METHOD FOR OPERATION OF A WIND PARK, WIND ENERGY PLANT AND WIND PARK

Description

[0001] The present invention relates to a method for operating a wind farm, a wind turbine and a wind farm.

[0002] Wind turbines are rarely erected as individual units anymore; instead, they are now usually built in groups of several turbines in a confined area. Such a group of wind turbines is called a wind farm, and the distance between individual turbines is typically only a few multiples of their diameter.

[0003] With a small number of turbines, they can be installed in just two rows; however, if there are a larger number of turbines in the wind farm, they must be arranged in three or more rows. In such a wind farm, individual turbines no longer operate independently, but are affected by the operation of neighboring turbines depending on the wind direction.

[0004] This becomes particularly evident when one turbine is positioned in the wake of another, i.e., when the two turbines are positioned one behind the other in the wind direction. Because the leading turbine slows the wind speed in the plane of the rotor blades to extract kinetic energy from the wind and convert it into electrical energy, the trailing turbine now has only a lower wind speed available for generating electricity. Furthermore, the wind field behind the leading turbine will have a different shape than the one in front of it with regard to characteristic wind field parameters such as turbulence intensity, vertical and horizontal shear, wind direction, and wind direction change with height.

[0005] The principles that apply in a wind farm differ significantly from those of a single turbine whose airflow is undisturbed. For example, the yield of a wind farm will generally not be the sum of the yields of the individual turbines within the farm if one considers the yield for each individual turbine as it would achieve in an undisturbed wind field. Similarly, the stability and load-bearing capacity of turbines within a wind farm typically need to be assessed, particularly if they are located in the wake of other turbines due to wind conditions.

[0006] According to current technology, it is often necessary to throttle turbines in a wind farm to ensure structural stability and compliance with design loads. Throttle operation means, for example, reducing the rated power or speed, or increasing the pitch angle. This can be done either on the turbine located in the front row relative to the wind direction (passive protection) or on turbines in the rear rows, i.e., in the wake of another turbine (active protection).

[0007] Regarding increasing wind farm yield, it is state of the art to operate turbines in the front row with, for example, a higher pitch angle to reduce blockage in the rotor blade plane, thus decreasing axial induction. This increases the wind speed behind the front turbine, thereby providing the rear turbine with a higher wind speed for energy conversion. Although the yield of the turbines in the front row decreases, this loss is more than compensated for by the increased yields of the turbines in the subsequent rows of the wind farm, resulting in an overall increase in wind farm yield.

[0008] Document US 2009 / 099702A1 describes a system and method for increasing the overall power output of a wind farm under conditions where the wake generated by an upstream turbine affects the power output of a downstream turbine. Minimizing the wake effects exerted on a downstream turbine increases the net power output of both the upstream and downstream turbines. This involves implementing an algorithm to determine the controller settings of one or more upstream turbines to increase the overall energy yield of the turbines in the wind farm. The algorithm also reduces fatigue stress on downstream turbines by mitigating turbulence caused by the wake effects of the upstream turbine.

[0009] Document WO 2019 / 138132A1 describes a method for controlling a wind turbine and an associated wind turbine. The wind turbine is operated according to an operating point, which is defined by at least a pitch angle and a tip speed ratio. One of the operating points corresponds to a maximum power coefficient. The wind turbine is operated in a partial load range at an operating point that differs from the operating point with the maximum power coefficient. The distance of the operating point from the operating point with the maximum power coefficient is adjusted depending on a measured turbulence measure.

[0010] Document WO 2019 / 197680A1 concerns a wind turbine with a wake control system configured to regulate the turbine based on wake effects caused by another wind turbine, wherein the wake control system is configured to regulate based on a turbulence measurement from a turbulence sensor of the other wind turbine. The document also concerns a wind turbine with a turbulence sensor configured to determine a turbulence measurement, wherein the turbulence measurement is indicative of turbulence and / or wind shear at the wind turbine, and wherein the wind turbine is configured to provide the turbulence measurement for the control of the wind turbine and / or another wind turbine.

[0011] Various approaches to optimizing the control of wind turbines in a wind farm were therefore attempted.

