IGBT Modules - Technologies, Driver and Application (Second Edition) - page 316

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
-monitor triggers
and turns off the IGBT. Thismay possibly be too late and the IGBT is destructed due to
the generated losses.
Fig. 7.10
Impact of the short circuit inductance in an SC2 for an 800A/600V IGBT
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
which charges the gate beyond the nominal gate voltage via the Miller capacitance.
Because not only is the
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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