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RE: OLTC update - primary IGBT loss
Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
At 11:08 AM 9/3/2002 -0700, you wrote:
>>Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>>Hi Bert, Paul, and All,
>>I checked it all out and the 3.8nH inductance and 0.4mOhm resistance of the
>>caps and it is just is not a factor at all. The leads are a concern but
>>there are ten in parallel and all that. However, I think I have "found"
>>some losses ;-))
>>I dropped two high voltage high bandwidth scope probes directly between the
>>CE leads of a center IGBT (on the leads, right up next to the plastic case)
>>and got this:
>>The red line is the CE voltage while the IGBT is on.
>That's an impressive bit of current to push through a PCB
>mountable package! Do you have 3 IGBTs in parallel here,
>as per the earlier sketch? How well do they share the
There are 10 IGBTs in the system. I have tested them to 700 amps "each"!!
So the whole thing could probably do 7000 amps. But they really only need
to do about 4500 amps when I go to 240VAC.
Here is the primary IGBT array:
Here is the single IGBT test:
>At 33kHz and 4500A pk that's a max dI/dt of about 940 A/uS.
>10nH will drop 9.4V at that speed, so a noticeable percentage
>your measured drops might be reactive, instead of purely
I do note that the Vce is about 90 degrees out of phase with the primary
voltage. The internal inductance of the emitter is speced at 13nH.
36500Hz and 450 amps gives a reactive voltage drop of... 1.34 volts. If
one can beleive the spec, I should hardly see that in the test I did (about
>It appears that the emitter voltage on the first scope trace
>starts out the pulse at 115 volts below ground? Or is this
>just a scope offset?
I was trying to differentially measure 10 volts out of 200VAC at 36500Hz
;-)) I was turning level knobs and all like crazy. Ignore any offsets.
>I was also wondering if the forward IGBT voltage drop and the
>reverse current drop due to the back diode are about the same?
>It's difficult to tell where zero is, on the math trace.
You can see it here:
The top glitches at about 6 volts is the IGBT Vdrop and the lower glitch at
about -5 volts (the scale in the chart is X10). The current is about 200
amps per IGBT. The reverse diode seems to work wonderfuly!