Siemens SINAMICS G130 Engineering Manual page 200

Fundamental Principles and System Description
Engineering Information
Parallel connection of S120 Active Line Modules supplied by a three-winding transformer
When a parallel connection is supplied by a three-winding transformer, up to four Active Line Modules are supplied
on the line side by the two secondary windings of the transformer. In order to ensure symmetrical loading of the
secondary windings, an even number of Active Line Modules ─ i.e. two or four ─ must be evenly distributed between
the two secondary windings. Since the input voltages are out of phase, it is essential that the Active Line Modules in
both subsystems are controlled by two Control Units operating according to the master-slave principle, see also
subsection "Redundant line supply concepts with SINAMICS Active Infeed" in section "Redundant line supply
concepts". This is necessary for Active Line Modules (as it is also for Smart Line Modules) because the firing pulses
for the IGBTs are synchronized by the Control Unit and therefore all Active Line Modules controlled by one Control
Unit must be connected to the same supply system with the same phasing. The current setpoint can be transferred
from the voltage-controlled master to the current-controlled slave by various methods: In systems with a higher-level
control, e.g. by PROFIBUS DP slave-to-slave communication, or in systems without a higher-level control via
SINAMICS Link using CBE20 Communication Boards or through analog channels using TM31 Terminal Modules.
Parallel connection of S120 Active Line Modules supplied by a three-winding transformer
The following measures help to ensure balanced currents in parallel connections of Active Line Modules:
·
Use of the master-slave operating principle between the two subsystems
·
Use of an electronic current sharing control (ΔI control) within the two subsystems
·
Reactors in the Clean Power Filters of the Active Interface Modules
·
Use of symmetrical power cabling between the transformer and the parallel-connected Active Interface
Modules / Active Line Modules (cables of identical type with the same cross-section and length)
To ensure symmetrical loading of the secondary windings of the transformer, no additional loads should be
connected to just one of the two low-voltage windings. Furthermore, it is not permissible to connect more than one
parallel connection with master-slave functionality to a three-winding transformer as connections of this kind cause
circulating currents.
As a result of the master-slave operating principle that ensures controlled current sharing between the subsystems,
there are (by contrast with 12-pulse parallel connections with line-commutated Basic Line Modules and Smart Line
Modules) no special requirements for the three-winding transformer with respect to the symmetry of the two
secondary windings. As a result, the use of alternative solutions (for example, two separate transformers with
different vector groups) is therefore completely acceptable.
The current reduction from the rated value for individual Active Interface Modules / Active Line Modules in a parallel
connection is 5%. This also applies to the simplest form of parallel connection supplied by a three-winding
transformer when only one Active Line Module with a separate Control Unit is connected to each secondary winding,
as the tolerances of the transformer and the master-slave control can also result in a slightly unequal current sharing
in this configuration.
SINAMICS Engineering Manual – November 2015
200/528
Ó Siemens AG