CONTROLLING WIND TURBINES IN PRESENCE OF WAKE INTERACTIONS

Abstract

It is described a method for controlling at least one considered wind turbine (5) in a wind park (1), comprising: determining, based on a wind condition (7b), in particular wind direction (7b), whether another wind turbine (9a, . . . ,9e) is in a wake region caused by the considered wind turbine; if another wind turbine (9b) is the closest wind turbine in the wake region (11b) and if the other wind turbine (9b) is in an operable state, applying a first control setting (15) to the considered wind turbine (5); if the other wind turbine (0b) is in a non-operable state applying a second control setting (17) to the considered wind turbine (5), wherein the first control setting is based on wind park level optimisation and the second control setting is based on wind turbine level optimisation.

Claims

1. A method for controlling at least one considered wind turbine in a wind park, the method comprising: determining, based on a wind condition, whether another wind turbine is in a wake region caused by the considered wind turbine; if the other wind turbine is a closest wind turbine in the wake region and if the other wind turbine is in an operable state, applying a first control setting to the considered wind turbine; if the other wind turbine is the closest wind turbine and the other wind turbine is in a non-operable state applying a second control setting to the considered wind turbine; and wherein the first control setting is based on wind park level optimisation and the second control setting is based on wind turbine level optimisation.

2. The method according to the preceding claim 1: wherein the first control setting has previously been determined for the given wind condition to optimize a first target function for the entire wind park based on a simulation model assuming that all wind turbines are operable; wherein the second control setting has been previously determined for the given wind condition to optimize a second target function for only the considered wind turbine; and/or wherein the other wind turbine is in the operable state, if the other wind turbine is producing electrical power or at least could produce electrical power, if the wind condition was appropriate; and/or wherein the other wind turbine is in the non-operable state, if the other wind turbine is stopped, in particular due to an error or due to maintenance.

3. The method according to claim 1, wherein the determining whether the other wind turbine is in the wake region comprises: utilizing a previously determined wind direction specific association of several other wind turbines to the considered wind turbine, which association designates one of the several other wind turbines to be in the wake region of the considered wind turbine depending on the wind direction.

4. The method according to the claim 1, wherein: the association defines for each of the several other wind turbines a wind direction angle sector for which the respective other wind turbine is considered to be in the wake region; wherein in particular, the other wind turbine is considered to be in the wake region, if the other wind turbine is located, depending on the wind direction, in a region downstream the considered wind turbine having a width of the diameter of the blades of the considered wind turbine, the width expanding downstream the considered wind turbine by an angle of between 2° and 6° on both sides; and and in particular and if a distance between the considered wind turbine and the other wind turbine is closer than threshold.

5. Method the method according to claim 1, wherein the first and second target function both comprise power output and/or load, of the entire wind park and the considered wind turbine, respectively.

6. The method according to claim 1, wherein the first and/or the second control setting comprises at least one set point of at least one parameter selected from: a rotor yaw angle, a rotor yaw offset, a rotor tilt angle, a rotational speed, an active power output, a reactive power output, at least one blade pitch angle, an active current, a reactive current.

7. The method according to claim 1, wherein the first and the second control setting are different in at least one set point of at least one parameter, in particular different in a set point for the yaw offset.

8. The method according to claim 1, wherein the second control setting comprises the set point of the yaw offset to be essentially zero; wherein the first control setting comprises the set point of the yaw offset to be different from zero.

9. The method according to claim 1, wherein the first control setting comprises the set point of blade pitch angle to be greater than the set point of the blade pitch angle of the second control setting.

10. The method according to claim 1, wherein the second control setting is based on at least one set point of rotational speed, pitch angle, yaw angle, a wind speed, each being selected for maximal power production of the considered wind turbine.

11. The method according to claim 1, further comprising: determining an operational state of the other wind turbine; communicating the operational state to the considered wind turbine, in particular via a park controller; and further comprising: determining the wind condition.

12. The method according to claim 1, further comprising: applying a wake model to the entire wind park determined previously to derive the first control setting.

13. A method for controlling wind turbines in a wind park, comprising: performing for each wind turbine of the wind park a method according to claim 1 as considered wind turbine.

14. An arrangement for controlling at least one considered wind turbine in a wind park, the arrangement configured: to determine, based on a wind condition, whether another wind turbine is in a wake region caused by the considered wind turbine; to apply a first control setting to the considered wind turbine, if the other wind turbine is a closest wind turbine in the wake region and if the other wind turbine is in an operable state; to apply a second control setting to the considered wind turbine, if the other wind turbine is in a non-operable state; and wherein the first control setting is based on wind park level optimisation and the second control setting is based on wind turbine level optimisation.

