Wind turbine rotor blade pitch control for tower fatigue reduction

A controller for a wind turbine having three rotor blades, the controller being for adjusting collective pitch of the three rotor blades, the controller being configured to:

• receive a sensor signal, from one or more sensors of the wind turbine, indicative of wind turbine rotor loading in a fore-aft direction;
• determine, based on the received sensor signal, a first component in the fore-aft direction, the first component including high frequency collective content, greater than 2P frequency content, from the received sensor signal;
• generate, based on the first component, a second component that is orthogonal to the first component;
• rotate the first and second components about a phase angle to obtain a first phase-shifted component and a second phase-shifted component;
• determine a collective pitch reference offset value for the three rotor blades based on the first phase-shifted component or the second phase-shifted component;
• and
• transmit a control signal to adjust pitch of the three rotor blades based on the determined collective pitch reference offset value.