RE: OLTC update - primary IGBT loss

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Greg,

At 11:08 AM 9/3/2002 -0700, you wrote:
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>>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:
>>
>>         http://hot-streamer-dot-com/temp/OLTC09-02-03.gif
>>
>>The red line is the CE voltage while the IGBT is on.
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>Hi Terry,
>
>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
>current?

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:
http://hot-streamer-dot-com/temp/OLTC08-31-03.jpg
http://hot-streamer-dot-com/temp/OLTC08-31-04.jpg

Here is the single IGBT test:
http://hot-streamer-dot-com/temp/OLTC08-30-01.jpg
http://hot-streamer-dot-com/temp/OLTC08-30-02.gif


>
>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
>resistive.

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
0.6 volts).

>
>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:

http://hot-streamer-dot-com/temp/OLTC09-02-06.gif

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!

Cheers,

	Terry


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>-GL
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