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Re: Terry's DRSSTC - The Bridge...



Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Steve,

At 04:42 AM 12/10/2004, you wrote:
> Important thought!!!  If we run our DRSSTC at 120
Hz,  We can take
> advantage of the AC line high peak currents and
vastly reduce the size of
> the filter electrolytic caps...  Why do all
that "filtering" when we can
> just run resonate with the AC line too...

Well as I'm sure Dan McCauley will point out... the
caps are there to provide energy storage just like in
a photo flash gun. So they have to be able to give a
number of joules equal to your desired bang energy,
without the voltage dropping too much.

The peak current drawn by the inverter is so high that
I think you would be on a hiding to nothing trying to
draw it straight from the 120v line. Even in a small
DRSSTC you have peak powers of around 50kW. (the big
ones are 300+ kW) How much do you think the voltage
would sag if you plugged a 50kW load into an ordinary
120 volt outlet?

I could do it with as little as 470uF of bus caps. But the waveforms looked real ugly in modeling. While it would be "possible", it would create too much trouble and added EMI problems and sync issues to be of any use.



I like your "No GDT" approach and I hope it all works
well...

That allows one to "play" with the IGBT timing and one can do a lot of experimenting with different digital timings. It also gets rid of the issues of trying to make gate drive transformers behave in many different situations. Hopefully, this method will work with any smaller IGBT without fiddling.


I wonder if a common lamp dimmer controller would work in place of a variac for input voltage control? It would be nice to get rid of the variac too and it may not be too hard in this case to make the input control electronic too... It seems like it all wants to be in one universal "box" that could be hooked to a wide variety of coils and just work...

Cheers,

        Terry


Steve
C.