Author Topic: Difference between DC Link and Snubber Capacitors  (Read 304 times)

Offline profdc9

  • High Voltage Technician
  • ***
  • Posts: 146
    • View Profile
Difference between DC Link and Snubber Capacitors
« on: February 09, 2018, 12:39:47 AM »
Hello,

I am a little confused about the terminology with DRSSTC.  The capacitor that goes between the high and low voltage rails I thought is called a DC Link capacitor.  It is intended to hold the voltage at the IGBT terminals constant despite the inductance of the connection from the electrolytic doubler capacitors to the IGBT terminals.   Snubbers I thought were on the part where the lower collector and the upper emitter of the half-bridge meet to the rails.  I thought that was intended to prevent spikes coming back from the load from spiking over the VCE limit of the IGBTs.

I am wondering this because I am using the Kaiser snubber calculator and if I place a value of capacitor between the collector/emitter junction and the rails (around 1 to 2 uF), it's going to basically short out the IGBT and the capacitor is going to blow up.  Do I have this wrong?

Thanks,

Dan

Offline Mads Barnkob

  • Administrator
  • High Voltage Senior
  • *****
  • Posts: 646
  • Denmark
    • View Profile
    • Kaizer Power Electronics
Re: Difference between DC Link and Snubber Capacitors
« Reply #1 on: February 09, 2018, 10:18:34 AM »
DC Link Capacitors and Snubber capacitors are really only differentiated by the amount of capacitance. To some extend there is also the difference in material (electrolytic vs. polypropylene)

The large capacitance that prevents DC bus voltage sagging by being able to supply a lot of peak current will just act as a energy storage, with its large capacitance and high ESR it does not take care of transients.

The small capacitance, high dv/dt, peak current ability of a snubber capacitor will absorb the switching transients from hurting the IGBT, this is why it should be mounted directly on the IGBT terminals, even the internal inductance of a large IGBT brick can give us problems when we push things above the limit.

current sharing in parallel capacitors is done capacitively, so if you have a 1000 uF electrolytic capacitor and a 1 uF snubber capacitor, the snubber capacitor will only supply 1/1000 of the current to the bridge.

Are you doing simulations since you say that 1-2 uF will short out the bridge?

It might not even be necessary with snubber capacitors if you only use MKP capacitors as DC link capacitance.


http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline Hydron

  • Administrator
  • High Voltage Technician
  • *****
  • Posts: 146
    • View Profile
Re: Difference between DC Link and Snubber Capacitors
« Reply #2 on: February 09, 2018, 11:39:51 AM »
I think there's a little confusion here with terminology.

A snubber capacitor can be either:
a) a suitably sized capacitor across the DC bus, e.g. a 1-2uF film cap with bolt-on terminals, used to provide a low impedance to minimise the magnitude of any switching transients at the IGBT terminals
b) a capacitor used together with resistor/diode on the half bridge output (C2E1 on IGBT module), used for reducing the stress on the IGBT or diode when hard-switching a lot of current by providing another path for some of the energy.

In DRSSTC use we normally just use type a), as it's easy and anything further isn't normally needed for a soft-switching. Obviously putting a large film cap from half-bridge output to ground is not a good idea, and this is not what is done in type b), as there are additional components involved as well!

Offline profdc9

  • High Voltage Technician
  • ***
  • Posts: 146
    • View Profile
Re: Difference between DC Link and Snubber Capacitors
« Reply #3 on: February 09, 2018, 04:25:51 PM »
Thanks for the explanation Mads and Hydron.  I get it now, I was just a bit confused.  Anyways, as a matter of interest, I am laying out this monster.  It is a half-bridge with 4 IGBTs on each side.  Not sure what I'm going to do with it yet, but I thought I would give it a go and see how wide I could get the traces on a 100 mm board.

Dan



High Voltage Forum

Re: Difference between DC Link and Snubber Capacitors
« Reply #3 on: February 09, 2018, 04:25:51 PM »

 


