What has the frequency got to do with any of this?,(reply>), Power electronics is an entire discipline of electrical engineering. They have applications in energy transmission, you can find inverters or rectifiers rated at several MW. <br>You can google more information about the power MOSFET or the IGBT, to basic semiconductors used in such systems.,(reply>), @*****   Thanks very much.  I didn't mean to suggest that brushless is bad, I agree with you that it can be great for both motors and generators, I was having trouble getting my head around just how big a diode (or 4) and capacitor(s) you need to do the conversion from ac to dc at such a high power level, and I've come across material speaking of slip rings, which are basically brushes to me (sliding contacts).  Forgive me, my experience is with low power electronics and the power levels involved here are about 100,000 times higher than anything that I actually know about.  Thanks again for the info.,(reply>), Let me say that you could run them synchronously, it is possible and not hard, with just pure electrical controls (even without blade or transmission adjustments), but it doesn't happen. Why? Don't know. Probably it is not the most efficient or cheap way, and that is all that matters.,(reply>), Hi, so most wind generators, and even some recent hydro generators don't run synchronously. They have AC generators ('cause DC motors are not a natural thing), then they electronically rectify to a DC bus and finally oscillate to grid frequency .  With this systems you have a big range of speeds in which you can run your generator, and the electronics efficiency is actually very good. I don't see what are you thinking about Brushless. Brushless generators "must" have magnets and you don't really use big brushless motors. Brushless motors are great! Just not for this. Answering your formal question: No. You never feather blades except if the wind speed is over your maximum allowed speed.,(reply>), +Nuno Gonçalves     Hi Nuno!  You seem to know about this.  I'm struggling, and perhaps you'll be kind enough to help.   Some turbines were installed here two years ago and friends said "you have a degree in physics, explain".   I said "give me a while with google...".   It seems to me that the biggest problems are phase synch and coping with 5 MW power levels if there are any brushes or semiconductors involved. Best to go brushless, best to avoid semiconductor AC/DC/AC conversion.  So I assumed rapid blade feathering and hydraulic continuously variable "gear" boxes.  A bit of googling suggests I'm wrong!   I get your point about phase synching of closely matched oscillators, it just happens automaticaly, I agree.  Sorry, my comment contains a lot of implicit questions, but I'll finish with one that I haven't seen the answer to: is blade feathering only used to protect the machine in high winds or is it twitched by the feedback loop for frequency/phase synch?