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Old 07-08-2016, 10:46 PM   #2792 (permalink)
e*clipse
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Thanks a bunch Paul - no worries about my troubles; this is the world of R&D

Yes, I was concerned about the out of phase (not 165 degrees out of phase, 165degrees instead of 180degrees) so, the problem was about 30 or 35 degrees. Still that could be the problem, and I couldn't figure out how to fix it; I tried adding some delays to the code or reversing the order of the switching, but that didn't help. One of the main issues may be the high frequency, and that any delay ends up being too much.

Also - regarding that DC bias in the driver & filter - can you see where hooking a 'scope across the output of the IXDN604 or possibly the "output" of the transformer could cause enough DC bias to fry things?

One possible solution might be to use one pin from the DSPIC to drive a pair of logic gates. They might put out little or no delay if the right combo of buffers and inverters were used. One thing I like about using the heartbeat circuit or some pin from the pic to drive the power supply for the driver circuit is that power will shut off if the the DSPIC latches up for some reason.

I also noticed what seemed like too much heat from the IXDN604's and the 5V regulator. During the successful part of the testing, I wasn't driving any IGBT's, so there shouldn't have been any significant current flow through the IXDN604's or the transformers.

That issue about the FOD8316 is very interesting. Was this causing any latch up or similar issues with the inverter that used it? When I connected and started switching the PWM circuits (at about 5kHz) For the tests, one part was always off, while I adjusted the pulse width of the second. I wasn't able to see any output of the circuit using my 'scope. There was nothing except the scope probes connected across the outputs of the driver circuit.

I'm also very interested in your new driver design; especially that they are all on the top. The current design is a bit "thick" considering the transformers on top and bottom. Also anything to build in some robustness would be good; Somehow it has to be robust enough to survive my experiments but also eventually run an EV.

Thanks again for your help - I'll look into the timing & FOD8316 pins.

-e*clipse


Quote:
Originally Posted by MPaulHolmes View Post
One possible guess is with the 165degree out of phase, it could get a DC bias going in the line filter, and maybe the line filter saturates, which would drastically reduce the inductance and makes the current coming from the driver too high. I moved to the ixdn604si that is surface mount, and has a metal tab on the underside for removing heat. I was noticing that the "no heat tab" version would get hot the touch (but not freakishly hot), but still worked. Hearing your results makes me think that there is too little headroom for that driver chip. But with the metal tab, they stay cool even switching 1200v 600amp IGBTs (I tested it over the last couple weeks on a grid tie). I'll be doing new driver boards that are all on the top side. They also use cheaper 10uF 1206 caps rather than the big fat 1210 caps.

Another issue I discovered about a week ago is, the FOD8316 pin 8 is sometimes NOT connected internally to ground, even though the datasheet says it is. So, I had to add a connection to ground from pin 8 (it allows turning on the LED inside) on the 3 phase grid tie board I recently did. I'm going to get new driver boards made. I'm very sorry it's causing you so much trouble.
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