Hi Nando,
I think I used non-standard terminology... when I wrote cut-in and cut-out, I meant for the booster circuit. Design parms are that the booster will turn on when the mill is making about 10 volts and 20 watts. Not sure what efficiency will be but I expect to be about .7 amps at 24 volts. I expect that alternator will be making about 175 watts when it makes 24 volts on it's own so that at the time the booster turns itself off, the output current is about 7 amps.
While using the coilcraft site, enter both different input voltages and different output currents that will give watts on a cubic curve between the two endpoints (like the blade will produce.) The results gives what I'll call a "nominal" PWM duty cycle along the curve. I expect that the maximum power point will be near those values but I won't hard-code them into the microcontroller, I'll use a search alogrithm to find them dynamically.
"Using Ton + Toff = T of the PWM frequency, get the time of one Hertz [...]"
fine, but
" L = Vin * dT / dI "
Considering that Vin and dI are determined by alternator and the wind, that leaves two variables (L and dT) in one equation... that isn't enough to generate a single number as "the answer." And considering that Vin and dI change with the wind, it appears that different L values are needed at different wind speeds.
As I understand the formula, the L value calculated is actually a minimum inductance required; higher values are okay so the higher inductor value calculated for the lower-power end of the curve will be more than enough for the higher-power end of the curve (and that's okay.) ... so a single L value is okay, it should be picked from the low end of the power curve, not the high end... but is has to be able to handle the amps at the the high end of the curve though it seems likely that if the wire doesn't melt, that even a derated inductor (due to high current) will still have enough inductance to work at the high end of the curve.
Flux uses about 500uH; that matches practically perfectly the results of the coilcraft app for low voltage in, low current out at 30KHz. IIRC, he got the core out of an old television. It's unlikely that I'll get that much inductance without winding a giant air core inductor. With what I've got, I can wind a high power inductor with about half that value. For less than cost of the wire I can buy a 100uH 10 amp inductor... so that's why (inductor requirements at the low end of the curve) I am asking about making up for a lack of inductance by raising the switching speed.
- Ed.