OPTIMAL WIND FARM OPERATION

Abstract

The present invention relates to a method of operating a wind farm comprising an upstream and a downstream turbine, wherein the upstream turbine is operated with current operation parameters under current wind conditions, wherein the method comprises the steps of: receiving future wind conditions for a time period for the wind farm, and evaluating required operation parameters for minimising wake effect of the downstream turbine under the future wind conditions, and determining a cost coefficient for changing the operation parameters to required operation parameters under consideration of fatigue effect of the wind turbine, calculating power productions P.sub.o and P.sub.c, in the predetermined time period, by the wind farm if operated with the current operation parameters under the current wind conditions and if operated with the required operation parameters under the future wind conditions, respectively, and operating the upstream turbine with the required operation parameters if the cost coefficient is lower than a cost that would be obtained by a power production increment P.sub.c-P.sub.o.

Claims

1-6. (canceled)

7. A method of operating a wind farm with an upstream turbine and a downstream turbine, wherein the upstream turbine is operated with a current upstream operation parameter value under current wind conditions, the method comprising the steps of: obtaining, for each time interval of a sequence of time intervals of a forecast time period, forecast wind conditions at the upstream wind turbine and at the downstream wind turbine, determining a candidate upstream operation parameter sequence minimizing a wake effect at the downstream turbine under the forecast wind conditions, estimating a parameter change expense indicative of a change from the current upstream operation parameter value to a first upstream operation parameter value of the candidate upstream operation parameter sequence, estimating wind farm productivity P.sub.0, P.sub.c during the forecast time period if the upstream turbine is operated under the forecast wind conditions with the current upstream operation parameter value or according to the candidate upstream operation parameter sequence, respectively, calculating a wind farm productivity gain as a difference (P.sub.c-P.sub.0) between the wind farm productivity according to the candidate upstream operation parameter sequence and the wind farm productivity with the current upstream operation parameter value, and operating the upstream turbine with the current upstream operation parameter value if the parameter change expense exceeds the productivity gain.

8. The method of claim 7, wherein wake effect, parameter change expense, productivity gain, and/or a fatigue effect are evaluated over the forecast time period.

9. The method of claim 7, wherein the wake effect, the parameter change expense, the productivity gain, and/or the fatigue are integrated or averaged over the forecast time period, preferably with a time interval or step size depending on the coarseness of the forecast wind conditions.

10. The method of claim 7, comprising: estimating a parameter change expense including an energy consumed by a driving motor for moving turbine parts of the upstream turbine when operating the driving motor according to a change in the upstream operation parameter from the current upstream operation parameter value to a first upstream operation parameter value of the candidate upstream operation parameter sequence.

11. The method of claim 7, comprising: estimating a parameter change expense including a component wear suffered by the driving motor or by the moving turbine parts, when operating the driving motor according to a change in the upstream operation parameter from the current upstream operation parameter value to a first upstream operation parameter value of the candidate upstream operation parameter sequence.

12. The method of claim 7, comprising: estimating a fatigue effect of the upstream wind turbine if operated according to the candidate upstream operation parameter sequence rather than with the current upstream operation parameter value under the forecast wind conditions during the forecast time period, and operating the upstream turbine based on a forecast balance including the parameter change expense, the productivity gain, and the fatigue effect.

13. The method of claim 7, wherein a length of the forecast time period is between one minute and three hours.

14. The method of claim 7, wherein the operation parameter comprises one of a yaw angle indicative of an alignment between a wind direction at the upstream turbine and a rotor axis of the upstream turbine, a pitch angle indicative of an alignment between the wind direction and a rotor blade orientation, a generator torque or a rotor speed.

15. A controller for operating a wind farm comprising an upstream turbine and a downstream turbine, wherein the upstream turbine is operated with a yaw angle y.sub.o under current wind conditions, wherein the controller is configured to: receive future wind conditions for a predetermined time period based on a wind forecast for the wind farm, calculate a yaw angle Y.sub.c for minimising wake effect at the downstream turbine under the future wind conditions, determine a cost for changing the yaw angle from Y.sub.0 to Y.sub.c, calculate power productions P.sub.0 and P.sub.c of the wind farm under the future wind conditions in the predetermined time period, assuming the upstream turbine being operated with the yaw angle Y.sub.0 and Y.sub.c respectively, set the yaw angle to Y.sub.c if the cost is lower than a profit of a power production increment a P.sub.c-P.sub.0.

