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The invention relates to a method of controlling a wind turbine having a rotor with pitchable wind turbine blades and a generator for producing power, where a pitch reference value for the wind turbine blades is determined, and an operational parameter representing a loading on the wind turbine roto

The invention relates to a method of controlling a wind turbine having a rotor with pitchable wind turbine blades and a generator for producing power, where a pitch reference value for the wind turbine blades is determined, and an operational parameter representing a loading on the wind turbine rotor exerted by the wind is measured at time intervals. A variation parameter reflecting a variation of the operational parameter over time is determined and used in the determination of a minimum pitch limit value of the pitch reference value. The wind turbine is then controlled according to the pitch reference value only if the pitch reference value is above or equal to the minimum pitch limit value, and otherwise according to the minimum pitch limit value. The invention further relates to a method of controlling the change in the operational parameter as measured in two successive time steps is determined and the turbine then being controlled according to a safety control strategy if the difference between the operational parameter change and the variation parameter is above a certain alert threshold. The invention further relates to a control system configured to perform the above control method, and a wind turbine comprising such system.

대표청구항 ▼

1. A method of controlling a wind turbine having a rotor with pitchable wind turbine blades and a generator for producing power, the method comprising: determining a pitch reference value for one or more of the pitchable wind turbine blades;measuring at time intervals at least one operational parame

1. A method of controlling a wind turbine having a rotor with pitchable wind turbine blades and a generator for producing power, the method comprising: determining a pitch reference value for one or more of the pitchable wind turbine blades;measuring at time intervals at least one operational parameter representing a loading on the rotor exerted by a wind;determining a variation parameter reflecting a variation of the at least one operational parameter over time;determining a minimum pitch limit value of the pitch reference value as a function of said variation parameter;controlling the wind turbine according to the pitch reference value only if the pitch reference value is greater than or equal to the minimum pitch limit value; andcontrolling the wind turbine according to the minimum pitch limit value if the pitch reference value is less than the minimum pitch limit value. 2. The method of claim 1, wherein the minimum pitch limit value reflects the minimum pitch for maintaining a thrust on the rotor less than or equal to a maximum allowable thrust level. 3. The method of claim 1, further comprising determining a power produced by a rotation of the rotor and a rotational speed of the rotor, and determining the minimum pitch limit value of the pitch reference value as a function of said power and said rotational speed of the rotor. 4. The method of claim 1, further comprising determining a maximum allowable thrust on the rotor as a function of the variation parameter, and determining said minimum pitch limit value of the pitch reference value as a function of said maximum allowable thrust. 5. The method of claim 4, further comprising determining a mean wind speed on the rotor, and determining the maximum allowable thrust as a function of said mean wind speed. 6. The method of claim 3, further comprising determining a maximum allowable thrust from predetermined look-up tables. 7. The method of claim 1, wherein measuring the at least one operational parameter comprises measuring loads on the one or more of the pitchable wind turbine blades. 8. The method of claim 1, wherein measuring the at least one operational parameter comprises measuring a sideways acceleration of the rotor, an axial acceleration of the rotor, and/or an angular acceleration of the rotor. 9. The method of claim 1, wherein measuring the at least one operational parameter comprises measuring a distance between one of the pitchable wind turbine blades and a wind turbine tower, an acceleration of the wind turbine tower or the nacelle, and/or a rotational speed of the generator or the rotor. 10. The method of claim 1, wherein the variation parameter is determined as a standard deviation of the at least one operational parameter. 11. The method of claim 1, wherein the variation parameter is determined by filtering the at least one operational parameter. 12. The method of claim 11, wherein the variation parameter is determined as a function of a difference between a fast and a slow low pass filtered operational parameter. 13. The method of claim 1, further comprising: determining a change in the at least one operational parameter as measured in two successive time steps; andoverruling the preceding control and controlling the wind turbine according to a safety control strategy if a difference between the at least one operational parameter change and said variation parameter is greater than an alert threshold. 14. The method of claim 13, wherein the safety control strategy comprises increasing the minimum pitch limit value. 15. The method of claim 2, wherein the safety control strategy comprises setting the maximum allowable thrust level to a pre-defined value. 16. The method of claim 13, wherein the alert threshold is a predefined constant. 17. A method of controlling a wind turbine having a rotor with pitchable wind turbine blades and a generator for producing power, the method comprising: determining a pitch reference value of one or more of the pitchable wind turbine blades;measuring at time intervals at least one operational parameter representing a loading on the wind turbine rotor exerted by a wind;determining the change in the at least one operational parameter as measured in two successive time steps;determining a variation parameter reflecting a variation of the at least one operational parameter over time;controlling the wind turbine according to the pitch reference value only if the difference between the at least one operational parameter change and said variation parameter is less than or equal to an alert threshold; andcontrolling the wind turbine according to a safety control strategy if a difference between the at least one operational parameter change and said variation parameter is greater than the alert threshold. 18. The method of claim 17, wherein the safety control strategy comprises increasing the pitch reference value. 19. The method of claim 17, wherein the safety control strategy comprises de-rating the wind turbine. 20. A method of controlling a wind turbine having a rotor with pitchable wind turbine blades and a generator for producing power, the method comprising: determining a pitch reference value for one or more of the pitchable wind turbine blades;measuring at time intervals at least one operational parameter representing a loading on the rotor exerted by a wind;determining a change in the at least one operational parameter as measured in two successive time steps;determining a variation parameter reflecting a variation of the at least one operational parameter over time;determining a minimum pitch limit value of the pitch reference value as a function of said variation parameter;controlling the wind turbine according to a safety control strategy if a difference between the at least one operational parameter change and said variation parameter is greater than or equal to an alert threshold;controlling the wind turbine according to the pitch reference value only if the difference between the at least one operational parameter change and said variation parameter is less than the alert threshold and the pitch reference value is greater than or equal to the minimum pitch limit value; andcontrolling the wind turbine according to the minimum pitch limit value if the difference between the at least one operational parameter change and said variation parameter is less than the alert threshold and the pitch reference value is less than the minimum pitch limit value. 21. A control system for a wind turbine configured to perform the steps of: determining a pitch reference value for one or more of the wind turbine blades;determining at least one operational parameter measured at time intervals and representing a loading on a wind turbine rotor exerted by a wind;determining a variation parameter reflecting a variation of the at least one operational parameter over time;determining a minimum pitch limit value of the pitch reference value as a function of said variation parameter;controlling the wind turbine according to the pitch reference value only if the pitch reference value is greater than or equal to the minimum pitch limit value; andcontrolling the wind turbine according to the minimum pitch limit value if the pitch reference value is less than the minimum pitch limit value. 22. A wind turbine, comprising: a rotor with pitchable wind turbine blades;a generator for producing power;a measuring unit placed in relation to the rotor and configured to measure at time intervals at least one operational parameter representing a loading on the rotor exerted by the wind; anda control system according to claim 21, comprising: a pitch controller for determining a pitch reference value for one or more of the wind turbine blades, anda processor for determining the at least one operational parameter as measured by the measuring unit, and for determining a variation parameter reflecting a variation of the at least one operational parameter over time, and for determining a minimum pitch limit value of the pitch reference value as a function of said variation parameter,wherein the pitch controller is further configured for controlling the wind turbine according to the pitch reference value only if the pitch reference value is greater than or equal to the minimum pitch limit value, and the pitch controller is further configured to control the wind turbine according to the minimum pitch limit value if the pitch reference value is less than the minimum pitch limit value.