METHOD OF OPERATING A WIND TURBINE, CORRESPONDING WIND TURBINE AND WIND FARM

Abstract

The present disclosure relates to a method of operating a wind turbine, a corresponding wind turbine, a method of controlling a wind farm and a corresponding wind farm. The method comprises the steps of: determining a target maximum active power to be fed by the wind turbine into a power grid, in particular into an electricity power grid; monitoring a current active power fed from the wind turbine into the power grid; determining a reference time period corresponding to the determined target maximum active power; deriving an average of the active power fed from the wind turbine into the power grid during the reference time period; comparing the average of the active power with the target maximum active power; and operating the wind turbine at a set operating point permitting active power above the target maximum active power in case the average of the active power is below the target maximum active power.

Claims

1. A method of operating a wind turbine, the method comprising: determining a target maximum active power to be fed by the wind turbine into an electric power grid, monitoring a current active power fed from the wind turbine into the electric power grid, determining a reference time period corresponding to the target maximum active power, deriving an average of the active power fed from the wind turbine into the electric power grid during the reference time period, comparing the average of the active power with the target maximum active power, and operating the wind turbine at a set operating point permitting active power above the target maximum active power while the average of the active power is below the target maximum active power.

2. The method according to claim 1, wherein the target maximum active power is determined under consideration of at least one of: a limitation specification from a grid operator or an energy marketer, a curtailment specification from operational control, a temperature management of thermally inert generator components, an official requirement, a nominal output of the wind turbine, and a maximum active power of the wind turbine in a specific operating mode.

3. The method according to claim 1, wherein the reference time period is determined as a time period during which an average of the active power does not exceed the target maximum active power.

4. The method according to claim 1, wherein the reference time period is a period of predetermined length up to the current time, wherein the predetermined length is between 1 second and 20 minutes or exactly 10 minutes.

5. The method according to claim 1, wherein the average of the active power is a moving average of the current active power that is monitored.

6. The method according to claim 1, wherein a deviation of the average of the active power from the target maximum active power is referred to as an average power deviation, and a deviation of the active power according to the operated operating point from the target maximum active power is referred to a target active power deviation, the method further comprising: setting the target active power deviation as a function of the average power deviation.

7. The method according to claim 6, wherein the setting the target active power deviation as a function of the average power deviation comprises setting the target active power deviation linearly proportional to the average power deviation.

8. The method according to claim 6, further comprising determining a proportionality factor between the active power deviation and the average power deviation under consideration of at least one environmental factor of a construction site of the wind turbine.

9. The method according to claim 6, wherein a predefined maximum target active power deviation limits an amount of the positive active power deviation.

10. The method according to claim 6, wherein a predefined proportionality factor for negative average power deviation is larger than a predefined proportionality factor for positive average power deviation.

11. The method according to claim 1, further comprising operating the wind turbine at an operating point ensuring active power below the target maximum active power while the average of the active power is above the target maximum active power.

12. The method according to claim 1, wherein a set active power of the set operating point is determined according to a power boost factor, the set active power being determined as a product of the target maximum active power and the power boost factor, wherein the power boost factor is at least one of: a) increased in response to the average of the active power being above the target maximum active power, and b) decreased in response to the average of the active power being below the target maximum active power.

13. The method according to claim 12, further comprising at least one of: determining a maximum of the power boost factor proportionally to a deviation of the average of the active power from the target maximum active power, and limiting a change rate of the power boost factor such that oscillations in wind turbine control are avoided.

14. The method according to claim 12, the wind turbine including a rotor comprising at least one rotor blade with an adjustable blade angle, the method further comprising: estimating whether the set operating point will result in a decrease of generated active power by anticipating future power drops, and reducing the power boost factor in response to the result of the estimating being positive, wherein the anticipating of future power drops includes that increased power generation will reduce a rotor speed of the rotor when the adjustable blade angle of the at least one rotor blade approaches a set minimum pitch angle.

15. The method according to claim 1, wherein the wind turbine includes a rotor comprising at least one rotor blade with an adjustable blade angle, wherein the operating the wind turbine at the set operating point permitting active power above the target maximum active power comprises: determining a current blade angle of the at least one rotor blade, determining a minimum blade angle as a minimum value of an operable blade angle range, and operating the wind turbine at the set operating point only if the current blade angle exceeds the minimum angle plus a predefined difference limit angle.

16. The method according to claim 15, wherein an increase in power above the target maximum active power is limited as a function of a difference between the current blade angle and a sum of the limit angle, and the predefined difference angle is limited proportionally to a difference or as a function of a predetermined characteristic curve.

17. The method according to claim 1, comprising stopping the operation of the wind turbine at the set point in response to at least one of: an average power being below a target maximum average is due to an intervention of a blade load limiter, an intervention by a storm control operation, and a noise optimization operation.

