Method and apparatus for controlling a wind turbine

1. A power system for a wind turbine, said power system comprising:

a measurement device configured to detect an overfrequency condition within an electrical system; and,

a controller communicatively coupled to said measurement device, said controller configured to switch the wind turbine between a power generation mode and a power consumption mode based on an existence of a detected overfrequency condition, wherein said controller is further configured to:

generate at least one of a negative torque command and a negative power command when the overfrequency condition is detected; and

generate at least one of a positive torque command and a positive power command when the overfrequency condition is not detected.

2. A power system in accordance with claim 1 , wherein said controller is further configured to switch the wind turbine from the power generation mode to the power consumption mode when the overfrequency condition is detected.

3. A power system in accordance with claim 1 , further comprising at least one blade, said controller being further configured to pitch said blade to a predefined position when the overfrequency condition is detected.

4. A power system in accordance with claim 3 , further comprising a generator communicatively coupled to said controller, said generator configured to use power from the electrical system to rotate said blade when the overfrequency condition is detected.

5. A power system in accordance with claim 4 , further comprising a four quadrant power converter coupled to said generator, said four quadrant power converter configured to rotate said generator and to brake said generator in both a clockwise direction and a counterclockwise direction, respectively.

6. A power system in accordance with claim 1 , wherein said measurement device comprises a current transformer coupled to the electrical system.

7. A wind turbine operatively coupled to an electrical system, said wind turbine comprising:

at least one blade;

a generator configured to be coupled to the electrical system;

a measurement device operatively coupled to the electrical system and configured to detect an overfrequency condition within the electrical system; and,

a controller communicatively coupled to said measurement device, said controller configured to switch said wind turbine between a power generation mode and a power consumption mode based on an existence of a detected overfrequency condition, wherein said generator is configured to consume power from the electrical system to rotate said blade when the overfrequency condition is detected.

8. A wind turbine in accordance with claim 7 , wherein said controller is further configured to switch said wind turbine from the power generation mode to the power consumption mode when the overfrequency condition is detected.

9. A wind turbine in accordance with claim 7 , wherein said controller is further configured to:

generate at least one of a negative torque command and a negative power command when the overfrequency condition is detected; and,

generate at least one of a positive torque command and a positive power command when the overfrequency condition is not detected.

10. A wind turbine in accordance with claim 7 , said controller being further configured to pitch said blade to a predefined position when the overfrequency condition is detected.

11. A wind turbine in accordance with claim 7 , further comprising a four quadrant power converter coupled to said generator, said four quadrant power converter configured to rotate said generator and to brake said generator in both a clockwise direction and a counterclockwise direction, respectively.

12. A wind turbine in accordance with claim 7 , wherein said measurement device comprises a current transformer coupled to the electric system.

13. A method for controlling a wind turbine, said method comprising:

coupling a generator to an electrical system;

detecting an overfrequency condition within the electrical system;

switching the generator between a power generation mode and a power consumption mode based on an existence of a detected overfrequency condition, wherein the generator is configured to consume power from the electrical system to rotate at least one blade when the overfrequency condition is detected.

14. A method in accordance with claim 13 , further comprising configuring a controller to switch the wind turbine from the power generation mode to the power consumption mode when the overfrequency condition is detected.

15. A method in accordance with claim 14 , further comprising configuring the controller to:

generate at least one of a negative torque command and a negative power command when the overfrequency condition is detected; and,

generate at least one of a positive torque command and a positive power command when the overfrequency condition is not detected.

16. A method in accordance with claim 13 , said method further comprising pitching the blade to a predefined position when the overfrequency condition is detected.

17. A method in accordance with claim 13 , further comprising:

coupling a four quadrant power converter to the generator; and,

configuring the four quadrant power converter to rotate the generator and to brake the generator in both a clockwise direction and a counterclockwise direction, respectively.