Method, park controller and program element for controlling a wind farm

1. A method for controlling a wind farm, the wind farm comprising a plurality of wind turbines, the method comprising:

determining the required power P R ;

determining fatigue load versus power curves for each of the plurality of wind turbines, and

based on the determined fatigue load versus power curves attributing different power settings P S,i to each of the wind turbines such that sum of the power settings P S,i of plurality of wind turbines is equal to the required power P R .

2. The method as set forth in claim 1 , further comprising for each of the plurality of wind turbines:

defining a mid power range P M,i comprising only one relative fatigue load maximum and wherein P A,i <P M,i <P B,I ;

defining a low power range P L,i ≦P A,i free of a relative fatigue load maximum;

defining a high power range P H,i ≧P B,i free of a relative fatigue load maximum; and

attributing the power settings such that P S,i ≠P M,i .

3. The method as set forth in claim 2 ,

wherein P A,i and/or P B,i correspond to relative or absolute fatigue load minima.

4. The method as set forth in claim 2 , further comprising for each of the plurality of wind turbines:

determining the current power settings P C,i , and

attributing new power settings P S,i such that |(P S,i −P C,i )/2|≦P A or |(P S,i −P C,i )/2|≧P B .

5. The method as set forth in claim 2 ,

wherein the low power ranges P L,i and/or mid power ranges P M,i and/or high power ranges P H,i are equal or different for all wind turbines.

6. The method as set forth in claim 2 ,

wherein at least some of the low power ranges P L,i for the plurality of wind turbines are different.

7. The method as set forth in claim 2 ,

wherein at least some of the high power ranges P H,i for the plurality of wind turbines are different.

8. The method as set forth in claim 2 ,

wherein determining fatigue load versus power curves comprises measuring wind turbine parameters.

9. The method as set forth in claim 2 ,

wherein determining fatigue load versus power curves comprises determining power versus pitch angle curves and fatigue load versus pitch angle curves.

10. The method as set forth in claim 2 ,

wherein attributing power settings to the wind turbine comprises attributing pitch angles to the wind turbines.

11. A park controller for controlling a wind farm, the wind farm comprising a plurality of wind turbines, the park controller comprising

a required power determination unit for determining the required power to be provided by the wind farm,

a fatigue load determination unit for determining the fatigue load versus power dependency of each wind turbine, and

an attribution unit for attributing different power settings to the wind turbines such that the sum of the power settings of all wind turbines is equal to the required power.

12. A program element for controlling a wind farm, the program element, when being executed by a data processer, is adapted for carrying out the method as set forth in claim 1 .