15. The wind park comprising an arrangement according to claim 14.

Description

BRIEF DESCRIPTION

[0047] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0048] FIG. 1 depicts a wind park including an arrangement for controlling at least one considered wind turbine in the wind park which is adapted to perform a method; and

[0049] FIG. 2 depicts a part of the wind park illustrated in FIG. 1.

DETAILED DESCRIPTION

[0050] The wind park 1 illustrated in FIG. 1 in a schematic plan view comprises plural wind turbines arranged substantially in a square area and labelled with reference signs A01 to A07 in a first row, B01 to B07 in a second row, . . . , and F01 to F07 in a last, sixth row. The wind park further comprises an arrangement 3 for controlling at least one considered wind turbine, for example wind turbine 5 (A07). Thereby, the arrangement 3 is adapted to determine, based on a wind direction 7 (7a, . . . , 7e denote examples of different wind directions), whether another wind turbine, for example one of the other wind turbines 9a (B07), 9b (B06), 9c (B05), 9d (B04) or 9e (A06) is in a wake region 11b caused by the considered wind turbine 5. In the present illustrated example, the other wind turbine 9b (B06) is located within the wake region 11b downstream the considered wind turbine 5 (A07) during the present wind condition, in which the wind blows in the direction 7b. For example, the other wind turbine 9a (B07) is in the respective wake region, if the wind blows in the direction 7a (and is closes to wind turbine 5). one of the other wind turbines 9b or 9c, 9d or 9e is in the wake region if the wind blows in the direction 7b, 7c, 7d and 7e, respectively, as indicated by dashed wind directions.

[0051] The arrangement is further configured to determine or request the operational states of the other wind turbines 9a, . . . , 9e which are potentially in the wake region depending on the wind direction. Therefore, the arrangement 3 is communicatively connected to all wind turbines of the wind park using a network connection 13. Furthermore, the arrangement 3 comprises a control output module which may also utilize the network connection 13 in order to supply control signals to all wind turbines in the wind park 1.

[0052] For example, in one scenario, the other wind turbine 9b within the wake region 11b is in an operable state, for example running and producing energy. In this case, the arrangement 3 supplies to the considered wind turbine 5 (A07) first control setting in order to control the operation of the considered wind turbine 5. If, however, the other wind turbine 9b (B06) is in a non-operable state, the arrangement 3 applies second control setting to the considered wind turbine 5.

[0053] FIG. 2 illustrates a portion of the wind park in more detail. The first control setting denoted by signal 15 in FIG. 2 has been determined for the given wind condition (for example characterized by the wind direction 7b) and also based on the wind speed, to optimize a first target function for the entire wind park 1 based on a simulation model assuming that all wind turbines are operable.

[0054] The second control setting, denoted by a control signal 17 in FIG. 2, has been determined for the given wind condition to optimize a second target function for only the considered wind turbine 5 (A07) without taking into account load and/or energy production of all other wind turbines of the wind park 1.

[0055] For determining whether the other wind turbine (for example 9b (B06)) is in the wake region 11b (depending on the current wind direction 7b), the arrangement 3 may have (for every wind turbine in the wind park) a wind direction specific association data structure 21 stored within an electronic storage 19. The association data structure 21 may, for each considered wind turbine 5, designate one of the several other wind turbines, for example the wind turbines 9a, . . . , 9e, to be in the wake region for the considered wind turbine depending on the wind direction 7b or 7a, . . . , 7e.

[0056] The respective association data structure 21 stored for each wind turbine of the wind park within the arrangement 3 is illustrated in a graphical manner as differently shaded angle sector map 21. In particular, the association data structure 21 comprises for each of several other wind turbines 9a, . . . , 9e a respective wind direction angle sector 23a, . . . , 23e, in a suitable format. The kind of shading in one wind direction angle sector is the same as applied to the dot showing the respective wind turbine.

[0057] For example, when the wind direction 7 is within an angle range covered by the wind direction angle sector 23a, the other wind turbine 9a (B07) would be considered to be in the wake region of the upstream wind turbine 5. For the wind direction 7b, however, the respective wind direction angle sector 23b identifies the other wind turbine 9b (B06) as the wind turbine within the wake region 11b. The association data structure 21 may be implemented in any suitable manner, such as a suitable data object or data table or database. The association data structure 21 may merely define an identity of the respective downstream wind turbine which is in the wake region for a wind direction angle range.

[0058] The wake region 11b may cover an area defined by the diameter d of the rotor blades of the considered wind turbine 5 which extends downstream the wind turbine 5 thereby, expanding the width w by an angle of between 2° and 6°, wherein the angle is denoted as a in FIG. 2. Other definitions are possible.

