Siemens SINAMICS DCM Operating Instructions Manual page 569

n+m mode
n+m converters are connected in parallel. When up to m converters fail (e.g. a fuse ruptures
in the power unit, a fault message occurs), operation is maintained without any interruption.
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 device 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 converters. The SINAMICS DCMs 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 devices continue to
operate uninterrupted. If several SINAMICS DCMs are parameterized as substitute masters,
the substitute master with the lowest bus address (p51806) that is ready for operation takes
over.
Parameter r53311.0 indicates whether the SINAMICS DCM is currently operating as master
(see FP9350).
During configuration, it is important to note that the power produced by n devices alone
(rather than n+m devices) 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.
Optimization runs:
n+m operation must be deactivated before starting the optimization runs. P51803 must be
set = 0 at the master and at the substitute master units.
Otherwise, during the optimization runs, monitoring functions can inadvertently respond
(e.g. for p51803 = 2, fault message F60105 with fault value 1 can be output).
Versions of the n+m operating mode:
1. n+m mode only in the armature circuit
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 devices, set p51803=1.
SINAMICS DCM Control Module
Operating Instructions, 12/2018, A5E34888669A
Descriptions of functions
10.26 Connecting units in parallel and in series
567