Help! IBGT 60N60 has been destroyed a lot by my coil

[VNTC]

IBGT 60N60 has been destroyed a lot by my coil
The amount of IBGT 60N60 that my Tesla coil destroyed was multiple 5 or 6 times than the number of IBGT in this picture.( Figure 1)
  I am very annoyed and frustrated because I am not yet solved this problem.
  I have applied almost protection components  to make safety for the IBGT’s for example:
  TVS diode, zener diode, ODC circuit, JK flip flop. . ext. But the IBGT still broken (all failure are short circuit by over current?)
  Until now I saw some main matter:
1-   Component IBGT 60N60 that I purchase have the input capacitor very different,that value from about 3nF to 26nF and almost higher x3 to x9 time the absolute maximum rating in the datasheet, the peak current they can drive also different  from 200A600A only. I  cannot approached 800A like that Steve ward wrote about 40N60 : I tested these IGBTs to over 1000A at 95khz so this should be no problem at all.
     2- Several starting pulses of burn-pulses always bad, bad signals means they are not enough level to make transistor turn on at saturate situation.( Figure 2)  Coupling capacitor 1uf cause this matter. This capacitor connects between the output of a pair gate drive chip UCC37322+UCC37321 and the GDT transformer, changing the value of this capacitor can’t solve this problem.
  I just find out the way to fix this. I used 20v zener diode instead of 33v zener diode to clamp the gate drive signals,  the ripple was minimized and become shortly 10us instead of 30us it is look beautifully (Figure 3) But another problem occurs: the oscillation of the coil become very hard to work.
    3-The output signals of the pair gate drive chip CC37322+UCC37321that I purchase in China is not rather good: with the load 30nf,the rising time 600ns the failing time 300ns for the 6.8us periods square wave30% so much loss! (Not include the effect of the characteristics of the 60N60 IBGT)..
  Terry Fritz said “the internal inductance of S pin of IBGT is10nH so to drive up to 800A-1000A peak  need to rise the gate control signals voltage up to 30V”.Is it true?.
If anybody has other good way to fix this problem please upload to help me and share.
  Thank you so much.

[sjsimmo]

Hi VNTC,

I'm not sure as to the exact reason that you're having failures (I'm fairly new to DRSSTCs myself), however I do notice a couple of things. It looks like you're using TO247 package FGH60N60SMD, and FGA60N65SMD igbts (am I correct?). These have a failure current of ~350A, opposed to the minibrick 60N60s which can typically take over 500A (what you seem to be trying to do).

I also agree with you that your gate waveform doesn't look great. Are you running half-bridge or full bridge? If you're running full bridge, it may be worth trying doubling the UCCs (stack two ICs on top of each other), to increase drive current.

Hope this helps (and sorry I can't help more),
-sjsimmo