IGBT Modules - Technologies, Driver and Application (Second Edition) - page 486

not cause amagnetic flux in the corematerial, provided the amount of both the currents
– forward and returning – does not differ. The DC-bus current, therefore, is only
subjected to a very low stray inductance of approximately 1% of L
. This means that
the current compensated choke does not affect the symmetrical currents, as the fields of
the forward and return winding compensate each other. If asymmetrical currents occur
in theDC-bus, then themagnetic field and, hence the choke, becomes effective. The X-
capacitors, again, have the job of attenuating occurring interference voltages and the Y-
capacitors are there to dissipate theasymmetrical currents.
In case chokes are not used at the input, a choke can be relocated into theDC+ or DC-
branch. The choke here can limit surge currents thatmay occur.
Fig. 13.14
Exampleof aDC-bus filter with complementingmains filter
13.10.3 Output filter
The output filter is connected in the shortest possible way directly to the inverter output.
The connections from the filter to the loadare generally cableswhichmay ormay not be
screened. The design of the filter depends partly on the length of the cable.
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