OPERATING A WIND POWER PLANT DURING A STORM

Description

[0001] The present invention relates to a method for controlling a wind turbine and the present invention relates to a corresponding wind turbine.

[0002] Wind turbines are occasionally operated even in storms, i.e., at wind speeds above 20 m / s. One approach is to operate the wind turbine using an operating characteristic curve, which defines the relationship between output power and rotor speed, and a wind speed-speed characteristic curve. The wind turbine is controlled in such a way that, based on the wind speed measured at the turbine and the wind speed-speed characteristic curve, a specific rotational speed is predetermined at which the turbine operates at the measured wind speed. This predetermined rotational speed is achieved by adjusting the blade angle of the wind turbine's rotor blades, a process also known as rotor blade pitching.

[0003] The operating characteristic curve then specifies the output power to be fed into the electrical grid, which can also be referred to simply as the power grid, of the wind turbine. Thus, the operating characteristic curve determines the wind turbine's output power based on its rotational speed and is then adjusted accordingly. Figures 2 and 3 The aforementioned characteristic curves show the storm control. Figure 2 This shows the wind speed-rotation characteristic curve and Figure 3 The operating characteristic curve shown is the characteristic curve that specifies the output power as a function of the rotational speed.

[0004] Particularly Figure 2This shows that the wind turbine operates at a constant rated speed Ntarget until the storm control begins, at which point the turbine delivers its maximum power output, namely the rated power, and feeds it into the electrical grid. From the wind speed VSA, which can also be referred to as the initial storm wind speed, storm control operation begins. The rotational speed is then linearly reduced from the rated speed Ntarget to a swirl speed Nt at a maximum wind speed Vmax, in order to limit the stresses on the wind turbine within specified limits. The maximum wind speed Vmax can also be referred to as the maximum wind speed or maximum storm wind speed.

[0005] Above this maximum wind speed Vmax, the wind turbine simply coasts and no longer feeds in any power. However, for this to occur, the wind speed must exceed the maximum wind speed Vmax over a 12-second average.

[0006] Characteristic values ​​for the initial storm wind speed and the maximum wind speed VSA or Vmax vary between different types of wind turbines. The initial storm wind speed ranges from 25 to 29 m / s, and the maximum wind speed, or maximum storm wind speed Vmax, ranges from 37 to 41 m / s.

[0007] The operating characteristic curve in storm operation, which is therefore in the Figure 3The curve shown is, according to the state of the art, identical to an operating characteristic curve in normal operation or in partial load operation. It runs from the rated speed Ntarget at rated power Pmax down to the idling speed Nt at minimum power Pmin = 0 kW. The reason why the speed is below the rated speed Ntarget is shown in the operating characteristic curve according to... Figure 3 not distinguished.

[0008] The described pitching of the rotor blades reduces the amount of power extracted from the wind, specifically the amount extracted at rated power. From an energy perspective, it is essentially irrelevant why less power than rated power is available, whether this is due to the pitching of the rotor blades during a storm or because the wind has weakened. Therefore, the same operating characteristic curve, i.e., the same speed-power curve, can be used for both partial load operation (when the wind has not yet reached rated wind speed and thus no rated power can be generated) and storm operation. Figure 3 shown.

[0009] The load during storm operation can still be high because, in addition to energy considerations, the forces acting on the rotor blades must also be taken into account.

[0010] To counteract this, the rotational speed, power output, or both can be further reduced during storm operation. However, this does not necessarily guarantee a reduction in stress, especially since the wind turbine remains exposed to the wind, in this case, the storm. Furthermore, this also results in the disadvantage of reduced power output, which must be accepted to protect the turbine.

[0011] The German Patent and Trademark Office has searched the following prior art in the priority application for the present PCT application: EP 2 063 111 A2, WO 2017 / 085156 A1 and WO 2017 / 178429 A1.

[0012] German patent DE 10 2011 006 670 A1 describes a method for operating a wind turbine, whereby the turbine is operated at an increased speed for a transitional period, relative to prevailing wind conditions and compared to an optimal operating point with an optimal rotational speed. In this operating mode, more kinetic energy is stored in the rotating parts of the wind turbine. Beyond the maximum wind speed, the power output is reduced to protect the turbine from further increases in wind speed.

[0013] The present invention is therefore based on the objective of addressing at least one of the aforementioned problems. In particular, a solution is to be proposed that results in the lowest possible stress on the wind turbine and / or the lowest possible power loss during storms. Specifically, an improvement on previously known storm control systems is to be proposed. At the very least, an alternative to existing solutions is to be proposed.

[0014] According to the invention, a method according to claim 1 is proposed. This method is based on a wind turbine for generating electrical power from wind. Such a wind turbine has a rotor with at least one, and in particular several, rotor blades whose blade angle is adjustable. The method therefore relates to a so-called pitch-controlled wind turbine. Furthermore, the wind turbine is one in which the rotor can be operated at a variable speed.

[0015] According to the proposed procedure, the wind turbine is controlled in part-load mode when the wind speed is below a rated wind speed. The wind turbine is controlled in storm mode when the wind speed exceeds a storm threshold. In both part-load and storm modes, the output power to be delivered by the wind turbine is set according to an operating characteristic curve. In both cases, the operating characteristic curve describes the relationship between rotational speed and output power, and thus specifies the output power as a function of rotational speed, or rather, it defines the relationship between these two quantities.

[0016] To control the wind turbine in partial load operation, a partial load operating curve is used as the operating characteristic. To control the wind turbine in storm operation, a storm operating curve is used as the operating characteristic, and these two operating characteristics, i.e., the partial load operating curve and the storm operating curve, are different.

[0017] It is proposed that the storm operating characteristic curve, compared to the partial load operating characteristic curve, exhibits lower rotational speed values ​​at least in sections, for the same power values.

[0018] Reducing the engine speed at the same power output during storm operation compared to partial load operation is by no means a trivial measure for load reduction, because this measure also means that higher power outputs are set at the same engine speed, which can fundamentally lead to an increase in load. However, it has been recognized that such an altered relationship also offers particular aerodynamic advantages.

