METHOD FOR OPERATING A WIND FARM AND WIND FARM

Abstract

A method for operating a wind farm having a plurality of wind power installations is provided. The installations each comprise an aerodynamic rotor, and the rotors each have an aerodynamic characteristic value. The method includes: obtaining a setpoint power value of the wind farm, in particular a setpoint value of the electrical power of the wind farm to be fed in, ascertaining an actual power value of the wind farm as the sum of actual electrical powers of the operated wind power installations, determining a permissibility of a power-reduced operating mode of each of the wind power installations of the wind farm on the basis of the associated aerodynamic characteristic value, and operating the wind power installations of the wind farm such that each operated wind power installation is operated in a permissible operating mode and the ascertained actual power value does not exceed the obtained setpoint power value.

Claims

1. A method for operating a wind farm having a plurality of wind power installations, wherein each wind power installation of the plurality of wind power installations includes an aerodynamic rotor having a respective aerodynamic characteristic value, and wherein the method comprises: obtaining a setpoint power value of the wind farm, the setpoint power value being a setpoint value of electrical power of the wind farm that is to be fed in; determining an actual power value of the wind farm as a sum of actual electrical powers of a plurality of operated wind power installations; determining a permissibility of a power-reduced operating mode of each wind power installation of the plurality of wind power installations of the wind farm based on the respective aerodynamic characteristic value; and operating the plurality of wind power installations of the wind farm such that each operated wind power installation is operated in a permissible operating mode and the actual power value does not exceed the setpoint power value.

2. The method according to claim 1, comprising: determining, based on the setpoint power value, whether to operate at least one of the plurality of wind power installations in power-reduced operation.

3. The method according to claim 1, wherein at least one of the plurality of wind power installations of the wind farm is not operated such that at least one of remaining wind power installation of the plurality of wind power installations is operated in the permissible operating mode.

4. The method according to claim 1, wherein the aerodynamic characteristic value indicates a flow separation.

5. The method according to claim 4, wherein the aerodynamic characteristic value indicates the flow separation on a pressure side of a rotor blade of the rotor.

6. The method according to claim 4, wherein the aerodynamic characteristic value includes a critical pitch angle, wherein the flow separation takes occurs when the critical pitch angle is exceeded.

7. The method according to claim 1, wherein the aerodynamic characteristic value is determined based on a characteristic map, wherein the characteristic map indicates the aerodynamic characteristic value as a function of a rotational speed of the wind power installation and a power stage.

8. The method according to claim 7, wherein the characteristic map indicates the aerodynamic characteristic value as a function of the rotational speed of the wind power installation and the power stage and a degree of soiling of the rotor.

9. The method according to claim 7, wherein each of the plurality of wind power installations is operated within a permissible area of the characteristic map.

10. The method according to claim 1, wherein an operating mode is selected from permissible operating modes of individual installations based on the basis of at least one of: tariff, load, or sound.

11. The method according to claim 1, wherein the aerodynamic characteristic value is determined individually for each of the plurality wind power installations.

12. The method according to claim 1, wherein determining the permissibility of the power-reduced operating mode of each of the plurality of wind power installations includes: determining a setpoint rotational speed of the aerodynamic rotor based on the aerodynamic characteristic value.

13. The method according to claim 12, wherein operating the wind power installation in the power-reduced operating mode includes reducing the setpoint rotational speed in a first operating range and increasing the setpoint rotational speed in a second operating range.

14. The method according to claim 1, wherein operating the wind power installation in the power-reduced operating mode includes changing a pitch angle of the rotor.

15. The method according to claim 1, wherein operating the wind power installation in the power-reduced operating mode includes reducing a pitch angle of the rotor.

16. The method according to claim 1, wherein the aerodynamic rotor is coupled to an electrical generator and operating the wind power installation in the power-reduced operating mode includes changing a generator torque of the electrical generator.

17. The method according to claim 16, wherein active electrical power at an output of the electrical generator in the power-reduced operating mode is reduced to a predetermined power value and/or by a predetermined absolute power value.

18. The method according to claim 17, wherein at least one of aerodynamic characteristic values is used in determining at least one setpoint rotational speed of one of aerodynamic rotors of the plurality of wind power installations.

