Method for operating a wind energy installation, and wind energy installation

Abstract

A method for operating a wind energy installation having a tower, a nacelle arranged on the tower, the azimuth of which can be adjusted, and a rotor having at least one rotor blade, the blade angle of which can be adjusted, in which tower oscillations are detected and monitored during operation using at least one measuring apparatus and power operation is switched off if a sliding average of the tower oscillations exceeds a tower oscillation limit value. The tower oscillation limit value is defined, at least during load operation of the wind energy installation, as at least one limit value function which is dependent on a sliding average of prevailing wind speed and/or a parameter associated therewith, and has different functional dependencies in a plurality of different value ranges of the prevailing wind speed or the parameter associated therewith. The invention also relates to a wind energy installation.

Claims

1. A method for operating a wind energy installation having a tower, a nacelle arranged on the tower, and a rotor having at least one rotor blade, wherein an azimuth of the nacelle is adjustable, wherein a blade angle of the at least one rotor blade is adjustable, the method comprising: detecting and monitoring tower oscillations during operation of the wind energy installation using at least one measuring apparatus; and switching off power operation of the wind energy installation if a measurement variable of the tower oscillations exceeds a tower oscillation limit value; wherein the tower oscillation limit value is defined, at least during load operation of the wind energy installation, as at least one limit value function which is dependent on prevailing wind speed and/or a parameter associated therewith, and which has different functional dependencies in a plurality of different value ranges of prevailing wind speed and/or the parameter associated therewith.

2. The method as claimed in claim 1, wherein the measurement variable is a sliding average.

3. The method as claimed in claim 2, wherein the sliding average is of prevailing wind speed and/or a parameter associated therewith.

4. The method as claimed in claim 3, wherein the tower oscillation limit value has different functional dependencies in a plurality of different value ranges of the sliding average of prevailing wind speed and/or the parameter associated therewith.

5. The method as claimed in claim 1, wherein the value of the limit value function corresponds to a first limit value a.sub.Grenz0 or runs below a first limit value a.sub.Grenz0 at wind speeds below a starting speed v.sub.Start of the wind energy installation, decreases toward wind speeds between v.sub.Start and a first wind speed limit value v.sub.Wind0, where v.sub.Wind0>v.sub.Start, and increases toward wind speeds between a second wind speed limit value v.sub.Wind1 and a third wind speed limit value v.sub.Wind2, where v.sub.Wind2>v.sub.Wind1>v.sub.Wind0, to a value which is greater than the limit value a.sub.Grenz0.

6. The method as claimed in claim 1, wherein the limit value function is dependent on at least one second parameter for one or more special meteorological conditions and/or special operating conditions, the limit value function comprising a constant correction term a.sub.GrenzOffset or a correction term, which is dependent on the wind speed and is added to the tower oscillation limit value when special meteorological conditions or special operating conditions occur.

7. The method as claimed in claim 1, wherein a positive additive term or offset is added in the event of a change from one operating state to another for a short period.

8. The method as claimed in claim 7, wherein the short period is from 1 to 10 minutes.

9. The method as claimed in claim 1, wherein the value of the limit value function does not undershoot a minimum first limit value a.sub.Grenz1.

10. The method as claimed in claim 9, wherein the minimum first limit value a.sub.Grenz1 is used at a medium wind speed or in a medium wind speed range.

11. The method as claimed in claim 1, wherein the value of the limit value function does not exceed a maximum second limit value a.sub.Grenz2.

12. The method as claimed in claim 11, wherein the maximum second limit value a.sub.Grenz2 is used at high wind speeds.

13. The method as claimed in claim 1, wherein an averaging duration for the tower oscillations is greater than an averaging duration for the prevailing wind speed by at least a factor of 5.

14. The method as claimed in claim 1, wherein an averaging duration for the tower oscillations is greater than an averaging duration for the prevailing wind speed by at least a factor of 10.

15. The method as claimed in claim 1, wherein the sliding average of the tower oscillations is averaged over a duration of between 2 and 20 minutes, and/or the sliding average of the prevailing wind speed is averaged over a duration of between 10 and 60 seconds.