[0019] It should also be noted that the rotational speed is initially set according to the wind speed during storm operation, and only then is the power setting adjusted.

[0020] However, it was recognized that the aerodynamic conditions in storm operation differ so significantly from those in partial load operation that lower rotational speeds are advantageous in storm operation for the same power output.

[0021] It is therefore specifically proposed that the storm operating characteristic curve, compared to the part-load operating characteristic curve, exhibits lower rotational speeds across its entire range for the same power values. Such a general statement does not automatically follow from a desire to reduce the load during storm operation. Rather, without a more detailed examination of the relationships, which will be done in more detail below, a person skilled in the art cannot expect any advantage from such a change in the speed-power characteristic curve. For load reduction during storm operation, it would be more logical to further reduce rotational speed and power with respect to high wind speeds if previous reductions proved insufficient to limit the load.

[0022] According to an unclaimed embodiment, it is proposed that a wind speed-rotation characteristic curve, starting from the initial storm wind speed, specifies a reduction in rotational speed with increasing wind speed, wherein the degree of reduction in rotational speed increases with increasing wind speed. Thus, the rotational speed is reduced more and more rapidly with increasing wind speed; consequently, the negative rotational speed gradient increases in magnitude with increasing wind speed, and the rotational speed gradient decreases. This allows the rotational speed to be reduced more slowly at the beginning.

[0023] Furthermore, it was recognized that one problem arises from the anticipated flow separation at the rotor blades. According to the invention, it is therefore proposed that the initial storm wind speed be selected based on the expected flow separation at the rotor blades. Such flow separations, in particular, can place a significant load on the corresponding rotor blade and thus on the rotor and the wind turbine. These flow separations can also occur on the pressure side of the rotor blade profile. Regarding such flow separations, it should also be noted that they can occur not only depending on the wind speed, but also depending on the blade angle and the rotor speed or rotational speed at the respective profile section under consideration. It is particularly important to note that such flow separations do not necessarily occur across the entire blade simultaneously, but can also occur only locally, especially in the outer region of the rotor.In this case, there are areas of the rotor blade where flow separation can occur and areas where flow separation is not expected. This can lead to particularly undesirable differential loads along the rotor blade.

[0024] Therefore, it is suggested that expected flow separations be taken into account.

[0025] It should be noted that such properties of rotor blades can be well investigated and therefore predicted in simulations or model tests. In particular, such studies or preliminary investigations based on operating conditions can allow for predictions as to whether, where, or to what extent flow separation is to be expected. Wind speed, rotational speed, and blade angle, in particular, allow for an assessment of whether flow separation is to be expected for specific sections of the rotor blade.

[0026] According to one embodiment, it is proposed that the initial storm wind speed be selected based on the power coefficient of the rotor blades. It has been recognized that aerodynamic conditions are particularly important in storm conditions, and considering the power coefficients can provide a criterion for this selection. It was observed that the power coefficient decreases with increasing wind speed during full-load operation, partly due to pitch adjustments during this full-load operation. As storm conditions approach, the power coefficient decreases steadily and can then serve as an indicator when storm conditions are reached. By specifying a limit value for the power coefficient, a clear, aerodynamically relevant criterion can be established to identify the onset of storm conditions.

[0027] The wind turbine is specifically designed and controlled in such a way that the power coefficient decreases with increasing wind speed, at least from the rated wind speed onwards, i.e., from the point of full-load operation. It is proposed that the initial storm wind speed be chosen as the wind speed at which the power coefficient falls below a predefined storm threshold. In particular, a corresponding study can be conducted beforehand to determine a wind speed-dependent power coefficient. This also takes into account the respective operating point and thus the pitch of the rotor blades, allowing such a determination to be made in advance. From the power coefficient, especially the decreasing power coefficient considered here with increasing wind speed, expectations regarding flow separation can also be derived.Therefore, the performance coefficient and, in particular, a correspondingly specified storm limit value are proposed here as criteria.

[0028] According to one embodiment, it is proposed that the storm operating characteristic curve is linear, decreasing linearly from a predetermined initial storm power value at a predetermined initial storm speed with increasing wind speed to a final storm power value at a predetermined final storm speed. Thus, a linear storm operating characteristic curve, namely one that decreases linearly with wind speed, is proposed. This allows for a reduction in rotational speed appropriate to the wind speed, and also enables a simple and practically feasible increase in rotational speed when the wind speed decreases again.

[0029] Alternatively, it is proposed that the storm operating characteristic curve decreases from the specified initial storm power value at the specified initial storm speed with increasing wind speed to an auxiliary storm power value at an auxiliary storm speed and from there further decreases to the final storm power value at the specified final storm power speed, whereby the auxiliary storm power value at the specified auxiliary storm speed is below a linear operating characteristic curve.

[0030] This means that the storm operating characteristic curve is flatter from the storm assistance speed to the storm end speed than from the storm start speed to the storm assistance speed. This allows for a rapid power reduction, especially at the beginning of a storm.

[0031] Preferably, it is proposed that the wind speed be measured and, during storm operation, the rotor blades' angle is adjusted according to the wind speed, starting at the initial storm wind speed, resulting in a lower rotational speed. It is then proposed that the output power be adjusted according to the storm operating characteristic curve, depending on the resulting rotational speed. Thus, a two-step method is proposed in which the rotor blades' angle is first adjusted, specifically by turning them out of the wind as the wind speed increases. This reduces the power extracted from the wind, resulting in a lower rotational speed. This lower rotational speed is then used in the next step to adjust the output power. The output power is adjusted according to the storm operating characteristic curve.This allows for immediate relief by adjusting the rotor blades and then adjusting the output power accordingly.

