Apparatus and method for determining a resonant frequency of a wind turbine tower
View Patent ↗An apparatus for determining a resonant frequency of a wind turbine tower is provided. The apparatus includes a processing unit configured to receive an acceleration measurement value, the acceleration measurement value representative of the acceleration of the wind turbine tower in the direction parallel to a rotor rotational axis of the wind turbine and/or in the direction perpendicular to both the rotor rotational axis and the tower axis of the wind turbine. The apparatus includes a memory configured to store a series of acceleration measurement values, and the processing unit includes a Fourier transform module configured to calculate a spectral vector based on calculating a convolution-based fast Fourier transform of the series of acceleration measurement values, and includes a resonant frequency calculation module configured to calculate the tower resonant frequency based on the calculated spectral vector.
1. An apparatus for determining a resonant frequency of a wind turbine tower, comprising:
a memory configured to store a series of acceleration measurement values, each acceleration measurement value representative of an acceleration of the wind turbine tower in a direction parallel to a rotor rotational axis and/or in a direction perpendicular to both the rotor rotational axis and the tower axis of the wind turbine; and
a processing unit that receives an acceleration measurement value, the processing unit comprising:
a Fourier transform module that calculates a spectral vector based on calculating a convolution-based fast Fourier transform of the series of acceleration measurement values, and
a resonant frequency calculation module that calculates the tower resonant frequency based on the calculated spectral vector.
2. The apparatus according to claim 1 , wherein the Fourier transform module calculates the convolution-based fast Fourier transform based on a chirp z-transform of the series of acceleration measurement values.
3. The apparatus according to claim 1 , wherein the processing unit further comprises a noise filter module to remove noise from the calculated spectral vector.
4. The apparatus according to claim 3 , wherein the noise filter module is based on a low-pass filter.
5. The apparatus according to claim 3 , wherein the noise filter module is based on a first-order-filter.
6. The apparatus according to claim 3 , wherein the noise filter module is configured such that a current filter output value accumulates a preceding filter output value and a bit-shifted difference between the preceding filter output value and the current acceleration measurement signal.
7. The apparatus according to claim 6 , wherein the bit-shift is performed by an arithmetic shift in the direction of the least significant bit.
8. The apparatus according to claim 3 , wherein the noise filter module is based on the programming expression
y +=( x−y )>>bitshift;
wherein bitshift is a specfic positive integer value.
9. The apparatus according to claim 3 , wherein the noise filter module operates based on the formula expression
y ( n )= y ( n− 1)+( x ( n )− y ( n− 1))· b 0 .
10. The apparatus according to claim 1 , wherein the Fourier transform module calculates the spectral vector based on calculating an absolute value of the convolution-based fast Fourier transform of the series of acceleration measurement values.
11. The apparatus according to claim 1 , wherein the resonant frequency calculation module calculates the tower resonant frequency based on determining a maximum value of the spectral vector.
12. A method of determining a resonant frequency of a wind turbine tower, comprising:
receiving an acceleration measurement value, the acceleration measurement value representative of an acceleration of a wind turbine tower in the direction parallel to a rotor rotational axis and/or in the direction perpendicular to both the rotor rotational axis and the tower axis of the wind turbine;
selecting a series of acceleration measurement values;
calculating a spectral vector based on calculating a convolution-based fast Fourier transform of the series of acceleration measurement values; and
calculating the tower resonant frequency based on the calculated spectral vector.
13. The method according to claim 12 , wherein the calculating the convolution-based fast Fourier transform is based on calculating a chirp z-transform of the series of acceleration measurement values.
14. The method according to claim 12 , further comprising filtering noise from the calculated spectral vector.
15. The method according to claim 14 , wherein a current filter output value is accumulated from a preceding filter output value and a bit-shifted difference between the preceding filter output value and the current acceleration measurement signal.
16. The method according to claim 14 , wherein the noise filtering is configured based on the programming expression
y +=( x−y )>>bitshift;
wherein bitshift is a specfic positive integer value.
17. The method according to claim 14 , wherein the noise filtering is based on the formula expression
y ( n )= y ( n− 1)+( x ( n )− y ( n− 1))· b 0 .
18. The method according to claim 12 , wherein the calculating the spectral vector comprises calculating an absolute value of the convolution-based fast Fourier transform of the series of acceleration measurement values.
19. The method according to claim 12 , wherein the tower resonant frequency is calculated based on determining a maximum value of the spectral vector.