Parallel Connection of SINAMICS S120 120 kW Active Line Modules

Overview

Two SINAMICS S120 Booksize Active Line Modules (ALM) in the 55 kW, 80 kW, and 120 kW frame sizes can be operated in parallel to increase the available line-side infeed power of a multi-axis drive lineup. The topology is officially supported in STARTER / SINAMICS S120 Application Example 109759667 and was added to the S120 firmware feature set with SINAMICS V5.2. The parallel ALM pair behaves as a single logical infeed referenced to one common DC link and one common Control Unit, which simplifies the surrounding cabinet design but introduces several hard-wired and firmware-level constraints that must be respected at the design stage.

The SIZER tool historically limited parallel selection because the configuration rules for line-side paralleling of booksize power units are stricter than those applied to motor-side paralleling. A SIZER entry that rejects the configuration does not, by itself, indicate that paralleling is impossible; it indicates that the tool does not have the design rule encoded. Final sizing and topology approval must be confirmed against the official Siemens application example and with the local Siemens presales contact.

Applicable Frame Sizes

Per Siemens Application Example 109759667, the parallel connection is permitted only for the following ALM booksize types:

• 6SL3130-7TE2x-1Axx / 6SL3130-7TE2x-0Axx family, 55 kW frame
• 6SL3130-7TE2x-1Axx / 6SL3130-7TE2x-0Axx family, 80 kW frame
• 6SL3130-7TE3x-1Axx / 6SL3130-7TE3x-0Axx family, 120 kW frame

Smart Line Modules (SLM), Basic Line Modules (BLM), and motor modules are not covered by this application example. The same frame-size rule applies to motor modules when they are paralleled on the load side, but the ALM parallel topology documented here is a separate, line-side configuration.

Mandatory Preconditions

All four preconditions below must be satisfied simultaneously. If any single one is violated, the parallel configuration is not approved and any commissioning attempt must be aborted.

1. Identical type / part number. Both ALM units must carry the same MLFB (order number) including all option suffixes. Mixed-option configurations are not permitted because internal control loop scaling, current sensor calibration, and pre-charge resistor sizing differ between options.
2. Identical frame size. Both units must be the same rated power (55, 80, or 120 kW). Pairing a 55 kW with an 80 kW ALM is explicitly not approved.
3. Identical firmware version. Both ALMs must run the same SINAMICS firmware version. The minimum approved versions are:
   • SINAMICS V5.2 for S120 stand-alone drive systems
   • SINUMERIK V4.91 for CNC-integrated configurations
   • SIMOTION V5.3 for motion-control-integrated configurations
4. Common Control Unit. Both ALMs must be connected to, and configured by, a single Control Unit (e.g., CU320-2 PN or CU320-2 DP). The two power units are addressed as a single logical infeed object and share the same DRIVE-CLiQ topology.

Line-Side Supply Requirements

The two paralleled ALMs must be supplied from a common, non-isolated line connection. Connecting the two ALMs to galvanically isolated line supplies (for example, two separate transformers with no common winding or grounding reference) is explicitly prohibited. The reason is the active infeed control algorithm: each ALM regulates the DC link by modulating its IGBT stage against a shared line voltage reference. If the two modules see phase-shifted or isolated supplies, circulating currents flow through the DC link, the IGBTs, and the pre-charge resistors, which can damage the modules within seconds of pre-charge completion.

Acceptable supply topologies include:

• Two ALMs connected in parallel to the same three-phase feeder terminals of a single transformer secondary.
• Two ALMs connected to a single busbar that is fed by one or more transformers whose secondary windings share a common star point or common delta node.

Not acceptable:

• Two separate transformers with isolated secondaries.
• Two feeds from different bus-tie sections of a plant distribution that can become islanded.
• Two feeds fed through different UPS or line-filter stages that introduce > 1° of relative phase shift under load.

DC Busbar and Current Sharing

The 120 kW booksize chassis uses an integrated DC busbar system whose continuous-current rating is limited to 200 A per end of the busbar segment. Two 120 kW ALMs each contribute up to 192 A DC to the common link, which means the entire 200 A budget of a single busbar end would be saturated by one module. The busbar must therefore be fed from both physical ends so that each end carries only the contribution of the ALM mounted at that end.

