Output Filters - Siemens 6SR41 series Product User Manual

Application Specific Features

7.6 Output Filters

7.6 Output Filters
Output filters are required for down-hole pumping with long cables and also must be
considered when shielded output cables are used. When required, the filter completely
avoids any problem with cable reflections. NXG control supports output filters for all control
modes. The output filter consists of an LC filter used to prevent the output cable dynamics
from interfering with the drive output. An output filter might also be used to address EMI or
DV/DT requirements. With the capacitors omitted, the filter can function as output reactors
for Synchronous Transfer used to limit the current that can circulate while the VFD output is
connected to the Medium Voltage input.
The output filter is designed to effectively remove all high frequency components in the drive
output voltage. Because Perfect Harmony is already free of low-order output harmonics, the
result is a nearly perfect sinusoidal output waveform.
Note that the filter adds losses proportional to the square of the RMS output current. The
filter inductance is in series with the VFD output and motor load and can reduce the output
voltage capability, depending on the load power factor. The filter also introduces an
amplifying resonance, which could limit the closed-loop gain for high-performance
applications. The filter consists of series inductors in each phase connected between the
drive outputs and the load (motor) terminals. Shunt capacitors in each phase connect
between the load terminals and are arranged in a floating wye configuration (capacitors are
omitted for Closed Synchronous Transfer applications). Refer to Chapter 4 for output filter
values.
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Operating Instructions, Version AE 12/2009, A5E01454341C
Product User Manual