# IGBT Modules - Technologies, Driver and Application (Second Edition) - page 339

327
Fig. 8.1
Output characteristics of an IGBT
Reducing the static total currents in a parallel connection is also called derating and can
be calculated according to
The factor
δ
der
is known as the derating factor and is
stated as apercentage.
%100
In
I
1
nom
tot
der
⋅

− = δ
Eq. 8.1
I
tot
: Total current in the parallel connection
I
nom
Nominal current of amodule (DC)
n: Number ofmodules connected in parallel
The values from the above example produce a derating factor
δ
der
for the parallel
connectionof twomodules, each of I
nom
= 1000A, of:
%12 %100
A 1000 2
A756 A 1000 1%100
In
I
1
nom
tot
der
=
⋅
+
− =
⋅

− = δ
For three modules, assuming that one module has a typical value and two modules
have themaximum value, thederating factor is:
%16 %100
A 1000 3
A756 A756 A 1000 1%100
In
I
1
nom
tot
der
=
⋅
+
+
− =
⋅

− = δ
The calculation shown here can be regarded as a worst case scenario. In reality,
however, there is oftenmuch less variance in theU
CEsat
values of the IGBTs. In addition,
somemanufacturers offer a classification system for their IGBTs usingU
CEsat
categories
or refer to the date code. It is preferable to use IGBTs from the same U
CEsat
category or
date code for parallel connection. Finally, static current mismatching is only part of the
picture, as the dynamic influencesmust be considered aswell.
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