Drsstc plz help

[otaKAREK]

hello, I'm new here, I need advice on what's causing the noise, I'm attaching a photo from the oscilloscope: yellow VGE blue primary current driver :2.7b mmc:100nf IGBT:CM300-24 Bus cap:6600uf400v

[AstRii]

The waveforms look good, the noise on the primary current is just an EMI picked up by the probes. You probably need to tune the phase lead for better soft switching so that it's not so noisy. Also get rid of all the loops in your measurements. If nothing helps, I would simply run the coil and see how hot the transistors are getting, but they are probably going to be fine if you don't push it too hard. I've had similar noise problems with all my coils and never really got rid of it. But the coils always worked:)

[otaKAREK]

I'm still not sure how much current I should set the OCD bricks to are CM300-24 full bridge I don't like the first wobbles excuse my English it was translated by google translator AstRii   ale vy jste čech   tak  klidne můžete česky

[AstRii]

AstRii   ale vy jste čech   tak  klidne můžete česky

I think it would be disrespectful to others to speak Czech on an English speaking forum:)

I'm still not sure how much current I should set the OCD

We usually over-drive the IGBTs to higher currents than what the datasheet claims. We can afford this thanks to soft-switching. A very nice guide to proper OCD setting can be found here: https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/

Although for some initial tests before the coil is properly tuned, I would recommend going lower with OCD. Perhaps sticking to the datasheet values. I think you can set 600A easily for testing, and going higher up once the coil is nicely tuned.

[otaKAREK]

didn't you look at the other images from the oscilloscope, I don't like the initial oscillations there

[AstRii]

Oh I'm so sorry I didn't see you posted another pictures. Well the new scope captures are very weird indeed. But the first picture you posted was looking decent. Is this random or can you make your coil oscillate as on the first picture?

It looks like if it didn't want to oscillate at the resonant frequency but maybe some multiple of it. Have you picked a correct capacitance value for capacitor C33? Perhaps try to make it a big bigger.

This is UD2.7C driver, but I assume UD2.7b will be the same in the feedback circuitry.

[davekni]

Have you picked a correct capacitance value for capacitor C33? Perhaps try to make it a big bigger.

That may help.  1nF should be fine for your ~140kHz frequency.  I'm guessing the issue is with UD2.7b layout.  Or with corona discharges coupling back to to UD2.7b circuitry.  Spikes occur between switching times, when current is high so comparitor input shouldn't be close to switching.  Would be useful to scope UD2.7b outputs (GDT inputs) to see if spikes occur there too.  More shielding and grounding may be the solution.

What value to you have for L1 (phase lead inductor)?  On the first scope trace where the coil is oscillating reasonably at ~140kHz, phase lead looks a bit high.  Presumes accurate current scoping.  Do you have a separate CT for scoping?  If so, what burden resistor and CT ratio?  Or are you measuring across R1 (which works well too)?