a relationship between the rotor rotational speed (n) and at least one operating variable (P), wherein - the operating characteristic (302) is implemented in the installation controller (103), and has - a first characteristic portion with a first rotational speed range (A1), and - a second characteristic portion with a second rotational speed range (A2), wherein - the operating characteristic (302) is adapted in relation to a previous operating characteristic (301) in such a manner that - values of the operating variable (P) of the first characteristic portion have been increased, and - values of the operating variable (P) of the second characteristic portion have been changed toward higher rotational speeds, and characterized in that - the operating characteristic (302) is adapted in such a manner that the wind power installation operated at a higher speed in the second characteristic portion and at a lower speed in the first characteristic portion, so that an expected total number of rotations of the rotor (106) over a predetermined lifetime of the wind power installation (100) has remained approximately the same.

16. The wind power installation (100) as claimed in claim 15, characterized in that - at least one detection device, for detecting a wind characteristic, in particular at least one measuring instrument, is provided on the wind power installation (100), and the detection device is used to detect at least one wind property from the list comprising - wind shear, - wind turbulence, and - a local wind speed distribution, wherein - the operating characteristic is adapted depending on the detected wind property.

17. A wind power installation (100), having a rotor (106) with rotor blades (108), the blade angle of which is adjustable, and an installation controller (103) for controlling the wind power installation (100), wherein - the rotor (106) is operable with a variable rotor rotational speed (n), and - in order to control the wind power installation (100), use is made of an operating characteristic (302) which describes a relationship between the rotor rotational speed (n) and at least one operating variable (P), wherein - the operating characteristic (302) is implemented in the installation controller (103), and - the wind power installation (100) is controlled by a method as claimed in one of claims 11 to 14, wherein optionally - the wind power installation (100) is designed according to claim 15 or 16.