Types Of Communication - Siemens SINAMICS S120 Function Manual

Function modules
8.9 Master/slave function for Active Infeed
Electrical isolation of infeeds
To successfully implement the structure, a means of electrically isolating the infeeds from the
line supply is required in addition to the SINAMICS components. This is to prevent circulating
currents from developing if the pulse patterns of the Active Line Modules are not
synchronized.
Two solutions are possible for the electrical isolation:
● Using an isolating transformer for each slave infeed train. The primary side of the
transformer is to be connected to the grounded or ungrounded line transformer. The
secondary side must never be grounded.
● Using a three-winding transformer for the master and slave infeeds. In this case, only the
neutral point of one winding may be grounded to prevent further electrical coupling via
ground.
Whichever solution is chosen, it must be noted that a separate transformer must be used for
each Active Line Module (slaves 1 to 3).
DC breaker
Note
When an infeed develops a fault it is disconnected on the line side by the line contactor, on
the DC-link side, using a DC breaker. Infeeds must not be switched in to a charged DC link.
The DC link must be discharged before another infeed train can be switched in.
An infeed may only be connected to a charged DC link if a DC breaker with pre-charging
branch is installed.
8.9.3

Types of communication

To implement master/slave operation, the CUs must be able to communicate with one
another. The master passes the active current setpoint to the slaves. To optimize V
(DC-link voltage), the dead times during communication must be kept to a minimum.
PROFIBUS slave-to-slave communication
The data is exchanged directly between the CUs without passing via the DP master. A
PROFIBUS master (higher-level controller) is required to act as a "clock generator" (e.g. an
S7-CPU). The minimum PROFIBUS cycle time that can be set depends on the PROFIBUS
master specifications.
Isochronous mode must be set for PROFIBUS. The PROFIBUS cycle time must not exceed
2 ms otherwise the closed-loop control may start to oscillate.
In order to ensure that other infeeds do not switch to fault status when one CU fails, the fault
message F01946 "Link to Publisher disconnected" must be deactivated.
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Function Manual, 11/2017, 6SL3097-4AB00-0BP5
control
dc
Drive functions