Provided is a method of controlling a pitch angle of at least one blade of a wind turbine by use of a hydraulic system, the hydraulic system including at least one reservoir configured to store a hydraulic fluid, and at least one pump configured to supply the hydraulic fluid from the reservoir to at least one accumulator, if a hydraulic fluid pressure in the accumulator falls below a lower threshold value and till the hydraulic fluid pressure in the accumulator exceeds an upper threshold value. The accumulator is configured to store the pressurized hydraulic fluid supplied by the pump and to supply the pressurized hydraulic fluid to at least one pitch control cylinder of the hydraulic system via at least one output valve of the hydraulic system. The pressurized hydraulic fluid in the pitch control cylinder drives at least one piston to change the pitch angle of the blade.

Method of controlling a wind turbine comprising a rotor comprising at least a first blade, the method comprising the step of varying an induction factor of the first blade over time by dynamically changing a pitch angle of the first blade over time between a first pitch angle and a second pitch angle while the first blade is rotating, wherein the first pitch angle is different from the second pitch angle, and wherein the dynamic change of the pitch angle over time is controlled such that the respective rotational position of the first blade at which the first blade is at the first pitch angle and the respective rotational positions of the first blade at which the first blade is at the second pitch angle are displaced in time and the varying induction factor of the blade occur at different angular positions in the rotor plane over time, such that a location and/or direction of a wake formed downstream of the wind turbine is dynamically changing with respect to the rotor of the wind turbine.

A method of controlling a wind turbine is provided, comprising identifying an out-of-vertical load acting in a first direction on the wind turbine. A direction of a wind load acting on the wind turbine is determined. If there is a degree of alignment between the direction of the wind load and the first direction, the wind turbine is controlled to reduce the wind load.

Provided is a method of determining a control setting of at least one wind turbine of a wind park, the method including: determining a free-stream wind turbulence and deriving the control setting based on the free-stream wind turbulence, wherein the control setting includes a yawing offset, and wherein the yawing offset is derived to be the smaller, the higher the free-stream wind turbulence is.

A method for reducing extreme loads acting on a component of a wind turbine includes measuring, via one or more sensors, a plurality of operating parameters of the wind turbine. Further, the method includes predicting at least one blade moment of at least one rotor blade of the wind turbine based on the plurality of operating parameters. The method also includes predicting a load and an associated load angle of the at least one rotor blade as a function of the at least one blade moment. Moreover, the method includes predicting a pitch angle of the at least one rotor blade of the wind turbine. In addition, the method includes generating a load envelope for the component that comprises at least one load value for the pitch angle and the load angle. Thus, the method includes implementing a control action when the load is outside of the load envelope.

A method of controlling a wind turbine, wherein a minimum required hydraulic pressure represents a hydraulic pressure of at least one accumulator of the wind turbine which is required to pitch at least one blade of the wind turbine which is associated with the accumulator into a stop position of the wind turbine, and wherein a pitch angle represents a pitch angle of a normal of the at least one blade of the wind turbine relative to an incoming wind direction. The method includes (a) determining a minimum requirement function of the minimum required hydraulic pressure dependent on the pitch angle, (b) detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade, and (c) controlling the wind turbine such that the current hydraulic pressure is above the minimum required hydraulic pressure at the current pitch angle.

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.

The present invention relates to 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.

Embodiments herein describe a hydraulic pitch system where a velocity (e.g., the velocity of a hydraulic cylinder or the piston rod in the cylinder) is fed forward and combined with a setting outputted by a pitch controller. The velocity of the hydraulic cylinder is derived from the reference pitch angle or a continuous pitch signal (e.g., a cyclic pitch or ramp rate) in the control system. In either case, the velocity can be determined by monitoring the change in the reference pitch angle or the continuous pitch signal. Using a gain control, the velocity is converted into a position setting of the hydraulic pitch system (e.g., a spool setting in a valve) which is combined with another position setting generated by the pitch controller.

The invention is about a method for controlling a wind turbine with a variable rotor area. The wind turbine comprises a rotor with one or more rotor blades which are arranged hinged at an adjustable pivot angle, where the variable rotor area depends on the pivot angle, and where the pivot angle is adjustable dependent on a variable pivot force provided by a pivot actuator. The method comprises determination of a maximal pivot force based on the input operational parameter which relate to an actual load or a predicted load of the wind turbine, determining a desired pivot force based on a desired operational performance of the wind turbine, and determining a pivot force set-point to be applied to the pivot actuator based on the desired pivot force so that the pivot force set-point is equal to or below the maximal pivot force.