18. A wind turbine comprising a controller configured to: determine a target maximum active power to be fed by the wind turbine into an electric power grid, monitor a current active power fed from the wind turbine into the electric power grid, determine a reference time period corresponding to the target maximum active power, derive an average of the active power fed from the wind turbine into the electric power grid during the reference time period, compare the average of the active power with the target maximum active power, and operate the wind turbine at a set operating point permitting active power above the target maximum active power while the average of the active power is below the target maximum active power.

19. A method for controlling a wind farm, the wind farm comprising a plurality of wind turbines, the method comprising: determining a combined target maximum active power to be fed by the plurality of wind turbines into a power grid, monitoring a combined current active power fed from the plurality of wind turbines into the power grid, determining a reference time period corresponding to the combined target maximum active power, deriving an average of the combined active power fed from the plurality of wind turbines into the power grid during the reference time period, comparing the average of the combined active power with the combined target maximum active power, and operating at least one of the wind turbines at a set operating point permitting an active power such that the combined active power is above the combined target maximum active power of the plurality of wind turbines when the average of the combined active power is below the combined target maximum active power.

20. A wind farm controller adapted to control the wind farm according to a method as defined in claim 19.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0125] Below the invention is explained by a way of examples using embodiments based on the attached figures.

[0126] FIG. 1 shows a wind turbine in a perspective view.

[0127] FIG. 2 shows a wind farm in a schematically view.

[0128] FIG. 3 shows a diagram illustrating power over time.

[0129] FIG. 4 shows a diagram illustrating modified power over time.

[0130] FIG. 5 illustrates a power increase factor for the time period of FIG. 4.

[0131] FIG. 6 shows two diagrams explaining the operation of a maximum power control.

[0132] FIG. 7 schematically and exemplarily illustrates a flowchart of a method.

[0133] FIG. 8 schematically and exemplarily illustrates a flowchart of a method.

DETAILED DESCRIPTION

[0134] FIG. 1 shows a schematic illustration of a wind power installation according to the invention.

[0135] The wind power installation 100 comprises a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 comprising three rotor blades 108 and a spinner 110 is provided on the nacelle 104. The aerodynamic rotor 106 is caused to effect a rotational movement by the wind during operation of the wind power installation and thereby also rotates an electrodynamic rotor of a generator, which is coupled to the aerodynamic rotor 106 directly or indirectly. The electrical generator is arranged in the nacelle 104 and generates electrical energy. The pitch angles of the rotor blades 108 can be varied by pitch motors on the rotor blade roots 109 of the respective rotor blades 108.

[0136] The wind power installation 100 comprises an electrical generator 101, indicated in the nacelle 104. Electrical power can be generated by means of the generator 101. An infeed unit 105, which can be configured as an inverter, in particular, is provided for feeding in electrical power. It is thus possible to generate a three-phase infeed current and/or a three-phase infeed voltage according to amplitude, frequency and phase, for infeed at a network connection point PCC. That can be effected directly or else jointly with further wind power installations in a wind farm. An installation controller 103 is provided for controlling the wind power installation 100 and also the infeed unit 105. The installation controller 103 can also acquire predefined values from an external source, in particular from a central farm computer.

[0137] FIG. 2 shows a wind farm 112 comprising for example three wind power installations 100, which can be identical or different. The three wind power installations 100 are thus representative of basically an arbitrary number of wind power installations of a wind farm 112. The wind power installations 100 provide their power, namely 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 and a transformer 116 is usually provided, which steps up the voltage in the farm in order then to feed it into the supply network 120 at the infeed point 118, which is also generally referred to as PCC. FIG. 2 is merely a simplified illustration of a wind farm 112. Moreover, by way of example, the farm network 114 can be configured differently, with for example a transformer also being present at the output of each wind power installation 100, to mention just one different exemplary embodiment.

[0138] The wind farm 112 additionally comprises a central farm computer 122. The latter can be connected to the wind power installations 100 via data lines 124, or in a wireless manner, in order thereby to exchange data with the wind power installations and in particular to acquire measured values from the wind power installations 100 and to transmit control values to the wind power installations 100.

[0139] In one example, the method according to the present disclosure can be expressed to comprising the following steps: [0140] (1) Determination of a target power (active power) to be aimed at. Possible sources for this are, for example: control specifications from the grid operator or energy marketer, control specifications from operational management (e.g., generator temperature management of thermally inert components), official requirements, design parameters (nominal power of a plant, maximum power of an operating mode). [0141] (2) Determination of an averaging period to which the target power from step (1) refers. A typical specification are 10 min averages, while also other periods are contemplated. [0142] (3) Measurement, in particular continuous measurement of the injected active power, and storage of the resulting time history. [0143] (4) Calculation of a moving average based on the stored time history on (3) over the selected period from (2). [0144] (5) Calculation of a power increase factor (boost factor), which indicates the measure of temporary power increase to be aimed at. For this purpose, the mean actual power known from step (4) is preferentially compared with the target power known from step (1). If the mean actual power is below the target power, a power increase factor, which is also referred to as power boost factor, is raised. If the actual power is above the target power, the power increase factor is lowered (this case occurs especially when the target power is changed).

