Method for the operation of a wind energy plant with voltage-dependent control of a reactive electric variable which is to be provided

1. A method for the operation of a wind energy plant in which a reactive electric variable (Q) reacts to voltage changes, the wind energy plant having a desired value of the grid voltage (U N ) and a real value of the grid voltage (U), comprising:

defining a first upper limit value of the grid voltage (U 1 ) and/or a first lower limit value of the grid voltage (U 3 );

adjusting the reactive electric variable (Q) when the real value of the grid voltage (U) exceeds the first upper limit value of the grid voltage (U 1 ), and/or falls below the first lower limit value of the grid voltage (U 3 ) such that the deviation of the real value of the grid voltage (U) from the desired value of the grid voltage (U N ) is counter-acted, characterised in that the desired value of the reactive electric variable (Q) is continuously increased or decreased further over time as long as the real value of the grid voltage (U) exceeds the first upper limit value of the grid voltage (U 1 ) or falls below the first lower limit value of the grid voltage (U 3 ).

2. The method according to claim 1 , characterised in that the first upper limit value of the grid voltage (U 1 ) is greater than or equal to the desired value of the grid voltage (U N ).

3. The method according to claim 1 , characterised in that the first lower limit value of the grid voltage (U 3 ) is smaller than or equal to the desired value of the grid voltage (U N ).

4. The method according to claim 1 , characterised in that the desired value of the reactive electric variable (Q) is increased or decreased until the desired value of the reactive electric variable (Q) has reached a maximum value (Q max ) or a minimum value (Q min ).

5. The method according to claim 1 , further comprising:

defining a second lower limit value of the grid voltage (U 2 ), the second lower limit value of the grid voltage (U 2 ) being smaller or equal to the first upper limit value of the grid voltage (U 1 );

continuously increasing or decreasing the desired value for the reactive electric variable (Q) when the real value of the grid voltage (U) falls below the second lower limit value of the grid voltage (U 2 ) until a first predetermined desired value for the reactive electric variable has been reached.

6. The method according to claim 1 , further comprising:

defining a second upper limit value of the grid voltage (U 4 ), the second upper limit value of the grid voltage (U 4 ) being greater or equal to the first lower limit value of the grid voltage (U 3 ),

continuously increasing or decreasing the desired value of the reactive electric variable (Q) when the real value of the grid voltage (U) exceeds the second upper limit value of the grid voltage (U 4 ) until a second predetermined desired value for the reactive electric variable has been reached.

7. The method according to claim 6 , characterised in that the first predetermined desired value for the reactive electric variable is equal to the second predetermined desired value for the reactive electric variable.

8. The method according to claim 7 , characterised in that the first and the second predetermined desired value for the reactive electric variable is zero.

9. The method according to claim 7 , characterised in that the first and the second predetermined desired value for the reactive electric variable is different from zero.

10. The method according to claim 1 , characterised in that when the real value of the grid voltage (U) falls below the first upper limit value of the grid voltage (U 1 ) again, and/or exceeds the first lower limit value of the grid voltage (U 3 ) again, the desired value for the reactive electric variable (Q) is set to a value which is constant over time.

11. The method according to claim 10 , characterised in that the value which is constant over time for the reactive electric variable (Q) is equal to the actual desired value of the reactive electric variable when exceeding the first lower limit value of the grid voltage (U 3 ) again or falling below the first upper limit value of the grid voltage (U 1 ) again, respectively.

12. The method according to claim 5 , characterised in that when the real value of the grid voltage (U) exceeds the second lower limit value of the grid voltage (U 2 ) again, and/or falls below the second upper limit value of the grid voltage (U 4 ) again, the desired value for the reactive electric variable is set to a value which is constant over time.

13. The method according to claim 12 , characterised in that the value which is constant over time for the reactive electric variable is equal to the actual desired value of the reactive electric variable when exceeding the second lower limit value of the grid voltage (U 2 ) again or falling below the second upper limit value of the grid voltage (U 4 ) again, respectively.

14. The method according to claim 5 , characterised in that the second lower limit value of the grid voltage (U 2 ) is greater or equal to the first lower limit value of the grid voltage (U 3 ).

15. A method according to claim 6 , characterized in that the second upper limit value of the grid voltage (U 4 ) is smaller or equal to the first upper limit value of the grid voltage (U 1 ).

16. The method according to claim 1 , characterised in that the reactive electric variable (Q) is a generated reactive power.

17. The method according to claim 1 , characterised in that the reactive electric variable (Q) is a generated reactive current.

18. The method according to claim 1 , characterised in that the reactive electric variable (Q) is the phase angle of a generated power.

19. The method according to claim 1 , characterised in that the reactive electric variable (Q) is a power factor of a generated power.

20. The method according to claim 1 , characterised in that the limit values of the grid voltage (U) are adjustable.