[0012] Against this background, it was an object of the present invention to propose a method for operating a wind farm, an associated wind energy plant and an associated wind farm, with which an increase in yield is possible.

[0013] According to the invention, the problem is solved by the independent claims. Preferred embodiments are specified in the dependent claims.

[0014] In one aspect, a method for operating a wind farm with a first wind turbine and a second wind turbine is proposed, wherein the second wind turbine is located in the wake of the first wind turbine in at least one wake wind direction, wherein a speed-of-speed coefficient is determined from the ratio of a second speed-of-speed number of the second wind turbine and a first speed-of-speed number of the first wind turbine, and wherein a pitch-angle coefficient is determined from the ratio of a second pitch angle of the second wind turbine and a first pitch angle of the first wind turbine.

[0015] The procedure comprises the following steps: determining a turbulence measure, in particular a turbulence intensity, at the second wind turbine, and operating the first wind turbine and the second wind turbine in the wake wind direction in a partial load range, wherein the speed coefficient and / or the pitch angle coefficient is a function of the turbulence measure at the second wind turbine and is greater than one.

[0016] In this configuration, the partial load range extends from 0 kW to the rated power of the wind turbine. It therefore includes both a range with a known, approximately constant tip speed and a range with a changing tip speed.

[0017] A wake wind direction is understood to be, in particular, a wind direction range in which the turbine located further downwind is influenced by the turbine located further upwind. In other words, a wake wind direction exists whenever the wind turbine in the wake experiences different wind conditions due to the presence of the turbine located further upwind than a turbine exposed to the wind would experience in a free-flowing environment. A wake wind direction is therefore a wind direction that lies within a range of wind directions relevant to the wake effect.

[0018] The other wind conditions caused by the wake can include, in particular, a different wind speed and / or a different turbulence level, especially a different turbulence intensity. Other parameters, such as a different wind direction due to deflection, are also conceivable.

[0019] The tip speed ratio λ indicates the ratio of the rotor's circumferential speed u to the wind speed v. The pitch angle, or setting angle, refers to the angle between the rotor plane of the wind turbine rotor and the chord line of the rotor blade.

[0020] A turbulence intensity is particularly suitable as a measure of turbulence, although other measures such as a turbulence degree, which is defined as a dimensionless quantity to describe the quality of an external flow, are also suitable.

[0021] Turbulence intensity is preferably defined as the ratio of the standard deviation of the wind speed to the mean wind speed over time intervals of, in particular, 10 minutes. Turbulence intensity is a measure of the variability of the wind speed within these time periods.

[0022] According to the invention, it is thus recognized that in the partial load range, the speed-of-flight ratio of the second wind turbine, which is positioned in the wake of the first wind turbine, is advantageously higher than the speed-of-flight ratio of the first wind turbine. Alternatively or additionally, the pitch angle of the second wind turbine can also be greater than the pitch angle of the first wind turbine with a similar advantage.

[0023] The functional relationship between the relatively increased speed-of-flight ratio and the relatively increased pitch angle is given by the turbulence coefficient. According to the invention, it has therefore been shown that optimized control of the entire wind farm, resulting in optimal yield, requires finely differentiated wake control.

[0024] The relevant factor is therefore not the absolute speed-of-flight ratio or the absolute pitch angle of the first and second wind turbines, but rather their ratio to each other. An advantageous ratio is such that the second wind turbine operates at a higher speed-of-flight ratio or pitch angle. This can be achieved by the second wind turbine increasing its speed-of-flight ratio and / or pitch angle; alternatively or additionally, the first wind turbine can decrease its speed-of-flight ratio and / or pitch angle, or at least increase it less significantly than the second wind turbine. A speed-of-flight coefficient or pitch angle coefficient greater than one can thus be achieved through a variety of control interventions.

[0025] The method particularly favors controlling the second wind turbine by increasing its speed-time and pitch angle essentially simultaneously, with the aim of keeping the thrust coefficient of the second wind turbine's rotor essentially unchanged. This allows the increase in yield in the wind farm to be achieved in a way that is essentially load-neutral.

[0026] Furthermore, it is essential according to the invention that the high-speed coefficient and / or the pitch angle coefficient are not only greater than one, but are also a function of the turbulence coefficient. This functional dependence on the turbulence coefficient allows the setting of the high-speed coefficient or the pitch angle coefficient to be specifically adjusted, thereby increasing the overall energy yield of the wind farm.