[0059] Furthermore, if several other wind turbines are within the thus defined cone, only the wind turbine closest to the considered wind turbine is considered to be within the wake region. Further, the wake region 11b does not need to extend indefinitely downstream the considered wind turbine 5 but may end at a maximal distance lmax from the wind turbine.

[0060] Both the first and the second control setting may comprise at least one set point of an operational parameter wherein, however, at least one value of the set point may be different.

[0061] According to an embodiment of the present invention, the control method may adapt to the situation that a turbine is stopped (or at least non-operable) by performing one or more of the following steps: [0062] 1) For each turbine A (for example wind turbine 5) in the wind farm, based on the wind direction (for example 7b) and the layout of the wind farm 1, determine which downstream turbines (for example which of the downstream turbines 9a, . . . , 9e) are effected by the turbine A through its wake (for example wake region 11b), in particular using some assumptions on the direction of the wake and its expansion in the flow downstream. [0063] 2) Check which of those downstream turbines is at the closest distance to turbine A along the wind direction. In the illustrated example, this is wind turbine 9b (B06). This closest wind turbine may be referred to as turbine B. These steps 1) and 2) may be performed beforehand offline and a mapping (for example the mapping 21 illustrated in FIG. 2) defining the closest downstream turbine for each wind direction could be stored on each turbine individually or at the arrangement 3, for example. [0064] 3) Perform a communication between turbines, to determine if the turbine B (for example turbine 9b) is operating (or at least operable) or stopped/stopping, because for example of a maintenance or because of an error in one of an essential component. [0065] 4) In case that the closest downstream turbine B is stopped, set the control settings of turbine A to the control settings that are optimal on the individual turbine level (i.e. the second control setting) thereby ignoring the wake effects of any downstream turbines. If turbine B is operating (or at least operable) use on turbine A the control settings that are optimal on the wind farm level assuming that all wind turbines are operating (or at least operable).

[0066] This approach follows from the simplifying assumption that for determining the optimal control settings, all wake interaction effects can be ignored, if the closest downstream turbine is stopped (or for example non-operable). This assumption follows from the fact that the distances between turbines and wind farm are generally large enough such that the wake will have recovered too close to the free stream conditions when they reach the turbines further downstream. In particular, wake interaction effects between turbine A and a turbine further downstream from turbine B may be negligible.

[0067] The association data structure 21 illustrates a mapping from wind direction to the closest downstream turbine for each turbine in a wind farm. Each turbine may be indicated by a code and/or identified by an identifier, for example A07 for the considered wind turbine 5 and also all the other wind turbines may be identified by a code or an identifier.

[0068] Further, in the illustration of FIGS. 1 and 2, each wind turbine is associated with a colour or a particular hatching type. The semi-circle sectors 21 around the dots indicate which turbine is the closest downstream turbine for each wind direction, using the same hatching type as use to fill the dot denoting the respective wind turbine. The wind direction is shown in a clockwise direction from due North and so a wind coming from the South have a wind direction of 180° and one from the East has 90°. When for example going from Southwest to North wind direction, the closest downstream turbine impacted by the wake of turbine A07 is first turbine B07 and then as the wind direction increases, respectively C06, B06, B05, B04 and A06.

[0069] The embodiments of the present invention may provide several advantages. The adaptation of the control settings to the case of one or more stopped (or non-operable) turbines within the wind farm level optimized wake control may result in a wind farm performance increase (increased electrical energy production and/or reduced wind turbine loads) compared to the case where the fact that some turbines could be stopped were ignored. Very little computational cost of dealing with the case of stopped (or at least non-operable) wind turbines within the wind farm level optimized wake control.

[0070] Embodiments of the present invention may comprise to determine the wind direction. This could be the local wind direction measured at the wind turbine or the wind direction of the inflow into the wind farm that could be determined by conventional methods for estimation of free stream inflow wind conditions in a wind farm. Based on the wind direction, a simple wake modelling algorithm may be applied, which may merely determine a wake expansion and direction, for example for determining the location and shape of the wake regions 11. The methodology may be retrofitted to existing wind parks.

[0071] A simple, widely-used wake model with a linear expansion of the wake that may be used in embodiments of the present invention is e.g. described in “A SIMPLE MODEL FOR CLUSTER EFFICIENCY” by I. KATIC. J. HØJSTRUP. N. O. JENSEN, European Wind Energy Association Conference and Exhibition 7-9 Oct. 1986, Rome, Italy.

[0072] It should be noted that the term “comprising” does not exclude other elements or steps and “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

[0073] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0074] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.