Lots of interesting points.
If you are in a good wind area then I tend to agree with your comments about low winds.
If wind is your only source of power then it is tempting to try and extract something on days with very low wind if they occur for a significant number of days but you are right the power available is very limited. With a 20 ft machine it makes reasonable sense to try and extract 100W or so if it occurs all day.
With smaller machines then it is a personal choice whether it is worth extracting 10W if it halves the machine output in a 20 mph wind.
Like me, you have grown up with machines that don't have the possibility of extracting power from those light winds and if you can get by without then you are very justified to adapt the machine to produce more efficiently in higher winds. The deciding factor eventually will probably whether you can actually use the higher output, the normal factor being fully charged batteries. If you plan your big loads for these times or want heat then ok.
If your main concern is reducing stator heating then again you do much better by steering clear of the very low cut in speed. If you furl at the same top end speed you can have less than 1/4 the stator heating.
If you keep stator heat down and you can solve the neo corrosion problem there is no reason why a machine shouldn't last many years .
Now having established that, anything you can do to still produce something in low winds is still worthwhile even though it may not be very efficient or elegant.
You can start simple and do something better later when you feel confident.
As you say, 2 slopes is a perfectly good enough approximation, the difficult bit being the low slope in low winds. Just used as a voltage changer, your converter will be very stiff and the slope will be near vertical and that is where you have trouble. Without electronic intervention low slope associated with low efficiency.
I tried a 2/1 tap change on a machine with just over an 8ft prop, the alternator was not desperately efficient so it would not be as bad a case as with your large alternator and efficient boost converter.
It held the blades fairly well stalled in the low wind setting but the speed did rise sufficiently to allow a speed sensor to change over to the high wind setting and it then speeded up and took over in high speed mode reasonably well.
The wind needed to drop to a very low speed to let it change back to the other mode and it was difficult to prevent it running unloaded for significant periods just at cut in for the high wind mode.
When it changed back there was a violent drop in speed with a sudden surge of current as the kinetic energy was dissipated and then it settled back into stall mode.
I am sure things could have been improved with a bit of resistance added in the low wind mode to reduce the slope and perhaps you could do the same to make something you consider good enough. I didn't carry on with trying to make it work as I already had far better ideas.
The state of charge of the battery does alter the optimum speed settings but probably not to the point that would make it unworkable. If you have a site with high wind days and low wind days then it may work fairly well. Conditions here are such that there are few occasions where the wind is sufficiently steady for it to want to be in one mode for long enough to be reasonably happy.
I am not sure if that converter could be run with external control of pwm, it seemed from the spec that it can at least be programmed for various inputs although you may not have direct access to the pwm.
The big problem is that there is no other application that needs a device to do this job and there is nothing readily available.
I can give you schematics to do the job but I am not in a position to do the layout and design work of the converter, these things are basically simple but are highly critical on layout and without an exact design to copy you may not have a lot of luck.
It is really a project for someone with a good grounding in power electronic converters.
I will have a look at a converter that I played with some months ago and see if it could be simplified to a form that could be copied.
You will find that with the fast winding and no converter you may pick up some power below 10 mph and although you will not be on peak production until about 12 mph, you should do quite well above 10mph.
A converter to handle the power from 6 to 10 mph should be fairly easy to manage.
If you were at 24V I think my test set up would do it, but the layout may need improving or higher voltage devices used to be sure of the higher voltage.
Flux
