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Methods for determining a yaw angle and a pitch angle cycle for a wind turbine are disclosed. The methods comprise measuring during a measuring time a wind speed and a wind direction at a plurality of measuring heights between the maximum and minimum height at the wind site, determining an average w

Methods for determining a yaw angle and a pitch angle cycle for a wind turbine are disclosed. The methods comprise measuring during a measuring time a wind speed and a wind direction at a plurality of measuring heights between the maximum and minimum height at the wind site, determining an average wind speed and an average wind direction for each of the measuring heights during the measuring time, and determining a wind speed distribution and wind direction distribution between the maximum height and the minimum height, and determining one or more yaw-pitch combinations of yaw angle and pitch angle cycles as a function of an azimuth position of a rotor blade that lead to a desired angle of attack along the rotor swept area. The present disclosure further relates to methods of operating a wind turbine and suitable wind turbines.

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1. A method of determining a yaw angle and a pitch angle cycle for a wind turbine located at a wind site, the wind turbine having a support structure,a nacelle rotatably mounted upon the support structure,a generator and a system for varying a torque of the generator,a rotor with a plurality of blad

1. A method of determining a yaw angle and a pitch angle cycle for a wind turbine located at a wind site, the wind turbine having a support structure,a nacelle rotatably mounted upon the support structure,a generator and a system for varying a torque of the generator,a rotor with a plurality of blades defining a rotor swept area between a maximum height and a minimum height, and operationally connected with the generator,a pitch mechanism for each of the blades for rotating the blades around their longitudinal axes, determining pitch angles for the blades and having a maximum pitch speed, anda yaw system for rotating the nacelle around a longitudinal axis of the tower,the method comprising: measuring during a measuring time a wind speed and a wind direction at a plurality of measuring heights between the maximum and minimum height at the wind site;determining an average wind speed and an average wind direction for each of the measuring heights during the measuring time;determining a wind speed distribution and wind direction distribution between the maximum height and the minimum height based on the average wind speed and average wind direction for each of the measuring heights and by assuming a wind speed distribution and wind direction distribution between the measured heights;determining a desired angle of attack cycle as a function of an azimuth position of a rotor blade along the rotor swept area for a representative portion of the blade based on the wind speed distribution;determining a yaw angle based on the wind direction distribution and taking into account the desired angle of attack cycle as a function of the azimuth position and the maximum pitch speed; anddetermining a pitch angle cycle as a function of the azimuth position of the rotor blade based on the desired angle of attack cycle and the determined yaw angle. 2. The method according to claim 1, wherein the desired angle of attack cycle, the yaw angle and the pitch angle cycle are determined online. 3. The method according to claim 1, wherein determining a desired angle of attack, a yaw angle and a pitch angle cycle are based on offline simulations. 4. The method according to claim 1, wherein the desired angle of attack cycle as a function of the azimuth position of the rotor blade along the rotor swept area for a representative portion of the blade is also based on the wind direction distribution. 5. The method according to claim 1, wherein determining the desired angle of attack cycle as a function of the azimuth position of the rotor blade along the rotor swept area comprises determining an angle of attack cycle that substantially maximizes energy yield. 6. The method according to claim 5, wherein the desired angle of attack cycle comprises maintaining the angle of attack substantially constant along the rotor swept area. 7. The method according to claim 1, wherein determining the desired angle of attack cycle as a function of the azimuth position of the rotor blade along the rotor swept area comprises determining an angle of attack that substantially minimizes a cyclic variation of loads over the rotor swept area. 8. The method according to claim 1, wherein the plurality of heights comprises at least three different heights. 9. The method according to claim 8, wherein the plurality of heights comprises a height of a hub of the wind turbine and further comprises a height corresponding to the height of the hub minus two thirds of a length of the blades, and a height corresponding to the height of the hub plus two thirds of the length of the blades. 10. The method according to claim 1, wherein measuring a wind speed and a wind direction at a plurality of measuring heights comprises measuring the wind speed and the wind direction using a LIDAR or anemometers. 11. The method according to claim 10, wherein the LIDAR and/or anemometers are positioned on a meteorological pole. 12. The method according to claim 10, wherein a measuring time for wind speed and wind direction is in a range from 1 minute up to and including 10 minutes. 13. The method according to claim 12, wherein the measuring time is in a range from 3 minutes up to and including 5 minutes. 14. The method according to claim 1, wherein the representative portion of each of the blades corresponds to the portion of each of the blades at approximately two thirds of the blade length. 15. The method according to claim 1, wherein assuming a wind speed distribution and wind direction distribution comprises representing the wind speed distribution and wind direction by a linear interpolation of the average wind speed and the average wind direction between each of the measuring heights. 