The job of the output filter is to reduce the electro-magnetic interference (EMI) as far as
possible, and to protect the load and the IGBT module. As depicted in
here is awide range of different filters. The design can be accompaniedwith
expensive EMC tests. Primarily there are three effects which an output filter should
As described before, the high switching speeds of the IGBTs can lead to
insulation and bearing damage in themotors. This can be avoidedwith a circuit
as exemplified i
(see also chapter
This filter is there to attenuate the voltage harmonics.
Output chokes are there to smooth the output current. To achieve a constant
sine-wave current for one, and also, to reduce capacitive charge reversal
effects and thus also to protect the IGBTs.
du filters or output chokes are used, then – as with the chokes of the mains filter –
calculate with a voltage drop across the inductances. The chokes must not reach
saturation and their inductance shouldbeas constant as possible.