Hi,Finn is adding a forward time prediction to compensate for the delay of the IGBT turn on. That is a predictable and constant time. It does not affect theoretical stability or anything like that. It is just a nice way to get a reliable stable forward signal to time the
IGBT switching. It really can be done in many other ways too, but this method is easier. It has been tested and seems to work fine ;) http://www.youtube.com/watch?v=S533gY4R_QIThere is no black magic to forward predicting the switching time. We all know what we want it to do. But getting a reliable easy forward timing signal really is the Holy Grail. Finn's circuit does this very well and simply.
http://www.youtube.com/watch?v=n5tj601tTrIThe dynamic or varying current does not effect Finn's circuit to any great degree and it works fine. Even in an extreme case like an IGBT failure, it would still work fairly well! Sometimes, seemingly difficult problems really can be solved with just a little coil of wire and a pot ;)
Terry
Any time the current is changing dynamically the inductance also changes --- it pure physics and basic E.E., not smoke and mirrors. Dan McCauley addressed some of these concerns in his book on Modern DRSSTCs which he wrote about 3 years ago. You will see the light when you try it. Been there, done that, about 7 years ago. D.C. Cox
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