Damping mechanical oscillations of a wind turbine

Abstract

Provided is a method of damping mechanical oscillations of plural wind turbines of a wind park commonly supplying electric energy to a grid, the method including: determining, for each of the plural wind turbines, a damping control signal for counteracting an oscillation of the respective wind turbine; supplying at least a subset of or a subset of modified versions of the damping control signals to respective wind turbines such that a sum of the supplied damping control signals is lower than a threshold.

Claims

1. A method of damping mechanical oscillations of a plurality of wind turbines of a wind park commonly supplying electric energy to a grid, the method comprising: determining, for each wind turbine of the plurality of wind turbines, a damping control signal for counteracting an oscillation of the respective wind turbine; selecting at least a subset of the damping control signals, the subset comprising at least a first damping control signal of a first wind turbine and a second damping control signal of a second wind turbine or a subset of modified versions of the damping control signals, the subset of modified versions comprising at least a first modified damping control signal of the first wind turbine and a second modified damping control signal of the second wind turbine, such that a sum of the selected damping control signals or a sum of the selected modified versions of the damping control signals is lower than a threshold; and supplying the selected subset of the damping control signals or the selected subset of the modified versions of the damping control signals to the respective wind turbines to counteract the oscillation of the respective wind turbines.

2. The method according to claim 1, wherein the oscillation of the respective wind turbine comprises a tower oscillation, the tower oscillation being a side-side oscillation of the tower and/or a drive train oscillation.

3. The method according to claim 1, wherein the oscillations of the respective wind turbines corresponding to the subset have a same frequency.

4. The method according to claim 1, wherein determining the damping control signal comprises: measuring an oscillation of the tower of the wind turbine; determining, based on the measured oscillation, an amplitude and a phase of the damping control signal such as to counteract the oscillation of the wind turbine.

5. The method according to claim 4, wherein determining the amplitude and the phase comprises determining a Fourier transform.

6. The method according to claim 4, wherein the selecting is performed based on the amplitude and phase of the plural damping control signals, to form the sub set.

7. The method according to claim 4, further comprising: selecting, based on the amplitude and phase of the plural damping control signals, at least two damping control signals with an amplitude that is equal and a phase that is opposite or has a same absolute value but different sign or a phase difference of 180.

8. The method according to claim 4, further comprising: supplying amplitude and phase of the plural damping control signals to a determining logic that outputs an enable or disable signal to define the subset.

9. The method according to claim 4, further comprising: determining, based on the amplitude and phase of the plural damping control signals, weighting factors; forming, using the weighting factors, a weighted sum of damping control signals having weighting factors, such that the weighted sum is smaller than the threshold.

10. The method according to claim 1, wherein measuring the oscillation of the wind turbines comprises: measuring the oscillation of the wind turbine using an accelerometer, or measuring an electrical output of the wind turbine.

11. The method according to claim 1, further comprising: supplying each of the damping control signal of the subset to the respective wind turbines to a blade pitch adjustment system and/or a converter connected to a generator.

12. The method according to claim 1, wherein supplying the selected subset of the damping control signals or the selected subset of the modified versions of the damping control signals to the respective wind turbines also reduces electrical oscillations from the wind park as a whole.

13. An arrangement for damping mechanical oscillations of a plurality of wind turbines of a wind park commonly supplying electric energy to a grid, the arrangement comprising: a determining module adapted to determine, for each wind turbine of the plurality of wind turbines, a damping control signal for counteracting an oscillation of the respective wind turbine; a supply module adapted to: select at least a subset of the damping control signals, the subset comprising at least a first damping control signal of a first wind turbine and a second damping control signal of a second wind turbine or a subset of modified versions of the damping control signals, the subset of modified versions comprising at least a first modified damping control signal of the first wind turbine and a second modified damping control signal of the second wind turbine, such that a sum of the selected damping control signals or a sum of the selected modified versions of the damping control signals is lower than a threshold, and supply the selected subset of the damping control signals or the selected subset of the modified versions of the damping control signals to the respective wind turbines.

14. A wind turbine park, including: the plurality of wind turbines; and an arrangement according to the claim 13 connected to control the plurality of wind turbines.

15. The wind turbine park according to claim 14, wherein the selected subset of the damping control signals or the selected subset of the modified versions of the damping control signals counteract the oscillation of the respective wind turbines.

