One needs to realized that the frequency capability ( response) of a transformer depends on the winding inductances and the core capabilities and losses at high frequencies.

So for 50/ 60 Hz the operating frequency may range from 40 to 800 HZ (at the designed input voltages).

If the input voltage is lower at lower frequencies, then the transformer may work well --the winding inductance has to be taken in consideration as well.

There are simple ways to use a regular transformer with a wind mill to vary the generator voltage as needed, using the 50/60 HZ transformers.

One is to isolate the DC resistance of the transformer to allow the wind mill to start rotating -- a large AC capacitor in series with the transformer inputs with a simple relay scheme to short circuit when the capacitor at certain generator voltage or frequency.

Enough for now

Ferrite is totally unsuited to this low frequency and would make them several times bigger.

The idea looks attractive but has many snags. If the transformers are reasonably efficient the power will rise rapidly and cause stall so you need to keep them inefficient. You then have a lot of wasted power in normal running which you have to live with or switch the transformers out when the main bridge is conducting. This makes it virtually a star delta scheme and needs a speed switch.

The result is an almost identical scheme to star delta with expensive transformers included.

I think that with the proper care and attention to detail,  and a little extra thought, you may well get this to a stage of complication that will have nasa scratching their heads.

Whilst the scheme would work, I can't help but feel that you have managed to introduce so many extra parts so as to make a simple mill, over complex and lossy.

It would be simpler to build a new stator..... or if you want to get serious, then do what Flux suggested in  "matching the load". By the simple use of the booster, you can wind the stator to 1/4th the R of the usual design .... 1/2 the turns, twice the sq mm. V squared /R gives you tons more power handling at the higher power levels with no loss devices in the way. At low power, the boost provides the lift, and mostly at 85-95%. The capacitors and transformers will likely be well under this, as the low frequencies will inhibit good transformer and cap characteristics. In fact you are relying on these losses to stop stall, so it cant be efficient , right where you need to harvest the most power from the least resources.

I'm sure you can make the transformer idea to work, but I doubt you will get near the efficiency of Flux's proposition, nor the bullet proof high power part of the equation.... where no parts are used between the alt and the recs.

It is fun to reinvent the wheel, and I'm guilty as hell, but in the end, simple is best.

I've proven that even a dill can design and build the booster in a day that will easily handle the lower speed power, so it's not wish-ware or vapour ware, it is doable and not that hard....... and even if it blows to bits, you still get power at medium and upper windspeeds while you fix it..... ever the optimist.

Just my thoughts on this one

...............oztules

I'm in very much agreement with the above.

With small permanent magnet axial flux alternators it is OK to use them without any kind of control system as battery chargers even with 50% efficiency.

But we have already seen that when the power of the alternator is reaching a few kilowatts, the heat in the coils is becoming a big problem. If your generator's output is 2 kW and the efficiency is only 50% there is 2 kW heat power heating the coils and the stator. It won't work well in the longer run.

I'm thinking that transformers and simple relays are one of the best technologies for home made systems. I don't like so much electronics with transistors, zener diodes etc. You can't make such things by yourself at home. Transformers you can make.