19. A wind farm, comprising: a plurality of wind power installations; and a wind farm controller configured to: obtain a setpoint power value of the wind farm, the setpoint power value being a setpoint value of electrical power of the wind farm that is to be fed in; determine an actual power value of the wind farm as a sum of actual electrical powers of a plurality of operated wind power installations; determine a permissibility of a power-reduced operating mode of each wind power installation of the plurality of wind power installations based on a respective aerodynamic characteristic value of an aerodynamic rotor of the wind power installation; and operate the plurality of wind power installations of the wind farm such that each operated wind power installation is operated in a permissible operating mode and the actual power value does not exceed the setpoint power value.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0057] Further advantages and particular configurations are described below with reference to the appended figures. In the figures:

[0058] FIG. 1 schematically shows a wind power installation by way of example;

[0059] FIG. 2 schematically shows a wind farm by way of example, and

[0060] FIG. 3 schematically shows a flowchart of a method by way of example.

DETAILED DESCRIPTION

[0061] FIG. 1 shows a schematic illustration of a wind power installation. 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 having 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 of a generator 101, 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.

[0062] 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 in 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.

[0063] 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 network 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 in the farm, is usually provided in order to then feed into the supply network 120 at the infeed point 118, which is also generally referred to as a point of common coupling (PCC). FIG. 2 is only a simplified illustration of a wind farm 112. By way of example, the farm network 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.

[0064] The wind farm 112 additionally has a central farm computer 122, which can also be referred to synonymously as central farm control system. This may be connected, via data lines 124 or wirelessly, to the wind power installations 100 in order to exchange data with the wind power installations via this connection and, in particular, to receive measured values from the wind power installations 100 and transmit control values to the wind power installations 100.

[0065] In this case, the central farm controller 122 is to be understood functionally as the component that is designed to execute the central farm control. The central farm controller 122 and/or individual components thereof can also be provided in a physically remote manner, for example in a server or in a cloud.

[0066] FIG. 3 schematically shows by way of example a flowchart of a method 300 for operating a wind farm 112, as is executed, for example, fully or partly on the central farm controller 122 and/or the individual wind power installations 100 of the wind farm 112. The dividing of the execution of the method steps between the central farm controller 122 and the individual wind power installations 100 may be different depending on the implementation.

[0067] An operator of a wind farm 112 guarantees a preferably smooth power limitation between 0-100% at the infeed point 118 or network connection point PCC. In this case, it is known to transmit the same active power control value from the farm controller 122 to all of the wind power installations 100 of the wind farm 112. The method 300 enables individual installation control by way of an operation of the individual wind power installations 100 with individual active power control values, wherein each wind power installation 100 can be supplied with different power limitations. In this case, the central farm controller 122 can either provide an active power control value to the wind power installations 100 directly or can provide or communicate an operating mode to be adjusted by the wind power installations 100 in another manner.

[0068] The power limitation can be carried out conventionally with a reduced rotational speed on the power-optimum operating characteristic curve, wherein other types of power limitation are also known.

[0069] The method 300 now makes it possible for the effects of the power limitation on the rotor blade aerodynamics to be taken into account and thus at high wind speeds in particular the risk of flow separation on the pressure side of the profiles of the rotor blades 108 in the outer region of the rotor blade 108. Such flow separations result amongst other things in severe wind noises and in aeroelastic instabilities and high loads. The sensitivity for this problem, which is dependent in particular on wind speed, varies across various types of wind power installations 100 and rotor blades 108.

[0070] The method 300 now enables individual installation control at different power levels while observing the boundary condition of separation-free profile flow around the rotor blade. In addition, while observing this boundary condition, a tariff-optimized operation can be carried out, for example when different wind power installations 100 obtain different infeed tariffs.

[0071] For this purpose, the method 300 initially comprises a step 310 of obtaining a setpoint power value of the wind farm 112, in particular a setpoint value of the electrical power of the wind farm 112 that is to be fed in. The setpoint power value is provided, for example, by the network operator of the electrical supply network and may require a power limitation of the wind farm or at least some of the wind power installations 100 given sufficient available wind power.

[0072] In a step 320, for this purpose an actual power value of the wind farm 112 is ascertained as the sum of actual electrical powers of the operated wind power installations 100. If the actual power value exceeds the setpoint power value, the farm controller 122 has to intervene and bring about a power limitation in order that the setpoint power value is observed as maximum value. If the actual power value is below the setpoint power value, the farm controller 122 can preferably ensure that each of the wind power installations 100 is operated in a power-optimized operating mode, provided this is not excluded by other additional conditions such as sound generation. The farm controller 122 thus attempts to generate as much active electrical power as possible in order to reach the setpoint power value, wherein this reaching of the setpoint power value is dependent on the wind speed.

