Medium Drsstc question

[unrealcrafter2]

Hi! I'm new here! I've been working on my cm300 drsstc for a couple years now and it's almost done. One thing I've been running into is that on the second pulse there is a large spike yet it stops right after and they go away with tuned lead. I can tune it to where the first one goes away but later parts start spiking as well. Is this first spike harmful? I have massively oversized 3.75uf snubbers.

Link to oscilloscope image
https://www.mediafire.com/view/6xxuzsilrbtrd5a/IMG_20240407_185545372.jpg/file

[flyingperson23]

The danger with voltage spikes is that they might exceed the voltage rating of the IGBT. It looks like your spikes are hitting 225v with 175Vbus, so it's unlikely to cause any damage. As long as your spikes aren't getting close to your IGBT's max voltage (likely 1200, possibly 600), it should be fine.

[markus]

Also note that even a perfectly tuned phase lead cannot get rid of all spikes - usually you tune phase lead for nice switching at the maximum expected current.

The UD2.7 instructions mention this (https://loneoceans.com/labs/ud27/#phaselead):

It will be impossible to completely eliminate all switching spikes. What I do is to ring up the primary (by adjusting the pulse width on my interrupter) until it hits a current I plan to run the coil at. In scope shot 2 [pasted here for your convenience], you can see the primary current (yellow) versus the bridge output (pink) with phase lead. At this point, the current ramps up to about 130A. I have also adjusted the phase lead such that the spikes are the smallest at the last few cycles when the current is the highest.

[unrealcrafter2]

Ok thanks! I appreciate the answers! My IGBTs are 1200 so Its probably fine! I plan to run at around 680V

[unrealcrafter2]

Alrighty the drsstc is functional! The current is ramping weird.
 It's not a smooth increase. It kind of pulsates. At first I thought it might be grounding or interference. It only does this with the secondary in place. With a dummy can it rings up much more smoothly. Improving  the shielding and GND didn't seems to fix it.


https://www.mediafire.com/view/xu5v7hi8hijpeqs/IMG_20240415_184442062.jpg/file
https://www.mediafire.com/view/jg7rf5eumetrf2r/IMG_20240415_184444974.jpg/file

[flyingperson23]

What you're seeing is notching https://richieburnett-co-uk-mirror.gitlab.io/operatn2.html
The energy is being transferred back and forth between primary and secondary. This is a good thing and indicative of good tuning.