The Frequency Converter As A High-Frequency Source Of Interference - Siemens SINAMICS G130 Engineering Manual

EMC Installation Guideline
Engineering Information

The frequency converter as a high-frequency source of interference

The main source of high-frequency interference is the fast switching of the IGBTs (Insulated Gate Bipolar
Transistors) in the motor-side inverter, which results in extremely steep voltage edges. Each voltage edge generates
a pulse-shaped leakage or interference current I via the parasitic capacitances at the inverter output.
I
Schematic representation of inverter output voltage V and interference current I
I
The interference current I flows from the motor cable and the motor winding to ground via the parasitic capacitances
I
C , and must return to its source (the inverter) via a suitable route. The interference current I flows back to the
P I
inverter via the ground impedance Z and the supply impedance Z , whereby the supply impedance Z
Ground Line Line
consists of the parallel connection of the transformer impedance (phase to ground) and parasitic capacitances of the
supply cable (phase to ground). The interference current itself as well as the interference voltage drops caused by
the impedances Z and Z can affect other devices connected to the same supply and grounding system.
Ground Line
Schematic representation of the generation of the interference current I and its route back to the inverter
I
Measures for reducing high-frequency conducted interference emissions
When unshielded motor cables are used, the interference current I flows back to the inverter via cable rack,
I
grounding system, and supply impedance and can generate high interference voltages via impedances Z and
Ground
Z due to its high frequency.
Line
The effect of interference on the grounding and supply system by the interference current I can be considerably
I
reduced by leading the high-frequency interference current I back to the inverter using a shielded motor cable in
I
such a way that the voltage drops via impedances Z and Z are minimized. In combination with the line
Ground Line
filter or EMC filter (RFI suppression filter) integrated as standard in SINAMICS devices (according to category
C3 of EMC product standard EN 61800-3), the high-frequency interference current I can flow via a low-resistance
I
route back to the inverter within the drive system. This means that most of the interference current I flows via the
I
shield of the motor cable, the PE or EMC shield busbar, and the line filter. The standard line filters are provided in
SINAMICS G130, G150, and S150 converters as well as in the infeeds of the SINAMICS S120 modular system
(Basic Line Modules, Smart Line Modules, and Active Line Modules including the associated Active Interface
Modules, in Chassis and Cabinet Modules format). As a result, the grounding and supply system are subject to much
lower interference currents and the interference emissions are considerably reduced.
SINAMICS Engineering Manual - May 2008
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