IGBT Modules - Technologies, Driver and Application (Second Edition) - page 484

Fig. 13.11
Simulationof themotor voltagewith a long cable
Several measures are available – all based on filter principles – in order to avoid or
minimise the unwanted over-voltages at themotor terminals:
Insert a series inductanceat the inverter terminals.
Insert a series inductanceat themotor terminals.
Insert snubber capacitors at themotor terminals.
Insert a lowpass filter (
Without such filters, long cables may lead to motor insulation problems. Also
displacement currents can pass via themotor bearings and this can lead to damage in
these bearings
shows the simulation of an IGBT inverter which is connected
to a motor via long cables. The simulation exemplifies the over-voltages at the motor
terminals which are significantly higher than the actual DC-bus voltages. Such effects
can be observed in a real application with cable lengths upwards of around 15m,
depending on the power rating and actual system design. They intensifywith increasing
cable length.
13.10 Filters
Important elements in power electronics are passive components. As mentioned, there
are parasitic capacitances and inductances, which – in conjunction with the fast-
switching power electronic components – bring along unwanted properties both for the
application and for the immediate environment. Filter circuits are used to minimise this
negative influence. These filter circuits consist mainly of inductors and capacitors.
Fig. 13.12
Cable conducted interferencemechanisms
Filter circuits are there to minimise the so-called symmetric (differential mode) and
asymmetric (common mode) current and voltage interferences. While the differential
mode currents occur in the cables due to the switching of IGBTs and diodes and show
high current rise times mainly at lower frequencies, the common mode currents are
generated by the
of the switching power electronic components and the coupling
depicts the asymmetric and symmetric interferences.
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