16. The method according to claim 1, wherein assuming a wind speed distribution and wind direction distribution comprises representing the wind speed distribution and wind direction by a linear extrapolation of the average wind speed and average wind direction below a minimum measuring height and above a maximum measuring height. 17. A method of operating a wind turbine as a function of wind speed comprising: the method of determining a yaw angle and a pitch angle cycle according to claim 1; anddetermining a uniform pitch angle and a uniform generator torque for a theoretically uniform wind distribution;determining an instantaneous azimuth position for each of the blades;determining an instantaneous pitch angle for each of the blades by combining the uniform pitch angle with a pitch angle corresponding to the instantaneous azimuth position according to the selected pitch angle cycle;rotating the blades according to the instantaneous pitch angle for each of the blades;rotating the nacelle according to the selected yaw angle; andapplying the uniform generator torque. 18. The method of operating a wind turbine according to claim 17, wherein determining a uniform pitch angle and uniform generator torque for a theoretically uniform wind distribution comprises following a power curve describing an operation of the wind turbine as a function of wind speed;the power curve comprising a sub-nominal zone of operation for wind speeds below a nominal wind speed and a supra-nominal zone of operation for wind speeds above the nominal wind speed, and whereinin the sub-nominal zone of operation, the uniform blade pitch angle is substantially equal to zero, and wherein the uniform generator torque is varied,the sub-nominal zone of operation comprises a first operational range, a second operational range and a third operational range, whereinthe first operational range extends from a cut-in wind speed to a first wind speed, wherein the rotor speed is kept substantially constant at a first value,the second operational range extends from the first wind speed to a second wind speed, wherein both the rotor speed and uniform generator torque are varied as a function of wind speed, andthe third operational range extends from the second wind speed to the nominal wind speed, wherein the rotor speed is kept substantially constant at a second value, andthe supra-nominal zone comprises a fourth operational range in which an aerodynamic torque of the rotor is maintained substantially constant by varying the uniform pitch angle. 19. A method of determining a yaw angle and a pitch angle cycle for a wind turbine located at a wind site, the wind turbine having a support structure,a nacelle rotatably mounted upon the support structure,a generator and a system for varying a torque of the generator,a rotor with a plurality of blades defining a rotor swept area between a maximum height and a minimum height, and operationally connected with the generator,a pitch mechanism for each of the blades for rotating the blades around their longitudinal axes, determining pitch angles for the blades and having a maximum pitch speed, anda yaw system for rotating the nacelle around a longitudinal axis of the tower,the method comprising: measuring during a measuring time a wind speed and a wind direction at at least three measuring heights between the maximum and minimum height at the wind site;determining an average wind speed and an average wind direction for each of the measuring heights during the measuring time;determining a wind speed distribution and wind direction distribution between the maximum height and the minimum height based on the average wind speed and average wind direction for each of the measuring heights and linearly interpolating between the measuring heights;determining a desired angle of attack cycle as a function of an azimuth position of a rotor blade along the rotor swept area for a representative portion of the blade based on the wind speed distribution;determining a yaw angle based on the wind direction distribution and taking into account the desired angle of attack cycle as a function of the azimuth position and the maximum pitch speed; anddetermining a pitch angle cycle as a function of the azimuth position of the rotor blade based on the desired angle of attack cycle and the determined yaw angle. 20. A wind turbine comprising a support structure,a nacelle rotatably mounted upon the support structure,a generator and a system for varying a torque of the generator,a rotor with a plurality of blades defining a rotor swept area between a maximum height and a minimum height, and operationally connected with the generator,a pitch mechanism for each of the blades for rotating the blades around their longitudinal axes and determining pitch angles for the blades, anda yaw system for rotating the nacelle around a longitudinal axis of the tower,a wind speed measurement system for directly or indirectly measuring a representative wind speed,an azimuth measurement system for determining an azimuth angle for each of the rotor blades, anda local wind turbine control system configured to receive a yaw angle and a pitch angle cyclereceive the representative wind speed from the wind speed measurement system,receive the azimuth angles for each of the rotor blades,determine a uniform pitch angle and a uniform generator torque for the representative wind speed,determining an instantaneous pitch angle for each of the blades by summing the uniform pitch angle with a pitch angle corresponding to the instantaneous azimuth position according to the selected pitch angle cycle, andsend control signals to the yaw system, the pitch mechanisms and the system for varying the torque of the generator, such that blades are rotated according to the instantaneous pitch angles for each of the blades,the nacelle is rotated according to the selected yaw angle, andthe uniform generator torque is applied to the generator.