SINAMICS G120: Multi-Motor Operation with Drive Data Sets (DDS)

Operating a single SINAMICS G120 modular inverter across motors of different ratings (for example 3 kW, 14 kW, and 37 kW on the same power module) is feasible, but only within defined power-ratio limits and with explicit Drive Data Set (DDS) management. This reference consolidates the engineering rules, parameter maps, and field commissioning steps required to swap motors on one drive without exceeding the converter's current measurement resolution or losing torque quality. The guidance also distinguishes two distinct multi-motor concepts that are often confused: (a) one drive running different motors one at a time via DDS switching, and (b) one drive running several identical induction motors simultaneously, a dedicated mode with its own preconditions.

1. SINAMICS G120 Modular Drive Architecture

The SINAMICS G120 family is a modular inverter composed of two physically separable units connected by a digital link:

• Control Unit (CU) – carries the firmware, I/O terminals, PROFIBUS/PROFINET interface (model dependent), and all parameter storage.
• Power Module (PM) – carries the rectifier, DC link, and IGBT inverter stage. Power ratings are fixed by frame size.

For multi-motor applications, the question is always "can one CU+PM pair serve multiple motors?" The answer depends on whether operation is sequential (one motor at a time) or simultaneous, and on the relative kW ratings of the motors.

Firmware V4.7 SP3 (or later V4.7.x maintenance release) is the minimum recommended baseline for multi-DDS applications with PROFINET name-of-station fallback; V5.2 is preferred for current production fleets. Verify the installed firmware via r0001 or the CU's P0018 on the BOP-2.

2. Multi-Motor Operating Modes — Terminology

Siemens documentation uses two distinct concepts that are easy to confuse:

1. DDS switching (single motor at a time): One CU + one PM drives any one of several physically different motors via index-switched parameters. Mechanical switching between motors is handled outside the drive (motor contactors). This is the subject of the present article.
2. Multi-motor operation (simultaneous, identical motors): A single drive powers several motors in parallel without contactors, but only identical standard induction motors are permitted. The Siemens knowledge base entry SINAMICS G: Preconditions to operate several motors on one converter states that up to 50 motors can be supported in this mode, subject to stationary or rotating identification of each unit.

3. Drive Data Set (DDS) Architecture

Each SINAMICS G120 Control Unit provides up to four Drive Data Sets: DDS0, DDS1, DDS2, DDS3. A DDS is an index slot for every motor-dependent parameter; switching DDS at runtime swaps the entire motor "personality" in one operation.

The selection of the active DDS is governed by two binary inputs:

• P0820 — BI: DDS bit 0
• P0821 — BI: DDS bit 1

4. DDS vs CDS — What Switches and What Doesn't

The Command Data Set (CDS) governs command sources (where ON/OFF1/REV/acknowledge come from) and setpoint sources (analog input, fixed setpoint, fieldbus). The DDS governs motor and controller parameters. Both are independently indexed.

A typical DDS-swap use case keeps the same CDS (same PLC, same bus, same wiring) and only swaps the motor data and ramp profile when contactor K1 closes for the 37 kW motor and K2 for the 3 kW motor.

5. Power Unit Sizing Rule — The 3× / 4× Limit

The power module's continuous output current is sized to the largest motor connected, but the converter's current measurement, current controller bandwidth, and ADC resolution are sized to that same rating. When the drive runs a much smaller motor, those scaling assumptions break down. Siemens formally recommends a maximum 4× ratio between the drive's rated output current and the smallest connected motor's rated current; many field engineers apply a stricter 3× rule for sensorless vector control (SLVC). V/f (scalar) control is more tolerant and ratios up to 8× are accepted in practice.

6. ADC Resolution — Why Oversized Drives Hurt Performance

The SINAMICS G120 current measurement is implemented on a 12-bit ADC per phase, giving 4096 discrete levels across the drive's full-scale current. As the operating current moves toward zero, the effective quantization step grows:

Quantization step:

I_LSB = I_drive_rated / 4096
       = 75 A / 4096   (for 37 kW PM240-2, FSE)
       = 18.3 mA per LSB

At 3 kW motor rated current (~5.5 A at 400 V, cos φ 0.85, η 0.92):

usable_steps = 5.5 A / 0.0183 A
             = 300 levels

The drive is left with the bottom ~7.3 % of its ADC range to encode a current that, in a properly-sized drive, would occupy the full scale. Torque ripple, audible noise, and oscillation at low speeds are the typical field symptoms. The threshold where these symptoms become unacceptable lies at roughly the 3× current ratio. At 12.3× (75 A drive vs. 6.1 A 3 kW motor), the symptoms are not a subtle nuisance; they will prevent stable closed-loop operation of the 3 kW motor.

