I try to build mazzili zvs with 2 IGBT toshiba MG75Q2YS40 75A 1200v. For the each fast diode, I use 2 pieces DSEC60-06 A 600v 30A in series to get 1200v.
for this, I use 2 power source:
12 volt for switch the gate.
0-80 volt (from variac + bridge diode + capacitor) for the main power
because the gate only use 12v power, I don't use zener. at first, no problem at all. it work normally.
Then I try to add the resonant capacitor by directly (without turn off the zvs) put second capacitor to the first capacitor in parallel, just by touch the second cap to the first cap (no solder,no screw).
when I do this, arc come out from the connection of the second capacitor and suddenly both IGBT failed together. at that time, I only use about 20 volt for the main power.I don't know exactly when the IGBT blown, when the second cap is connected or disconnected. because it's happened very fast.
I try to re-read the schema, but still don't find reason why both IGBT failed together, but the fast diodes is OK. maybe someone know why both IGBT suddenly failed ? thank you.