School project : First DRSSTC

[Nijin]

Hello Everybody i'm proud to introduce you my first DRSSTC built for an engineer project school !

Last year I decided to built a large SGTC but the price of my 942C MMC was to high for my budget and I don't have a 220V/32A power source. So I decided to change the technology of my Tesla in order to supply it with a 3phase power source.

(video of my SGTC last year)


I use the plan of F. Franzoli for his DRSSTC III for the full bridge, driver, PSU and interrupter. I saw that his OCD is at 1200A. Due to the low impedance of my primary I think it will reach 1000A peak. I need to find an IGBT module wich can handle this curent at the resonant frequency of my secondary.

I made a simulation on JavaTC3D. I saw that the surge impedance of the secondary need to be close to 50kOhm. I have two size of wire : 0.4 and 0.475mm. With my actual secondary and size of the coil (200*1080mm) I can reach a couple of values for frequency and surge impedance :

Size of wire | Number of turns | Frequency |  Z surge
0.475            1850                    63.41 kHz   52 kOhm
0.475            2000                    60.95 kHz   54.6 kOhm
0.4                2100                    52.6 kHz    61.6 kOhm
0.4                2400                    49.8 kHz    66.5kOhm

My first question is witch case I should take ? I prefer the first for the low impedance but I'm affraid that at 63kHz it would be hard to find an IGBT module for 1000Apeak.

So the second question is which module I should use ? I saw CM300DY-24NFH and SKM400GB125D. I think the SKM is really good for my DRSSTC but it is more expensive. Do you have seen an other model for a DRSSTC at this frequency and this peak current ?


Thanks you for your help. I have one month to finish the circuit ^^. I will post more information about this project.

PS : i'm sorry, it's my first time on a forum, i don't know how to post pictures of my tesla... :/

[futurist]

For my DRSSTC I'm using SKM400GB123DH6 in half-bridge configuration, bought it used for ~30€. Kizmo tested those bricks and I think he said they can handle up to 1500 Apk before blowing up
My predicted secondary fres was around 70 kHz, but after tuning I end up around 57 kHz which turned out to be completely fine with that brick

Check it out
https://highvoltageforum.net/index.php?topic=78.0

[Mads Barnkob]

Welcome to HVF Nijin!

Good to see that you have previous experience with high voltage and a good plan for your next project.

If you want to dig deep down in IGBT current/frequency handling, I suggest you take a look at that part of my DRSSTC guide (or just scroll to the bottom to see the table of proven speeds and currents): http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/

Since you have already planned for a low inductance primary circuit, your secondary coil should fit that in order to not need excessive long on-times to grow good sparks, so go for either of the coil specs with 0.475 wire diameter. As long as you stay below 100 kHz, most of those mid-range IGBT bricks will do just fine, as a huge ball park figure estimate, if you want to be sure, do the math

To attach pictures to your posts, just click on the attachments part below the text box when making a new thread/writing a reply. Here you can select files, see with formats and sizes are allowed.

Looking forward to see much more about your project!

[Nijin]

Thanks you for your answers.
The photo of my TC. I know the primary coill tube is not enough large but I will change it later.


I made more maths yesterday.

I choose 1800 turns of 0.0475mm for the secondary. I think the low impedance will less detune the secondary Fres.



For a frequency of 55kHz when the an arc appears ( 14% detuning), the period is 18us. If I take a 470nF primary capacitor, Xc= 6.1Ohm. I want a maximum current of 1200A. The MMC voltage will be equal to 7320V. The DC bus has a voltage of 620VDC so the n cycles is equal to 6 cycles. Finally the On-time is 108us max.

What do you think about these values ?

The schematics of my DRSSTC based on Franzoli DRSSTC III :