Method of operating a wind turbine
Method of operating a wind turbine having a tower, a rotor with a plurality of blades arranged on the tower, one or more pitch systems for pitching the blades, a system for determining an instantaneous representative wind speed, and a system for determining a distance between a blade and the tower. The method comprises determining the instantaneous representative wind speed, and determining the distance between the tower and one of the blades when said blade is in the shadow of the tower. The method further comprises determining a tower distance pitch adjustment depending on the determined distance between the tower and the blade in the shadow of the tower and on the determined instantaneous representative wind speed. The method still further comprises the one or more pitch systems applying the determined tower distance pitch adjustment to at least the next blade to be in the shadow of the tower.
1. A method of operating a wind turbine having a tower, a nacelle, a rotor with a plurality of blades arranged on a rotor hub on the tower, one or more pitch systems for pitching the blades to a pitch angle, a system for determining an instantaneous representative wind speed, and a system for determining a distance between a blade and the tower;
the method comprising:
determining the instantaneous representative wind speed from a wind sensor mounted on the nacelle;
determining the distance between the tower and one of the blades when the blade is in front of the tower;
determining a tower distance pitch adjustment to pitch angle of the blades depending on the determined distance between the tower and the blade in front of the tower and on the determined instantaneous representative wind speed;
the one or more pitch systems applying the determined tower distance pitch adjustment to at least a next blade to be in front of the tower;
wherein the blades are rotatable relative to the rotor hub and the pitch angle of the blades is adjusted by rotating the rotor blade around a rotational pitch axis of the rotor blade relative to the rotor hub;
the step of determining the pitch adjustment comprising:
defining, a distance threshold as a percentage of a static distance between the tower and the blade in front of the tower, the distance threshold varying depending on the instantaneous representative wind speed;
at the determined instantaneous wind speed, when distance of the blade in front of the tower is determined to be less than the distance threshold, determining a magnitude of the pitch adjustment based on actual distance of the blade to the tower and the determined instantaneous wind speed.
2. The method according to claim 1 , wherein the distance threshold increases as the instantaneous representative wind speed increases, when the instantaneous representative wind speed is above a nominal wind speed.
3. The method according to claim 1 , wherein
when the distance between the tower and the blade in front of the tower is above the distance threshold, the pitch angle is a predefined pitch angle according to a conventional control strategy.
4. The method according to claim 1 , wherein the one or more pitch systems comprise a collective pitch system, and wherein the pitch adjustment is applied to all the blades of the wind turbine.
5. The method according to claim 1 , wherein the wind turbine comprises an individual pitch control for each blade, and wherein the pitch adjustment is only applied to the next blade of the wind turbine to be in front of the tower.
6. The method according to claim 1 , wherein the instantaneous representative wind speed is determined based on a wind speed measurement of a nacelle mounted anemometer.
7. The method according to claim 6 , wherein the wind speed measurement of the nacelle mounted anemometer is an average wind speed measured over a period of time.
8. The method according to claim 7 , wherein the period of time is between 1-5 seconds.
9. The method according to claim 1 , wherein the system for determining the distance between a blade and the tower comprises an emitter arranged on each blade and a receiver arranged on the tower; wherein each of the emitters and the receiver are arranged in such a way that, at least when any of the blades is in front of the tower, a distance between the emitter of the blade in front of the tower and the receiver can be inferred from a signal transmission between the emitter of the blade in front of the tower and the receiver.
10. The method according to claim 9 , wherein the tower's receiver is arranged at a given height with respect to the ground, and each blade's emitter is arranged in such a way that, when the blade is in front of the tower, the blade's emitter achieves a position at the substantially same height as the tower's receiver.
11. The method according to claim 9 , wherein each blade's emitter is arranged in a position closer to a tip of the blade than to the rotor hub.
12. The method according to claim 1 , wherein the system for determining the distance between a blade and the tower comprises a receiver arranged on each blade and an emitter arranged on the tower; wherein each of the receivers and the emitter are arranged in such a way that, at least when any of the blades is in front of the tower, a distance between the receiver of the blade in front of the tower and the emitter can be inferred from a signal transmission between the emitter and the receiver of the blade in front of the tower.
13. A wind turbine configured to perform the method according to claim 1 .