16. The controller of claim 15, wherein said controller is further configured to determine a cost for changing the yaw angle from Y.sub.0 to Y.sub.c under consideration of driving motor involvement.

17. The controller of claim 15, wherein said controller is further configured to determine a cost for wear and fatigue effects at the upstream turbine.

18. The controller of claim 15, wherein said controller is further configured to evaluate wake effect, parameter change expense, productivity gain, and/or a fatigue effect over the forecast time period.

19. The controller of claim 18, wherein said controller is further configured to integrate or average wake effect, parameter change expense, productivity gain, and/or a fatigue effect over the forecast time period, preferably with a time interval or step size depending on the coarseness of the forecast wind conditions.

20. The method of claim 9, comprising: estimating a parameter change expense including an energy consumed by a driving motor for moving turbine parts of the upstream turbine when operating the driving motor according to a change in the upstream operation parameter from the current upstream operation parameter value to a first upstream operation parameter value of the candidate upstream operation parameter sequence.

21. The method of claim 20, comprising: estimating a parameter change expense including a component wear suffered by the driving motor or by the moving turbine parts, when operating the driving motor according to a change in the upstream operation parameter from the current upstream operation parameter value to a first upstream operation parameter value of the candidate upstream operation parameter sequence.

22. The method of claim 21, comprising: estimating a fatigue effect of the upstream wind turbine if operated according to the candidate upstream operation parameter sequence rather than with the current upstream operation parameter value under the forecast wind conditions during the forecast time period, and operating the upstream turbine based on a forecast balance including the parameter change expense, the productivity gain, and the fatigue effect.

23. The method of claim 22, wherein a length of the forecast time period is between one minute and three hours.

24. The method of claim 23, wherein the operation parameter comprises one of a yaw angle indicative of an alignment between a wind direction at the upstream turbine and a rotor axis of the upstream turbine, a pitch angle indicative of an alignment between the wind direction and a rotor blade orientation, a generator torque or a rotor speed.

25. The method of claim 13, wherein a length of the forecast time period is between three and five minutes.

26. The method of claim 25, wherein the operation parameter comprises one of a yaw angle indicative of an alignment between a wind direction at the upstream turbine and a rotor axis of the upstream turbine, a pitch angle indicative of an alignment between the wind direction and a rotor blade orientation, a generator torque or a rotor speed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The subject matter of the invention will be explained in more detail in the following text with reference to preferred exemplary embodiments that are illustrated in the attached drawings, in which:

[0029] FIG. 1 schematically shows top view of the wind farm wake configuration, where (a) is before yawing and (b) after yawing, wherein the turbine 1 and 2 are yawed in (b) leading to a decrease in produced energy by turbines I and 2, but an increase in produced energy by turbines 3-6;

[0030] FIG. 2 illustrates the power productions of turbines before and after yawing for the farm configuration shown in FIG. 1, where yawing turbine 1 and 2 reduces their energy capture, however, it can also result in downwind turbines gaining energy due to reduced ‘shadowing’ as depicted in FIG. 1b;

[0031] FIG. 3 schematically shows the trends of the total farm power, upwind and downwind turbines power as a function of the changing yaw angles of upwind turbines 1 and 2;

[0032] FIG. 4 shows turbine 3 and 4 being shut off and hence do not produce any wakes that will affect turbines 5 and 6, thus, turbines 5 and 6 are affected only by wakes produced by upwind turbines 1 and 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0033] According to an exemplary embodiment, the present invention analyses the wind changes and the forecast predicts in a stable and long-term change. If the wind forecast predicts stable wind situations for a sufficiently long period of time and the cost of changing the yaw angle is lower than the accompanying increase in energy production and/or decrease in fatigue loads, then it makes economic sense to change the yaw angle. However, if such effects can only be observed for shorter periods of time, the change of yaw angles may not be advisable.

[0034] Additionally, yawing can even be used pro-actively in such a way that anticipated wind direction and speed changes that the wind farm control knows about (through wind forecasts) can lead to earlier movements of the yawing. This particularly addresses the slow yaw angle changes that are currently existing (about 8 degrees per minute).

