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Registered Member #2989
Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94
I can't see the under side of those caps but maybe Solder a copper strip on to them so it goes out towards the bus, then fold it 90Deg and use the bus bolt holes already there. So the caps will be in the same place but sit higher up.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hydron wrote ...
nzoomed wrote ...
Kizmo wrote ...
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Dont think this is even possible since both are connected internally and there is no connection possible.
Kizmo is 100% correct. On dual-IGBT bricks capacitor goes between C1 and E2, across the DC bus (skip the C2E1 connection that is one leg of the bridge output). On single IGBT bricks you need to connect the cap between the two bricks, across the DC bus connections (it ALWAYS goes across the DC bus).
edit: second set of scope shots look OK, I had similar questions when first starting to use CM300s:
Yes he is correct, i was on a different wavelength sorry. Here is a photo of my inverter ive just completed assembly of. Orac12, you can see how the snubbers should be fitted to a Dual IGBT module. I see yours are single modules?
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
orac12 wrote ...
nzoomed wrote ...
orac12 wrote ...
Yeah mine are single. Next one will use dual igbt module.
After re-reading the replies this morning it all makes a lot more sense and my original configuration was correct.
Now the snubber caps I have, I've made up of a series parallel string of 3x2 20uF 350VDC which gives 13.2 uF at 1050V.
Im not sure how having them in series will affect their performance but I suspect it will..
Should I be looking for something more suitable?
I would recommend the Aerovox RGPB series 2uf 1000v, thats what ive got on mine and they seem to be very popular amongst coil builders.
More reliable to have a single cap rates at a higher voltage than stringing several together, however if they are good quality caps it should be OK.
I was going with the general rule of thumb 1uF per 100A, so that means I would need multiple anyway..
OK, you may need more then possibly, i can see some 4uf on ebay but are only rated around 630v. You could put 2x 2uf in parallel each side of the bus and you would get 4UF, which should do the trick for you.
Registered Member #57545
Joined: Wed Oct 21 2015, 01:28AM
Location:
Posts: 8
In this link:
There is a weird "skip" where the 5th drive wave seems twice as long, then the whole thing is 1/2 cycle out of phase. It seemed strange to me, and possibly indicated some sort of control issue...
Registered Member #9879
Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37
meawoppl wrote ...
In this link:
There is a weird "skip" where the 5th drive wave seems twice as long, then the whole thing is 1/2 cycle out of phase. It seemed strange to me, and possibly indicated some sort of control issue...
I believe that is where the IGBT's are turned off, and the residual voltage in the MMC and such things rings back and forth through the free wheel diodes, hence it shows out of phase.
Thats how I believe it works, if anyone can explain it better than me then I'd be learning something.
Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
orac12 wrote ...
I was going with the general rule of thumb 1uF per 100A, so that means I would need multiple anyway..
I'd just go with what seems to work, if 2uF is enough to keep the ringing manageable then don't worry about stuffing more on there. Layout, inductance etc are probably far more critical than how much capacitance you have.
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