[0027] Preferably, the second speed-of-flight number is increased such that, taking into account a maximum permissible thrust coefficient, a maximized power coefficient of the second wind turbine is achieved.

[0028] In particular, an increase in the high-speed rotational speed can be accompanied by an operationally driven increase in load. This is only permissible to the extent that the system's design loads are reached or any residual safety margins are fully utilized.

[0029] The design loads of the system are maintained if the speed-of-speed ratio, and in particular the combination of speed-of-speed ratio and pitch angle, is selected such that the thrust coefficient at the resulting operating point lies within a permissible range. It is important to note that the thrust coefficient must not deviate significantly from standard operating conditions so that any predicted loads on the system itself and on downstream systems remain valid.

[0030] It is particularly advantageous to increase the speed-of-flight ratio or the combination of speed-of-flight ratio and pitch angle in such a way that the thrust coefficient remains essentially constant. This achieves power-maximized operation while adhering to the design loads, even in the wake of a wind turbine.

[0031] Alternatively or in addition to the shear coefficient, a forward-backward bending moment of the wind turbine tower can be determined to infer the shear.

[0032] Preferably, the increase in the top-up speed is limited in such a way that the rated speed is not exceeded. This ensures that the wind turbine does not overspeed.

[0033] Preferably, the second speed ratio and the second pitch angle are increased such that, taking into account a maximum permissible thrust coefficient, a maximized power coefficient of the second wind turbine is achieved.

[0034] Preferably, the maximum permissible shear coefficient is a site-dependent shear coefficient, which depends in particular on air density and / or wind speed.

[0035] Other factors influencing the thrust coefficient include, for example, those from aerodynamics and control systems, particularly pitch angle and torque. For the location-dependent thrust coefficient, wind speed and air density are especially important.

[0036] Preferably, a decision as to whether the pitch angle coefficient is increased in addition to the speed-of-speed coefficient is made depending on the operating conditions at the location of the first and / or second wind turbine.

[0037] The operating conditions at the site of the first and / or second wind turbine preferably include wind conditions and environmental conditions. The wind conditions include at least one factor consisting of wake-disturbed turbulence, wind speed, oblique flow, a vertical wind speed profile, and air density. The environmental conditions preferably include at least one factor consisting of temperature and humidity, for example, to detect possible icing of the rotor blade. The conditions mentioned are, of course, examples and not exhaustive.

[0038] The data on operating conditions can be based on a forecast, i.e., in particular as a combination of statistics and modeling, and / or be measured, in particular directly or indirectly.

[0039] Preferably, the decision is made depending on site loads at the location and / or the type of plant of the second wind turbine.

[0040] In this interpretation, the site loads are specifically the mechanical loads acting on the structure of the second wind turbine. These mechanical loads can be based on a forecast, such as an aeroelastic forecast, or they can be measured, particularly directly or indirectly.

[0041] In principle, only the rear turbine, i.e., the second wind turbine, is relevant. However, since this wind turbine is affected by the wake of the front turbine, the site loads of the rear wind turbine are also dependent on those of the front wind turbine.

[0042] The smaller the relative distance between the first and second turbines, the greater the impact of wake turbulence and, consequently, the higher the site loads. Therefore, the relative distance between the wind turbines is preferably used to correct or improve the site loads on the second wind turbine.

[0043] Furthermore, the higher the thrust coefficient of the leading turbine, the greater the wake turbulence and consequently the site loads. Therefore, wake turbulence is also preferably used to correct or improve, in particular, the predicted site loads.

[0044] In addition to the site loads, the reserves of the wind turbine play a particularly important role, especially the aerodynamic reserves and the load-related reserves.

[0045] Preferably, the permissible range for increasing the speed-of-flight ratio and / or the pitch angle of the second wind turbine can be specified via a live control system, in particular a central wind farm computer. For this purpose, the grid connection point is preferably taken into account and / or monitored. Furthermore, load monitoring of the second wind turbine, preferably performed at least approximately in real time, is preferably used. In this case, the operating point of the second wind turbine, i.e., in particular the permissible range for increasing the speed-of-flight ratio and / or the pitch angle, can be defined for a maximized power coefficient.

