bob
I don't go back to the Old Board era but I did a diary entry called matching the load in which I covered virtually every method of load matching that I could think of. I concentrated most on using a boost converter at the low speed end because that was the scheme that I had tried and proved effective at that time. I did include the mixed diode/mosfet boost circuit.
Since then I have done some work on the buck converter approach starting at cut in volts and leaving the alternator volts rise with speed.
I can assure you that both schemes work effectively. The buck converter is better in that it is far less affected by line resistance, but if you have short low resistance lines there is not a lot to choose.
I don't have a site of my own so I have to do tests as and when I can at other peoples convenience( or perhaps inconvenience) so it doesn't give me the chance to get as much data as quickly as I would sometimes like.
I am not prepared to give results unless they have been measured under reasonable conditions and are likely to be fairly accurate. I had hoped by now to have more performance figures for the buck converter.
You may have seen this before, it was an early test I did on a 6ft machine under poor and turbulent wind conditions. The top end wind speeds were few and far between and the result is undoubtedly skewed in such a way as to make the high wind end come out low. It does at least show that the converter gains you power all the way up the wind speed range although the big improvement only starts to come at wind speeds beyond that test.
Recently the thing has been doing over 30A into a 24 v battery. Unfortunately I don't have wind measurements but they must be below 30mph as that was the highest gust figures from a local airfield located in better surroundings.
The top curve is with converter. Bottom is alternator direct to battery and the middle one is with some series resistance added to hold the prop out of stall ( usually done with a lower efficiency alternator direct).
Adding series resistance doesn't have much effect on the low wind end but does raise the high wind results by holding prop out of stall.
Whatever you do in the low wind region the prop curve is so flat that it can never effectively match the steep slope of a high efficiency alternator. The improvement in the lower winds from the converter is more due to matching the prop than alternator efficiency. The top end gains on both scores with the prop on design tsr and the electrical efficiency still over 70% including the alternator rectifier and converter.
Hope this goes part way to answering your question.
Flux
