Method of and device for determining a common blade frequency of a rotor of a wind turbine, and method of operating a wind turbine

1. A method regarding a wind turbine, the method comprising:

determining a common blade frequency resulting from a common vibrational movement due to mutual interactions between members of a rotor in a wind turbine, the wind turbine comprising a tower, a nacelle, and a plurality of rotatable blades, each rotatable blade having a blade edge frequency;

measuring, using an accelerometer or a strain gauge, a vibration quantity indicative of a vibration of the tower or nacelle of the wind turbine,

wherein the determining of the common blade frequency is performed by way of signal processing in a frequency domain or in a time domain with a determining unit and a peak detector, wherein the common blade frequency is based on the measured vibration quantity, and wherein the determining of the common blade frequency comprises:

determining a respective frequency quantity indicative of a vibration of each of the plurality of rotatable blades, and

calculating an average of the determined respective frequency quantities of the plurality of rotatable blades, the calculated average indicative of the common blade frequency,

wherein the peak detector determines at least in part the common blade frequency by selecting a frequency value from blade edge frequency values whose associated frequency spectrum comprises a highest signal value in a region around the common blade frequency,

wherein the frequency spectrum of the vibration quantity comprises at least one peak corresponding to a vibration quantity having a maximum signal in a frequency range of the peak being equal to or approximating the common blade frequency, and

setting in a controller of the wind turbine an operational mode of the wind turbine based on the determined common blade frequency, the setting of the operational mode comprising at least one of setting the wind turbine in a shutdown mode, setting the wind turbine in a standby mode, and changing a rotor rotational speed.

2. The method according claim 1 , the method further comprising:

measuring a quantity representative of a rotational angle value of a rotational angle of the rotor,

wherein the determining of the common blade frequency is further based on the quantity representative of the rotational angle value.

3. The method according claim 2 ,

wherein the measuring of the quantity representative of the rotational angle value comprises measuring an azimuth angle value of an azimuth angle of at least one of the blades of the rotor, a rotor rotational speed value of a rotor rotational speed of the rotor, or a generator rotational speed value of a generator rotational speed of a generator attached to the blades.

4. The method according claim 1 , wherein the determining of the common blade frequency comprises multiplying the vibration quantity with a trigonometric function of a term related to a rotational angle quantity indicative of a rotational angle of the rotor.

5. The method according claim 1 , wherein the determining of the common blade frequency comprises performing a frequency analysis of the vibration quantity.

6. The method according claim 1 ,

wherein the determining of the common blade frequency comprises determining a frequency quantity representative of a common vibration of the plurality of blades.

7. The method according to claim 6 , wherein the measuring of the vibration quantity comprises measuring the vibration quantity in an idle mode of the wind turbine.

8. The method according claim 1 , wherein the measuring of the vibration quantity comprises measuring the vibration quantity during a time period, and wherein the determining of the common blade frequency comprises averaging vibration quantities at frequency quantities associated with a frequency quantity and a rotor rotational frequency of the rotor measured at a predefined rotational speed of the rotor.

9. The method according to claim 1 , wherein the common blade frequency is indicative of at least one of a mass distribution of at least one blade, and a shape of the at least one blade.

10. The method according claim 1 further including adapting an operational mode of the wind turbine based on the determined common blade frequency.

11. The method according claim 10 wherein the adapted operational mode comprises at least one of a shutdown mode, and a standby mode.

12. A system for a wind turbine, the system comprising:

a device for determining a common blade frequency resulting from a common vibrational movement due to mutual interactions between members of a rotor of a wind turbine, the wind turbine comprising a tower, a nacelle, and one or more rotating blades, the device comprising:

a measuring unit configured to measure a vibration quantity representative of a vibration of a component of the wind turbine;

a determining unit and a peak detector configured to determine the common blade frequency based on the measured vibration quantity,

wherein the determining unit is configured to determine a respective frequency quantity representative of a vibration of each of the plurality of rotatable blades, and is further configured to calculate an average of the determined respective frequency quantities of the plurality of rotatable blades, the calculated average indicative of the common blade frequency

wherein the peak detector at least in part determines the common blade frequency by selecting a frequency value from blade edge frequency values whose associated frequency spectrum comprises a highest signal value in a region around the common blade frequency,

wherein the frequency spectrum of the vibration quantity comprises at least one peak corresponding to a vibration quantity having a maximum signal in a frequency range of the peak being equal to or approximating the common blade frequency; and

a controller configured to set an operational mode of the wind turbine based on the determined common blade frequency, the operational mode of the wind turbine comprising at least one of a shutdown mode, a standby mode, and a change in a rotor rotational speed.

13. A method regarding a wind turbine, the method comprising:

determining a common blade frequency resulting from a common vibrational movement due to mutual interactions between members of a rotor in a wind turbine, the wind turbine comprising a tower, a nacelle, and a plurality of rotatable blades, each rotatable blade having a blade edge frequency;

wherein the determining of the common blade frequency is performed by way of signal processing in a frequency domain or in a time domain with a determining unit and a peak detector, wherein the determining of the common blade frequency comprises:

determining a respective frequency quantity indicative of a vibration of each of the plurality of rotatable blades, and

calculating an average of the determined respective frequency quantities of the plurality of rotatable blades, the calculated average indicative of the common blade frequency,

wherein the peak detector at least in part determines the common blade frequency by selecting a frequency value from blade edge frequency values whose associated frequency spectrum comprises a highest signal value in a region around the common blade frequency,

wherein the frequency spectrum of the vibration quantity comprises at least one peak corresponding to a vibration quantity having a maximum signal in a frequency range of the peak being equal to or approximating the common blade frequency, and

setting in a controller of the wind turbine an operational mode of the wind turbine based on the determined common blade frequency, the setting of the operational mode comprising at least one of setting the wind turbine in a shutdown mode, setting the wind turbine in a standby mode, and changing a rotor rotational speed.