[0046] Preferably, a maximum power coefficient is determined for the specific turbulence intensity at the second wind turbine, wherein the operating parameters speed ratio and pitch angle are determined for the operating point corresponding to the maximum power coefficient, and the second wind turbine is operated at the operating point with maximum power coefficient if the resulting thrust coefficient is permissible for the specific location.

[0047] Preferably, air density is taken into account when setting the second speed setting and / or the second pitch angle.

[0048] In another aspect, a wind turbine in a wind farm is proposed, wherein the wind farm contains the wind turbine and another wind turbine, wherein the wind turbine is located in the wake of the other wind turbine in at least one wake wind direction, wherein a speed-of-flight coefficient is determined from the ratio of a speed-of-flight number of the wind turbine and a speed-of-flight number of the other wind turbine, and wherein a pitch-angle coefficient is determined from the ratio of a pitch angle of the wind turbine and a pitch angle of the other wind turbine, comprising a control device configured to determine a turbulence intensity at the wind turbine and to operate the wind turbine in a partial load range in the wake wind direction.that the high-speed coefficient and / or the pitch angle coefficient is a function of the turbulence intensity at the second wind turbine and is greater than one.

[0049] The wind turbine according to the invention, in this respect, makes it possible to achieve the same advantages as disclosed with reference to the method described above. In particular, it enables the operation of the wind turbine in the wind farm with optimized overall yield.

[0050] The combination of the wind turbine with the special configurations of the process described as preferred is also advantageous.

[0051] In another aspect, a wind farm is proposed with one wind turbine according to the previous aspect and another wind turbine.

[0052] The wind farm according to the invention, in this respect, makes it possible to achieve the same advantages as those disclosed with reference to the method described above or the wind turbine disclosed above. In particular, it enables the operation of the wind farm with optimized overall yield.

[0053] The combination of the wind farm with the special configurations of the process described as preferred is also advantageous.

[0054] Preferably, the control device of the wind turbine or of one of the wind turbines of the wind farm is configured to increase the speed-of-flight ratio and / or the pitch angle in such a way that a maximum permissible thrust coefficient of the wind turbine is achieved.

[0055] Preferably, the maximum permissible thrust coefficient of the wind turbine or one of the wind turbines of the wind farm is site-specific and depends in particular on the air density.

[0056] Preferably, the wind turbine or one of the wind turbines of the wind farm comprises a turbulence measuring unit for determining a turbulence intensity, wherein the control device is configured to take the determined turbulence intensity into account when setting the speed-of-flight number and / or the pitch angle of a rotor of the wind turbine.

[0057] All known units for measuring turbulence intensity are conceivable. Preferably, the turbulence intensity is derived from the measured wind speed using the turbulence measurement unit. Particularly preferably, the turbulence intensity is even calculated with spatial resolution at several locations. The functional dependence of the speed coefficient or the pitch angle coefficient can then be directly determined by the multiple turbulence intensities; alternatively, a single mean or average value representing the multiple spatially resolved turbulence intensities can be determined by the turbulence measurement unit.

[0058] Preferably, the control device of the wind turbine or of one of the wind turbines of the wind farm is configured to adjust the speed ratio and / or the pitch angle, taking into account the turbulence intensity, in such a way that a substantially maximum power coefficient is achieved at one rotor of the wind turbine.

[0059] Preferably, the wind turbine or one of the wind turbines of the wind farm comprises an air density measuring unit for determining an air density, wherein the control device is configured to take the determined air density into account when setting the speed-of-flight rate and / or the pitch angle.

[0060] The present disclosure is particularly applicable to variable-speed, pitch-controlled wind turbines that are operated in the wake of another wind turbine. The turbines must be operable in such a way that the rotational speed and pitch angle can be adjusted independently of each other. The turbines must have a sensor for determining turbulence intensity.

