Method for operating a wind farm, wind power installation and wind farm

Abstract

A method for operating a wind farm having a first wind power installation and a second wind power installation, to an associated wind power installation and to an associated wind farm. The second wind power installation is located in the wake of the first wind power installation in at least one wake wind direction. A tip-speed coefficient is determined from the ratio of a second tip-speed ratio of the second wind power installation and a first tip-speed ratio of the first wind power installation and a pitch-angle coefficient is determined from the ratio of a second pitch angle of the second wind power installation and a first pitch angle of the first wind power installation. The method comprises: determining a turbulence metric, in particular a turbulence intensity, at the second wind power installation; operating the first wind power installation and the second wind power installation in the wake wind direction in a part-load range, 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 and are/is greater than one.

Claims

1. A method for operating a wind farm having a first wind power installation and a second wind power installation, wherein the second wind power installation is located in a wake of the first wind power installation in at least one wake wind direction, the method comprising: determining a tip-speed coefficient from a ratio of a second tip-speed ratio of the second wind power installation to a first tip-speed ratio of the first wind power installation, determining a pitch-angle coefficient from a ratio of a second pitch angle of the second wind power installation to a first pitch angle of the first wind power installation, determining a turbulence metric at the second wind power installation, and operating the first wind power installation and the second wind power installation in a part-load range, wherein at least one coefficient chosen from the tip-speed coefficient and the pitch-angle coefficient is a function of the turbulence metric at the second wind power installation and is greater than one.

2. The method according to claim 1, comprising increasing the second tip-speed ratio 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. The method according to claim 1, comprising increasing the second tip-speed ratio and the second pitch angle 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.

4. The method according to claim 3, wherein the maximum permissible thrust coefficient is a location-dependent thrust coefficient which is dependent on at least one ambient condition chosen from an air density and wind speed.

5. The method according to claim 3, comprising determining whether to increase the pitch-angle coefficient, wherein the determining whether to increase the pitch-angle coefficient depends on operating conditions at a site of the first and/or second wind power installation.

6. The method according to claim 5, wherein the determining whether to increase the pitch-angle coefficient depends on location loads at the site and/or on an installation type of the second wind power installation.

7. The method according to claim 1, comprising: determining a maximum power coefficient for the turbulence metric at the second wind power installation, wherein an operating point related to the maximum power coefficient and the operating parameters tip-speed ratio and pitch angle are determined, and operating the second wind power installation at the operating point having the maximum power coefficient if a resulting thrust coefficient is permissible at the location of the wind power installation.

8. The method according to claim 1, comprising setting the second tip-speed ratio and/or the second pitch angle depending on air density.

9. A wind power installation, wherein the wind power installation is located in a wake of a further wind power installation in at least one wake wind direction, wherein a tip-speed coefficient is determined from a ratio of a tip-speed ratio of the wind power installation to a tip-speed ratio of the further wind power installation and wherein a pitch-angle coefficient is determined from a ratio of a pitch angle of the wind power installation to a pitch angle of the further wind power installation, the wind power installation comprising: a tower, a nacelle, and a controller configured to determine a turbulence intensity at the wind power installation and to operate the wind power installation in the wake wind direction in a part-load range in such a way that at least one coefficient chosen from the tip-speed coefficient and the pitch-angle coefficient is a function of the turbulence intensity at the wind power installation and is greater than one.

10. The wind power installation according to claim 9, wherein the controller 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 first wind power installation is obtained.

11. The wind power installation according to claim 10, wherein the maximum permissible thrust coefficient is location-specific and is dependent on air density.

12. The wind power installation according to claim 9, comprising a turbulence measuring unit for ascertaining a turbulence intensity, wherein the controller is configured to take the turbulence intensity into consideration when setting the tip-speed ratio and/or the pitch angle of a rotor of the wind power installation.

13. A wind farm comprising: a first wind power installation and a second wind power installation, wherein the first wind power installation is located in a wake of the second wind power installation in at least one wake wind direction, wherein a tip-speed coefficient is determined from a ratio of a tip-speed ratio of the first wind power installation to a tip-speed ratio of the second wind power installation, and wherein a pitch-angle coefficient is determined from a ratio of a pitch angle of the first wind power installation to a pitch angle of the second wind power installation, and a controller configured to determine a turbulence intensity at the first wind power installation and to operate the first wind power installation and the second wind power installation in a part-load range in such a way that at least one coefficient chosen from the tip-speed coefficient and the pitch-angle coefficient is a function of the turbulence intensity at the first wind power installation and is greater than one.

14. The wind farm according to claim 13, wherein the controller 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 first wind power installation is obtained.

15. The wind farm according to claim 14, wherein the maximum permissible thrust coefficient is location-specific and is dependent on air density.

