Method of controlling a wind turbine, and a wind turbine

1. A method of controlling a wind turbine having a blade and a controller to effect removal of foreign material from the blade, the method including:

detecting, using sensors mounted on the blade and communicatively coupled with the controller, a location of the foreign material that is adhered to the blade;

selecting, using the detected location of the foreign material, a resonance mode of a plurality of predefined resonance modes of the blade, wherein the selected resonance mode is greater than a first order resonance mode; and

exciting the blade to the selected resonance mode.

2. The method according to claim 1 , wherein selecting the resonance mode includes:

comparing the detected location of the foreign material with a plurality of locations corresponding to a plurality of resonance nodes of the blade under the plurality of predefined resonance modes.

3. The method according to claim 2 , wherein the resonance mode is selected based on one or more resonance nodes of the plurality of resonance nodes that are closest to the detected location of the foreign material.

4. The method according to claim 2 , wherein the foreign material is ice.

5. The method according to claim 1 , wherein selecting the resonance mode includes:

comparing the detected location of the foreign material with a plurality of positions of maximum displacement of the blade under the plurality of predefined resonance modes.

6. The method according to claim 5 , wherein the resonance mode is selected based on one or more positions of the plurality of positions that are closest to the detected location of the foreign material.

7. The method according to claim 5 , wherein the foreign material is dirt.

8. The method according to claim 1 , wherein selecting the resonance mode of the plurality of predefined resonance modes comprises selecting at least two resonance modes, and

wherein exciting the blade to the selected resonance mode comprises exciting the blade to the at least two selected resonance modes.

9. The method according to claim 8 , wherein the blade is excited to the selected resonance mode using a blade pitch system, and

wherein the blade pitch system is communicatively coupled with the controller and configured to rotate the blade around its axis at frequencies close to natural frequencies of the at least two selected resonance modes.

10. The method according to claim 1 , wherein exciting the blade to the selected resonance mode comprises:

when the detected location corresponds to one of a blade root, a blade tip, and a middle area of the blade, exciting the blade to a second order resonance mode; and

when the detected location indicates that an extent of the foreign material corresponds to at least a predetermined portion of the blade, exciting the blade to a fourth or higher order resonance mode.

11. The method according to claim 1 , wherein the plurality of predefined resonance modes includes at least one of flapwise, edgewise, or torsional resonance.

12. The method according to claim 1 , wherein the blade is excited to the selected resonance mode using a blade pitch system, wherein the blade pitch system is configured to rotate the blade around its axis and is communicatively coupled to the controller.

13. The method according to claim 12 , wherein exciting the blade to the selected resonance mode comprises:

pitching, using the blade pitch system, the blade around its axis at or near a natural frequency of the selected resonance mode for a first period of time,

pausing the pitching for a second period of time, and

repeating the pitching and pausing.

14. The method according to claim 1 , wherein the blade is excited to the selected resonance mode using one or more external exciters communicatively coupled with the controller, and

wherein the one or more external exciters are one of attached onto the blade or independent of the blade.

15. The method according to claim 1 , wherein the sensors are optical sensors.

16. The method according to claim 1 , wherein the controller stores data related to a plurality of resonance nodes of the blade.

17. A wind turbine, including:

at least one blade having sensors mounted thereon, the sensors configured to detect at least one location of foreign material that is adhered to the at least one blade;

a blade pitch system configured to rotate the at least one blade around its axis; and

a controller communicatively coupled to the blade pitch system and to the sensors, wherein the controller is operable to:

select, using the detected at least one location of the foreign material, one or more resonance modes of a plurality of predefined resonance modes of the blade, wherein the one or more resonance modes are greater than a first order resonance mode; and

control the blade pitch system to excite the blade to the selected one or more resonance modes.

18. The wind turbine according to claim 17 , wherein the controller stores data related to a plurality of locations of a plurality of resonance nodes of the blade, and wherein the controller is further operable to:

compare the detected at least one location of the foreign material with the plurality of locations of the plurality of resonance nodes of the blade, and

select the one or more resonance modes based on the comparison of the plurality of locations with the detected location of the foreign material.

19. The wind turbine according to claim 17 , wherein the sensors are arranged along a span of the at least one blade.