Redundant Line Supply Concepts - Siemens SINAMICS G130 Engineering Manual

Fundamental Principles and System Description
Engineering Information

Redundant line supply concepts

General
Certain applications require redundant infeeds for multi-motor drives or common DC link configurations to increase
availability. This demand can basically be fulfilled by using several independent Infeed units working in parallel on the
common DC link. If one Infeed unit fails the common DC link can be supplied by the remaining Infeed unit, usually
without interruption. Depending on the power rating of the Infeed units the common DC link can continue to operate
at between half and full power. The difference between redundant Infeeds and the parallel connection of Infeeds for
increasing the power rating, as described in the section "Parallel connections of converters", is the arrangement of
the Control Units. At redundant Infeeds each Infeed is controlled by its own Control Unit. Therefore, each Infeed is
completely autonomous. At the parallel connection of Infeeds, a single Control Unit controls and synchronizes all
power units in the parallel configuration, which behaves as a single Infeed with a higher power rating.
Note:
When several independent infeeds are used, this can considerably increase the availability of the DC busbar. In
practice, however, 100% fault tolerance is impossible since certain fault scenarios can still cause an interruption in
operation (such as a short circuit on the DC busbar). Even if these fault scenarios are extremely unlikely to occur, the
risk of their occurring cannot be completely eliminated in practice.
Depending whether the demand for redundancy is related only to the Infeed units or also to the supplying
transformers or the supply systems, different circuit concepts are possible, which are shown and explained below.
Supply
Control
Unit 1
Infeed 2
Infeed 1
M
Variant 1:
Supply from a single supply system
with a double-winding transformer
At variant 1, both redundant Infeeds with the same power rating are supplied from one supply system via a two-
winding transformer. As both infeeds are supplied with exactly the same voltage on the line side, in normal operation
the current distribution is largely symmetrical, even with unregulated infeeds. The infeeds can, therefore, be
dimensioned so that each infeed can provide half of the total current taking into account a small current derating
factor. If one infeed fails, only half of the power required will be available. If the full power is required when one infeed
fails, each infeed must be dimensioned to provide the full power.
SINAMICS Engineering Manual – May 2008
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Supply
Phase Shift
Control
Control
of 30 (elec.)
Unit 2
Unit 1
Infeed 1
Variant 2:
Supply from a single supply system
with a three-winding transformer
Control
Unit 2
Infeed 2
M
Variant 3:
Supply from two independent supply
systems with two transformators