Method for operating a wind farm and wind farm

1. A method for operating a wind farm, the method comprising:

determining a power setpoint for the wind farm;

determining a group curtailment setpoint for each of at east two groups of wind turbines, each of the at least two groups of wind turbines comprising at least one wind turbine of the wind farm, each of the wind turbines of the wind farm belonging to one of the at least two groups of wind turbines;

determining a power production value of each of the at least two groups of wind turbines;

determining for each of the at least two groups of wind turbines a power reference value using the respective group curtailment setpoint and the respective power production value;

determining for each of the at least two groups of wind turbines a group power setpoint which is proportional to the respective power reference values and determined as a product of the respective power reference value and the power setpoint divided by a sum of the power reference values; and

operating the at least two groups of wind turbines by using the respective group power setpoints to determine individual power setpoints for the wind turbines of the at least two groups of wind turbines, wherein each of the respective group power setpoints is related to each of the respective power reference values by a uniform proportion, and

wherein determining the group curtailment setpoint comprises at least one of considering a power demand of at least one energy trader for at least one of the at least two groups of wind turbines, relaxing at least one of a previously calculated group curtailment setpoint to allow an overproduction, or limiting a group power reduction in accordance with a group slew rate limit.

2. The method of claim 1 , wherein determining the power reference value comprises determining the minimum of the respective group curtailment setpoint and the respective power production value.

3. The method of claim 1 , wherein determining the power setpoint comprises at least one of receiving a power limit; and limiting a reduction of the power setpoint in accordance with a slew rate limit.

4. The method of claim 1 , wherein each of the group curtailment setpoints is in a range from zero to a rated power of the respective group of the at least two groups of wind turbines; and wherein relaxing at least one of the group curtailment setpoint comprises at least one of forming a sum of available group power production values; and comparing the sum with the power setpoint.

5. The method of claim 1 , further comprising dividing the wind farm into the at least two groups of wind turbines.

6. The method of claim 1 , wherein the group power setpoints are determined iteratively as a product of the respective power reference values and the power setpoint divided by a sum of power reference values determined in a previous iteration step.

7. The method of claim 1 , wherein the method is closed-loop controlled.

8. A method for curtailing a wind farm, the method comprising:

dividing the wind farm into at least two groups of wind turbines so that each of the at least two groups of wind turbines comprises at least one wind turbine, and that each of the wind turbines belongs to one of the at least two groups of wind turbines;

receiving a power setpoint for the wind farm Which is lower than a rated power of the wind farm;

receiving a set of curtailment setpoints comprising, a group curtailment setpoint for each of the at least two groups of wind turbines;

determining a power production value of each of the at least two groups of wind turbines;

determining for each of the at least two groups of wind turbines a power reference value using the respective group curtailment setpoint and the respective power production value;

determining an updated set of curtailment setpoints comprising relaxing at least one of the group curtailment setpoints to allow an overproduction of at least one of the at least two groups of wind turbines; using the updated set of curtailment setpoints for determining for each of the at least two groups of wind turbines a group power setpoint such that a sum of the group power setpoints substantially matches the power setpoint; and

operating the at least two groups of wind turbines by using the respective group power setpoints to determine individual power setpoints for the wind turbines of the at least two groups of wind turbines, wherein each of the respective group power setpoints is related to each of the respective power reference values by a uniform proportion.

9. The method of claim 8 , further comprising:

determining a power production value for each of the at least two groups of wind turbines,

wherein relaxing the at least one of the group curtailment setpoints comprises at least one of:

determining a sum of the power production values;

subtracting the sum of the power production values from the power setpoint to form a difference value; and

dividing the difference value by the rated power of the wind farm.

10. The method of claim 8 ,

wherein dividing the wind farm is performed in accordance with an ownership and/or with a contract with an energy trader.