304

however, the current rises to approx. 3.7kA which is 4.6 times the nominal module

current of 800A. Not before a pulse time of 14µs will the IGBT go into desaturation at a

current of approx. 5.7kA. Therefore, more energy is converted in the IGBT in case of a

large short circuit inductance rather than a small one, before the U

CEsat

-monitor triggers

and turns off the IGBT. Thismay possibly be too late and the IGBT is destructed due to

the generated losses.

Impact of the short circuit inductance in an SC2 for an 800A/600V IGBT

module

If, in the case of an SC2 short circuit, there is an extremely low inductance, as may

occur for example with shorted inverter terminals, this would constitute themost critical

case. Due to the very low inductance, the IGBT desaturates rapidly creating a high

dt

du

,

which charges the gate beyond the nominal gate voltage via the Miller capacitance.

Because not only is the

dt

du

very high (higher than the ones looked at in the previous

short circuits) but also the Miller capacitance is very large (because the IGBT is

saturated) hence the resulting gate voltage is much higher. This means, however, that

the short circuit current peaks at a value which may destruct the IGBT despite the

protection circuit.

ompares a short circuit SC1 as well as an SC2 with a low

and a very low short circuit inductance. The scaling in all three diagrams is identical and

was created using a simplified simulation. It is notable that the peak short circuit current

rises according to the short circuit type.

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