[0032] The proposed storm operating characteristic is particularly advantageous here, as it exhibits lower rotational speeds for the same power output compared to the part-load operating characteristic. This means that the power is reduced less in this second step than would be the case when using the part-load operating characteristic. Here, it is specifically proposed to adjust the rotational speed reduction by changing the blade angle of the rotor blades to match the advantageous storm operating characteristic.

[0033] According to one embodiment, it is proposed that during storm operation, starting at the initial storm wind speed, the rotor blades are adjusted in their blade angle to achieve a rotational speed corresponding to a predetermined wind speed-rotation speed characteristic curve. This measure thus allows for the predefined wind speed-rotation speed characteristic curve. The wind speed-dependent rotational speed, in particular, has a direct impact on the aerodynamic forces acting on the rotor blade. Especially when the blade angle and, of course, the known geometry of the rotor blade are also taken into account, the effects of flow separation can be considered. In particular, such effects can be detected in advance, and it is even preferable to select a corresponding wind speed-rotation speed characteristic curve based on these findings, in which undesirable flow separations do not occur or are at least reduced.

[0034] According to one embodiment, it is proposed that the wind speed-speed characteristic curve be linear, decreasing linearly from a predetermined initial storm speed at a predetermined initial storm wind speed to a predetermined final storm speed at a predetermined final storm wind speed as the wind speed increases. Thus, a linear wind speed-speed characteristic curve is proposed in which the rotational speed decreases linearly with increasing wind speed, i.e., it decreases proportionally to an increase in wind speed. This establishes a clear relationship between wind speed and rotational speed, which can be readily implemented by the wind turbine and its control system. With such a linear wind speed-speed characteristic curve, the rotational speed can also be increased again when the wind speed decreases.The rated speed is particularly preferred as the initial speed during a storm. Accordingly, with the proposed linear wind speed-speed characteristic curve, the speed can be easily reduced linearly with increasing wind speed immediately following full-load operation.

[0035] A linear wind speed-rotation curve combined with a linear rotation speed-power curve is particularly preferred. This allows for a linear relationship between output power and wind speed. Consequently, in stormy conditions, as wind speed increases, both rotation speed and output power can be reduced linearly, thereby simultaneously reducing or limiting the corresponding loads. A reduction in rotation speed has a particularly significant impact on the mechanical loads of the rotor blades, whereas a reduction in output power primarily affects the loads on the drivetrain. With the proposed linear reduction of both rotation speed and power, a reduction in both areas can thus be implemented equally and transparently.

[0036] Alternatively, it is proposed that the wind speed-speed characteristic curve, starting from the predetermined initial storm speed (preferably the rated speed), decreases with increasing wind speed to an intermediate storm speed at a predetermined intermediate storm speed when the initial storm wind speed is higher than the predetermined (i.e., unincreased) initial storm wind speed. This intermediate storm speed preferably corresponds to the auxiliary storm speed of the storm operating characteristic curve. In any case, it is proposed that the speed decrease further from the intermediate storm speed at the predetermined intermediate storm wind speed to the predetermined final storm speed at the predetermined final storm wind speed, with the intermediate storm speed at the predetermined intermediate storm wind speed preferably being above the linear wind speed-speed characteristic curve.

[0037] Preferably, this wind speed-speed characteristic curve begins at an increased initial storm wind speed. It therefore starts later than the predetermined initial storm wind speed, relative to an increasing wind speed. This allows for a correspondingly later reduction in power output. This preferred wind speed-speed characteristic curve will preferably, in every case—whether the initial storm wind speed is increased or not—initially have a shallower slope than later on; that is, a shallower slope at lower wind speeds than at higher wind speeds.

[0038] It was particularly noted that premature or excessive pitching, or both, can lead to negative angles of attack, especially in the outer area of ​​the rotor blade, i.e., towards the blade tip. Such negative angles of attack can then lead to stall effects, particularly on the pressure side of the rotor blades. Since these negative angles of attack do not occur across the entire blade, from the root to the tip, but primarily in the outer area, flow separation occurs mainly there. This results in differential loads in the outer and inner areas of the rotor blade, which can also lead to blade torsion. Such torsion can further amplify or mitigate the effect, ultimately leading to torsional vibrations. These differential loads, especially the aforementioned torsional vibrations, can place a high stress on the rotor blade.The proposed measures are aimed precisely at counteracting this. In particular, by avoiding premature adjustment of the blade angles, which would also reduce the rotational speed, such negative angles of attack in part of the rotor blade can be avoided.

[0039] According to one embodiment, it is proposed that the wind speed-rotation curve, starting at the initial storm wind speed, specifies a reduction in rotational speed with increasing wind speed, with the degree of reduction increasing with increasing wind speed. Thus, the rotational speed is reduced with increasing wind speed during a storm, as is generally known. However, it is further proposed that this reduction also increases more sharply with increasing wind speed. The rotational speed therefore falls more and more steeply. This results in a wind speed-rotation curve that is curved upwards. This can be achieved incrementally, in the simplest case by implementing an initial reduction gradient up to a storm intermediate wind speed, and then a steeper reduction, i.e., an increase in the degree of reduction.However, it can also be carried out in several steps, or preferably continuously, so that the wind speed-rotation curve forms a continuous, upwardly curved characteristic curve.

[0040] This also helps prevent prematurely and rapidly reducing the rotational speed, which, surprisingly, does not necessarily relieve stress on the wind turbine. In fact, due to the aerodynamic loads described above, particularly the risk of torsional vibrations, such a reduction can even be detrimental, at least with regard to direct aerodynamically induced stresses. This wind speed-rotation curve, with its progressively increasing rotational speed reduction, thus achieves an initially advantageous, less pronounced reduction in rotational speed.

[0041] According to a further embodiment, it is proposed that as wind speed increases, the blade angle is increased in relation to the wind speed, moving towards a flag position that is not initially reached, thus increasing the angle to reduce the rotational speed. It is specifically assumed here that the blade angle is defined such that the flag position corresponds to a blade angle of approximately 90° (and not 0°), which is a common definition of the blade angle, also known as the pitch angle. Adjusting the blade angle towards the flag position therefore represents an increase in the blade angle.

