If you use a step up converter you would design your alternator to match the blade characteristics in high winds using less turns and thicker wire. This would give optimum efficiency in high winds and would reduce stator losses so that you could push it to a higher wind speed before limiting output.
As usual there is a snag, as you boost from lower volts the diode drops have a bigger effect on the alternator output. this may be a problem with a 12v system when you are boosting from 4 to 6 v where the diode drop is serious. It is not much of a problem with 24v systems and would be negligible with 48v.
You also have the converter efficiency reducing the available power in low winds so you will only get about 90% of what is left after the rectifier.
If done properly it is probably the best scheme for 24v machines and above but you can't just use any old boost converter, its output must be controlled to keep the prop tracking optimum tsr.
With any form of electronic overload control there is a risk of failure, with a 4 ft machine it is unlikely you would come to any harm if you lost load, it would be extremely noisy but would self limit its speed to a fairly safe value. I wouldn't risk it with any bigger prop.
You could retain furling, but bring it in in much higher winds or devise some sort of shut down mechanism such as turning the tail at right angles with a pull rope.
Large machines use tip air brakes but would be complicated for small machines and you may have trouble making them reliable. Disc brakes etc need to be over engineered to be sure of results and are complicated. I prefer to be able to turn the tail at right angles.
If you keep the electronics at ground level you can short the alternator as a brake but even this could fail if you have a cable or winding fault so for anything above 4 ft you still need a backup if it is run near habitation.
Flux