* Recent Topics and Posts

post Re: MMC configuration advice
[Dual Resonant Solid State Tesla coils]
zizzer
June 19, 2018, 06:45:59 PM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils]
Netzpfuscher
June 19, 2018, 08:14:00 AM
post Re: CM200DU-24F woes
[Dual Resonant Solid State Tesla coils]
Usernametaken
June 19, 2018, 07:28:22 AM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils]
profdc9
June 19, 2018, 03:19:15 AM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils]
Hydron
June 18, 2018, 11:18:56 PM
post Re: Bach on sparks!
[Vacuum tube Tesla coils]
pentode
June 18, 2018, 11:03:47 PM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils]
profdc9
June 18, 2018, 09:07:28 PM
post Re: The hobo's SSTC
[Solid state Tesla coils]
Mads Barnkob
June 18, 2018, 08:47:15 PM
post Re: Bach on sparks!
[Vacuum tube Tesla coils]
Mads Barnkob
June 18, 2018, 07:39:58 PM
post Re: The hobo's SSTC
[Solid state Tesla coils]
Hydron
June 18, 2018, 04:36:18 PM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils]
Hydron
June 18, 2018, 04:27:14 PM
post The hobo's SSTC
[Solid state Tesla coils]
Spuriosity_
June 18, 2018, 04:17:13 PM
post Re: IGBT selection - TO-247 or minibrick?
[Dual Resonant Solid State Tesla coils]
Hydron
June 18, 2018, 04:07:44 PM
post Re: Bach on sparks!
[Vacuum tube Tesla coils]
pentode
June 18, 2018, 03:32:39 PM
post Re: MMC configuration advice
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
June 18, 2018, 02:02:50 PM
post Re: IGBT selection - TO-247 or minibrick?
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
June 18, 2018, 01:53:12 PM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
June 18, 2018, 01:48:11 PM
post Re: Bach on sparks!
[Vacuum tube Tesla coils]
Mads Barnkob
June 18, 2018, 12:41:18 PM
post Re: Drsstc 3
[Dual Resonant Solid State Tesla coils]
Hydron
June 18, 2018, 12:31:42 PM
post Re: Glass and shellac
[Radio frequency]
Mads Barnkob
June 18, 2018, 12:13:42 PM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils]
Hydron
June 18, 2018, 11:46:44 AM
post Re: Drsstc 3
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
June 18, 2018, 11:13:39 AM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils]
Netzpfuscher
June 17, 2018, 08:35:38 PM
post Re: Bach on sparks!
[Vacuum tube Tesla coils]
pentode
June 17, 2018, 01:15:28 PM
post Re: IGBT selection - TO-247 or minibrick?
[Dual Resonant Solid State Tesla coils]
TDAF
June 17, 2018, 01:06:30 PM
post Re: Bach on sparks!
[Vacuum tube Tesla coils]
oneKone
June 17, 2018, 12:15:59 PM
post Bach on sparks!
[Vacuum tube Tesla coils]
pentode
June 17, 2018, 09:14:12 AM
post Re: IGBT selection - TO-247 or minibrick?
[Dual Resonant Solid State Tesla coils]
profdc9
June 17, 2018, 06:07:55 AM
post Re: IGBT selection - TO-247 or minibrick?
[Dual Resonant Solid State Tesla coils]
oneKone
June 17, 2018, 01:59:48 AM
post Glass and shellac
[Radio frequency]
gar3thling
June 17, 2018, 01:41:54 AM
post Re: MMC configuration advice
[Dual Resonant Solid State Tesla coils]
Hydron
June 16, 2018, 10:53:34 PM
post Re: IGBT selection - TO-247 or minibrick?
[Dual Resonant Solid State Tesla coils]
Hydron
June 16, 2018, 10:12:08 PM
post Cheap, small signal, through-hole P-channel MOSFETs?
[Electronic circuits]
profdc9
June 16, 2018, 07:29:31 PM
post Re: IGBT selection - TO-247 or minibrick?
[Dual Resonant Solid State Tesla coils]
TDAF
June 16, 2018, 06:28:20 PM
post IGBT selection - TO-247 or minibrick?
[Dual Resonant Solid State Tesla coils]
Spuriosity_
June 16, 2018, 06:20:26 PM
post Re: MMC configuration advice
[Dual Resonant Solid State Tesla coils]
zizzer
June 16, 2018, 04:49:44 PM
post Re: MMC configuration advice
[Dual Resonant Solid State Tesla coils]
Hydron
June 16, 2018, 03:38:06 PM
post MMC configuration advice
[Dual Resonant Solid State Tesla coils]
zizzer
June 16, 2018, 01:39:41 PM
post Re: New Tesla Coil songs
[Dual Resonant Solid State Tesla coils]
oneKone
June 16, 2018, 10:38:22 AM
post Re: Drsstc 3
[Dual Resonant Solid State Tesla coils]
oneKone
June 16, 2018, 09:45:09 AM
post New Tesla Coil songs
[Dual Resonant Solid State Tesla coils]
profdc9
June 16, 2018, 03:38:50 AM
post Re: Online Electronic Resources - A library of books, websites and online calculator
[Beginners]
the_anomaly
June 16, 2018, 02:07:39 AM
post Re: Best of the best Ebay sellers!
[Sell / Buy / Trade]
StaticBuildup
June 15, 2018, 01:24:19 PM
post Best of the best Ebay sellers!
[Sell / Buy / Trade]
Mads Barnkob
June 14, 2018, 08:57:49 AM
post Ericsson RBS 2216 900 MHz base station teardown (part 1 & 2)
[Radio frequency]
Mads Barnkob
June 13, 2018, 10:13:16 AM
post Re: Newbie on a learning curve
[Solid state Tesla coils]
Andy Kay
June 12, 2018, 06:21:14 PM
post Re: Newbie on a learning curve
[Solid state Tesla coils]
Mads Barnkob
June 12, 2018, 02:45:51 PM
post Re: Newbie on a learning curve
[Solid state Tesla coils]
Andy Kay
June 12, 2018, 01:48:13 PM
post Re: Replacing a HV Transformer
[Transformer (iron core)]
Mads Barnkob
June 12, 2018, 01:14:54 PM
post Re: Newbie on a learning curve
[Solid state Tesla coils]
Mads Barnkob
June 12, 2018, 10:00:24 AM