QCW questions

[Rafft]

David

I have placed all my electronics 'in a box' except for the dc-dc boost, 16v8 battery -> 330vdc. I have tried placing the C=23uF(4u7 5parallel mkp x2) on the inverter full-bridge side. It serves as the C from buck LC. Inductor is around 4inches(end to end) wire connection from inductor L -> full-bridge. And also serves as full-bridge snubber.

In my head, its 'calculated' as a snubber of single 4u7 only? Or as a whole ~23uF? Is it ok though this kind of arrangement? Though ive also soldered a single 4u7(same make/type) of the 5p placed underneath the board. Just making sure(?) I still have a proper 'snubber'  on the bridge.. So in total, C on bridge is 4u7 6p. With the single 4u7 wired (top of board)to be 'as close as possible to ecb(as snubber low lead inductance).

Added are some scope shots during phase lead tuning.
Yellow = bridge output
Magenta = Iprim

Single shot of Iprim, with ch1 probe physically detached from scope.it affects the other channel/s reading. Bottom shots show as 'tuned' , by getting a cleaner Iprim and not minding of 'spike' at bridge output

[davekni]

I have tried placing the C=23uF(4u7 5parallel mkp x2) on the inverter full-bridge side. It serves as the C from buck LC. Inductor is around 4inches(end to end) wire connection from inductor L -> full-bridge. And also serves as full-bridge snubber.

In my head, its 'calculated' as a snubber of single 4u7 only? Or as a whole ~23uF? Is it ok though this kind of arrangement? Though ive also soldered a single 4u7(same make/type) of the 5p placed underneath the board. Just making sure(?) I still have a proper 'snubber'  on the bridge.. So in total, C on bridge is 4u7 6p. With the single 4u7 wired (top of board)to be 'as close as possible to ecb(as snubber low lead inductance).

Presuming I understand correctly, this is ideal.  Wire inductance between inductor and caps is no issue at all.  Just adds a tiny bit to buck inductance.  BTW, I have ~20inches of wire from buck inductor to H-bridge on my new QCW experiment platform, with caps on H-bridge board.

I have tried placing the C=23uF(4u7 5parallel mkp x2) on the inverter full-bridge side. It serves as the C from buck LC. Inductor is around 4inches(end to end) wire connection from inductor L -> full-bridge. And also serves as full-bridge snubber.

In my head, its 'calculated' as a snubber of single 4u7 only? Or as a whole ~23uF? Is it ok though this kind of arrangement? Though ive also soldered a single 4u7(same make/type) of the 5p placed underneath the board. Just making sure(?) I still have a proper 'snubber'  on the bridge.. So in total, C on bridge is 4u7 6p. With the single 4u7 wired (top of board)to be 'as close as possible to ecb(as snubber low lead inductance).

All looks good.

[Rafft]

David

For reference I will use MBQ60T65PES

If I use IGBT internal diode(across CE), how do I determine its forward current? Can I safely assume x10 current to be its peak(qcw use)? Same as whats done/calculated on real fast diodes.

What do I look for in the datasheet?  Should I ask for more questions im not aware of?

Is this 'diode' affected by switching speed?

Pls take note IGBT gate=gnd.

[davekni]

For reference I will use MBQ60T65PES

Spec. sheet for this part looks great.  However, I don't see any in normal electronics distribution.  Haven't since I first heard of this part.  No evidence of this, but I'd guess that any parts you purchase are counterfeit.  So no way to know actual spec's.

If I use IGBT internal diode(across CE), how do I determine its forward current? Can I safely assume x10 current to be its peak(qcw use)? Same as whats done/calculated on real fast diodes.

IGBT diodes generally can't handle 10x current.  Look at spec peak current, but even that is usually for only 1ms, shorter than QCW.

Is this 'diode' affected by switching speed?

Yes, at least if you run buck inductor current in continuous mode, where current doesn't ramp all the way to 0 between pulses.  Most IGBT diodes will be fast enough.

[Rafft]

hi again

since I have switched into using (TOSLINK)fiber optic for INT(inverter) and pwm ramp(buck), I have finally acheived real isolation between int/ramp controller and inverter&buck.

my initial hardware had ramp gen GND connected to buck GND.using audio shielded wire. INTerrupt was isolated by PC817 opto only.

but I have also noticed something!

it has totally eliminated my previous "glitches" with Iprim.

BUT it has also become "less forgiving" at tuning part. like changing the MMC from 12.57nF to 9.8nF immediately showed something, whereas my -before GNDed- hardware config, those to MMC values showed little effect only(like shorter spark).

using 12.57nF result in early branching. going back 9.8nF resulted in straight sparks. it seems to "visualy" show that its more in-tune with later mmc value. scope shots below. with the "hump" (12.57nF), Vbus around 150v only. the cleaner Iprim is 220vdc(9.8nF).

any idea what that hump is?

im also planning to change my gapped-ferrite (LC buck) to powdered iron torroid. waiting for part to arrive.

edit:
those above scopeshots, was using MKP10 series-parallel connection. I also remember using CBB81 10s1p 9.6nF for mmc , and also got similar hump at around ramp-up portion. but 9.6nF(cbb81) and 9.8nF(mkp10) are close-enough values, but why no hump on mkp10? capacitor materials maybe?