16. The method as claimed in claim 1, wherein tower acceleration is measured as the measurement variable for the tower oscillations.

17. The method as claimed in claim 1, wherein two different limit value functions are used for tower oscillations in a direction of a rotor axis and for tower oscillations in a plane perpendicular to the rotor axis.

18. A wind energy installation comprising: a tower; a nacelle arranged on the tower, wherein an azimuth of the nacelle is adjustable; a rotor having at least one rotor blade, wherein a blade angle of the at least one rotor blade is adjustable; at least one measuring apparatus configured and arranged to detect tower oscillations; and an operation control device comprising a data processing system with operation control software set up to monitor the tower oscillations and to switch off power operation of the wind energy installation if a tower oscillation limit value is exceeded by the tower oscillations; wherein at least one limit value function is defined as the tower oscillation limit value in the operation control software, which limit value function is dependent on prevailing wind speed and/or a parameter associated therewith, and wherein the at least one limit value function, which is dependent on prevailing wind speed and/or a parameter associated therewith, has different functional dependencies in a plurality of different value ranges of prevailing wind speed and/or a parameter associated therewith.

19. The wind energy installation as claimed in claim 18, wherein the operation control software is set up to monitor the tower oscillations and to switch off power operation of the wind energy installation if a tower oscillation limit value is exceeded by a sliding average of the tower oscillations.

20. The wind energy installation as claimed in claim 18, wherein the limit value function is dependent on a sliding average of prevailing wind speed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described below, without restricting the general concept of the invention, using exemplary embodiments with reference to the drawing, in which case, with respect to all details according to the invention which are not explained in any more detail in the text, reference is expressly made to the drawing, in which:

(2) FIG. 1 shows a wind energy installation 1 having a tower 2, a nacelle 3 which is arranged on the tower and the azimuth of which can be adjusted, and a rotor 4 having at least one rotor blade 5, the blade angle of which can be adjusted, tower oscillations being detected and monitored during operation of the wind energy installation using at least one measuring apparatus 6; and

(3) FIG. 2 shows a graph of a limit value function aGrenz according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) The limit value a.sub.Grenz1 is plotted on the Y axis of the graph, and the wind speed v.sub.Wind is plotted on the X axis. The possible range of limit values is restricted by a lower limit value a.sub.Grenz1 and an upper limit value a.sub.Grenz2, below or above which the limit value function a.sub.Grenz does not deviate.

(5) At a wind speed below the starting wind speed which, depending on the wind energy installation, is a few meters per second, the base value of the function a.sub.Grenz, which is indicated with a bold line, has a value a.sub.Grenz0 and is constant. The endpoint of this constant range of the function is indicated by P.sub.1. At this point, the limit value a.sub.Grenz0 is normally between 5 and 30 mG (the unit mG denotes one thousandth of the gravitational acceleration) depending on the wind energy installation type. In a similar manner, the tower acceleration as the measurement variable for tower oscillations may also be replaced with other suitable measurement variables, for instance strain gauges, position sensors or the like.

(6) Between the points P.sub.1 and P.sub.2, that is to say at wind speeds between the installation-specific starting wind speed and a wind speed v.sub.Wind0 which corresponds, for instance, to a lower variable-speed range, the value of the limit value function decreases continuously, and in a linear manner in the exemplary embodiment, until the lower limit value a.sub.Grenz1 is reached at point P.sub.2. Depending on the installation, the wind speed v.sub.Wind0 is between 3 and 10 m/s and may be included as a value for v.sub.Wind0 up to the nominal wind speed v.sub.rated, for example. At point P.sub.2, the lower limit value a.sub.Grenz1 is reached, which lower limit value is between 3 and 30 mG in an installation-specific manner. It is advantageously lower than the value a.sub.Grenz0.

(7) In the example according to FIG. 1, the value of the limit value function a.sub.Grenz between the points P.sub.2 and P.sub.3 is constant at the value a.sub.Grenz1, the point P.sub.3 corresponding to a wind speed v.sub.Wind1 which is between 10 and 15 m/s in an installation-specific manner and corresponds approximately to the nominal wind for the wind energy installation.

