Siemens Sinamics S120 Function Manual page 406

Function modules
7.11 Parallel connection of power units
Figure 7-26 Parallel connection of power units - overview
Note
For further information about parallel connection of power units, especially instructions on
how to configure them, see "SINAMICS Configuration Manual for G130, G150, S120
Chassis, S120 Cabinet Modules, S150".
Infeed concepts - parallel (one CU) and redundant parallel (two CUs)
Some applications require redundant infeeds for a DC line-up. This requirement can be
fulfilled through the implementation of multiple, independent infeeds which are connected in
parallel to the DC-line-up. Depending on how the drive is dimensioned, the DC line-up can
continue operating at between 50 % to 100 % output when one infeed fails. With the
redundant variant of the infeed parallel connection, each infeed is controlled by a separate
Control Unit and is thus completely independent. With the non-redundant variant, a single
Control Unit generally controls all parallel-connected power units which then, from a practical
viewpoint, function like a single, high-output infeed.
The type of circuit required depends on whether the redundancy requirement applies only to
the infeed itself or also includes the supply-side transformers or the supply systems (see
"SINAMICS Configuration Manual G130, G150, S120 Chassis, S120 Cabinet Modules,
S150").
6-pulse infeed
With a 6-pulse infeed, the two redundant infeeds with the same power rating are supplied
from a line supply via a two-winding transformer. As both infeeds are supplied with exactly
the same line voltage, the current distribution is largely symmetrical in normal operation,
even with uncontrolled infeeds. The infeeds can thus be dimensioned such that, taking into
account a minor current derating factor, each can carry 50 % of the total current. However, if
one infeed fails, only half the output remains available. If the full output needs to be available
when one infeed fails, then each infeed must be dimensioned to carry the full current.
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Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
Drive functions