[0061] The invention is explained in more detail below by way of example embodiments with reference to the accompanying figures. Figure 1 shows a schematic and exemplary perspective view of a wind turbine. Figure 2 shows a schematic and exemplary view of a wind farm. Figure 3 shows a schematic and exemplary comparison of the tip speed ratio and pitch angle versus wind speed for the front and rear wind turbines. Figure 4 shows a schematic and exemplary view of the tip speed ratio and pitch angle at the point of maximum power coefficient versus a turbulence measure. Figure 5 shows a schematic and exemplary view of contour lines of the power coefficient, the thrust coefficient, and their ratio versus tip speed ratio and pitch angle for a first combination of turbulence intensity and turbine type. Figure 6 shows a schematic and exemplary view of contour lines of the power coefficient, the thrust coefficient, and their ratio versus tip speed ratio and pitch angle for a second combination of turbulence intensity and turbine type.

[0062] Figure 1 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 into 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 electric 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.

[0063] The wind turbine 100 has an electric 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 is provided for feeding electrical power into the grid; this unit can be specifically designed as an inverter. This allows a three-phase feed-in current and / or a three-phase feed-in voltage with amplitude, frequency, and phase to be generated for feeding into a grid connection point (PCC). This can be done directly or in conjunction with other wind turbines in a wind farm. A plant control unit 103 is provided for controlling the wind turbine 100 and the feed-in unit 105. The plant control unit 103 can also receive setpoint values ​​from external sources, in particular from a central park computer.

[0064] Figure 2Figure 112 shows a wind farm with three exemplary wind turbines 100, which can be identical or different. The three wind turbines 100 thus represent, in principle, any number of wind turbines in a wind farm 112. The wind turbines 100 supply their power, namely the generated electricity, via an electrical park grid 114. The currents or power outputs of the individual wind turbines 100 are added together, and a transformer 116 is usually provided to step up the voltage in the park in order to feed it into the supply grid 120 at the feed-in point 118, which is also generally referred to as PCC. Fig. 2 This is only a simplified representation of a wind farm 112. For example, the park network 114 can be designed differently, for instance by including a transformer at the output of each wind turbine 100, to name just one other embodiment.

[0065] In order to increase the yield of wind farms, an alternative method is proposed according to the present disclosure, which is to be applied as soon as there are at least two rows of wind turbines in a wind farm 112 and thus the turbines of the rear row are at least partially in the wake of the turbines in the front row depending on the wind direction.

[0066] It is proposed here that the high-speed number λ in the partial load range of the rear systems is greater than the high-speed numbers λ of the front systems, i.e., the ratio of the high-speed numbers in the partial load range of the rear systems to the front system is always greater than one.

[0067] It is further proposed that, optionally, the pitch angles γ in the partial load range should also be increased from the front system to the rear system when the high-speed numbers λ are increased.

[0068] It is therefore proposed that the wind turbine 100 in a wind farm 112, which is located in the wake of another wind turbine 100, be operated in the partial load range with a higher speed ratio λ and / or with a higher pitch angle γ than the turbines that are located upstream in the wind and cause the wake.

[0069] Fig. 3 Figure 1 schematically and exemplarily shows the comparison of the speed-of-flight number λ and the pitch angle γ on the vertical axis over the wind speed v on the horizontal axis for turbines in a wind farm 112, where lines 200 indicate the operating management for the turbines in the front row, i.e. for turbines that are in free flow, and lines 300 indicate the operating management for turbines that are placed in a rear row, i.e. in the wake of the turbines in the front row.

[0070] It can be seen that the inventive procedure proposes operating the systems in the rear row, cf. line 300, with a higher speed-of-flight ratio λ, or with a higher pitch angle γ, than the systems in the front row, cf. line 200. This difference exists in a partial load range 250 with wind speeds v that are below a rated wind speed vn, at which the system is operated at rated power.

[0071] The Fig. 3The diagram is to be understood schematically, and accordingly, the rated wind speed vn is also schematically depicted at a transition between the partial load range of 250 and the full load range of 260. While in the full load range of 260 there are wind speeds at which lines 200 and 300 run parallel, meaning that the operating conditions of the turbines in the rear row are the same as those of the turbines in the front row, in the partial load range of 250 there is a difference between the respective operating conditions; that is, lines 200 and 300 run differently in the partial load range of 250.