7. Applied Scenario — 3 kW, 14 kW, 37 kW Motors

Assume 400 V three-phase motors, 50 Hz, 4-pole, cos φ 0.85, efficiency 0.92:

I_rated = P / (sqrt(3) * V_LL * cos_phi * eta)
I_3kW   = 3000  / (1.732 * 400 * 0.85 * 0.92) = 5.5  A
I_14kW  = 14000 / (1.732 * 400 * 0.85 * 0.92) = 25.7 A
I_37kW  = 37000 / (1.732 * 400 * 0.85 * 0.92) = 68.0 A

Only the second architecture (one 14 kW drive for 3 kW + 14 kW motors, separate small drive for the 37 kW motor) keeps every ratio inside the 4× rule. The 14 kW power module has a continuous output of 32 A, which is 1.4× the 3 kW motor current (acceptable) and 1.2× the 14 kW motor current (ideal).

8. Parameter Map — What Is Indexed per DDS

The following parameters must be reconfigured per DDS. Indexed parameters carry four slots (one per DDS); the slot is the array index, not the active DDS index. Use P0010 = 30 (commissioning factory settings) only when starting from a known-good state, then re-enter each DDS data set.

9. Step-by-Step DDS Commissioning Procedure

Use SINAMICS StartDrive in TIA Portal or the STARTER tool with a CU230P-2 PN / CU240E-2 PN connected via PROFINET. The procedure is identical whether commissioning offline or online.

1. Restore factory settings: P0010 = 30, P0970 = 21. Wait for the CU to complete the reset (fault F00518 will self-clear once complete).
2. Enter quick commissioning on DDS0: P0010 = 1. Set P0100 = 0 (Europe, 50 Hz, kW), P0205 = 0 (no DC braking applied), then motor data P0304..P0311 from the 14 kW motor nameplate.
3. Set control mode P1300 = 20 for SLVC if motor decoupler loads allow; otherwise P1300 = 0 (linear V/f) on the larger motor slots.
4. Set ramp times P1120/P1121 indexed per DDS.
5. Exit quick commissioning: P0010 = 0. Run P1900 = 2 (stationary motor identification) once with the 14 kW motor connected.
6. For each additional DDS, select the slot via P0820/P0821 first, then change the motor data block. Example: drive ON disabled, P0820 = 1, P0821 = 0 ⇒ DDS1 active. Edit P0304[1], P0305[1], P0307[1], P0308[1], P0310[1], P0311[1] from the 3 kW motor nameplate. Adjust P1120[1]/P1121[1] and P1300[1] to suit.
7. Repeat for DDS2 (37 kW motor).
8. Wire P0820 and P0821 to digital inputs or PROFINET control word bits.
9. Test each DDS individually with the corresponding motor, no load, jogging 5 s in each direction. Verify actual current in r0027 against the nameplate value at 50 Hz, no load (expect 30–50 % of rated for a typical induction motor).

10. Motor Output Switching — Contactor Interlocking

A single G120 power module has one three-phase output. To drive more than one motor, external motor contactors switch the output between motors. Each motor must be protected by its own thermal overload (OLR) because the drive's i²t model fits only the motor whose data are currently in the active DDS.

Interlock rules — apply at the contactor control level (relay logic or PLC safety logic):

• Only one of K1, K2, K3 may be closed at any instant.
• A drive OFF1 must be issued before a contactor is opened or closed.
• STO (Safe Torque Off, when wired to a CU240E-2 F or CU250S-2) must be active while contactors operate to suppress any residual output pulse.
• OLR for each motor set to the nameplate current of that motor (not the drive's rated current).
• Mechanical interlock between contactors is mandatory as a backup to the electrical interlock.

