Siemens SINAMICS DCM Operating Instructions Manual page 457

For n+m operation, a SINAMICS DCM is defined as master. Additional SINAMICS DCM are
defined as substitute masters. As with the standard mode, the unit defined as the master
carries out the closed-loop speed control, the closed-loop armature current control, the line
synchronization tasks and determines the firing points.
If a slave fails (due to a fuse blowing in the power unit or a fault being output, for example),
operation continues with the remaining converter units. The SINAMICS DCM units that are
still in proper working order continue to operate uninterrupted.
If a master fails (due to a fuse blowing in the power unit or a fault being output, for example)
a substitute master automatically becomes the master and the remaining units continue to
operate uninterrupted.
During configuration, it is important to note that the power produced by n units alone (rather
than n+m units) must also be sufficient for the application in question.
When operating the SINAMICS DCM together with a SIMOREG DC-MASTER Converter
Commutation Protector (CCP), n+m operation must be deactivated.
Versions of the n+m operating mode:
1. n+m mode only in the armature circuit
2. n+m mode in the armature circuit and in the field circuit
SINAMICS DCM DC Converter
Operating Instructions, 1.2012, C98130-A7066-A1-05-7619
In this operating mode, when the master fails, only the armature firing pulses and the
upstream closed-loop control (setpoint channel, speed control, armature-current control)
are transferred to the substitute master; however, not the field firing pulses and the
upstream control (EMF control, field current control).
The main application for the operating mode is to supply large inductances (e.g. field
windings of synchronous generators) with the SINAMICS DCM armature converter.
Activation:
At the master and substitute master units, set p51803=1.
In this operating mode, when the master fails
 the armature firing pulses and the upstream control (setpoint channel, speed control,
armature current control) and
 the field firing pulses and the upstream control (EMF control, field current control)
are transferred to the substitute master.
Activation:
At the master and at the substitute master units, set p51803=2.
Connection:
Outputs 3C and 3D (field DC voltage output) of the master and all substitute masters
must be connected to the motor field winding in parallel.
Descriptions of functions
10.25 Connecting units in parallel and in series
455