[0072] In other words, it is proposed that the ratio of the speed-of-flight ratio λ or the pitch angles γ of the trailing turbine to the leading turbine should always be greater than one. The turbine trailing another should therefore be operated with a higher speed-of-flight ratio and / or higher pitch angles than the turbine causing the trail.

[0073] The inventive method is proposed because it can be assumed that the similarly configured systems in the rear row generate more yield than systems that are operated in the rear row with identical speed settings λ and pitch angles γ compared to the front row.

[0074] The proposal is based on the understanding that a measure of turbulence, for example expressed by the turbulence intensity, increases in the wake of a plant, i.e., the turbulence intensity for the plants in the rear row is greater than the turbulence intensity of the plants in the front row.

[0075] Furthermore, it was recognized that the maximum power coefficient of a rotor blade or the entire system shifts to higher tip speed ratios λ or higher pitch angles γ with increasing turbulence intensity.

[0076] Fig. 4 The figure schematically and exemplarily shows the tip speed ratio λ cpmax or the pitch angle γ cpmax at which the maximum power coefficient of the rotor blade is present, plotted against the turbulence intensity Ti of the oncoming wind on the horizontal axis.

[0077] Out of Fig. 4It becomes apparent that with increasing turbulence intensity, the tip speed ratio λ or the pitch angle y, at which the rotor blade exhibits the maximum power coefficient c pmax, also increases. This means that the turbine located in the wake of another and exposed to increased turbulence intensity must be operated with a higher tip speed ratio and / or a higher pitch angle to achieve maximum energy yield from the turbines in the rear row, i.e., to be operated at the maximum power coefficient c pmax.

[0078] The specific procedure in the inventive proposal, in particular whether only the speed-of-flight ratio is increased or whether the speed-of-flight ratio λ and also the pitch angle γ are increased, depends on the load situation at the site, which must be taken into account. It may be expected that the inventive proposal will generate comparatively higher loads at the turbines in the rear rows. This is especially likely if only the speed-of-flight ratio λ is increased at the turbines in the rear row, while the pitch angle γ remains unchanged.

[0079] However, a combined approach of increasing the speed-time ratio and the pitch angle can also be chosen, which may not lead to an increase in the system loads. The inventive proposal must be adapted to the load conditions at the wind farm site, and it must be site-specifically examined which operating mode can be implemented.

[0080] Fig. 5schematically and exemplarily shows contour lines of the power coefficients cp, the thrust coefficients ct and the ratio of power and thrust coefficient cp / ct as a function of tip speed λ and pitch angle γ for a specific type 1 of wind turbines 100 at a turbulence intensity Ti=A%, for example at a low turbulence intensity where no wake effects are to be expected.

[0081] Fig. 6 schematically and exemplarily shows contour lines of the power coefficients cp, the thrust coefficients ct and the ratio of power and thrust coefficient cp / ct as a function of tip speed λ and pitch angle γ for a type 2 wind turbine 100 at Ti=B%.

[0082] The power coefficient cp is a dimensionless parameter of a wind turbine. It describes, at any given time, what proportion of the power contained in the wind can be converted into mechanical power of the rotor, or is converted at a specific operating point. The power coefficient is therefore not a constant design parameter, but rather depends on varying influencing factors.

[0083] The power of the wind depends primarily on the wind speed. The mechanical power of the turbine, in turn, depends on the wind speed in front of and behind the rotor. Furthermore, the power of the wind and the mechanical power of the rotor depend on the air density and the rotor disc area. In simplified terms, the power coefficient can therefore be calculated using the wind speed in front of and behind the rotor. According to Betz's law, air cannot be completely slowed down. Thus, a maximum power coefficient is achieved when the wind speed behind the rotor is one-third of the wind speed in front of the rotor. However, due to losses at the rotor, wind turbines typically only achieve power coefficients between approximately 0.4 and 0.5 during normal operation.

[0084] Rotor thrust is the force exerted horizontally by the airflow on the hub of the wind turbine 100, or conversely, by the wind turbine 100 on the airflow. Normalized by the axial force of the wind, this yields the thrust coefficient. The feedback effect of a wind turbine on the airflow depends, among other things, on its dimensionless thrust coefficients (ct). Thrust coefficients are therefore essential input parameters for modeling shading in wind farms. The thrust coefficients used are generally calculated by the turbine manufacturers. The highest thrust coefficients occur during power operation at low wind speeds and decrease steadily at medium and higher speeds. Consequently, the mutual influence of wind turbines is relatively greatest at low wind speeds.Since the energy contained in the wind is then low and increases disproportionately with wind speed, the absolute mutual interference is ultimately greatest at medium wind speeds.

