Why do paralleled MOSFETs/IGBTs show huge oscillations during short circuit?

[Bakez]

When you short circuit a module with paralleled MOSFETs or IGBTs, the gate voltage shows huge oscillations, potentially destroying the device.

Why does this happen? This is the reason why manufacturers place additional gate resistors inside the module. They use these additional gate resistors to provide impedence between the different gates of the mosfets/igbts and it lessons the oscillations.

But why do the oscillations happen in the first place? Something is happening between the gates of the igbt/mosfet during short circuit that causes the oscillations to happen

 

[andre_luis]

Power switching MOSFETs leads a large amount of current to inductive components in series to the load. A short-circuit there generate a high dv/dt surge voltage in opposite direction against the Drain, so that a peak current can cross the parasitic capacitance ( Cdg ) able to even burn the gate driver circuitry.

 

[Bakez]

I dont think that is the problem

In a short circuit there are huge and high frequency oscillations on the gate voltage

 

[andre_luis]

Although no details were provide concerning the circuit topology under test, my opinion is that the picture seems somewhat feasible to a resonant oscillation due to some parasitic capacitance of the MOSFET in series with a leakage inductance of a transformer or inductor.

 

[Bakez]

Probably, but the issue is what is starting the oscillations, and why they don't occur when a large impedence is placed inbetween the gates of the paralleled IGBT/mosfet

You are right, if you change the leakage inductance of the short circuit pathway then the frequency of the oscillations change, and if you change the parasitic capacitances of the MOSFET then the frequency also changes slightly.

 

[FvM]

General speaking, circuit inductance (bond wires and external wiring) is causing the oscillations. You should be able to see it in a simulation with reasonable parameters.

But your test setup isn't clear at all, for a detail discussion please show a circuit.