11. PROFINET / PROFIBUS DDS Selection

The two DDS bits can be sourced from digital inputs (default on CU230P-2: P0820 = r722.0, P0821 = r722.1) or from PROFINET control-word bits. For PROFIdrive telegrams 1, 2, 3, or 20, the control word STW1 occupies bits 0–15 of PZD1 (output from PLC to drive). Common mapping on G120:

PLC code sample (TIA Portal SCL, SIMATIC S7-1500):

// "driveWord" is the STW1 sent to the G120
IF ("motorSelect" = 1) THEN              // 14 kW motor
  "driveWord".%X14 := FALSE;
  "driveWord".%X15 := FALSE;
ELSIF ("motorSelect" = 2) THEN           // 3 kW motor
  "driveWord".%X14 := TRUE;
  "driveWord".%X15 := FALSE;
ELSIF ("motorSelect" = 3) THEN           // 37 kW motor
  "driveWord".%X14 := TRUE;
  "driveWord".%X15 := TRUE;
END_IF;

// Sequencer
IF ("motorSelect" <> "lastSelect") THEN
  "driveWord".%X0 := FALSE;              // OFF1 while swapping
  "driveCmd"     := "driveWord";         // send STW1
  WAIT_FOR("driveState.r52.zsw1.bit3");  // inhibit pulse (ZSW1 bit 3 = 0)
  // Engage new contactor here
  "lastSelect" := "motorSelect";
END_IF;
"driveWord".%X0 := "runEnable";           // ON after contactor made

In StartDrive, the equivalent mapping is set in "Control Word / Status Word" mapping (free interconnect via BICO).

12. Motor Identification After DDS Switch

Whenever motor parameters are changed substantially (different kW, different manufacturer, different frame), run the identification routine for that DDS slot:

• P1900 = 2 — stationary identification. Drive measures stator resistance, leakage inductance, and saturation curves without rotating the shaft. Safe for uncoupled loads. ~30–60 s. Required after every DDS edit where P0305 changes by more than ~10 %.
• P1900 = 1 — rotating identification. Requires mechanical decoupling. Measures rotor time constant and magnetizing curve. Best accuracy. Triggered automatically after first ON with P0340 > 0 in some firmware builds.

13. Multi-Motor Operation (Identical Motors) — Reference

For a use case where several identical induction motors must run in parallel from a single G120 (typical in pumps or fans where each branch motor is a redundant unit), refer to the Siemens knowledge base article SINAMICS G: Preconditions to operate several motors on one converter. Key constraints:

• Up to 50 identical standard induction motors can be supported.
• All motors must be the same type (same manufacturer, same kW, same frame, same winding).
• Stationary (P1900 = 2) or rotating (P1900 = 1) identification must be run; the procedure differs from single-motor commissioning.
• Thermal protection is collective; no individual i²t per motor.
• This is not the same as DDS switching. Multi-motor operation does not use DDS — the motors share a single set of parameters.

14. Verification and Commissioning Checklist

For each configured DDS, run the following checklist before declaring the system operational:

1. Confirm nameplate data match the parameters: printout P0304..P0311 indexed at each slot.
2. No-load current at 50 Hz in r0027 should be 25–50 % of P0305; if lower than 15 % the motor may be wired delta/star wrongly.
3. Rotation direction: command +5 Hz via JOG, verify mechanical rotation matches STW bit 11. Reverse two phases if mismatched.
4. Ramp times P1120/P1121: verify no F0001 (overcurrent) on full ramp.
5. Load step response: apply rated load, check r0027 settles within 1 s. Excessive oscillation indicates ADC-resolution issues (oversized drive).
6. Thermal model: after 1 hour at rated load, drive temperature (r0037) should be below 80 % of overtemperature threshold. Inspect motor OLR trip indicators.
7. PROFINET diagnostics: trigger PLC-CPU stop; drive must continue on last setpoint (configurable) or coast to stop (P1142 = 1 default).
8. Safe Torque Off (STO) test if CU240E-2 F variant: pull STO inputs; output must drop within 5 ms.

15. Troubleshooting Matrix

16. Recommended Architecture for the Example Project

For the 3 kW + 14 kW + 37 kW motor set, the engineering-correct architecture is:

• Drive A: SINAMICS G120 with PM240-2 18.5 kW (45 A) + CU240E-2 PN-F. Serves the 3 kW and 14 kW motors via DDS0 / DDS1, switched by contactors K1 / K2. Current ratio 14 kW motor: 1.75× (acceptable). 3 kW motor: 8.2× — borderline; consider reducing PM to 11 kW (FSB, 26 A) which gives 4.7× for the 3 kW motor (still slightly over the 3× rule for SLVC; suitable for V/f).
• Drive B: SINAMICS G120 with PM240-2 45 kW (90 A) + CU230P-2 PN. Dedicated to the 37 kW motor, single DDS0. Current ratio 1.3×.
• PLC S7-1500 arbitrates contactor K1/K2/K3 selection, ensures exclusive operation, manages DDS bits on PROFINET.