16. The wind turbine park according to claim 14, wherein the selected subset of the damping control signals or the selected subset of the modified versions of the damping control signals reduce electrical oscillations from the wind park as a whole.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 illustrates graphs showing power output of wind turbines of a wind park;

(3) FIG. 2 schematically illustrates a wind park according to an embodiment of the present invention including an arrangement for damping mechanical oscillations of plural wind turbines according to an embodiment of the present invention; and

(4) FIG. 3 schematically illustrates an arrangement for damping mechanical oscillations of plural wind turbines for a wind park, for example the wind park illustrated in FIG. 2, according to an embodiment of the present invention.

DETAILED DESCRIPTION

(5) The graphs 1, 3, 5 illustrated in FIG. 1 show the active power output 7, 9, 11 of three wind turbines of a wind park which commonly supply energy to a utility grid. Thereby, the abscissas 2 indicate time, while the ordinates 4 indicate the power. As can be observed from FIG. 1, the power trace 7 of the graph 1 exhibits a 0.3 Hz oscillation with amplitude of between 80 kW and 100 kW. The power trace 9 of the graph 3 does not contain a visible oscillation. However, the power trace 11 in graph 5 contains both tower oscillation and drive train oscillation. Herein, the tower oscillation may have a frequency of around 0.3 Hz which is comprised in the traces 7 and 11 of graphs 1 and 5.

(6) Embodiments of the present invention are capable of damping drive train oscillations or tower oscillations of plural wind turbines which are commonly included in a wind park and are commonly connected to a utility grid. When the wind turbine whose power traces are illustrated in FIG. 1 are connected to a point of common coupling, especially during past fault and during wind gust, an oscillation of the electrical power at the point of common coupling may be conventionally observed which may be undesired and which may in particular violate requirements set by the grid operator.

(7) FIG. 2 schematically illustrates a wind park 13 according to an embodiment of the present invention including plural wind turbines 15.1, . . . , 15.n and an arrangement 17 for damping mechanical oscillations of the plural wind turbines 15 according to an embodiment of the present invention. Thereby, the arrangement 17 is arranged to perform a method of damping mechanical oscillations of the plural wind turbines 15 according to an embodiment of the present invention.

(8) The arrangement 17 comprises a determining module 19 which is adapted to determine, for each of the plural wind turbines 15.1, . . . , 15.n, a respective damping control signal 21.1, . . . 21.n for counteracting an oscillation of the respective wind turbine 15. The arrangement 17 further comprises a supply module 23 adapted to supply at least a subset (e.g. for wind turbines 15.1, 15.2) or a subset of modified versions of the damping control signals 21.1, 21.2 to the respective wind turbines 15.1, 15.2, such that a sum of the supplied damping control signals 21.1, 21.2 is lower than a threshold or is substantially zero.

(9) The wind park comprises the wind turbines 15.1, 15.2, 15.3, 15.4, . . . , 15.n, wherein n may be between 10 and 300. The damping control signals 21.1, 21.2, . . . , 21.n may also be referred to as P.sub.TD1, P.sub.TD2, . . . P.sub.TDn. The damping control signal may be derived using corresponding active tower damping modules 25.1, 25.2, . . . , 25.n which receive at input terminals oscillation signals 27.1, 27.2, 27.n relating to the oscillations of the wind turbines 15.1, 15.2, 15.3, . . . , 15.n, respectively. For measuring the oscillations and generating the oscillation signals 27.1, . . . , 27.n, the respective wind turbines may comprise for example an accelerometer.

(10) Based on the measured oscillation signals 27.1, 27.2, . . . , 27.n, respectively, the active tower damping modules 25.1, 25.2, . . . , 25.n determine the active damping control signals 21.1, 21.2, . . . , 21.n.

(11) The arrangement 17 is comprised in a high performance park pilot 29 which controls all the wind turbines 15.1, 15.2, . . . , 15.n of the wind park 13. The high performance park pilot 29 outputs enable signals 31.1, . . . , 31.n to the respective active tower damping modules 25.1, . . . , 25.n. Based on these enable signals 31.1, . . . , 31.n, the high performance park pilot 29 outputs the damping control signals 21.1, 21.2, . . . , 21.n to the particular subset of wind turbines, for example the subset comprised of wind turbines 15.1 and 15.2.

