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DRSSTC Tuning, UD2.7C

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orac12

Thu Apr 28 2016, 08:20AM

Registered Member #9879 Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37

Kepp forgetting to convert images from .bmp ....

Closer up shot.. I tuned the inductor so current crossed as close to zero as possible, this minimised spikes in the current and you can hear a noticeable increase in noise from the breakout point (gets louder)

20a6t1e

Blackcurrant

Thu Apr 28 2016, 10:06PM

Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94

Have you had a look at the gate drive waveform? (careful with the scope ground lead)
It took me some time to optimize the GDT
A small gate resister may drive it too fast and ring
maybe try an ohm or two more see if the ringing goes down
also keep the GDT twisted wires all the way up, minimize leakage inductance.

I take it those black things are snubber caps across the bridge

One thing I would tune the coils at the same frequency to start with, then fine tune (shift pri res lower) after it was running ok

orac12

Thu Apr 28 2016, 10:25PM

Registered Member #9879 Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37

Blackcurrant wrote ...

Have you had a look at the gate drive waveform? (careful with the scope ground lead)
It took me some time to optimize the GDT
A small gate resister may drive it too fast and ring
maybe try an ohm or two more see if the ringing goes down
also keep the GDT twisted wires all the way up, minimize leakage inductance.

I take it those black things are snubber caps across the bridge

One thing I would tune the coils at the same frequency to start with, then fine tune (shift pri res lower) after it was running ok

Where should the snubber caps be across? I have seen schematics that show them across the DC bus, and then pictures and other information showing them across collector and emitter.
Will check gate signals.

nzoomed

Thu Apr 28 2016, 10:36PM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

orac12 wrote ...

AFAIK, they go across the DC bus, but thats essentially the same thing as collector and emitter anyway.
The negative rail connects the emitters from both IGBT's together and same with the collectors to the positive rail respectively.

Most people bolt them to the collector and emitter terminals such as this:
WIMG 2769

orac12

Fri Apr 29 2016, 02:58AM

Registered Member #9879 Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37

Have done some experimenting with different snubbers etc and taken shots of gate signal.

Gate signal
2wd2hye

Gate signal close up
351h7qq

10uF snubber across collector emitter
2ekrme8

10uF snubber across collector emitter close up
N5fz7t

20uF across collector emitter:
Xc3vo9

With no snubber
2chb02q

With no snubber close up
20a6t1e

Kizmo

Fri Apr 29 2016, 06:47AM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

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

orac12

Fri Apr 29 2016, 07:18AM

Registered Member #9879 Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37

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

Ok, thanks for the clarification. I have tryed all sorts of things (but at low power, and lucky the cm600's are resistant to abuse) and haven't damaged anything catastrophically yet.

It was just pictures and caps recommended for CM600's stated they bolted across the IGBT, but they may have been dual IGBT modules.

Kizmo

Fri Apr 29 2016, 08:05AM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

I cleaned up your double post mistake :)

But yeah, regarding your switching spikes, dont be too worried about them. There is a interesting physics thing going on in your bridge which is causing most of these spikes. And they are much more visible large bridges like yours.

Have a look at CM600 datasheet:

We are now interested in the "Coes" value

prx app note wrote ...

Coes â€“ Output Capacitance
This is the output capacitance measured between the
collector and emitter terminals with the gate shorted to
the emitter for AC voltages. Coes is made up of the
collector to emitter capacitance (CCE) in parallel with
the gate to collector capacitance (CGC), or

Coes = Cce + Cgc

For soft switching applications, Coes is important
because it can affect the resonance of the circuit.

As you can see the IGBT open state capacitance is largely depending on the voltage that is applied over Collector-emitter! And imagine what happens at your bridge when for example high side transistor turns on and low side transistor turns off. The emitter of the low side brick is tied to negative bus rail, and collector is quickly whacked to the full bus voltage which means the parasitic capacitance inside of the brick will be charged to your dc bus voltage at very high voltage rise time. And that charge current must travel through all parasitic inductances that your bridge has.

As you increase your bus voltage, your parasitic capacitance will decrease and amplitude of these transients related to the bus voltage will go down. My big coil does that too, at 100V bus the transients are almost 200% above bus voltage. But at 650V they are only maybe 20% over.

I would tune the phase lead for switching ever so slightly before zero crossings and leave it there.

nzoomed

Fri Apr 29 2016, 11:53AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

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.

Hydron

Fri Apr 29 2016, 09:19PM

Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208

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:

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