IGBT Modules - Technologies, Driver and Application (Second Edition) - page 337

8.2 Parallel connection
While themotivation for connecting chips in parallel within an IGBTmodule results from
the availability of chips with specific current handling capacities, other factors can play
an important rolewhen IGBTmodules are connected inparallel in theapplication:
No IGBT module of the required current rating is available. For example, the
requirement is to switch a current of nominally 5kA, but the largest IGBT
module currently offered by suppliers in the voltage range up to 1.7kV has a
nominal value of 3.6kA. It will therefore be necessary to connect two or more
modules inparallel, dependingon the current rating actually selected.
There is no IGBTmodule available in the desired package configuration in the
correct current rating. For example, the requirement is to use only modules
with a particular package configuration. Each package configuration has a
maximum limit for the current within the package family, e.g. currently 900A for
62mm IGBT modules. If, for any reason, it is not possible to use a different
configuration instead, this will also be a case of having to use parallel
connection, if the expected load exceeds the properties of the individual
There is a need to scale the inverters so as to have only a few specific
mechanical platforms. What usually happens in this case is that a particular
module package is chosen, which means that the amount of current an
individual module can utilise is limited, as describedabove.
Static current symmetry
Dynamic current symmetry
DC-bus stray inductance
ACoutput inductance
Temperature difference
between IGBTmodules
Saturation voltageU
Forward voltageU
Gate-emitter threshold voltage
ACoutput resistance
DC-link resistance
Gate drive voltageU
Gate turn-on and turn-off delay
Gate loop resistance
Gate loop induction
Magnetic field influence
Tab. 8.1
Static anddynamic dependencies of currentmismatching in parallel connection
Where IGBTmodules are used connected in parallel, there are many specific points to
be noted. If the parallel connection is not set up properly – including selection of the
correct IGBT modules, the design of the IGBT gate drive and DC-bus and, where
relevant, the output filter – slight or severe current mismatching can occur in the
modules. This can eventually cause overloading of a module and failure of the
application. When connecting in parallel, it is therefore important to ensure that, in both
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