[0042] Depending on the reduction in rotational speed, the output power is then reduced. Therefore, there is first a reduction in rotational speed that depends on the wind speed, and this then forms the basis for the reduction in output power, as already described above.

[0043] It has now been recognized that the increase in angle, relative to the decrease in output power, forms an angle-power change coefficient. The angle-power change coefficient CWP can thus be defined as the ratio of the angle increase ΔW, proposed for a given increase in wind speed, to the decrease in output power ΔP, proposed for the resulting change in rotational speed, as CWP = ΔW / ΔP. It is proposed that this angle-power change coefficient should increase in magnitude with increasing wind speed. This allows for advantageous behavior of the wind turbine in stormy conditions, since the proposed increase in the angle-power change coefficient also results from the corresponding change in output power.Specifically, it is proposed here that the power output should be adjusted more quickly, and then more slowly, relative to the blade angle as wind speed increases. This approach helps to avoid excessively rapid adjustments to the blade angle and rotational speed, which can lead to the aforementioned aerodynamic problems, while simultaneously allowing the power output and associated loads to be reduced quickly from the outset.

[0044] It is preferably proposed that the angle-power change coefficient decreases from a predetermined first reversal wind speed during storm operation and, in particular, increases again from a second reversal wind speed that is greater than the first. It has been recognized that at high wind speeds during storm operation, especially in the range of 25 to 26 m / s, an excessively rapid angle increase can result in a negative, particularly a strongly negative, angle of attack. To avoid this, the angle-power change coefficient is reduced from the first reversal wind speed, meaning the angle decreases less rapidly from that point onward. From the second reversal wind speed onward, the power and / or rotational speed may have decreased sufficiently to allow the angle to decrease more rapidly again.

[0045] The invention also proposes a wind turbine. Such a wind turbine is designed to generate electrical power from wind and has a rotor with rotor blades whose blade angle is adjustable, and the rotor can be operated at variable speeds. The wind turbine comprises A control unit for controlling the wind turbine in partial load operation when the wind speed is below a rated wind speed, and for controlling the wind turbine in storm operation when the wind speed is above a storm initial wind speed, wherein the control device is prepared to control the wind turbine such that, in partial load operation and in storm operation, an output power to be delivered by the wind turbine is set as a function of an operating characteristic curve, wherein the operating characteristic curve specifies a relationship between the rotational speed and the output power, a partial load operating characteristic curve is used as the operating characteristic curve for controlling the wind turbine in partial load operation, and a storm operating characteristic curve is used as the operating characteristic curve for controlling the wind turbine in storm operation.and wherein the storm operating characteristic and the part-load operating characteristic are different and the storm operating characteristic exhibits lower rotational speeds at least section by section for the same power values ​​compared to the part-load operating characteristic, and / or the control device is prepared to specify a wind speed-rotational speed characteristic which, starting from the initial storm wind speed, specifies a reduction in rotational speed with increasing wind speed, wherein a measure of the reduction in rotational speed increases with increasing wind speed, i.e., a negative rotational speed gradient increases in magnitude with increasing wind speed, thus decreasing the rotational speed gradient.

[0046] Such a wind turbine is also specifically designed to execute a method described above, as described at least according to one embodiment. For this purpose, a control unit is provided, which can also be designed as a process computer, on which the functions are implemented and which can transmit the corresponding control commands to actuators of rotor blades, exciters, or frequency inverters intended for feeding power into an electrical supply network.

[0047] Preferably, such a wind turbine has at least one wind speed sensor. This wind speed sensor is used particularly during stormy conditions, where it measures the wind speed and controls the wind turbine accordingly, especially with regard to its rotational speed. Preferably, several different wind speed sensors are provided to achieve redundancy and / or increase measurement accuracy.

[0048] In particular, the control unit, at least according to one embodiment, is designed to have characteristic curves stored within it. Specifically, it is proposed that the control unit contain a partial load operating characteristic curve and a storm operating characteristic curve, and preferably also a wind speed-rotational speed characteristic curve, particularly for storm operation. Based on this, i.e., using one or more of these characteristic curves, the control unit, and thus the wind turbine, can execute at least one method as described above with reference to at least one embodiment of the method.

[0049] The invention will now be explained in more detail below by way of example embodiments with reference to the accompanying figures. Figure 1 shows a perspective view of a wind turbine. Figure 2 illustrates a wind speed-rotation curve for storm operation. Figure 3 shows a rotational speed-power curve, and thus an operating characteristic. Figure 4 shows, by way of example, the angle of attack for storm operation along a rotor blade from the blade root to the blade tip as a function of the radius. Figure 5 shows an improved wind speed-rotation curve. Figure 6 shows a proposed operating characteristic. Figure 7 shows another proposed operating characteristic. Figure 8 compares different blade angle profiles for various designs as a function of wind speed. Figure 9 shows different angles of attack in an outer region of a rotor blade for different designs. Figure 10 explains the meaning of the blade angle and the angle of attack.

[0050] Figure 1 Figure 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 110 is mounted on the nacelle 104. During operation, the wind sets the rotor 106 into rotation, thereby driving a generator in the nacelle 104.

[0051] Figure 1 Figure 130 also illustrates a control unit 130 that can control the wind turbine 100. A wind speed sensor 132, which can be mounted on the spinner 110, is provided for controlling the wind turbine 100 depending on the wind speed. It sends its signals to the control unit 130. The control unit 130 can evaluate these signals and use them, for example, to control a pitch motor 134, which in Figure 1This is shown for illustrative purposes only. Specifically, only one pitch motor 134 is shown, although of course each of the rotor blades 108 can have its own pitch motor 134, allowing its blade angle to be adjusted. A generator 136 is also shown. Figure 1 indicated and can, if necessary, be controlled by the control unit 130 to adjust the output power.