[0073] The method now relates in a step 330 to checking whether a power-reduced operation of one of the wind power installations is fundamentally necessary. If not, no limitation of a wind power installation 100 is necessary and each of the wind power installations 100 can be operated in the power-optimized operating mode in a step 335.

[0074] If a limitation, that is to say a power-reduced operation, of at least one of the wind power installations 100 is necessary, in a further step 340 a permissibility of a power-reduced operating mode of each of the wind power installations 100 of the wind farm is determined on the basis of an associated aerodynamic characteristic value. The aerodynamic characteristic value is preferably formed as a characteristic map and a function of a plurality of input variables, for example a rotational speed of the wind power insulation 100, a power stage and/or a degree of soiling of the rotor. An aerodynamic characteristic value that indicates whether or not flow separation on the pressure side occurs during operation in the operating mode to be checked under the current wind conditions can then be obtained on the basis of the prevailing wind speed.

[0075] An operating mode is fundamentally permissible when the aerodynamic characteristic value for the current wind conditions indicates that no flow separation occurs.

[0076] The aerodynamic characteristic value can be tabulated or available in the central farm controller 122 or it can be available on the individual wind power installations 100 that then independently determine the permissibility of an operating mode.

[0077] In this step 340, the permissibility of only one determined, desired operating mode can be determined. For example, the central farm controller 122 can determine a permissibility of an operating mode with a determined power limitation. As an alternative, a plurality of different permissibilities of operating modes can also be determined in step 340. For example, the permissibility can be determined using the aerodynamic characteristic value for various stages of the power limitation.

[0078] The permissibility of all of the operating modes particularly advantageously does not have to be checked at all times but the check is limited to operating modes that may potentially arise. As a result, the demand for computation power, for example by the central farm controller 122, can be kept low and the processing time until the result of step 340 is available can be reduced.

[0079] In a particularly preferred example, the aerodynamic characteristic value is a critical pitch angle that may not be exceeded under the given conditions for a determined operating mode in order that said operating mode is determined as permissible.

[0080] Finally, using the permissibilities determined in step 340, the wind power installations 100 are operated, that is to say the operating modes of the wind power installations 100 are set, in a step 350 in such a way that each of the operated wind power installations 100 is operated in a permissible operating mode and the ascertained actual power value does not exceed the obtained setpoint power value.

[0081] Here, depending on the case, at least one of the wind power installations 100 of the wind farm is not operated in order that at least one of the remaining wind power installations 100 is able to be operated in a permissible operating mode. This is relevant in particular for severely limited scenarios and/or high wind speeds.

[0082] The selection of the respective operating mode from a plurality of permissible operating modes can be made in particular according to a) tariff, b) load and/or c) sound.

[0083] Several operating scenarios are thus advantageously able to be achieved.

[0084] At low wind speeds, wind power installations 100 in the wind farm run in power-reduced operation, for example with a reduced rotational speed. If the wind speed increases, successive wind power installations 100, depending on installation type, run in a critical operating state. In this scenario, the critical operation can be shifted to higher wind speeds by increasing the rotational speed from a critical wind speed. This is achieved by determining the permissible operating modes.

[0085] At high wind speeds, the wind power installations 100 run, for example, in a power-optimized operation at full load. If a power limitation is now required, wind power installations 100, depending on installation type and demanded power level, can run in a critical operating state. In this scenario, the nominal rotational speed is preferably retained in the case of power reduction. A critical operation is accordingly shifted to smaller power stages and/or higher wind speeds.

[0086] The determination of the permissible operating modes can thus permit an operation at reduced rotational speed up to storm control mode that is applied at a wind speed that exceeds a threshold value since no negative stall occurs during operation. In comparison with previously known control modes, the rotational speed is preferably increased from a predetermined wind speed up to the storm control mode. As an alternative, the rotational speed is initially increased, which is then followed by a decrease in the rotational speed to a non-critical value for the occurrence of negative stall in the case of further increasing wind speed.

[0087] In summary, the power reduction at high wind speeds in wind farms 112 must thus take into account aerodynamic boundary conditions. For this purpose, the solution proposed is, for example, an increase to or a retaining of the nominal rotational speed for shifting critical operating points to higher wind speeds or smaller power stages.

[0088] As an alternative, the combination of the described method with a controllable aerodynamic brake in the inner rotor region and/or with energy storage solutions is conceivable. The controllable aerodynamic brake may comprise, for example, flaps or similar movable add-on parts. Both additional concepts expand the field of use of the wind farm 112 or the range of permissible operating modes of the individual wind power installations 100.

[0089] 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.