[0035] According to an exemplary embodiment, the present invention analyses the wind changes and the forecast predicts in a short-term effect. If the wind forecast predicts wind situations to change only for a short period of time, the yaw angle should not be changed (in contrast to pitch/yaw control) as the time and the costs for the changes would be too large compared with the short period of increasing the energy production of the overall wind farm.

[0036] According to an exemplary embodiment, the present invention analyses changing the yaw angles of up-wind turbines to reduce the impact of wakes on down-wind turbines.

[0037] As shown in FIG. 1, the yaw angle of the upwind turbines arc changed such that the wakes do not ‘shadow’ the full rotor areas of the down-wind turbines anymore. This reduces the power production of the upwind turbine but increases the power production at downwind turbines due to reduced impact of wakes. This can potentially lead to a higher energy production for the overall wind farm.

[0038] FIG. 2 shows the power productions of several wind turbines in sequence for a given initial wind speed and direction and then for the yaw optimized version.

[0039] In FIG. 3, the corresponding power productions and the sum are plotted as a function of the yaw angles of the upwind turbines. Since upwind turbines power decreases with the yaw angles and the downwind turbines power increases with the yaw angles, the total farm power goes through a maximum as a result of this trade-off. This demonstrates the achievable benefits.

[0040] According to an exemplary embodiment, the present invention analyses changing the yaw angles of upwind turbines to reduce the impact of wakes on downwind turbines. As shown in FIG. 4, when some of the turbines are switched off, e.g. operation stopped, they do not produce wakes anymore. Thus, the previous and the next row of turbines have fewer limitations. Especially in low wind conditions, the power generation of the overall wind farm can be similar to the case where all turbines are used but in this setup life-time effects can be optimized for the rows that are not operating.

[0041] In an embodiment of the present invention, the integration of short, e.g. a second to a minute, and medium-term, 1 minute to an hour, forecasts to decide pro-actively on yaw angle changes while accounting for the trade-off between the cost/time of realizing the proposed yaw angle change vs. the projected energy capture benefit and the accompanying increase in fatigue effects on all the wind farm equipment.

[0042] The same effect of reducing wakes between turbines can be achieved the by pitch control, torque control, or by choosing either all or any combination of yaw control, pitch control, torque control.

[0043] According to a further embodiment, the present invention can decide if it is advantage to temporarily switch off selected turbines to achieve similar wake savings.

[0044] According to a further embodiment, assuming the settings for optimal yaw control, the present invention uses a dynamic identification of yaw angle errors and subsequent decision regarding correction of these errors using wind forecasts, based on the projected cost/time of doing so vs. the energy benefit it will bring if yaw error is indeed corrected.

[0045] According to a further embodiment, the present invention observes a steady state, e.g. constant wind conditions, the system can once optimize the yaw angles for the whole wind farm to optimize the given wind farm owner's objective. The optimization can use any combination of yaw angles, pitch control, and torque control.

[0046] While the invention has been described in detail in the drawings and foregoing description, such description is to be considered illustrative or exemplary and not restrictive.

[0047] Variations to the disclosed embodiments can be understood and effected by those skilled in the art and practising the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain elements or steps are recited in distinct claims does not indicate that a combination of these elements or steps cannot be used to advantage, specifically, in addition to the actual claim dependency, any further meaningful claim combination shall be considered disclosed.

[0048] The features of the method of operating a wind farm and the wind farm controller as described herein may be performed by way of hardware components, firmware, and/or a computing device having processing means programmed by appropriate software. For instance, the wind farm controller can include any known general purpose processor or integrated circuit such as a central processing unit (CPU), microprocessor, field programmable gate array (FPGA), Application Specific Integrated Circuit (ASIC), or other suitable programmable processing or computing device or circuit as desired. The processor can be programmed or configured to include and perform features of the exemplary embodiments of the present disclosure such as a method of operating a wind farm. The features can be performed through program or software code encoded or recorded on the processor, or stored in a non-volatile memory accessible to the processor, such as Read-Only Memory (ROM), erasable programmable read-only memory (EPROM), or other suitable memory or circuit as desired. In another exemplary embodiment, the program or software code can be provided in a computer program product having a non-transitory computer readable recording medium such as a hard disk drive, optical disk drive, solid state drive, or other suitable memory device or circuit as desired, the program or software code being transferable or downloadable to the processor for execution when the non-transitory computer readable medium is placed in communicable contact with the processor.