[0052] Figure 2 A simple wind speed-speed characteristic curve (202) is shown. This curve indicates the rated speed N at wind speeds below a minimum wind speed V min. The range before this minimum wind speed represents the full-load range or full-load operation of the wind turbine, at least as long as the wind speed is not below a rated wind speed, which is shown in the Figure 2This curve is not shown because it only depicts the wind speed-speed characteristic curve, primarily for storm operation. In fact, no wind speed-speed characteristic curve is provided for other operating conditions. While there are known relationships between wind speed and rotational speed, these are not typically used to control the system during full-load and partial-load operation. Only for storm operation is it proposed to adjust the rotational speed according to the wind speed-speed characteristic curve 202, based on a measured wind speed.

[0053] In the example of the Figure 2Storm operation begins at the storm wind speed, designated VSA. From there, the rotational speed decreases linearly according to the wind speed-rotational speed curve 202 until the maximum wind speed Vmax is reached, at which point it reaches the idling speed Nt. There is also an exception where the wind turbine can be shut down at the safety wind speed V* if the average wind speed over 10 minutes exceeds the safety wind speed V*.

[0054] The wind speed-rotation characteristic curve 202 falls linearly here and its linear fall can also be defined via a virtual starting value, which is located at the minimum wind speed and 1.2 times the rated wind speed.

[0055] Figure 3Figure 302 shows a speed-power characteristic curve, also known as an operating characteristic curve (BKL). This curve illustrates the relationship between the speed N and the power P. At essentially maximum speed, namely the rated speed Ntarget, the rated power PN is also present. At correspondingly lower speeds, the power is also lower and reaches a value of 0 at the idle speed Nt. In this case, the system operates at the idle speed without generating any power. This operating characteristic curve 302 of the Figure 3The relationship between rotational speed N and power P can be represented or specified in both partial load and storm operation. However, in partial load operation, the rotational speed would increase with increasing wind speed, whereas in storm operation, the rotational speed would decrease with increasing wind speed. In storm operation, the operating characteristic would thus be reversed with respect to wind speed.

[0056] The following points should now be noted. During storms, the air flowing through the rotor disc has very high kinetic energy, and only a small portion of this needs to be converted into rotational energy by the wind turbine to generate the power required according to the operating characteristic curve.

[0057] It was recognized that the necessary torque is essentially only generated in the inner area of ​​the blade, which results in a fundamentally different angle of attack distribution over the rotor radius compared to normal operation.

[0058] To illustrate this, shows Figure 4 A typical angle of attack profile for a given wind speed during storm operation. The angle of attack, in this context, refers to the angle at which the airflow actually strikes the chord line of the rotor blade section in the relevant area. This angle of attack therefore depends on the actual position of the rotor blade at that point, the prevailing wind, and the rotational speed of the rotor blade at that point.

[0059] To illustrate the blade angle y and the angle of attack α, these are shown in the Figure 10This is shown for a profile section 1000. This profile section 1000 thus represents a rotor blade segment. By rotating the rotor blade in the rotor plane R at the rotational speed ω, a blade segment velocity VBA results for the considered profile section 1000, which is therefore parallel to the rotor plane. The actual wind speed Vw, taking into account the blade segment velocity VBA, leads to an apparent or relative wind speed Urel. This is in Figure 10 The diagram is shown schematically as a vector representation in an inset area. Only the corresponding relative wind direction Urel is marked on the profile section 1000. The angle between this relative wind direction Urel and the profile chord line c is the angle of attack α. It also depends directly on the set blade angle γ, which is referenced to the rotor plane R. A small blade angle γ corresponds to a setting in partial load operation.

[0060] In the Figure 4 It can be seen that positive angles of attack are only found in the inner part of the leaf and that the value of the angle of attack decreases sharply towards the outside and becomes clearly negative towards the leaf tip. It should be noted that the Figure 4 The abscissa indicates the respective position on the rotor blade relative to the total length of the rotor blade. At the blade tip, the position corresponds to the length of the rotor blade, so the value there is 1. The position is considered as the radius r of the rotor and relative to the total radius R of the rotor. The abscissa therefore does not extend all the way to 0, because the value 0 lies on the axis of rotation and thus in the spinner or hub.

[0061] The Figure 4This is just one example, but it has been observed that the higher the wind speed and the less power the wind turbine feeds into the turbine during storm operation at these higher wind speeds, the more pronounced this trend or phenomenon becomes. It has been recognized that this can be problematic because, at high negative angles of attack, there is a risk of so-called negative stall occurring on the airfoil sections where these high negative angles of attack are present. Depending on the airfoil and structural design of the rotor blade, there is a risk that undesirable aeroelastic phenomena can occur on the rotor blade due to operation in sections of the blade experiencing negative stall. This means that feedback loops can develop between the forces exerted on the rotor blade by the airflow and the resulting elastic deformations.Such deformations can in turn result in a changing airflow with changing aerodynamically induced forces.

[0062] It was also recognized that such feedback loops, in one form, can lead to an oscillating movement around the longitudinal axis of the rotor blade. In this case, the rotor blade would twist with high frequency and amplitude. Such rotor blade vibrations could even reach amplitudes that could damage the rotor blade. Therefore, preventative measures are proposed. It has been particularly noted that such flow separation can occur during stormy operation of a wind turbine at negative angles of attack on the rotor blade. Accordingly, it is proposed to counteract this phenomenon, i.e., such negative angles of attack, and to avoid them whenever possible.

[0063] Figure 4This shows the angle of attack α over the length of a rotor blade with total length R, where R is actually the maximum radius of the rotor in which the blade operates. Therefore, the maximum radius R represents the distance from the rotor's axis of rotation to the blade tip. The radius r under consideration is normalized to this maximum radius R, so the graph extends to the value 1 on the abscissa.