(8) Beyond the nominal wind speed or wind speed v.sub.Wind1, the value of the function a.sub.Grenz again increases continuously, and in a linear manner in the exemplary embodiment, to the point P.sub.4 at which the upper limit value a.sub.Grenz2 is reached, which upper limit value is generally between 10 and 40 mG. Above the point P.sub.4, the value of the limit value function a.sub.Grenz is then constant at this value a.sub.Grenz2. The wind speed v.sub.Wind2 at the point P.sub.4 is approximately 22 to 30 m/s and corresponds approximately to the switch-off speed of the wind energy installation and should be greater than the nominal wind speed.

(9) A somewhat thinner line is used to represent the function a.sub.Grenz, for which a constant offset a.sub.GrenzEisOffset is added, which is taken into account in the case of an iced state of the rotor blades of the wind energy installation. In this case, greater imbalances and greater tower oscillation states occur for a relatively short time. In order to avoid the wind energy installation being unnecessarily switched off in an undesirable manner in this case, the limit value function a.sub.Grenz is increased by the offset a.sub.GrenzEisOffset. The curve also ends with the offset a.sub.GrenzEisOffset at a maximum at the upper limit value a.sub.Grenz2 which, however, is already reached in this case at lower wind speeds, that is to say before reaching v.sub.Wind2.

(10) In this case, one preferred development provides for an offset which varies with the wind speed or a parameter associated with the latter. In order to reduce high oscillation amplitudes, provision is preferably made in this case for the offset to be continuously reduced in the range between v.sub.Wind1 and v.sub.Wind2, with the result that the limit value a.sub.Grenz2 is reached only at v.sub.Wind2, that is to say at the point P4.

(11) The exemplary embodiment which is illustrated in FIG. 1 and has a plurality of linear curve sections which are continuously placed next to one another forms a method which is particularly simple to implement. Alternatively, it is naturally also possible to select another function which has fewer bends or no bends, for example a spline-interpolated function over a plurality of supporting points or a function which is completely continuous also in the first derivative and possibly also the second derivative.

(12) The table below explains the parameter ranges in FIG. 2. The X direction is used to denote the oscillations in the direction of the rotor axis and Y is used to denote the oscillations transverse to the rotor axis. For each individual parameter, a preferred embodiment comprises the choice of the parameter in the range between minimum and maximum. In particularly preferred embodiments, an individual parameter or a selection of parameters is set in the range of the normal range.

(13) TABLE-US-00001 Normal Parameter Unit MIN Range MAX Note V.sub.Wind0 m/s V.sub.Start 3-10 V.sub.Rated 2) a.sub.Grenz0 mG 10 5-30 50 1) V.sub.Wind1 m/s >a.sub.0 10-15 20 3) a.sub.Grenz1 mG a.sub.0 3-30 50 V.sub.Wind2 m/s V.sub.Rated 22-30 30 4) a.sub.Grenz2 mG 10 10-40 50 a.sub.GrenzEisOffset mG 0 3-20 30 In this case, note 1) means that the limit value is possibly dependent on the hub height, 2) means the lower variable-speed range, 3) means the nominal wind range, and 4) means the switch-off speed.

(14) The parameters v.sub.Wind0, v.sub.Wind1 and v.sub.Wind2 are the first, second and third wind speed values in the characteristic curve of the maximum permissible tower oscillation, whereas a.sub.Grenz0, a.sub.Grenz1 and a.sub.Grenz2 respectively denote the first, second and third limit values in the characteristic curve of the maximum permissible tower oscillation. a.sub.GrenzEisOffset is the offset for maximum permissible tower oscillations for the special condition of icing of the rotor blades. The individual parameters may each be defined differently for the X and Y directions parallel and transverse to the rotor axis of rotation.

(15) All of the features mentioned, including the features which can be gathered from the drawing alone and individual features which are disclosed in combination with other features, are considered to be essential to the invention alone and in combination. Embodiments according to the invention may be complied with by individual features or a combination of a plurality of features.