16. The wind farm according to claim 13, comprising a turbulence measuring unit for ascertaining a turbulence intensity, wherein the controller is configured to take the turbulence intensity into consideration when setting the tip-speed ratio and/or the pitch angle of a rotor of the wind power installation.

17. The wind farm according to claim 13, wherein the controller 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 maximum power coefficient at a rotor of the wind power installation is obtained.

18. The wind farm according to claim 13, comprising an air density measuring unit for ascertaining an air density, wherein the controller is configured to take the air density into consideration when setting the tip-speed ratio and/or the pitch angle.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention is explained in more detail below by way of example on the basis of exemplary embodiments with reference to the accompanying figures.

(2) FIG. 1 schematically shows, by way of example, a perspective illustration of a wind power installation.

(3) FIG. 2 schematically shows, by way of example, a wind farm.

(4) FIG. 3 schematically shows, by way of example, a comparison of the tip-speed ratio and the pitch angle, respectively, against the wind speed for front and rear wind power installations.

(5) FIG. 4 schematically shows, by way of example, the characteristics of the tip-speed ratio and the pitch angle at the point of the maximum power coefficient against a measure of turbulence.

(6) FIG. 5 schematically shows, by way of example, altitude lines for the power coefficient, the thrust coefficient and the ratio thereof against tip-speed ratio and pitch angle for a first combination of turbulence intensity and installation type.

(7) FIG. 6 schematically shows, by way of example, altitude lines for the power coefficient, the thrust coefficient and the ratio thereof against tip-speed ratio and pitch angle for a second combination of turbulence intensity and installation type.

DETAILED DESCRIPTION

(8) FIG. 1 shows a schematic illustration of a wind power installation according to the invention. The wind power installation 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 having three rotor blades 108 and a spinner 110 is provided on the nacelle 104. During the operation of the wind power installation, the aerodynamic rotor 106 is set in rotational motion by the wind and thereby also rotates an electrodynamic rotor or armature of a generator, which is coupled directly or indirectly 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 may be varied by pitch motors at the rotor blade roots 109 of the respective rotor blades 108.

(9) The wind power installation 100 in this case has an electric generator 101, which is indicated in the nacelle 104. Electric power is able to be generated by way of the generator 101. Provision is made for an infeed unit 105, which may be designed in particular as an inverter, to feed in electric power. It is thus possible to generate a three-phase infeed current and/or a three-phase infeed voltage in terms of amplitude, frequency and phase, for infeed at a grid connection point PCC. This may be performed directly or else together with other wind power installations on a wind farm. Provision is made for an installation control system 103 for the purpose of controlling the wind power installation 100 and also the infeed unit 105. The installation control system 103 may also receive predefined values from an external source, in particular from a central farm computer.

(10) FIG. 2 shows a wind farm 112 having, by way of example, three wind power installations 100, which may be identical or different. The three wind power installations 100 are thus representative of basically any desired number of wind power installations of a wind farm 112. The wind power installations 100 provide their power, specifically in particular the generated current, via an electrical farm grid 114. In this case, the respectively generated currents or powers of the individual wind power installations 100 are added together and a transformer 116, which steps up the voltage on the farm, is usually provided in order to then feed into the supply grid 120 at the infeed point 118, which is also generally referred to as a PCC. FIG. 2 is only a simplified illustration of a wind farm 112. By way of example, the farm grid 114 may also be designed in another way by virtue of for example a transformer also being present at the output of each wind power installation 100, to mention just one other exemplary embodiment.

(11) In order to improve the yield from wind farms, the present disclosure proposes an alternative method which is meant to be used whenever at least two rows of wind power installations are located on a wind farm 112 and at least some of the installations of the rear row are therefore located in the wake of the installations in the front row, depending on the wind direction.

(12) It is proposed here that the tip-speed ratio ? in the part-load range of the rear installations is greater than the tip-speed ratios ? of the front installations, that is to say the ratio of the tip-speed ratios in the part-load range of the rear installations to the front installation is always greater than one.

(13) It is furthermore proposed that, optionally, further to the raising of the tip-speed ratios ?, the pitch angles ? in the part-load range are also raised from the front installation to the rear installation.

(14) It is thus proposed that the wind power installation 100 on a wind farm 112, which is in the wake of another wind power installation 100, is operated in the part-load range with a higher tip-speed ratio ? and/or with a higher pitch angle ? than the installations which are upstream in the wind and cause the wake.

(15) FIG. 3 schematically shows, by way of example, a comparison of the tip-speed ratio ? and the pitch angle ?, respectively, on the vertical axis against the wind speed v on the horizontal axis for installations on a wind farm 112, wherein the lines 200 indicate the operational management for the installations in the front row, that is to say for installations with freely inflowing wind, and the lines 300 indicate the operational management for installations placed in a rear row, that is to say in the wake of the installations of the front row.