[0064] It can be seen that this angle of attack curve 402 assumes negative values ​​from about halfway along the rotor blade, i.e., from approximately the value 0.5 for the radial position on the rotor blade, and these values ​​become even more significant towards the blade tip, thus falling further below 0. This is an example of a rotor blade whose angle of attack was adjusted too drastically during stormy operation in an attempt to reduce the rotational speed too much. With a smaller adjustment of the blade angle and a correspondingly smaller or later reduction in rotational speed, the angle of attack would not transition so far into the negative range, or perhaps not at all.

[0065] Based on this finding, the task for the operation of a wind turbine in stormy conditions is therefore to avoid the occurrence of flow separation at negative angles of attack on the rotor blade.

[0066] To achieve this, it is therefore proposed to adjust the operational management accordingly during storms. Specifically, it is suggested that the operating characteristic curve, the wind speed-speed characteristic curve, or both simultaneously be modified compared to previously used variants. The following, in particular, should be considered. Figures 5 to 7 They should explain the proposed improvements or possibilities for improvement.

[0067] Figure 5 shows, among other things, the wind speed-rotation characteristic curve 202 of the Figure 2It is now specifically proposed to deviate from this wind speed-speed characteristic curve 202 and to this end, an improved wind speed-speed characteristic curve 502 is proposed. This improved wind speed-speed characteristic curve 502 only begins to reduce the rotational speed at an increased initial storm wind speed VSA2. From there, the rotational speed then decreases with a lower initial speed slope until the second minimum wind speed Vmin2. At this point, it reaches the first minimum rotational speed Nmin1. From there, the improved wind speed-speed characteristic curve 502 decreases with an increased slope to the spin-down speed Nt at the maximum wind speed Vmax. This ensures, in particular, that this improved wind speed-speed characteristic curve 502 lies above the wind speed-speed characteristic curve 202.The first minimum speed N min1 can also represent an intermediate storm speed or a storm assistance speed, which may correspond in value to a storm assistance speed used in a later operating characteristic curve. This improved wind speed-speed characteristic curve 502 thus reduces the speed relatively late and then only relatively slightly, at least initially. Only later, namely from the second minimum wind speed V min2 or upon reaching the first minimum speed N min1, does the speed then drop sharply.

[0068] The shutdown of the wind turbine, if the 10-minute average wind speed is above the safety wind speed V*, can also take place at a higher rotational speed, namely the second minimum rotational speed N min2.

[0069] The aim of the proposal, according to the improved wind speed-speed characteristic curve 502, is to increase the rotational speed during storm operation compared to previous approaches. The rotational speeds should therefore be reduced later and / or less significantly with increasing wind speed, at least at the beginning of storm operation. The cut-off wind speed, which can also be referred to as the maximum wind speed Vmax, remains constant, and a linear relationship between wind speed and rotational speed can also be used, at least according to one embodiment. However, it is proposed to define the relationships section by section, specifically in two sections, the first of which, i.e., at lower wind speeds, is flatter, and the second, later section, i.e., at higher wind speeds, is steeper.

[0070] Such first and second sections 504 and 506 respectively are in the Figure 5As shown, it is proposed that the start of storm operation be shifted from the initial storm wind speed to an increased initial storm wind speed VSA2. Furthermore, a sectionally linear characteristic curve with varying slopes is proposed, with the aim of ensuring that the rotational speeds throughout storm operation are lower compared to the variant shown. Figure 2 be raised.

[0071] This also includes the proposal for preferably adapted operating characteristics, which are included in the Figures 6 and 7 The goal of modifying the operating characteristics is to increase the power output at a given speed. One way to achieve this is to shift an operating characteristic curve, as illustrated in [reference]. Figure 6The diagram shows a first operating characteristic curve for comparison, which can also be referred to as the normal operating characteristic curve 602. This curve, indicated by an arrow, is essentially shifted to the left towards the improved operating characteristic curve 604. This shift means that, as a result, the power P exhibits the same curve as before, only at a lower speed. Consequently, the power is increased at the same speed. However, the rated power PN is maintained even at a slightly lower speed due to this shift.

[0072] For the specific course of the operating characteristic curve, it is specifically provided here that the improved operating characteristic curve 604, which here forms a storm operating characteristic curve, should initially fall from the specified storm initial power value PN at the specified storm initial speed N with increasing wind speed Vw to a storm auxiliary power value PH at a specified storm auxiliary speed NH and from there further fall to the storm final power value, namely 0, at the specified storm final power speed Nt.

[0073] In another embodiment, a linear relationship between power and speed can be provided from the rated speed Ns up to the idling speed Nt. This is in Figure 7This is explained, and for comparison, a normal operating characteristic curve 702 is also shown, which does not represent a straight line, i.e., no linear relationship between power and speed. This normal operating characteristic curve 702 is modified according to the indicated arrow to the improved linear operating characteristic curve 704. It was also particularly recognized here that such a linear relationship is suitable for an operating characteristic curve for storm operation, but less suitable for partial load operation.

[0074] Particularly in partial load operation, it is aerodynamically advantageous to increase the rotational speed as quickly as possible with rising wind speeds, as this can lead to aerodynamically favorable high-speed ratios at low wind speeds. However, it has been recognized that in stormy conditions, it can be beneficial not to reduce the power output too drastically, even when the rotational speed decreases with increasing wind. Furthermore, the potential for the wind turbine to stall in stormy conditions is irrelevant, allowing the power output to be maintained at a comparatively high level during these conditions. This is precisely what the proposed improved linear operating characteristic curve 704 achieves. Additionally, this ensures that a comparatively high power output can still be generated despite the reduction in rotational speed and power output during stormy conditions, which serves to protect the turbine. The proposed improved linear operating characteristic curve 704 can provide this advantage.

[0075] At the same time, it was recognized that, with appropriate consideration of the characteristics of the generator used, especially its maximum, speed-dependent power output, a comparatively high power output can still be generated.

[0076] Achievable effects are in the Figure 8 and 9 shown. Figure 8 This illustrates the behavior of a blade angle γ as a function of the wind speed V w during storm operation for three different cases, such that Figure 8 Figure 802 shows three blade angle profiles: 804, 804, and 806. The first blade angle profile, 802, can also be referred to as the normal blade angle profile and essentially corresponds to the wind speed-rotation characteristic curve 202 according to [reference missing]. Figure 2 . At the same time, an operating characteristic curve according to the normal operating characteristic curve 602 or 702 of the Figure 6 or 7 as a basis.