[0145] How far the power increase factor can be raised (or lowered) preferentially depends on how much the average power falls below (or exceeds) the target power.

[0146] A proportional coupling is particularly suitable here (e.g., the power increase factor is increased up to 102% if the target power was undercut by 1%, and increased to 104% if the target power was undercut by 2%, etc.).

[0147] The rate of change of the power increase factor is preferentially chosen sufficiently low to avoid oscillations in the resulting control loop (e.g., 10 kW/s).

[0148] The power increase factor is preferentially limited to an adjustable range (e.g., to compensate for previous underpower situations, subsequently feed in a maximum of 110% of the target power).

[0149] The power increase factor is preferentially reduced when an operating state is reached in which increased power consumption resulted in a subsequent power drop. This happens in particular when it becomes apparent that the wind speed drops to such an extent that the target rotor speed could no longer be maintained with an increased power input (i.e., coming out of speed control operation with high wind speeds, the blade angles advance to a minimum blade angle). [0150] (6) The maximum power that would otherwise be set and the associated power setpoint are adjusted (typically increased by a few percent) via the power increase factor. The increased power is fed in.

[0151] In particular, the upper limit for the power increase factor (e.g., maximum 110%) and the proportional coupling factor between target power undershoot power increase factor limit are useful parameters for site-specific parameterization.

[0152] The method according to the present disclosure is beneficial in the dynamic determination of the maximum power of a wind turbine. An application on wind farm level is also conceivable in some embodiments.

[0153] This will be illustrated by the example of a 10 min time series with a wind turbine, which can generate technically 5500 kW power. In the time series, the technically generated power fluctuates between 1900 kW (during a negative gust) and 5500 kW (technical limitation of the WEA).

[0154] An exemplary target power of 4000 kW (e.g., network operator specification) leads according to the classic procedure to a limitation of the power setpoint to 4000 kW. This results (due to gusts/turbulence) in that the average power within exemplary 10 min time interval results below the aimed power set point.

[0155] FIG. 3 illustrates a situation 300 before introducing the “Temporary Power Boost” according to the present invention, wherein every maximum power was understood as an immediate and short-term limit. On a vertical axis, generated power is drawn. The unit is arbitrary and may, for instance, be in kW. On a horizontal axis, a time is drawn. The unit is also arbitrary and may, for instance, be in seconds (s).

[0156] A first dashed line 310 illustrates the technically available power, which fluctuates between approx. 1900 kW and 5500 kW. Using a limitation of the power setpoint to 4000 kW results in a line 320 indicating the generated power. In this example, an average value 330 of the generated power reaches only 3604 kW, i.e., well below the target power of 4000 kW, for instance.

[0157] FIG. 4 illustrates a situation 400 after introducing the “Temporary Power Boost” in a drawing similar to FIG. 3. Again, a first dashed line 410 illustrates the technically available power and a solid line 420 indicates the generated power. The target average value is indicated with a second dashed line 430 and the average value 440 of the generated power can be seen to be closed to the target power than in the example of FIG. 3.

[0158] In a first time period 402, the generated power corresponds to the target power set point, for instance, of 4000 kW. After a short reduction of power production, for instance due to a negative gust, the generated power is increased during a second time period 404 to compensate for the prior drop in power production. The generated power during this period is below the technically available power so that the target average power but not more than the target average power is generated.

[0159] After a longer period 406 of low generated power, for instance of low wind speed, during a period 408 the generated power lies well above the target average power.

[0160] In a period 409, a limit for the increased generated power above the target power can be seen as the generated power 430 proceeds horizontally. The upper limit for the power boost, i.e., the increase of the generated power above the target power, may be for instance 130% of the target power.

[0161] FIG. 5 schematically and exemplarily illustrates the corresponding power increment factor, referred to as power boost factor, in a diagram 500 for the same time period as illustrated in FIG. 4. In this example, the power boost factor can be between 100% and 130% of the target active power.

[0162] FIG. 6 schematically and exemplarily illustrates a further example graph 610 of generated power over time and a graph 620 of a corresponding pitch angle of the rotor blades of the wind turbine for the same time period.