For a 120 kW + 120 kW parallel pair, mount the two ALMs at opposite ends of the line-up and route their DC link power connections to the corresponding ends of the DC busbar. The total infeed capability becomes approximately 240 kW (subject to de-rating for ambient temperature, altitude, and simultaneity factor) while each busbar end sees only one ALM's contribution.

Optional Voltage Sensing Module (VSM10)

The VSM10 Voltage Sensing Module is optional for the ALM booksize parallel topology, unlike in some motor-module parallel configurations where it is mandatory. The ALM derives its line voltage measurement internally through its own IGBT stage synchronization, which is sufficient when the two modules are fed from a common, low-impedance bus. Install a VSM10 if any of the following apply:

• The line impedance between the two ALM line terminals is greater than the value published in the S120 equipment manual for the frame size in use.
• The drive system includes a braking module or active line filter between the two ALM feed points.
• The plant has known line-voltage transients above 1.1 × Vrated that could trigger DC link over-voltage (F30002) under load.

When used, the VSM10 must be connected to the Control Unit via DRIVE-CLiQ and assigned to the infeed object that represents the parallel ALM pair, not to a single physical module.

Commissioning Procedure

1. Pre-power checklist. Verify MLFB equality, firmware equality (read out with STARTER, Online → Accessible Nodes → Device Identification), Control Unit presence, DRIVE-CLiQ topology, and common supply wiring. Verify that the busbar feed points are at opposite ends of the DC link.
2. Topology in STARTER. Insert the two ALM power units in the STARTER project under a single infeed object. STARTER automatically assigns DO numbers; do not edit the DO numbers manually. Configure the line voltage (p0210) and line frequency (p0211) for the common supply.
3. Pre-charge verification. With the line contactor open, command pre-charge via p0009 = 2 → 0 transition. Both ALMs should reach the pre-charge-complete state within 500 ms of each other. A skew greater than 1 s typically indicates a firmware mismatch or a DRIVE-CLiQ fault on one of the units.
4. First energization. Close the line contactor. Monitor the DC link voltage (r0070) on both ALMs. The displayed values should match within 0.5 V. A larger deviation indicates that one ALM is in current-controller saturation, usually because the parallel configuration parameter (p7000 ff.) has not been correctly set.
5. Current sharing check. Apply 30 % load through the DC link (for example, by enabling a motor module with a connected motor). Monitor r0027 (smoothed DC link current) on both ALMs. Current sharing should be within 5 % of the average.
6. Full load test. Ramp to 100 % motor-side load. Verify that neither ALM reports F30001 (overcurrent), F30002 (DC overvoltage), or F30003 (DC undervoltage). Verify that the cabinet temperature stabilizes below the derating curve.

Parameterization Highlights

The following STARTER / Startdrive parameters must be set identically on both ALMs of the parallel pair. A mismatch is the most common cause of circulating current and DC link fault trips on first commissioning.

Fault and Warning Matrix

SIZER vs. STARTER Tool Behavior

A common point of confusion is that SIZER may not offer a parallel-ALM option for booksize frames, while STARTER / Startdrive accepts the configuration once the project is created. This is a tool-coverage difference, not a topology restriction. The SIZER tool database at the time of writing does not encode the parallel-ALM booksize rule defined in Application Example 109759667, so a manual design is required. Document the manual selection in the project functional specification and have it countersigned by Siemens presales.

Verification Checklist Before Energization

• ☐ Both ALM MLFBs match (read at the rating plate and verified in STARTER Device Identification).
• ☐ Both ALMs report the same SINAMICS firmware version (r0018).
• ☐ Control Unit firmware supports parallel ALM (≥ V5.2 for SINAMICS stand-alone).
• ☐ DRIVE-CLiQ cabling connects each ALM to the Control Unit directly.
• ☐ Line supply is common and non-isolated; transformer secondary is shared.
• ☐ DC busbar feed points are at opposite ends of the line-up.
• ☐ VSM10 installed (if required by line impedance criteria above).
• ☐ STARTER configuration wizard re-run for parallel infeed topology.
• ☐ Pre-charge symmetry verified within 1 s.
• ☐ Current sharing verified within 5 % at 30 % load.
• ☐ Siemens presales sign-off on the design recorded in the project file.

FAQ