[0077] Furthermore, a second and thus improved blade angle profile 804 is shown, which also corresponds to the wind speed-rotation characteristic curve 202 of the Figure 2 The third, further improved blade angle curve 806 is based on the wind speed-speed curve 202, but an improved operating characteristic curve was used. This could have been an improved operating characteristic curve 604 or 704, or a similar one. In contrast to the second improved blade angle curve 804, the improved wind speed-speed curve 502 is also used for the third, further improved blade angle curve 806.

[0078] It is in Figure 8It is particularly noticeable that the use of an improved operating characteristic curve and, additionally, an improved wind speed-speed characteristic curve results in smaller blade angles. The blade angles are the same at the beginning of storm operation, i.e., at the initial storm wind speed VSA, and then increase at varying rates with increasing wind speed. The proposed measures, both individually and in combination, thus lead to a reduction in the blade angle during storm operation compared to variants that do not use such an improved operating characteristic curve and / or an improved wind speed-speed characteristic curve.

[0079] One key reason for this is that the proposed measures generally result in increased power output compared to variants that do not implement these measures. This increased output is also fed into the electrical grid. More power is thus extracted from the wind, and the wind turbine therefore requires less throttling. This is reflected in the reduced blade angles, which can also be referred to as pitch angles or rotor blade angles. Smaller blade angles directly result in higher angles of attack. This has been recognized as an advantageous effect, helping to avoid areas of very low angles of attack where there is a risk of flow separation.

[0080] This is in Figure 9 explained. Figure 9Figure 802, 804, and 806 show the angle of attack in the outer region of the rotor blade for a given wind speed, specifically from 70 to 100 percent of the radius r relative to the maximum radius R. Corresponding angle of attack curves 902, 904, and 906 are shown for blade angles 802, 804, and 806. Figure 9 shown. Thus, the Figure 9 also the angle of attack distribution in the leaf tip area, which results from the Figure 8 the aforementioned operational management results.

[0081] Would the rotor blade design, for example, be in the range for 0.96 <r / R<1 Profile einsetzen, die bei Anstellwinkeln kleiner als -11° zum Strömungsabriss neigen und damit die angeführten aeroelastischen Probleme auslösen, wäre es durch die vorgeschlagenen Maßnahmen möglich, einen Betrieb der Anlagen in diesem Anstellwinkelbereich mit Werten kleiner als -11° zu vermeiden und damit potenzielles Aufschwingen und möglicherweise einhergehende Schädigung der Rotorblätter zu verhindern. Figure 9 This shows that only the angle of attack curve 902, which results from unchanged operating conditions, achieves a significantly lower angle of attack than the angle of attack curves 904 and 906 according to the improved operating conditions.

[0082] The invention is therefore particularly intended to increase the angle of attack, especially in the blade tip region. In stormy conditions, negative angles of attack can occur in the blade tip region, meaning the stagnation point of the flow is then located on the suction side of the airfoil. At high negative angles of attack, flow separation typically occurs on the pressure side. Under certain circumstances, when the system is operating in flow separation on the pressure side, also known as negative stall, an aeroelastic oscillation of the rotor blade can occur, which can lead to blade damage. The proposed invention aims, through a modified operating procedure, to avoid reaching critical negative angles of attack in stormy conditions and thus ensure, or at least improve, the integrity of the rotor blade.

[0083] As a result, the proposed measures can thus relieve the rotor blades during storm operation, while at the same time enabling a higher power output.

Claims

1. A method of controlling a wind power plant (100) for generating electrical power from the wind, wherein - the wind power plant (100) comprises a rotor (106) having rotor blades (108) which are adjustable in respect of the blade angle thereof and - the rotor (106) can be operated at a variable rotational speed (N), said method comprising the steps of: - controlling the wind power plant (100) in a partial load mode when the wind has a wind speed (Vw) below a nominal wind speed, - controlling the wind power plant (100) in a storm mode when the wind has a wind speed (Vw) above a storm commencement wind speed (VSA), wherein - an output power to be output by the wind power plant (100) in partial load mode and in storm mode is adjusted according to an operating characteristic curve, wherein the operating characteristic curve determines a relationship between the rotational speed (N) and the output power (P), - a partial load characteristic curve (602, 702) is used as the operating characteristic curve for controlling the wind power plant (100) in partial load mode, and - a storm mode characteristic curve (604, 704) is used as the operating characteristic curve for controlling the wind power plant (100) in storm mode, and wherein - the storm mode characteristic curve and the partial load characteristic curve are different and the storm mode characteristic curve (604, 704), in comparison with the partial load characteristic curve (602, 702), has lower rotational speed values (N) for the same power values (P), at least in sections, characterized in that - the storm commencement wind speed (VSA) is selected according to an expected stalling of the rotor blades (108).

2. The method according to claim 1, characterised in that the storm mode characteristic curve, in comparison with the partial load characteristic curve, has lower rotational speed values (N) for the same power values (P) over its entire range.

3. The method according to claim 1 or 2, characterised in that - the storm commencement wind speed (VSA) is selected according to a power coefficient (Cp value) of the rotor blades (108), in particular such that - the wind power plant (100) is designed and configured in such a way that the power coefficient (Cp value) decreases with increasing wind speed (Vw) at least from the nominal wind speed, and - the wind speed (Vw) at which the power coefficient (Cp value) falls below a predefined storm threshold for the power coefficient (Cp storm threshold) is selected as the storm commencement wind speed (VSA).

