one basicly simple way to control blade angle i have seen on web site of french producer Eoltec
http://www.eoltec.com/English/Main_en.htm
if i get it properly, on every blade there is spring and small metal plate with weight at the end of it.
when turbine is turning on desired speeds, all is in balance. but, when stronger wind cause faster and faster turning, weight on the blade becomes stronger than spring and starts to "pull" out blade from basic attack angle to reduce rotation speed.
this picture is from their site, showing two blades and weights on them.