[0163] A lack of generated power during period 612 is indicated with the surface area below target power under the curve A1. The surface area corresponds to a surface area A2 during a period 614, in which more than target power is generated. This period 614 can be referred to as a power boost period.

[0164] An average generated power 630 corresponds to the generated power without power boost and a generated power 640 includes the power boost. It can be seen that the generated power 640 approximates the target power, while the generated power 630 remains at approximately 95% due to the lack of generated power during the period 612.

[0165] After compensating the lack of generated power, i.e., P.sub.avg equals the desired target power, potential excess power would be available during a period 616. In this period 616, the generated power 618 may be reduced so that an average generated power, for instance a moving average over the preceding 10 minutes, does not exceed the target power.

[0166] The set value of the blade pitch angle is indicated in graph 620. During periods of negative gusts or low wind, a minimum blade angle 622 is set. This angle is also referred to as α.sub.min. More available wind will result in an increased pitch angle to limit the generated power to the desired power value. At point in time 624, the wind dropped to nominal wind, for instance, such that the 25 pitch angle is reduced. At point in time 626, the blade angle might be increased in order, for instance, to limit oscillations or load on the wind turbine.

[0167] FIG. 7 schematically and exemplarily illustrates a flowchart of a method 700 of operating a wind turbine 100. The method 700 comprises the steps 710 to 760 and optionally at least one of the optional steps 762 to 770 described in the following.

[0168] A step 710 of determining a target maximum active power to be fed by the wind turbine 100 into a supply network 120 such as a power grid, in particular into an electricity power grid. The target maximum active power is in particular determined under consideration of at least one of, preferentially more than one of and in particular all of: a limitation specification from a grid operator or an energy marketer, a curtailment specification from operational control such as a temperature management of thermally inert generator components, an official requirement, a nominal output of the wind turbine, and a maximum active power of the wind turbine 100 in a specific operating mode.

[0169] A step 720 of monitoring a current active power fed from the wind turbine 100 into the power grid 120, for instance at an input of a transformer of the wind turbine 100.

[0170] A step 730 of determining a reference time period corresponding to the determined target maximum active power. The reference time period is in particular determined as the time period during which an average of the active power shall should not exceed the target maximum active power. The reference time period is in particular a period of predetermined length up to the current time, wherein the predetermined length is in particular between 1 second and 20 minutes and preferably about or exactly 10 minutes.

[0171] A step 740 of deriving an average of the active power fed from the wind turbine into the power grid 120 during the reference time period. The average of the active power may be determined as a moving average of the monitored current active power of the wind turbine.

[0172] A step 750 of comparing the average of the active power with the target maximum active power.

[0173] A step 760 of operating the wind turbine at a set operating point permitting active power above the target maximum active power in case the average of the active power is below the target maximum active power.

[0174] A deviation of the average of the active power from the target maximum active power may be referred to as an average power deviation and a deviation of the active power according to the operated operating point from the target maximum active power is referred to a target active power deviation. The step 760 of operating may optionally include a step 762 of setting the target active power deviation as a function of, in particular linearly proportional to, the average power deviation.

[0175] Further, the step 760 may include an optional step 764 of determining a proportionality factor between the active power deviation and the average power deviation under consideration of at least one environmental factor of a construction site of the wind turbine 100.

[0176] If the wind turbine 100 includes a rotor 106 comprising at least one rotor blade 108 which is adjustable in its blade angle, the step 760 may further comprise:

[0177] A step 766 of determining the current blade angle of at least one of the rotor blades.

[0178] A step 768 of determining a minimum blade angle as a minimum value of the operable blade angle range, and

[0179] A step 770 of operating the wind turbine at the set operating point only if the current blade angle exceeds the minimum angle plus a predefined difference limit angle.

[0180] FIG. 8 schematically and exemplarily illustrates a flowchart of a method 800 for controlling a wind farm 112, for instance using a central farm computer 122. The wind farm 112 comprises a plurality of wind turbines 100, and the method 800 comprises steps 810 to 860 described in the following.

[0181] A step of determining 810 a combined target maximum active power to be fed by the plurality of wind turbines 100 into a power grid 120, in particular into an electricity power grid.

[0182] A step of monitoring 820 a combined current active power fed from the plurality of wind turbines 100 into the power grid 120,

[0183] A step of determining 830 a reference time period corresponding to the determined combined target maximum active power,

[0184] A step of deriving 840 an average of the combined active power fed from the plurality of wind turbines 100 into the power grid 120 during the reference time period,

[0185] A step of comparing 850 the average of the combined active power with the combined target maximum active power, and

[0186] A step of operating 860 at least one of the wind turbines 100 at a set operating point permitting an active power such that the combined active power is above the combined target maximum active power of the plurality of wind turbines 100 in case the average of the combined active power is below the combined target maximum active power.

[0187] 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.