Imbalance estimation for the wind rotor of a wind turbine

1. A method for compensating an imbalance of a wind rotor of a wind turbine, the method comprising

applying at least two test-offsets, one after the other, to a parameter characterizing a state of the wind rotor, wherein the imbalance depends on the parameter;

measuring for the at least two test-offsets an acceleration of the wind turbine, wherein the acceleration depends on the imbalance; and

determining a compensation-offset based on the acceleration, wherein the imbalance is at least partially compensated, when the compensation-offset is applied to the parameter, wherein determining the compensation-offset comprises;

determining, for each of the at least two test-offsets, a frequency component of a frequency spectrum of the acceleration,

mapping each of the frequency components to a coordinate system,

determining a center defined by each of the frequency components, wherein the center is defined as a center of gravity of a geometric shape defined by each of the frequency components, and

calculating the compensation-offset based on the center, wherein the parameter comprises a plurality of blade parameters, each characterizing a different blade of a plurality of blades of the wind rotor, wherein each blade parameter comprises a blade pitch.

2. The method of claim 1 , wherein determining the compensation-offset comprises determining, for each of the at least two test-offsets, a magnitude and/or a phase of the frequency component of the frequency spectrum of the acceleration.

3. The method of claim 1 , wherein frequencies of each of the frequency components are based on a rotor frequency of the wind rotor.

4. The method of claim 1 , wherein determining the compensation-offset comprises fitting a circle based on each of the frequency components, and calculating the compensation-offset based on the circle, wherein the circle is fitted on a basis of at least three frequency components.

5. The method of claim 1 , wherein determining the compensation-offset comprises setting the compensation-offset to a test-offset corresponding to the frequency component with the smallest magnitude.

6. The method of claim 1 , wherein, after determining the compensation-offset, the method further comprises:

applying the compensation-offset to the parameter;

applying at least one further test-offset to the parameter, wherein each of the at least one further test-offset is smaller than a corresponding test-offset;

measuring for the at least one further test-offset the acceleration of the wind turbine; and

determining a further compensation-offset based on the acceleration.

7. The method of claim 1 , wherein applying the at least one test-offset comprises sequentially applying a plurality of test-offsets.

8. The method of claim 7 , wherein each of the plurality of test-offsets comprises a blade test-offset for each of a plurality of blades of the wind rotor, wherein values of the blade test-offsets are permuted for different test-offsets and/or wherein signs of the values of the blade test-offsets are reversed for different test-offsets.

9. The method of claim 1 , wherein each blade parameter comprises a blade balance mass of the respective blade.

10. The method of claim 1 , wherein at least one test-offset comprises a blade pitch test-offset with an absolute value between 0.05 and 0.6 degrees.

11. The method of claim 1 , wherein the acceleration comprises a fore-aft acceleration and/or a side-to-side acceleration of a tower of the wind turbine and/or of a nacelle of the wind turbine.

12. The method of claim 1 , wherein the imbalance comprises an aerodynamical imbalance, which is compensated based on the fore-aft acceleration, and the imbalance comprises a mass imbalance, which is compensated based on the side-to-side acceleration.

13. The method of claim 1 , wherein the compensation-offset is determined in dependence of a blade pitch angle of the wind rotor and/or of a blade loading of the wind rotor.

14. A wind turbine for generating electrical power, the wind turbine comprising

a tower;

a wind rotor, which is arranged at a top portion of the tower and which comprises at least one blade;

an electrical machine configured as an electric generator, which is mechanically coupled with the wind rotor; and

a control unit configured to carry out the method of claim 1 .