Operating instructions

Introduction
MICROMASTER 420 / 440 – DC link coupling between several
Frequency inverters
A&D SD Page 7/32
Copyright © Siemens AG 2005 All rights reserved
4.1 Frequency inverter versions and power ratings which can be
coupled
MICROMASTER 420 and MICROMASTER 440 frequency inverters can be
operated together as well as mixed in a DC link group. In mixed operation,
both frequency inverter types can be used as the supply inverter connected
to the line supply. The DC link coupling is possible with frequency inverters
which can be connected to the following line supplies:
o 1-ph. 200-240V AC
o 3-ph. 200-240V AC
o 3-ph. 380-480V AC
Notes:
o It must be ensured that only frequency inverters having the same
voltage level 1/3-ph. 200-240V AC and 3-ph. 380-480V AC are
connected through the DC links.
o When using the DC link coupling, only frequency inverters with a
maximum rated power of 75kW (CT) or 90kW (VT), (frame size F) may
be used.
o In order not to overload the frequency inverter connected to the line
supply during pre-charging, a maximum load of 300% of the supply
inverter power may be connected to its DC link.
o The maximum number of frequency inverters coupled via the DC link is
10 .
When engineering the drive system it is important to ensure that the rated
input current of the frequency inverter connected to the line supply is not
exceeded. The rated input currents are specified in Catalog DA51.2 and
Tables 2-1 and 2-2. However, the overload capacity of the frequency
inverter, specified in Catalog DA51.2, can be utilized. In practice, it
therefore makes sense to connect - as a maximum - the same power as
the supply inverter rating at its DC link.
This means, that in total, for the complete DC link group, only the power of
the supply frequency inverter can be drawn from the line supply. The DC
link coupling, described here, with one supply inverter is therefore practical
for applications where the frequency inverters connected to the DC link of
the supply inverter predominantly operate in the regenerative mode or the
power rating of the supply inverter is significantly higher than the connected
frequency inverters.