A wind turbine is provided, having a wind turbine tower and at least one rotatable blade, and further comprising a system for measuring rotor blade vibration of said wind turbine. The system comprises at least one Doppler radar unit operatively configured to emit and receive radar signals, the radar unit being mounted on the wind turbine tower at a position above the lowest position of the at least one blade, the radar unit being positioned so as to measure reflections of an emitted radar signal from the turbine blade. A processing unit is configured to receive measurement data from the radar unit and to determine, by analysis of Doppler shift in received radar signals relative to transmitted signals due to movement of the blade towards or away from the turbine tower, the velocity of the blade in the direction towards or away from the turbine tower. Using a radar unit to measure blade velocity allows a determination to be made of the vibrations occurring in the blade without needing an internal sensor in the blade. This reduces manufacturing and maintenance costs of the blades since sensors in the blades will not need to be replaced, and sensors positioned on the tower are easier to replace in the field.

Method and blade monitoring system for monitoring bending moment of a wind turbine blade. The method comprises obtaining a first sensor set signal indicative of a first bending moment at a first sensor position different from the tip end along the longitudinal axis of the wind turbine blade, and estimating a bending moment at a first estimation position along the longitudinal axis based on the first sensor set signal, wherein the first sensor position is different from the first estimation position along the longitudinal axis. The blade monitoring system comprises a processing unit and an interface connected to the processing unit, the processing unit being configured for performing the method.

A method is provided for determining a deflection of a rotor blade of a wind turbine including the following steps: fixing at least one electrical conductor loop via fixing points to at least one surface of the rotor blade, wherein the at least one electrical conductor loop is arranged such that due to the deflection of the rotor blade an extension of the at least one conductor loop is forced between at least two of the fixing points, the extended electrical conductor loop keeps closed if the deflection of the rotor blade is below the defined threshold, the extended conductor loop opens if the deflection of the rotor blade is beyond the defined threshold. Further an arrangement, a sensor, a rotor blade and a wind turbine are also provided.

The present invention relates to a method for controlling a wind turbine comprising a pitch of one or more blades and collecting first data indicative of a dynamic condition of the first wind turbine blade and a rotor, the first data comprising rotor data and first deflection data, the rotor data indicative of the azimuth position and rotational velocity of the rotor in a rotor plane perpendicular to the rotor axis, and the first deflection data indicative of the position, speed and acceleration of one or more parts of the first wind turbine blade. The method comprises calculating an expected tower clearance distance at a later time of tower passage for the first blade based on the first data including acceleration of one or more parts of the first blade, and performing measures to prevent tower collision, if the expected tower clearance distance fulfills a collision risk criterion.

A method of calibrating a load measurement apparatus for measuring a load on a wind turbine blade on the basis of strain data based on strain of a wind turbine blade includes: a strain-data acquisition step of, during a startup of a wind turbine, obtaining a plurality of the strain data for each of a plurality of conditions among which at least one of an azimuth angle or a pitch angle of the wind turbine blade is different from one another; a theoretical load-value acquisition step of obtaining a theoretical load value applied to the wind turbine blade due to own weight of the wind turbine blade, for each of the plurality of conditions, on the basis of the azimuth angle and the pitch angle of the wind turbine blade in each of the plurality of conditions; and a calibration-parameter calculation step of calculating a calibration parameter representing a relationship between the strain data obtained by the load measurement apparatus and the load on the wind turbine blade, on the basis of a correlation between each of the strain data and the theoretical load value.

A load mitigation arrangement of a non-mounted rotor blade, includes at least one actuatable lift-modification device arranged on a surface of the rotor blade; a monitor configured to estimate the magnitudes of loads acting on the non-mounted rotor blade; a controller configured to actuate the lift-modification device on the basis of the estimated magnitudes to mitigate the loads acting on the non-mounted rotor blade. Further provided is a rotor blade assembly, and a method of performing load mitigation on a non-mounted rotor blade.

Method and blade monitoring system for monitoring bending moment of a wind turbine blade. The method comprises obtaining a first sensor set signal indicative of a first bending moment at a first sensor position different from the tip end along the longitudinal axis of the wind turbine blade, and estimating a bending moment at a first estimation position along the longitudinal axis based on the first sensor set signal, wherein the first sensor position is different from the first estimation position along the longitudinal axis. The blade monitoring system comprises a processing unit and an interface connected to the processing unit, the processing unit being configured for performing the method.

A method for controlling a wind turbine to decrease blade deflection during tower passage is disclosed. A blade flap moment of the wind turbine blades is measured. A blade flap moment of the wind turbine blades and a rotor tilt moment in a situation where the pitch offset has not been added are estimated, based on the measured blade flap moment. In the case that the estimated blade flap moment exceeds a first activation threshold value and the estimated rotor tilt moment exceeds a second activation threshold value, individual pitch angle adjustment of the wind turbine blades is initiated by adding a pitch offset, at azimuth angles within an azimuth adjustment region corresponding to tower passage of the wind turbine blades.

A method of determining a distance between a rotor blade tip and a tower of a wind turbine includes: estimating the distance based on a strain measurement; measuring the distance; correcting an estimation procedure based on the estimated distance and the measured distance; and deriving a corrected distance based on the corrected estimation procedure.

The present disclosure relates to methods for installing and uninstalling devices for reducing vibrations in wind turbines and to such devices. More particularly, the present disclosure relates to methods for installing and uninstalling devices for reducing vortex induced vibrations and stall induced vibrations when the wind turbine is parked, especially during wind turbine installation and/or maintenance, and to such devices. A method for installing a vibration mitigating device for mitigating wind turbine vibrations on a wind turbine blade of a parked wind turbine is provided. The method comprises moving the vibration mitigating device at least partially around the wind turbine blade using one or more drones; and securing the vibration mitigating device to the wind turbine. In some examples, the vibration mitigating device may be carried to the wind turbine blade using the one or more drones.