Pitch Control

From Wind wiki

When a wind turbine is pitch-controlled, the power flow is regulated through the pitch angle of the blade. Pitch control generally provides users both positive and negative effects. Among the positive ones are good power control, flat-wise aerodynamic damping, loads reducing with wind speed, assisted start and built-in breaking. Its negative effects, on the other hand, include extra complexity, reduced reliability, and the expensive cost of pitch mechanism and control systems.

If power is well-controlled, it means that the mean value of the power output is kept close to the rated power of the generator at wind speeds from rated wind speed up to the shut-down wind speed.