[0085] Fig. 5 and Fig. 6 The statements made are intended to clarify the information presented. As mentioned, the figures show contour lines for the aerodynamic performance coefficients cp, the thrust coefficients ct, and the ratio of performance to thrust coefficient cp / ct versus the tip speed ratio and the pitch angle. The explicit values, especially those for pitch angle and tip speed ratio, but also the stated performance coefficients cp and thrust coefficients ct, are merely examples and not to be understood as limiting.

[0086] The illustrations are for two different plant types and for different turbulence intensities Ti, which are in the range of 10%. <Ti<30% bewegen, erstellt.

[0087] Point 410 in Fig. 5 and Fig. 6 Each value indicates the point of maximum aerodynamic power coefficient for turbulence-free flow with Ti=0%.

[0088] In Fig. 5 It can first be seen that the maximum aerodynamic performance coefficient shifts from the speed-to-speed ratio λ=7.5 and the pitch angle γ=-1° at Ti=0%, represented by point 410, to λ=9 and γ=1.5° at Ti=A%, indicated by point 420.

[0089] If the system were operated at turbulence intensity A% at point 420, the thrust coefficient would also increase from ct=0.8 to ct=0.9, but the ratio of power and thrust coefficient (contour line cp / ct ) would remain constant; therefore, when changing the operating conditions in the turbulent flow, the power coefficient would increase in the same proportion as the thrust coefficient.

[0090] Therefore, in order to operate the plant at maximum power even at Ti=A%, circumstances must exist that compensate for the operational load increase, such as operation at a low-density site where the plant's design loads are typically not reached. If this is not the case, alternatively, the plant could be operated at point 430 at λ=8.5 and y=3°. Point 430 was chosen so that, with a constant thrust coefficient ct=0.8, the ratio of cp / C t is maximized.

[0091] The point is therefore chosen such that a maximum power coefficient is achieved under load neutrality. Compared to the state of the art, in which the operation of the system would remain unchanged at point 410 under an inflow with increased Ti=A%, the aerodynamic power coefficient increases significantly.

[0092] For plant type 2 ( Fig. 6The situation is somewhat different in that, when the maximum aerodynamic power coefficient shifts from turbulence-free flow Ti=0%, again represented by point 410, to turbulent flow with Ti=B%, represented by point 420, only the tip speed ratio λ changes, while the pitch angle γ remains almost unchanged. Therefore, if one wants to operate the system at its optimum power output under turbulent flow, the corresponding increase in the thrust coefficient ct must be checked for site-specific compliance.

[0093] For operation at a constant thrust coefficient, a combination of speed-time speed and pitch angle increase must again be implemented, here in this example for system type 2 to approximately λ=9.25 and γ=0.3°, represented by point 430 in Fig. 6For constant thrust ct=0.86, the power coefficient is at its maximum here, but lower than the optimum for this turbulence intensity and still higher than at the operating point of system type 2 with turbulence-free flow Ti=0%, i.e. at point 410.

[0094] It follows that, depending on site loads and turbine type, the operation of the turbine under flow conditions with increased turbulence intensity, for example in a wind farm when a turbine is operated in the wake of another turbine, must be adjusted with regard to the tip speed and pitch angle in the partial load range, such that a tip speed increase or a combined increase of tip speed and pitch angle is implemented. The combined increase is particularly preferred as a function of the turbulence intensity as the turbulence measure.

Claims

1. Method for operating a wind farm (112) having a first wind power installation (100) and a second wind power installation (100), wherein the second wind power installation (100) is located in the wake of the first wind power installation (100) in at least one wake wind direction, wherein a tip-speed coefficient is determined from the ratio of a second tip-speed ratio of the second wind power installation (100) and a first tip-speed ratio of the first wind power installation (100) and wherein a pitch-angle coefficient is determined from the ratio of a second pitch angle of the second wind power installation (100) and a first pitch angle of the first wind power installation (100), comprising the steps of: - determining a turbulence metric, in particular a turbulence intensity, at the second wind power installation (100), characterized by - operating the first wind power installation (100) and the second wind power installation (100) in the wake wind direction in a part-load range (250), wherein the tip-speed coefficient and / or the pitch-angle coefficient are / is a function of the turbulence metric at the second wind power installation (100) and are / is greater than one.