(16) It is recognized that the procedure proposes operating the installations in the rear row, cf. line 300, with a higher tip-speed ratio ?, or with a higher pitch angle ?, than the installations in the front row, cf. line 200. This difference is present in a part-load range 250 at wind speeds v below a rated wind speed v.sub.n, at which the installation is operated at rated power.

(17) FIG. 3 should be understood to be schematic overall and the rated wind speed v.sub.n is accordingly also shown schematically at a transition between part-load range 250 and full-load range 260. While the full-load range 260 has wind speeds for which the lines 200 and 300 are of identical shape, that is to say the operational management of the installations in the rear row is identical to the operational management of the installations in the front row, there is a difference between the respective operational managements in the part-load range 250, that is to say that the lines 200 and 300 in the part-load range 250 are of different shape.

(18) In other words, it is proposed that the ratio of the tip-speed ratios ? or the pitch angles ? of the rear installation to the front installation is always greater than one. The installation which is in the wake of another installation is thus intended to be operated with a higher tip-speed ratio and/or higher pitch angles than the installation which causes the wake.

(19) The procedure is proposed since it can be assumed that the installations in the rear row that are set in this way generate more yield than installations which are operated in the rear row with tip-speed ratios ? and pitch angles ? that are identical in comparison with the front row.

(20) The proposal is based on the recognition that a measure of turbulence, for example expressed by the turbulence intensity, increases in the wake of an installation, i.e., the turbulence intensity for the installations of the rear row is greater than the turbulence intensity of the installations of the front row.

(21) Furthermore, it has been recognized that the maximum power coefficient of a rotor blade or of the whole installation shifts towards higher tip-speed ratios ? or higher pitch angles ? when turbulence intensity increases.

(22) FIG. 4 schematically shows, by way of example, the tip-speed ratio ?.sub.cpmax and the pitch angle ?.sub.cpmax for which in each case the maximum power coefficient of the rotor blade is present, plotted against the turbulence intensity Ti of the inflowing wind on the horizontal axis.

(23) It can be seen from FIG. 4 that the tip-speed ratio ? or the pitch angle ? at which the rotor blade has the maximum power coefficient c.sub.pmax increases as turbulence intensity increases. Thus, that is to say that the installation which is in the wake of another and is subject to inflowing wind with an increased turbulence intensity has to be operated with an increased tip-speed ratio and/or an increased pitch angle in order to harvest the maximum yield at the installations in the rear row, that is to say in order to be operated at the maximum power coefficient c.sub.pmax.

(24) The specific procedure in the proposal, in particular whether only the tip-speed ratio is raised or the tip-speed ratio ? and additionally the pitch angle ?, is dependent on the load situation at the location which has to be taken into consideration. It may therefore be expected that, in the proposal, comparatively larger loads are generated at the installations in the rear rows. This can be expected especially if only the tip-speed ratio ? at the installations of the rear row is increased, with the pitch angle ? remaining unchanged.

(25) However, a combined procedure of increasing the tip-speed ratio and the pitch angle can also be chosen, which may lead to no increase in the installation loads. The proposal needs to be adapted to suit the load conditions at the location of the wind farm, and the operational management that can be implemented needs to be checked at the specific location.

(26) FIG. 5 schematically shows, by way of example, altitude lines for the power coefficients c.sub.p, the thrust coefficients c.sub.t and the ratio of the power coefficient and the thrust coefficient c.sub.p/c.sub.t against tip-speed ratio ? and pitch angle ? for a determined type 1 of wind power installations 100 at a turbulence intensity Ti=A %, for example at a low turbulence intensity, for which no wake effects are to be expected.

(27) FIG. 6 schematically shows, by way of example, altitude lines for the power coefficients c.sub.p, the thrust coefficients c.sub.t and the ratio of the power coefficient and the thrust coefficient c.sub.p/c.sub.t against tip-speed ratio ? and pitch angle ? for a type 2 of wind power installations 100 at Ti=B %.

(28) The power coefficient c.sub.p is a dimensionless index for a wind power installation. It describes, at any point in time, what proportion of the power contained in the wind can be converted, or is converted at a certain operating point, into mechanical power of the rotor. The power coefficient is accordingly not a constant constructive index, but rather is dependent on changing influencing variables.

(29) The power of the wind is primarily dependent on the wind speed. The mechanical power of the installation is in turn dependent on the wind speed upstream and downstream of the rotor. Additionally, the power of the wind and the mechanical power of the rotor are dependent on the density of the air and the rotor circle area. Simply put, the power coefficient can therefore be calculated using the wind speed upstream and downstream of the rotor. According to Betz' law, the air cannot be slowed down completely. A maximum power coefficient is thus reached when the wind speed downstream of the rotor corresponds to a third of the wind speed upstream of the rotor. Due to losses at the rotor, wind power converters only reach power coefficients of between approximately 0.4 and approximately 0.5 during normal operation, however.

