Pitch control strategy before the rated power for variable speed wind turbines at high altitudes

The wind turbines in the world's highest wind farm with an altitude of over 4 000 m in Naqu county of China were put into operation in 2014.Compared with the wind turbines at lower altitudes,the rated wind speed of these wind turbines are much larger,and the corresponding tip-speed ratio at the rated power reduces significantly due to the lower air density.Hence,the power coefficient at the point of the rated power is decreased to a rather low level.To improve the performance of the wind turbines at very high altitudes,this paper proposes a new pitch control strategy for variable speed wind turbines at the constant-speed phase,especially at the rated-speed phase before the rated power is reached.It is shown that the new pitch control strategy works very well for the wind farms at very high altitude and with low air density,with the catch of the wind energy enhaneed and the aerodynamic loads significantly reduced.