Asynchronous Generator Control

Wind turbines use asyn, generators . the rpm in a wind turbine can vary quite a bit. what I understand about
slip is it is very limited, that its ability to be flexible is only a few percent.
How exactly can the voltage be controlled outside of this limited range if the wind pushes quickly
and adds rpm to the turbine. ?? I know the blades can be pitched out, but I heard that blade pitch is only
used for extreme wind situations and mostly to completely cut out the turbine, like stop it.
Also, how do the cycles stay right ,60 ,while the generator poles are varying a little or more than a little??