2. Method according to Claim 1, wherein the second tip-speed ratio is increased in such a way that a maximized power coefficient of the second wind power installation is obtained in consideration of a maximum permissible thrust coefficient.

3. Method according to Claim 2, wherein the second tip-speed ratio and the second pitch angle are increased in such a way that a maximized power coefficient of the second wind power installation (100) is obtained in consideration of a maximum permissible thrust coefficient.

4. Method according to Claim 3, wherein the maximum permissible thrust coefficient is a location-dependent thrust coefficient which is dependent in particular on an air density and / or the wind speed.

5. Method according to one of the preceding claims, wherein a decision about whether the pitch-angle coefficient is increased in addition to the tip-speed coefficient is made depending on operating conditions at the site of the first and / or second wind power installation (100).

6. Method according to Claim 5, wherein the decision is made depending on location loads at the site and / or on the installation type of the second wind power installation (100).

7. Method according to one of the preceding claims, wherein a maximum power coefficient is determined for the determined turbulence intensity at the second wind power installation (100), wherein the operating point (430) related to the maximum power coefficient the operating parameters tip-speed ratio and pitch angle are determined, wherein the second wind power installation (100) is operated at the operating point (430) having the maximum power coefficient if the thrust coefficient obtained is permissible at the specific location.

8. Method according to one of the preceding claims, wherein an air density is taken into consideration when setting the second tip-speed ratio and / or the second pitch angle.

9. Wind power installation (100) on a wind farm (112) having the wind power installation (100) and a further wind power installation, wherein the wind power installation (100) is located in the wake of the further wind power installation (100) in at least one wake wind direction, wherein a tip-speed coefficient is determined from the ratio of a tip-speed ratio of the wind power installation (100) and a tip-speed ratio of the further wind power installation (100) and wherein a pitch-angle coefficient is determined from the ratio of a pitch angle of the wind power installation (100) and a pitch angle of the further wind power installation (100), comprising a control apparatus (103) which is designed to determine a turbulence intensity at the wind power installation (100) and characterized by that the control apparatus (103) is configured to operate the wind power installation (100) in the wake wind direction in a part-load range (250) in such a way that the tip-speed coefficient and / or the pitch-angle coefficient are / is a function of the turbulence intensity at the wind power installation (100) and are / is greater than one.

10. Wind farm (112) having a wind power installation (100) according to Claim 9 and the further wind power installation (100).

11. Wind power installation (100) according to Claim 9 or wind farm (112) according to Claim 10, wherein the control apparatus (103) is configured to increase the tip-speed ratio and / or the pitch angle in such a way that a maximum permissible thrust coefficient of the wind power installation (100) is obtained.

12. Wind power installation (100) or wind farm (112) according to one of preceding Claims 9 to 11, wherein the maximum permissible thrust coefficient is location-specific and is dependent in particular on the air density.

13. Wind power installation (100) or wind farm (112) according to one of preceding Claims 9 to 12, comprising a turbulence measuring unit for ascertaining a turbulence intensity, wherein the control apparatus (103) is configured to take the ascertained turbulence intensity into consideration when setting the tip-speed ratio and / or the pitch angle of a rotor (106) of the wind power installation (100).

14. Wind power installation (100) or wind farm (112) according to one of preceding Claims 9 to 13, wherein the control apparatus (103) is configured to set the tip-speed ratio and / or the pitch angle in consideration of the turbulence intensity in such a way that a substantially maximum power coefficient at a rotor (106) of the wind power installation (100) is obtained.

15. Wind power installation (100) or wind farm (112) according to one of preceding Claims 9 to 14, comprising an air density measuring unit for ascertaining an air density, wherein the control apparatus (103) is configured to take the ascertained air density into consideration when setting the tip-speed ratio and / or the pitch angle.