(12) All the wind turbines 15.1, 15.2, . . . , 15.n are connected to a point of common coupling 37 which is connected via a wind park transformer 39 to a utility grid 41.

(13) The proposed solution may be called a de-synchronization of active tower oscillation caused by active tower damping in individual turbines so that there is no significant oscillation seen at the point of common coupling 37 thus fulfilling grid code requirements at the point of common coupling 37.

(14) FIG. 3 schematically illustrates the arrangement 17 in more detail. Digital signal processing modules 33.1, 33.2, . . . , 33.n receive the damping control signals 21.1, 21.2, . . . , 21.n, respectively and derive therefrom amplitudes A.sub.1, A.sub.2, . . . , A.sub.n and phases .sub.1, .sub.2, . . . , .sub.n or a frequency of oscillation of the respective wind turbines 15.1, 15.2, . . . , 15.n, for example a side-side tower oscillation.

(15) A determining logic 35 receives the amplitudes A.sub.1, A.sub.2, A.sub.n and phases .sub.1, .sub.2, . . . , .sub.r, and derives the enable signal 31.1, 31.2, . . . , 31.n, respectively therefrom. Thereby, the digital signal processing modules 33.1, 33.2, . . . , 33.n may comprise a Fast Fourier Transformation algorithm to derive a Fourier transform of the damping control signals 21.1, 21.2, . . . , 21.n. The determining logic 35 sets the enable signals 31.1, 31.2, . . . , 31.n such that the sum of the associated damping control signals 21.1, 21.2, . . . , 21.n is lower than a threshold.

(16) Thereby, e.g. the enable signals 31.1, 31.2 may, according to an exemplary embodiment, be true, while all other enable signals may be false. Thus, the subset, to which the damping control signals are supplied may be the wind turbines 15.1 and 15.2. Therefore, the damping control signals 21.1 and 21.2 are supplied, in particular from the high performance park pilot 29 to the wind turbines 15.1 and 15.2, respectively.

(17) Thereupon, a not illustrated blade pitch adjustment system or/and a converter are controlled such as to respectively counteract the wind turbine oscillations of the respective wind turbines.

(18) The proposed solution may be applied during normal operation as well as during grid faults or after grid faults. The tower oscillation de-synchronization algorithm may be located in a high performance power plant controller, such as HPPP 29 illustrated in FIG. 2, as part of a wind farm controller. Each wind turbine 15.1, 15.2, . . . , 15.n in the wind farm may send the needed damping power 21.1 (or an oscillation signal 27.1, 27.2, . . . , 27.n) through the communication network to the HPPP. The tower oscillation de-synchronization algorithm may collect the required active power damping for active power damping in HPPP and may select/enable the active tower damping features for these turbines (for example the turbines 15.1, 15.2) such that the sum of the active power demand of these wind turbines is close to zero.

(19) The detailed setup of the de-synchronization algorithm shown in FIG. 3 utilizes a digital signal processing method such as FFT, to derive the amplitude and the phase of the damping power in real-time. For the wind turbine 15.1, the calculated amplitude and phase are A.sub.1 and .sub.1. For wind turbine 15.n, the amplitude and phase are A.sub.n and .sub.n. The amplitude and phase of all the wind turbines are used to determine the subset of wind turbines in which active power damping control shall be enabled. For example, if A.sub.1=A.sub.2 and .sub.1=.sub.2, both turbines 15.1 and 15.2 shall be enabled. In this way, there is no sufficient power oscillation at the point of common coupling 37 or the oscillation can at least be reduced and nevertheless tower damping may be enabled for at least a subset of the wind turbines.

(20) A similar method may be used to reduce power oscillation after grid fault due to drive train oscillations.

(21) Embodiments of the present invention may achieve the following advantages: Cancellation of power oscillation at PCC to fulfil grid code requirements No additional hardware required Expand mechanical system life span Stabilize grid due to less/no post fault oscillation especially for weak grid

(22) Further an advantage of the present invention may be that requirements of the stability of the tower may be less demanding, thereby saving manufacturing costs and material.

(23) Although the present invention has been described in detail with reference to the preferred embodiment, it is to be understood that the present invention is not limited by the disclosed examples, and that numerous additional modifications and variations could be made thereto by a person skilled in the art without departing from the scope of the invention.

(24) It should be noted that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements. 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.