Device and method of damping front and backward movements of a tower of a wind turbine

A device for damping front and backward movements of a tower of a wind turbine, wherein the wind turbine comprises the tower and a rotor, the rotor being mounted at the top of the tower to rotate about a rotational axis in which the front and backward movements of the tower occur, and the rotor has a plurality of blades, wherein each blade has at least one corresponding active add-on member which is actuated by a corresponding actuator to alter aerodynamic properties of the blade;

• wherein each add-on member is actuated by the corresponding actuator to alter the aerodynamic properties of the blade in a manner that the rotor is configured to damp the front and backward movements of the tower of the wind turbine,
• wherein the device further comprises:
• a measuring device configured to measure a time signal which represents a front and backward acceleration, velocity or position of the tower or a nacelle mounted to the tower;
• a filtering device configured to extract at least one frequency component by filtering the time signal;
• and
• a generating and supplying device configured to generate an actuating signal for each actuator based on the at least one extracted frequency component and to supply the actuating signals to the actuators to actuate the corresponding add-on member, and
• wherein the filtering device further comprises:
• an applying device configured to apply gains to obtain individual actuating signals for each actuator to act on the at least one frequency component, wherein the gains have variable values which are determined based on a sensitivity of the corresponding active add-on member at a certain operating point and which apply a damping only at a selected operating point.