The lower curves are just what you were talking about adding series resistance to improve the performance when in stall. The bottom curve shows severe stall from 15 mph upwards. That is the low wind end as far as I am concerned. If I chose a much lower cut in then the stall would come in earlier.

I doubt that the thing would ever get out of that stall in any wind. By adding resistance you can extend the operation to a higher wind speed.

Although there is no obvious bad stall below 15mph, there is still some reduction of prop efficiency almost from cut in and you can see that with the converter there is increased output in the region below 15mph. That was what I meant when I said that the added resistance has little effect.

If any normal machine hits stall bad stall under 15mph then I would suggest that the cut in speed is too low. I think most people go for cut in speeds lower than necessary in the belief that it will help low wind results. Only on a very low wind site is this a benefit. The first step with stall is to try to increase cut in speed, if it high enough and you start to loose out in low winds then is the time to add resistance.

Raising cut in speed by increasing air gap is a useful dodge for fine tuning but it is not a good idea to deliberately aim for too low a cut in. It is better to raise cut in with less turns of thicker wire and keep efficiency up. If you have to compensate with added resistance at least the heat is not in the stator.

With the boost converter, stator heating is no longer a problem.