The snubber of this thread title was described by:
Domb, Redl and Sokal,
"Nondissipative turn-off snubber alleviates switching power dissipation, second-breakdown stress and VCE overshoot: Analysis, design procedure and experimental verification"
Published 1982
Paywalled by IEEE, not a member, I might try to get a copy through Engineers Australia
The latest converter project here is mostly completed and running. it is a converter from 32V DC link to 14V 20Amp part of the 85 A.h. DC Ups for ham radio gear.
The converter presently has what I call "floating" snubber.
Here is qucs showing the "floating" snubbers. They do return part of the energy to the DC link, and they only dissipate about 2 Watt in this converter.
https://app.box.com/s/2orjo7boyqa74c0siq88yy8ydzspus4i"Floating" Snubbers only conduct when the collector voltage is > 2 * 36V
So they do not reduce the off dv/dt which is set by the IGBTs.
Here is the spectrum today of the converter with "floating" snubbers running at 7.9 Amp output.
Measuring on the DC(+12V) output bus via a pad: Level is about -88dBm to the pad,from 2 to 20 MHz
marker at 18 MHz. (Note this spectrum is using snubbbers different from subject of this thread !)
https://app.box.com/s/vtljdvw7wqwh1odq3h1zqvxo0m695j9g----------------------------
Thanks Tim for your post #11,
I will continue with that in qucs with R being of the transformer and the ESR of the DC Link capacitor.
Here is qucs circuit for the "Domb" snubbers that are subject of this thread:
https://app.box.com/s/vw2jfnoy2ejb40ch5be32pc9va1fc8nbI am presently having difficulty (long solving time, instability) with the transient solver due to snubber di/dt .
Time steps are down to 5 ns but using the whole inverter circuit, it take 600 us for the start transients to die out sufficiently to zoom in on snubber.
Also note that I have added Miller capacitors to the IGBTs to slow down the voltage rise time.
That is for qucs solution and I might try it on next real converter too.