306

Destruction of a 1.5kA/3.3kV IGBT module when turning off an SC2 short

circuit due to an insufficient driver stage

When selecting an IGBT or IGBTmodule, one has to bear inmind that not all IGBTs are

specified for a short circuit, i.e. their behaviour and robustness during a short is

indeterminate.

The stray inductance L

σ

influences the switching behaviour of an IGBT significantly. All

parasitic inductances in the commutation path are combined in the stray inductance.

Therefore, the load inductance is not part of it. Sources of the stray inductance are:

•

Parasitic inductance of theDC-bus capacitors.

•

Parasitic inductance of the connection of theDC-bus capacitors to the IGBT or

IGBTmodule.

•

Internal stray inductance of the IGBT or IGBT module. This comprises of the

parasitic inductance of the connection terminals, the bond wires and a DCB (if

implemented) with copper layer.

What influence the stray inductance will have in particular exemplifying the measuring

diagrams i

During the IGBT turn-onprocess the following applies:

•

The more L

σ

there is, the more distinct will the drop of the collector-emitter

voltagebewhen the collector current sets in.

•

The more L

σ

there is, the slower will the collector current rise. Meaning the

same as a reduced

dt

di

C

.

•

Themore L

σ

there is, the smaller the turn-on losses E

on

. In the example o

the turn-on losses with L

σ

≈

70nH are approx. 190mJ. Whereas only

140mJ of switchingenergy occurswithL

σ

≈

155nH.

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