(30) The rotor thrust is the force which is exerted on the hub of the wind power installation 100 horizontally by the flow of air, or conversely on the flow by the wind power installation 100. Normalized with the axial force of the wind, the thrust coefficient is calculated therefrom. The retroactive effect of a wind power installation on the flow is dependent, inter alia, on its dimensionless thrust coefficients c.sub.t. Thrust coefficients are therefore essential input variables for modelling shadowing in wind farms. The thrust coefficients used are generally calculated by the installation manufacturers. The highest thrust coefficients arise during power operation at low wind speeds and they fall constantly at medium and higher speeds. Accordingly, seen in relative terms, the mutual influence of wind power installations is greatest at low wind speeds. However, 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.

(31) FIG. 5 and FIG. 6 are intended to clarify the statements made. The images each present, as mentioned, altitude lines for the aerodynamic power coefficients c.sub.p, the thrust coefficients c.sub.t and the ratio of the power coefficient and the thrust coefficient c.sub.p/c.sub.t against the tip-speed ratio and the pitch angle. The explicit values, in particular the values for pitch angle and tip-speed ratio, but more specifically the specified power coefficients c.sub.p and thrust coefficients c.sub.t, should be understood merely as examples and not in a restrictive sense.

(32) The images are compiled for two different installation types and for different turbulence intensities Ti, which are in the range 10%<Ti<30%.

(33) The point 410 in FIG. 5 and FIG. 6 indicates in each case the point of the maximum aerodynamic power coefficient for the turbulence-free inflow at Ti=0%.

(34) In FIG. 5 it will initially be seen that the maximum aerodynamic power coefficient shifts from the tip-speed ratio ?=7.5 and the pitch angle ?=?1? at Ti=0%, represented by the point 410, to ?=9 and ?=1.5? at Ti=A %, indicated by point 420.

(35) If the installation were now operated at the turbulence intensity A % at the point 420, the thrust coefficient would also increase from c.sub.t=0.8 to c.sub.t=0.9; the ratio of power coefficient and thrust coefficient (altitude line c.sub.p/c.sub.t) would, however, remain constant and consequently, in the case of the operational management change in the turbulence-rich inflow, the power coefficient would increase in the same proportion as the thrust coefficient.

(36) Thus, in order to be able to operate the installation at the maximum power at Ti=A % too, circumstances have to exist which compensate for the operational-management-related load increase, such as, for example, operation at a reduced-density location at which the designed loads of the installation are typically not reached. If this is not the case, operation of the installation at the point 430 at ?=8.5 and ?=3? is alternatively possible. The point 430 has been selected such that the ratio of c.sub.p/c.sub.t reaches its maximum at a constant thrust coefficient c.sub.t=0.8.

(37) The point is accordingly selected such that a maximum power coefficient is realized for load neutrality. In contrast to the prior art, in which the installation would continue to operate at point 410 in the case of an inflow with increased Ti=A %, the aerodynamic power coefficient is significantly increased.

(38) For installation type 2 (FIG. 6) the situation is somewhat different in this respect, since the shift of the maximum aerodynamic power coefficient from turbulence-free inflow Ti=0%, again represented by point 410, to turbulence-rich inflow at Ti=B %, represented by point 420, only changes the tip-speed ratio ?; the pitch angle ? is virtually unchanged, however. Thus, if the installation is required to be operated at the optimum power in the case of turbulence-rich inflow, the relevant increase in the thrust coefficient c.sub.t needs to be checked for permissibility at the specific location.

(39) For operation with a constant thrust coefficient, a combination of tip-speed ratio increase and pitch angle increase again needs to be realized, in this example here for installation type 2 with approximately ?=9.25 and ?=0.3?, represented by point 430 in FIG. 6. For constant thrust c.sub.t=0.86 the power coefficient is at the maximum here but lower than the optimum for this turbulence intensity and furthermore higher than at the operating point of installation type 2 for turbulence-free inflow Ti=0%, that is to say at point 410.

(40) Thus, it turns out that, depending on location loads and installation type, the operational management of the installation when subjected to inflow conditions with increased turbulence intensity, for example on a wind farm when an installation is operated in the wake of another installation, has to be adjusted in terms of the tip-speed ratio and the pitch angle in the part-load range in such a way that an increase in the tip-speed ratio or a combined increase in tip-speed ratio and pitch angle is implemented. Particularly preferably, the combined increase takes place as a function of the turbulence intensity as the measure of turbulence.

(41) The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.