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

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.

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.