Bleeder resistor for MMC

[Unrealeous]

Hi,

Just double checking that I'm interpreting this comment correctly - as I'm about to put a bleeder resistor across my MMC, but it looks like I can just put it across the output of the two IGBT bricks?

A comment from Mads: https://highvoltageforum.net/index.php?topic=722.msg5143#msg5143

"A simpler and quicker fix for the MMC residual charge, is to place a 5-10K power resistor across the output of the inverter, this removed instability problems with my large DRSSTC."

Am I correct to assume I can update his schematic to the following:

[AstRii]

Yes you can do it this way. Just make sure to properly rate the resistor for the voltage and power (I recommend highly overrate it). Because in case the resistor fails short circuit (which might be rare but it's possible), then the resistor will blow your bridge.

[flyingperson23]

When you put it across the bridge output, it discharges the MMC through the primary instead of directly. Same effect, but it means the resistor sees less voltage during operation.

[Unrealeous]

Thanks for the replies.

These forum posts need a 'like' button 

[Mads Barnkob]

Yes you can do it this way. Just make sure to properly rate the resistor for the voltage and power (I recommend highly overrate it). Because in case the resistor fails short circuit (which might be rare but it's possible), then the resistor will blow your bridge.

Luckily it is rare that a large ceramic power resistor fails short. The currents that IGBTs can withstand for 1ms is quite insane, with a bit of luck, the DC bus charge is enough to blow it into piece and not maintain a short circuit for very long.

[AstRii]

These forum posts need a 'like' button 

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Luckily it is rare that a large ceramic power resistor fails short. The currents that IGBTs can withstand for 1ms is quite insane, with a bit of luck, the DC bus charge is enough to blow it into piece and not maintain a short circuit for very long.

It is rare, however I think relying on luck to prevent destruction of IGBTs is not the path I'd take

[davekni]

It is rare, however I think relying on luck to prevent destruction of IGBTs is not the path I'd take

Rare is a relative term.  For normal axial-leaded wire wound power resistors, I think "rare" is close enough to never.  Meteorite impacts are rare too.  I spend no time being concerned about coil destruction by meteorite impact.

[Edi]

I need some help with GDT. Im using FGY75N60SMD with min treshold voltage of 3.5 V and max 6.5V. GE volage is rated for +-20V. How should I wind my GDT if my UD2.7C driver has an output of +-24V for GDT. If I rewind the coil for turn ratio 15:6:6:6:6 (24V:9.6V), would that be good for my drsstc?

[Hydron]

Please keep questions on-topic, this question has nothing to do with Bleeder resistors.

You've also already asked this in other threads - be patient and someone will likely answer a reasonable question (as I did in the other thread where you asked). I suggest going and reading the forum rules, specifically #3.