Method for operating a wind energy converter, control device for a wind energy converter, and wind energy converter

1. A method for operating a wind energy converter having

a variable-ratio gear system mechanically coupled between

a rotor and

a generator,

the variable-ratio gear system including

a first transmission unit coupled to a first shaft and

a second transmission unit coupled to a second shaft,

the method comprising:

adjusting the variable-ratio gear system to a first gear ratio at which the first shaft substantially does not rotate;

determining a wind speed or a related parameter;

detecting whether the wind speed or the related parameter has crossed a first threshold value in a first direction; and

adjusting the variable-ratio gear system, when the wind speed has crossed the first threshold value in the first direction, to a second gear ratio at which the second shaft substantially does not rotate.

2. The method of claim 1 , wherein the first and second transmission units comprise a first and a second hydraulic unit.

3. The method of claim 2 , wherein at least one of the first gear ratio and the second gear ratio corresponds to one of a minimum operational speed and a nominal maximum speed of the rotor.

4. The method of claim 2 , further comprising uncoupling the first shaft from the first hydraulic unit when the wind speed or the related parameter has crossed the first threshold value in the first direction.

5. The method of claim 4 , further comprising braking the first hydraulic unit when the wind speed or the related parameter has crossed the first threshold value in the first direction.

6. The method of claim 5 , further comprising adjusting a swivel angle of the first hydraulic unit to substantially stop a hydraulic flow through the first hydraulic unit.

7. The method of claim 4 , wherein the first and second hydraulic unit are connected by at least one hydraulic conduit, the method further comprising blocking the at least one hydraulic conduit when the wind speed or the related parameter has crossed the first threshold value in the first direction.

8. The method of claim 2 , further comprising:

detecting whether the wind speed or the related parameter has crossed a second threshold value in a direction opposite to the first direction; and

adjusting the variable-ratio gear system, when the wind speed or the related parameter has crossed the second threshold value in a direction opposite to the first direction, to the first gear ratio.

9. The method of claim 8 , further comprising uncoupling the second shaft from the second hydraulic unit when the wind speed or the related parameter has crossed the second threshold value in a direction opposite to the first direction.

10. The method of claim 9 , further comprising braking the second hydraulic unit when the wind speed or the related parameter has crossed the second threshold value in a direction opposite to the first direction.

11. A wind energy converter comprising:

a rotor;

a generator;

a variable-ratio gear system mechanically coupled between the rotor and the generator, the variable-ratio gear system including

a first transmission unit coupled to a first shaft and

a second transmission unit coupled to a second shaft;

a first control unit, which is arranged to adjust the variable-ratio gear system to a first gear ratio at which the first shaft substantially does not rotate;

a wind speed determiner, which is arranged to determine a wind speed or a related parameter;

a threshold detector, which is arranged to detect whether the wind speed or the related parameter has crossed a first threshold value in a first direction; and

a second control unit, which is arranged to adjust the variable-ratio gear system to a second gear ratio at which the second shaft substantially does not rotate, when the wind speed or the related parameter has crossed the first threshold value in the second direction.

12. The wind energy converter of claim 11 , wherein

the generator is a constant-speed generator, and

the variable-ratio gear system is configured such that at least one of the first gear ratio and the second gear ratio corresponds to one of a minimum operational speed and a nominal maximum speed of the rotor.

13. The wind energy converter of claim 11 , further comprising

a clutch for uncoupling the first shaft from the first transmission unit when the wind speed or the related parameter has crossed the first threshold value in the first direction.

14. The wind energy converter of claim 13 , wherein the clutch is a double clutch comprising

a first clutch position configured to couple the first shaft to the first transmission unit, and

a second clutch position configured to brake the first transmission unit.

15. The wind energy converter of claim 13 , further comprising

a brake for braking the first transmission unit when the wind speed or the related parameter has crossed the first threshold value in the first direction.

16. The wind energy converter of claim 15 , further comprising

a safety brake activator arranged to activate the brake in an event of the first or the second transmission unit becoming inoperational along with activating a bypass.

17. The wind energy converter of claim 13 , wherein the first and second transmission units comprise first and second hydraulic units.

18. The wind energy converter of claim 17 , further comprising:

at least one hydraulic conduit connecting the first and second hydraulic unit; and

a valve for blocking the at least one hydraulic conduit when the wind speed or the related parameter has crossed the first threshold value in the first direction.

19. The wind energy converter of claim 18 , further comprising a bypass that interconnects the at least one hydraulic conduit.