4. The method according to any one of the preceding claims, characterised in that - the storm mode characteristic curve forms a linear storm mode characteristic curve which - decreases with increasing wind speed (Vw) from a predefined storm commencement power value (PN) at a predefined storm commencement rotational speed (Nset) - linearly to a final storm power value, in particular to the value 0, at a predefined final storm rotational speed (Nt), or that - the storm mode characteristic curve decreases initially, with increasing wind speed (Vw), from the predefined storm commencement power value (PN) at the predefined storm commencement rotational speed (Nset) - to a storm auxiliary power value (PH) at a predefined storm auxiliary rotational speed (NH) and from there - to the final storm power value at the predefined final storm rotational speed (Nt), wherein - the storm auxiliary power value (PH) at the predefined storm auxiliary rotational speed (NH) lies below a / the linear operating characteristic curve, and the storm mode characteristic curve is flatter from the storm auxiliary rotational speed (NH) to the final storm rotational speed (Nt) than from the storm commencement rotational speed (Nset) to the storm auxiliary rotational speed (NH).

5. The method according to any one of the preceding claims, characterised in that - the wind speed (Vw) is measured and, - in storm mode from the storm commencement wind speed (VSA), - the rotor blades (108) are adjusted in respect of their blade angle according to the wind speed (Vw), such that a lower rotational speed (N) is reached, and - the output power (P) is set in accordance with the storm mode characteristic curve (604, 704) depending on the rotational speed (N) that is reached.

6. The method according to any one of the preceding claims, characterised in that - in storm mode from the storm commencement wind speed (VSA), - the rotor blades (108) are adjusted in respect of their blade angle such that a rotational speed (N) according to a predefined wind speed / rotational speed characteristic curve (502) results.

7. The method according to any one of the preceding claims, characterised in that - a / the wind speed / rotational speed characteristic curve (202) - forms a linear wind speed / rotational speed characteristic curve (202) which - decreases linearly with increasing wind speed (Vw) from a / the predefined storm commencement rotational speed (Nset) at the predefined storm commencement wind speed (VSA) - to a / the predefined final storm rotational speed (Nt) at a predefined final storm wind speed (Vmax), or that - the wind speed / rotational speed characteristic curve (502) - decreases initially with increasing wind speed (Vw) from the predefined storm commencement rotational speed (Nset) at the storm commencement wind speed (VSC2), in particular at a higher storm commencement wind speed (VSC2) that is greater than the predefined storm commencement wind speed (VSA), - to an intermediate storm rotational speed (Nmin1) at a predefined intermediate storm wind speed (Vmin2), wherein the intermediate storm rotational speed is equal to the storm auxiliary rotational speed, and from there - to the predefined final storm rotational speed (Nt) at the predefined final storm wind speed (Vmax), wherein it is preferable that - the intermediate storm rotational speed (Nmin1) at the predefined intermediate storm wind speed (Vmin2) is above a / the linear wind speed / rotational speed characteristic curve (202), and / or the wind speed / rotational speed characteristic curve (502) decreases from the intermediate storm wind speed (Vmin2) to the final storm wind speed more steeply than from the storm commencement wind speed (VSA) to the intermediate storm wind speed (Vmin2).

8. The method according to any one of the preceding claims, characterised in that - a / the wind speed / rotational speed characteristic curve (502) - specifies with increasing wind speed (Vw) a reduction of the rotational speed (N) from the storm commencement wind speed (VSA), wherein - a measure of the reduction in rotational speed (N) increases with increasing wind speed (Vw).

9. The method according to any one of the preceding claims, characterised in that - with increasing wind speed (Vw) the rotor blade angle is increased according to the wind speed (Vw) towards a feathered position such that the blade angle increases in order to reduce the rotational speed (N), and - the output power (P) is reduced according to the reduction in rotational speed (N), and - the ratio of the blade angle increase (ΔW) to the reduction in output power (ΔP) forms an angle / power change coefficient (CWP), wherein - the angle / power variation coefficient (CWP) increases in magnitude with increasing wind speed (Vw), and preferably decreases from a predetermined first reversal wind speed in storm mode and in particular increases again from a second reversal wind speed that is greater than the first reversal wind speed.

10. A wind power plant (100) for generating electrical power (P) from the wind, comprising - a rotor (106) having rotor blades (108) which are adjustable in respect of the blade angle, wherein - the rotor (106) can be operated at a variable rotational speed (N), - a control unit (130) for controlling the wind power plant (100) in a partial load mode when the wind has a wind speed (Vw) below a nominal wind speed, and - for controlling the wind power plant (100) in a storm mode when the wind has a wind speed (Vw) above a storm commencement wind speed (VSA), wherein - the control means (130) is configured to control the wind power plant (100) in such a way that - an output power (P) to be output by the wind power plant (100) in partial load mode and in storm mode is adjusted according to an operating characteristic curve (604, 704), wherein the operating characteristic curve (604, 704) determines a relationship between the rotational speed (N) and the output power (P), - a partial load characteristic curve (602, 702) is used as the operating characteristic curve for controlling the wind power plant (100) in the partial load mode, and - a storm mode characteristic curve (604, 704) is used as the operating characteristic curve for controlling the wind power plant (100) in storm mode, and wherein - the storm mode characteristic curve (604, 704) and the partial load characteristic curve (602, 702) are different and - the storm mode characteristic curve (604, 704), in comparison with the partial load characteristic curve (602, 702), has lower rotational speeds (N) for the same power values (P), at least in sections, characterized in that - the storm commencement wind speed (VSA) is selected according to an expected stalling of the rotor blades (108).

11. The wind power plant (100) according to claim 10, characterised in that - the wind power plant (100), in particular the control unit (130), is configured to perform a method according to any one of claims 1 to 9.

12. The wind power plant (100) according to claim 10 or 11, characterised in that a wind speed sensor (132) is provided to record the wind speed (Vw), wherein the wind power plant (100), in particular its control means (130), is configured to use the wind speed (Vw) recorded by means of the wind speed sensor (132) as an input variable in order to adjust a blade angle in storm mode according to said variable, in order to reduce to reduce the rotational speed (N) of the rotor (106) with increasing wind speed (Vw).