Hello,

with 2 CU Three-winding transformer or one isolated transformer for every infeed is necessary.

1.15.4 Parallel connection of S120 Smart Line Modules

https://support.industry.siemens.com/cs/de/en/view/83180185

Hello,

2 CU with 2 SLM require two galvanic isolated supplies to prevent from circular currents, so your setup would not work.
If you would use 1 CU with 2 SLM in parallel, you could operate a single SLM in an emergency by following the steps shown in the commissioning manual 3.10:
"Power units should only be activated and deactivated in the event of a fault, for example, after replacing a failed power unit. This approach is unsuitable for variable power control, because the Control Unit recalculates the drive line-up control parameters after every change. Optimal, highly dynamic control behavior of the drive line-up can only be ensured by recalculation.
The power units can be monitored and parameterized individually:

• Using p0125, you activate or deactivate a power unit from the topology (select using the topology number).● With p0895, you specifically activate or deactivate power units via an interconnected digital input (BI).
• The number of currently active power units in a parallel connection is displayed in r7000.
• After a fault or replacement, parameter p7001 allows you to specifically deactivate or activate connected power units....."