Parallel connection of SINAMICS DC MASTER units

SINAMICS DC MASTER units can be connected in parallel to increase the power rating. The following secondary conditions must be fulfilled:

The hardware and plug connectors necessary to transmit the firing pulses and to establish the higher-level communication are provided on the CUD.

A maximum of 6 units can be connected in parallel. When connecting several units in parallel, the master unit should be positioned centrally due to the signal runtimes. Maximum cable length of the parallel-connection interface cable between master and slave units at each end of the bus: 15 m.

Identical, separate commutating reactors (u_K min. 2 %) are required for each SINAMICS DC MASTER unit in order to evenly distribute the current. The difference in reactor tolerances determines the current distribution. For operation without derating (current reduction), a tolerance of 5 % or better is recommended.

Only units with the same DC current ratings are permitted to be connected in parallel.
The permissible output current when connecting units in parallel is, when maintaining the secondary conditions:

I_max = n ? I_{N(SINAMICS DC MASTER)}

n = number of SINAMICS DC MASTER units

Redundant operation (mode "(n+m) operation“)

SINAMICS DC MASTER can also be used in a redundant configuration as a special operating mode of the parallel connection. In this operating mode, it is possible to maintain operation with the remaining SINAMICS DC MASTER units if one unit fails (e.g. if a fuse fails in the power section). When appropriately configured and interconnected, both the armature circuit as well as the field circuit can be redundantly operated.

SINAMICS DC MASTER units that can still function, continue to operate without any interruption when a unit fails. When configuring the system, it is important to note that in redundant applications, the power rating of only n units (instead of n+m units) must be sufficient.

In the case of a fault, the master functionality is automatically transferred. As a consequence, this operating mode is possible both when power sections of the slaves fail and when the power section of the master fails. (MTBF data in redundant operation are available on request.)

Connection schematic of the armature circuit when connecting SINAMICS DC MASTER units in parallel

(1) The same phase sequence is required between 1U1/1V1/1W1.

(2) The same phase sequence is required between 1C1/1D1.

(3) The units are connected using (8-pin) shielded patch cables of type UTP CAT5 in acc. with ANSI/EIA/TIA 568, such as those that are used in PC network technology. A standard 5 m long cable can be directly purchased from Siemens (Article No.: 6RY1707-0AA08). (n-1) cables are required to connect n units in parallel. The bus termination must be activated at the units/devices connected at the start of the bus and at the end of the bus.

(4) These fuses may only be used with units up to 850 A.

(5) Only for units up to 850 A in four-quadrant operation.