Azimuth-domain detection of an occurring rotor imbalance in a wind turbine

1 . A method for detecting an occurring imbalance in a pitchable rotor of a wind turbine during operation, comprising:

measuring a dynamic characteristic of the wind turbine;

defining a sequence of dynamic values (a(ψ))) by sampling the dynamic characteristic when the rotor is at each of a plurality of azimuth angles (ψ n ), the sequence of dynamic values includes dynamic values obtained for the immediate at least one full rotation prior to a current azimuth angle of the rotor;

applying an azimuth-domain transform to the sequence of dynamic values (a(ψ) to generate at least one inverse-angle component (A(γ k ));

detecting the imbalance based on the at least one inverse-angle component (A(γ k )); and

initiating a pitching of the pitchable rotor to stop the rotation of the rotor.

2 . The method of claim 1 , wherein the at least one inverse-angle component (A(γ k )) is a fundamental inverse-angle component (A(γ k )), and detecting the imbalance comprises:

comparing a value of the fundamental inverse-angle component (A(γ k )) to a fundamental inverse-angle threshold; and

determining the imbalance exists in response to the value of the fundamental inverse-angle component (A(γ k )) exceeding the fundamental inverse-angle threshold.

3 . The method of claim 1 , wherein the at least one inverse-angle component (A(γ k )) is a fundamental inverse-angle component (A(γ k )), and detecting the imbalance comprises:

determining a difference between a current value of the fundamental inverse-angle component (A(γ k )) and a previous value of the fundamental inverse-angle component (A(γ k ));

comparing the difference to a fundamental inverse-angle rate of change threshold; and

determining the imbalance exists in response to the value of the difference exceeding the fundamental inverse-angle rate of change threshold.

4 . The method according to claim 1 , further comprising:

updating the sequence of dynamic values (a(ψ)) by adding a new dynamic value (a(ψ n )) to the sequence of dynamic values (a(ψ)) and removing an oldest dynamic value (a(ψ n )) from the sequence of dynamic values (a(ψ)) each time the rotor reaches one of the plurality of azimuth angles (ψ n ).

5 . The method according to claim 1 , wherein the number of dynamic values (a(ψ n )) in the sequence of dynamic values (a(ψ)) is equal to an integer multiple of the number of azimuth angles (ψ n ) in one full rotation of the rotor.

6 . The method according to claim 1 , wherein the dynamic characteristic includes a component aligned with a rotor plane of the rotor.

7 . The method according to claim 1 , wherein each dynamic value is a measured acceleration of a nacelle of the wind turbine.

8 . The method according to claim 1 , further comprising:

in response to detecting the imbalance, pitching one or more blades of the rotor toward a feathered position in accordance with a selected pitch trajectory.

9 . The method of any of claim 1 , further comprising:

in response to detecting the imbalance, adjusting a blade pitch rate from a first rate to a second rate higher than the first rate.

10 . The method according to claim 1 , wherein the pitching of the pitchable rotor to stop the rotation of the rotor is handled by a safety control system.

11 . A system for detecting an occurring imbalance in a pitchable rotor of a wind turbine, comprising:

one or more processors; and

a memory coupled to the one or more processors and including program code that, when executed by the one or more processors, causes the system to perform an operation, comprising:

measure a dynamic characteristic of the wind turbine;

define a sequence of dynamic values (a(ψ)) by sampling the dynamic characteristic when the rotor is at each of a plurality of azimuth angles (ψ n ), the sequence of dynamic values includes dynamic values obtained for the immediate at least one full rotation prior to a current azimuth angle of the rotor;

apply an azimuth-domain transform to the sequence of dynamic values (a(ψ) to generate at least one inverse-angle component (A(γ k ));

detect the imbalance based on the at least one inverse-angle component (A(γ k )); and

initiate a pitching of the pitchable rotor to stop the rotation of the rotor.

12 . The system of claim 11 , wherein the at least one inverse-angle component (A(γ k )) is a fundamental inverse-angle component (A(γ k )), and detect the imbalance comprises:

compare a value of the fundamental inverse-angle component (A(γ k )) to a fundamental inverse-angle threshold; and

determine the imbalance exists in response to the value of the fundamental inverse-angle component (A(γ k )) exceeding the fundamental inverse-angle threshold.

13 . The system of claim 11 , wherein the at least one inverse-angle component (A(γ k )) is a fundamental inverse-angle component (A(γ k )), and detecting the imbalance comprises:

determine a difference between a current value of the fundamental inverse-angle component (A(γ k )) and a previous value of the fundamental inverse-angle component (A(γ k ));

compare the difference to a fundamental inverse-angle rate of change threshold; and

determine the imbalance exists in response to the value of the difference exceeding the fundamental inverse-angle rate of change threshold.

14 . A computer program product for detecting an occurring imbalance in a rotor of a wind turbine, comprising:

a non-transitory computer-readable storage medium; and

program code stored on the non-transitory computer-readable storage medium that, when executed by one or more processors, causes the one or more processors to perform an operation, comprising:

measure a dynamic characteristic of the wind turbine;

define a sequence of dynamic values (a(ψ)) by sampling the dynamic characteristic when the rotor is at each of a plurality of azimuth angles (ψ n ), the sequence of dynamic values includes dynamic values obtained for the immediate at least one full rotation prior to a current azimuth angle of the rotor;

apply an azimuth-domain transform to the sequence of dynamic values (a(ψ)) to generate at least one inverse-angle component (A(γ k ));

detect the imbalance based on the at least one inverse-angle component (A(γ k )); and

initiate a pitching of the pitchable rotor to stop the rotation of the rotor.

15 . The computer program product of claim 14 , wherein the at least one inverse-angle component (A(γ k )) is a fundamental inverse-angle component (A(γ k )), and detecting the imbalance comprises:

compare a value of the fundamental inverse-angle component (A(γ k )) to a fundamental inverse-angle threshold; and

determine the imbalance exists in response to the value of the fundamental inverse-angle component (A(γ k )) exceeding the fundamental inverse-angle threshold.

16 . The computer program product of claim 14 , wherein the at least one inverse-angle component (A (γ k )) is a fundamental inverse-angle component (A (γ k )), and detecting the imbalance comprises:

determine a difference between a current value of the fundamental inverse-angle component (A (γ k )) and a previous value of the fundamental inverse-angle component ( 4 (γ k ));

compare the difference to a fundamental inverse-angle rate of change threshold; and

determine the imbalance exists in response to the value of the difference exceeding the fundamental inverse-angle rate of change threshold.