# IGBT Modules - Technologies, Driver and Application (Second Edition) - page 312

300
apply for the gate resistor, the stray inductance and the gate inductance. (For example,
if the stray inductance is higher than in the datasheet then the gate resistor should also
be chosen with a higher value.) In the end the voltage or current gradient
dt
du
or
dt
di
is
crucial and the voltage overshoot across the diode which must not exceed the
breakdown voltageand theSOA (chapte
of the semiconductor.
This is quite different for the turn-off process of the IGBT. Here the limiting factor is the
IGBT blocking capability (voltage rating). Over-voltages are effected originating from the
current gradient during turn-off and the stray inductance in the commutation path. These
combined with the supply (DC-bus) voltage may not exceed the voltage rating U
CES
of
the IGBT. The values for the maximum blocking voltages in the datasheets are
referenced to chip level. The maximum blocking voltages of the module are below that
and somemanufacturers refer to them in theRBSOAdiagrams (chapte
.
The maximum permissible current gradient can be calculated from the basic conditions
of the application in normal and overload operation. The case of a short circuit is not
taken into account here and it is taken care of by other protective measures. An
example below:
Lets assume an inverter with amains voltage of 690V and a voltage tolerance of
±
10%,
a stray inductance in the commutation path of 80nH (excluding themodule internal stray
inductance), a nominal load current of 350A and amaximum overload current of 525A.
The IGBT module used is the one described in
Goal is to find the maximum
possible current gradient for this application.
Fig. 7.8
The DC-bus voltage results from
V 1100 1.12 V690
U
DC
≈ ⋅
=
(the factor 1.1 stems
from the voltage tolerance of
±
10%). The voltage rating of the IGBT module quoted in
the datasheet is 1700V at chip level. At module level the blocking capability is around
1560V, having taken the internal module stray inductance into account. Following
ne finds amaximum current gradient during turn-off of
.
s
kA 75.5
nH80
V 1100 V 1560
L
U U
dt
di
DC
CES
max
µ
−=
−=
−=
σ
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