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Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
Insulation can actually make the problem worse - the E-field gets concentrated in the airgap (due to the dielectric constant of the insulation being significantly higher than air's 1) and the air gap is now smaller due to the insulation you just put there. My vote would be to start the primary a little further away.
Another thing to check, is the inner of the primary connected to one bridge output? The end of the primary with the capacitor connection has significantly higher voltages present on it.
Edit: forgot to ask, where about in NZ is this coil? Good to see a few more NZ coilers on here - I'm living in the UK right now but the stuff I built is still in Auckland; am looking forward to having a go at getting my QCW working when I'm back in August.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hydron wrote ...
Insulation can actually make the problem worse - the E-field gets concentrated in the airgap (due to the dielectric constant of the insulation being significantly higher than air's 1) and the air gap is now smaller due to the insulation you just put there. My vote would be to start the primary a little further away.
Another thing to check, is the inner of the primary connected to one bridge output? The end of the primary with the capacitor connection has significantly higher voltages present on it.
Edit: forgot to ask, where about in NZ is this coil? Good to see a few more NZ coilers on here - I'm living in the UK right now but the stuff I built is still in Auckland; am looking forward to having a go at getting my QCW working when I'm back in August.
Yes good question! I was going to ask the same thing. Im in Tauranga Orac12, send me a PM if you like to get in contact.
I am working on my first DRSSTC and i have no idea what problems i will encounter, i may come across the same issues no doubt, but we can at least exchange some information on what we both learn with our coils.
Registered Member #9879
Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37
The inner of the primary is connected to the MMC, so thats a good point. I will take some turns off the inner to give a bigger gap and connect it to the bridge output at the same time. Hopefully that should solve that problem.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
orac12 wrote ...
The inner of the primary is connected to the MMC, so thats a good point. I will take some turns off the inner to give a bigger gap and connect it to the bridge output at the same time. Hopefully that should solve that problem.
I'm in Hamilton.
OK, thats pretty handy to me. I have had no experience in tuning them either so i dont know what i will encounter when i fire mine up first go.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
You need to do a serious double check of your bridge. The fact that you have a negative going spike during the rectification period (when the IGBTs are not driven) means that it has nothing to do with your controller.
I would recommend posting a photo of the bridge. Folks here will be able to tell very quickly if you have something out of place.
You need to do a serious double check of your bridge. The fact that you have a negative going spike during the rectification period (when the IGBTs are not driven) means that it has nothing to do with your controller.
I would recommend posting a photo of the bridge. Folks here will be able to tell very quickly if you have something out of place.
That's right; also another point - it's hard to see from the current shots you have - could you zoom in into one of the transition points? You're having some quick transitions on the gate drive at each turn on. Initial guess could be that your IGBTs are turning on too slowly - what gate resistor are you using and which specific IGBTs? Otherwise the driver looks like it's doing just fine.
Registered Member #9879
Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37
Ok, I'm going to change the polarity of the primary and get some new scope shots. Those ones in the first post are a bit old now.
Just to be sure I'm doing the right thing ( and not getting different waveforms because I've done something different), how is everyone scoping their bridges? I have a x10 probe on the output of the bridge and a CT on the output connected to the primary coil.
The IGBT's are CM600HA-24H and using 4.7 ohm gate resistors.
Registered Member #57545
Joined: Wed Oct 21 2015, 01:28AM
Location:
Posts: 8
Big thing: It looks like you drop a half cycle in the control somehow. Your LC and drive seem out of phase, which will damp the oscillation...
A couple little things:
CM600's get pretty hot during operation. I would make sure your drive wires aren't sandwitched b/t them
It is also common to add a bias to the charge/discharge cycle on these to minimize shoot-through.
I have a CM600 face-mounting board that incorporates these (and nice connectors), our coil became more reliable when we replaced the deadbugs in that segment of our design.
Make sure you have read the application notes for the UD27, there are a couple components to adjust for the big brick IGBT's
Registered Member #9879
Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37
meawoppl wrote ...
Big thing: It looks like you drop a half cycle in the control somehow. Your LC and drive seem out of phase, which will damp the oscillation...
A couple little things:
CM600's get pretty hot during operation. I would make sure your drive wires aren't sandwitched b/t them
It is also common to add a bias to the charge/discharge cycle on these to minimize shoot-through.
I have a CM600 face-mounting board that incorporates these (and nice connectors), our coil became more reliable when we replaced the deadbugs in that segment of our design.
Make sure you have read the application notes for the UD27, there are a couple components to adjust for the big brick IGBT's
Where it has the gap / dropped half cycle, I believe that is where the drive has stopped / IGBT's are off and current is ringing back and forth? Thats why current is out of phase at that point?
The drive wires do go between them, but there is room and are not sandwiched tightly. Will keep an eye on it and make sure they don't get hot though.
What do you mean by bias on the charge / discharge cycle?
I have changed C33 to 2.2nF on the UD. Is there anything else that needs adjusting? I have gone over the notes multiple times, but its a lot to learn all at once and I may have missed something.
Registered Member #9879
Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37
OK, I have changed the polarity of the primary so that the MMC is connected to the outside of the primary and the bridge output connected to the inside, I also removed two turns from the side to give more room. I then retuned the primary to about 35kHz (slightly lower than secondary).
These scope shots were taken at 90VDC bus, 100uS on time. Scope probe connected across bridge output, current transformer on the bridge output to the outside of the primary. Still seem to be having large spikes, have tried a whole range of inductors and only seem to make it worse by winding the inductor all the way to the bottom and bottoming it out. Other than that, cannot seem to make it any better.
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DRSSTC Tuning, UD2.7C
