The invention presents a method for operating a horizontal axis wind turbine, the wind turbine comprising a tower and a rotor with at least one rotor blade, the rotor being connected to the tower, and being adapted to drive a generator connected to a utility grid, wherein a pitch angle of each rotor blade is adjustable, the method comprising detecting, when the wind turbine is in an idling power producing situation in relation to the utility grid, a tower oscillation, and controlling, when the wind turbine is in the idling power producing situation, the pitch angle of the at least one rotor blade so as to produce aerodynamic forces counteracting the detected tower oscillation.

There is provided a method (40) of correcting blade pitch in a wind turbine (10) having a tower (12) and a plurality of rotor blades (18). The method (40) comprises: receiving (410) sensor output data from one or more wind turbine sensors (141), the sensor output data including data indicative of excitation of the tower (12) for a plurality of different pitch angles of a particular one of the blades (18); determining (420) a corrected pitch reference of the particular blade (18), the corrected pitch reference corresponding to a minimum tower excitation based on the received sensor output data; and, sending (430) the corrected pitch reference to a pitch actuator system (24) of the particular blade (18).

A method for controlling a wind power installation, wherein the wind power installation has an aerodynamic rotor with rotor blades that are individually adjustable in their blade angle and the rotor can be operated with a variable rotational rotor speed, and the wind power installation has a generator coupled to the aerodynamic rotor, for generating a generator output, comprising the steps of: individually adjusting each blade angle in a way corresponding to an individual setpoint blade angle, wherein each setpoint blade angle is made up of a common basic angle, which is specified for all of the rotor blades, and an individual compensatory angle, to allow for individual load torques, detecting in each case at least one load torque on each of the rotor blades, or a variable that is representative of this, wherein for each rotor blade considered, there is a preceding rotor blade and the setpoint blade angle of each rotor blade considered is determined in dependence on the at least one load torque of its preceding rotor blade.

Provided is a method for adjusting a pitch angle of a rotor blade connected to a rotor of a wind turbine, the method includes: pitching the rotor blade towards a target blade pitch angle, the manner of pitching depending on a load on a pitch bearing and/or an azimuthal position of the rotor.

The present invention relates to control of a wind turbine in a stop process in response to a rotor stop signal. The rotor stop process comprises the steps of prior to receipt of the rotor stop signal, generating a stored pitch angle signal by storing pitch angle signals for at least a fraction of a rotor revolution, and determining at least one periodic component of the stored signal. The rotor blades of the wind turbine are controlled towards a feathering position using a pitch control signal containing the at least one periodic component.

A system for measuring displacements of a blade root of a rotor blade of a wind turbine includes a hub, and a rotor blade coupled to the hub by a pitch bearing. The system further comprises a reference plane and at least one displacement sensor. The reference plane is configured to move with the rotor blade as the rotor blade moves relative to the hub while the displacement sensor is fixed to the hub and the displacement sensor is configured to detect a displacement of the reference plane relative to the hub without physical contact. Alternatively, the reference plane has a fixed position with respect to the hub while the displacement sensor is fixed to the rotor blade and the displacement sensor is configured to detect a displacement of the reference plane relative to the rotor blade without physical contact.

A blade pitch arrangement of a wind turbine is provided having a number of blade shafts extending radially outward from a hub and a rotor blade mounted around each blade shaft, which blade pitch arrangement includes a toothed ring arranged at the root end of each rotor blade; and a pitch drive unit for each rotor blade, having a driver body and a pinion realized to engage with the toothed ring of a rotor blade; wherein a pitch drive unit is arranged relative to its corresponding rotor blade such that the pinion is positioned closest to the hub, and the driver body extends in a direction radially outward from the hub. A wind turbine is also described.

A method for controlling a wind turbine is disclosed, the wind turbine comprising a set of wind turbine blades (1), each wind turbine blade (1) being provided with at least one air deflector (2) being movable between an activated position in which it protrudes from a surface of the wind turbine blade (1) and a de-activated position. The occurrence of an event causing a change in operational conditions is registered, and a new operating state for the wind turbine is determined, the new operating state meeting requirements of the changed operational conditions. The air deflectors (2) of the wind turbine blades (1) and pitch angles of the wind turbines blades (1) are controlled in order to reach the new operating state for the wind turbine, and in such a manner that the control of the pitch angles of the wind turbine blades (1) is performed while taking information regarding the control of the air deflectors (2) into account.

A method for rotating the rotor of a wind turbine, in particular in still air conditions. The rotor rotates about a rotor axis and comprises at least three rotor blades, each having a center of gravity located outside of the respective axes of rotation. To create an imbalance in the rotor, the blade pitch angle of a first rotor blade is systematically set to be different from the blade pitch angle of a second rotor blade in such a way that a gravitational torque about the rotor axis is generated as a result of the change in the position of the center of gravity of the first rotor blade. The invention also relates to a computer program product and a wind turbine, which are designed to carry out this method.

Control of a wind turbine in a stop process where a stop controller is used to pitch the blades at a number of pre-set pitch rates including a first pitch rate and a second pitch rate. The stop controller is arranged to access desired pitch angles of the stopping process and add an envelope band to the desired pitch angles. In the stop process, pitching at a selected pitch rate among the number of pre-set pitch rates is performed, and the pitch rate is changed according to criteria to keep the pitch value within the envelope band.