To prevent wind turbines from overloading and to ensure that they have constant output, part of the power has to be throttled when the wind velocity exceeds nominal wind velocity. The following two principles are the most commonly used methods of controlling power output:
· Stall control (aerodynamic turbulence): if the wind velocity exceeds a certain limit, the rotor blades are designed to cause a turbulence at the edge of the blade to limit speed. In active stall control, the pitch of the rotor blades can also be changed.
· Pitch control: Electronics and hydraulics are used to infinitely adjust the pitch of each blade. This reduces the lift, so that the rotor continues to generate power at nominal capacity even at high wind speeds.