Controlling wind power plant with negative power capability to respond to grid frequency instability

1. A method of controlling a wind power plant, the wind power plant comprising a plurality of wind turbines and being connected to a power grid, the method comprising

detecting a grid frequency instability,

selecting a subset of wind turbines,

modifying a power reference for each wind turbine in the selected subset of wind turbines to respond to the grid frequency instability, and

applying the modified power references to the corresponding wind turbines in the selected subset of wind turbines,

wherein the detected frequency instability is an over frequency situation, and wherein modifying the power reference for each wind turbine in the selected subset of wind turbines comprises reducing the power reference for each wind turbine in the selected subset of wind turbines; and

wherein a second wind turbine in the selected subset of wind turbines is idling or standing still when the grid frequency instability is detected, and wherein the power reference for the second wind turbine is reduced to a negative value.

2. The method according to the claim 1 , wherein a first wind turbine in the selected subset of wind turbines is producing active power when the grid frequency instability is detected.

3. The method according to claim 1 , wherein reducing the power reference for each wind turbine in the selected subset of wind turbines is limited by a protective limit value.

4. The method according to claim 1 , further comprising

selecting a further subset of wind turbines, and

increasing internal power consumption in each wind turbine in the selected further subset of wind turbines by modifying state signals for each wind turbine in the selected further subset of wind turbines.

5. The method according to claim 4 , further comprising

increasing internal power consumption in each wind turbine in the selected further subset of wind turbines by increasing heating or cooling in each wind turbine in the selected further subset of wind turbine.

6. The method according to claim 1 , wherein selecting a subset of wind turbines is based on lifetime consumption and/or load considerations for each wind turbine in the wind power plant.

7. A wind power plant controller comprising a processing unit to perform a method comprising:

detecting a grid frequency instability,

selecting a subset of wind turbines from a plurality of wind turbines,

modifying a power reference for each wind turbine in the selected subset of wind turbines to respond to the grid frequency instability, and

applying the modified power references to the corresponding wind turbines in the selected subset of wind turbines,

wherein the detected frequency instability is an over frequency situation, and wherein modifying the power reference for each wind turbine in the selected subset of wind turbines comprises reducing the power reference for each wind turbine in the selected subset of wind turbines; and

wherein a second wind turbine in the selected subset of wind turbines is idling or standing still when the grid frequency instability is detected, and wherein the power reference for the second wind turbine is reduced to a negative value.

8. A wind power plant comprising a plurality of wind turbines, and a wind power plant controller according to claim 7 .

9. The wind power plant according to claim 8 , further comprising an energy storage for providing additional active power to the grid in case of an under frequency situation.

10. The wind power plant according to claim 8 , wherein each wind turbine of the plurality of wind turbines comprises an internal wind turbine controller adapted to perform at least a part of the control functions for the wind power plant.

11. The wind power plant controller according to claim 7 , wherein reducing the power reference for each wind turbine in the selected subset of wind turbines is limited by a protective limit value.

12. The wind power plant controller according to claim 7 , wherein selecting a subset of wind turbines is based on lifetime consumption and/or load considerations for each wind turbine in the wind power plant.

13. A computer program product comprising a non-transitory computer readable data carrier loaded with a computer program comprising computer executable instructions adapted to, when executed by a computer processor, perform a method comprising:

detecting a grid frequency instability,

selecting a subset of wind turbines,

modifying a power reference for each wind turbine in the selected subset of wind turbines to respond to the grid frequency instability, and

applying the modified power references to the corresponding wind turbines in the selected subset of wind turbines,

wherein the detected frequency instability is an over frequency situation, and wherein modifying the power reference for each wind turbine in the selected subset of wind turbines comprises reducing the power reference for each wind turbine in the selected subset of wind turbines; and

wherein a second wind turbine in the selected subset of wind turbines is idling or standing still when the grid frequency instability is detected, and wherein the power reference for the second wind turbine is reduced to a negative value.

14. The computer program product according to claim 13 , wherein reducing the power reference for each wind turbine in the selected subset of wind turbines is limited by a protective limit value.

15. The computer program product according to claim 13 , wherein selecting a subset of wind turbines is based on lifetime consumption and/or load considerations for each wind turbine in the wind power plant.

16. The computer program product according to claim 13 , wherein the computer program is for a wind power plant controller.