A method for decreasing blade deflection during tower passage in a wind turbine

A control unit for controlling blade deflection during tower passage in a wind turbine, the control unit comprising:

• an input for receiving a measured blade flap moment of wind turbine blades of the wind turbine,
• a blade flap moment estimating module being adapted to estimate a blade flap moment of the wind turbine blades in a situation where a pitch offset has not been added, based on the measured blade flap moment,
• a rotor tilt moment estimating module being adapted to estimate a rotor tilt moment in a situation where a pitch offset has not been added, based on the measured blade flap moment,
• a comparing unit being adapted to compare the estimated blade flap moment to a first activation threshold value, and to compare the estimated rotor tilt moment to a second activation threshold value, and
• a control output adapted to provide an activation signal for initiating individual pitch angle adjustment of the wind turbine blades by adding a pitch offset, at azimuth angles within an adjustment region, the adjustment region including an azimuth position corresponding to tower passage of the wind turbine blades, in the case that the estimated blade flap moment exceeds the first activation threshold value and the estimated rotor tilt moment exceeds the second activation threshold value.

A wind turbine, comprising:

• a tower;
• a nacelle mounted rotatably on the tower;
• one or more pitchable wind turbine blades mounted rotatably on the nacelle via a hub, the wind turbine blades thereby performing azimuth rotations relative to the nacelle, along with the hub;
• and
• a control unit for controlling blade deflection during tower passage, the control unit comprising:
• an input for receiving a measured blade flap moment of wind turbine blades of the wind turbine;
• a blade flap moment estimating module being adapted to estimate a blade flap moment of the wind turbine blades in a situation where a pitch offset has not been added, based on the measured blade flap moment;
• a rotor tilt moment estimating module being adapted to estimate a rotor tilt moment in a situation where a pitch offset has not been added, based on the measured blade flap moment;
• a comparing unit being adapted to compare the estimated blade flap moment to a first activation threshold value, and to compare the estimated rotor tilt moment to a second activation threshold value;
• and
• a control output adapted to provide an activation signal for initiating individual pitch angle adjustment of the wind turbine blades by adding a pitch offset, at azimuth angles within an adjustment region, the adjustment region including an azimuth position corresponding to tower passage of the wind turbine blades, in the case that the estimated blade flap moment exceeds the first activation threshold value and the estimated rotor tilt moment exceeds the second activation threshold value.