Commissioning Siemens SINAMICS G120 Sensorless Vector Control

Commissioning Siemens SINAMICS G120 in Sensorless Vector Control Mode (SLVC)

On a basic truck-assembly conveyor line, two SINAMICS G120 drives (1 kW and 4 kW) operated on PROFIBUS, parameterized for V/f control, showed large speed errors across the 0–100 % setpoint range — only the 0 % and 100 % setpoints matched the actual speed. After verifying the motor nameplate data and re-running quick commissioning, the V/f accuracy remained insufficient. Sensorless vector control (SLVC) is the next step because it closes a speed loop on a flux-model-estimated speed, providing far better speed accuracy at low rpm and improved load disturbance rejection than linear V/f with slip compensation.

This reference documents the exact parameter set, motor identification procedure, PROFIBUS setpoint normalization, fault handling, and verification steps required to switch a SINAMICS G120 CU240E-2 DP (or equivalent) from V/f to SLVC, while keeping the existing PLC, PROFIBUS telegram, and motor cabling untouched.

1. Application Profile and Why V/f Is Not Sufficient

Conveyor applications with light-to-medium mechanical loading and modest dynamic requirements are usually fine with linear V/f (P1300 = 0). Accuracy problems appear when:

• The load varies (boxes of different mass on the belt), causing real-time slip that V/f cannot compensate fast enough.
• Operation is required below 10 % of rated speed — V/f's speed estimate is open-loop below this band on SINAMICS.
• The motor runs at partial load with non-linear torque curves (typical of induction motors driving gearboxes).

V/f with linear characteristic is intrinsically an open-loop frequency controller; it does not measure or estimate rotor speed. SLVC adds a software model of the asynchronous motor and regulates the torque-producing current component (Iq) and the flux-producing component (Id), deriving speed from the model. This delivers:

2. Prerequisites Before Changing P1300

1. Confirm Control Unit. Read the rating label on the front of the Control Unit. Only CU240E-2, CU240E-2 DP, CU240E-2 PN, CU240E-2 F, and CU250S-2 support P1300 = 20. Attempting SLVC on a CU240B-2 results in fault F01505 "Closed-loop control not supported by this Control Unit".
2. Read the motor nameplate. Capture: motor type, rated voltage (V), rated current (A), rated power (kW), cos φ, rated frequency (Hz), rated speed (rpm), and the connection (star/delta). The PM240-2 / PM250 Power Modules use the induction motor data — not synchronous — unless a 1FK7 / 1FT7 synchronous servo is being driven (which requires P1300 = 21/22 and additional commissioning).
3. Mechanical decoupling for rotating measurement. If you intend to run a rotating motor identification (P1900 = 2 or 3), the motor shaft must be uncoupled from the gearbox and conveyor. The rotating ID accelerates the motor up to roughly rated speed and back, which is unsafe if the load is attached. Plan for the time the line is offline.
4. Back up the current parameter set. Save with the IOP, BOP-2, or STARTER / Startdrive to a memory card or project file so you can roll back if commissioning fails.
5. Document the PROFIBUS configuration. Note the slave address (P0918), the configured telegram (P0922), the reference speed (P2000), and the ramp times (P1120, P1121). The vector-control change must not alter the PLC program.

3. Quick Commissioning: From Factory Reset to SLVC

Sequence used to put both the 1 kW and 4 kW G120 drives into SLVC. Parameter numbers are SINAMICS G120 (firmware V4.7 SP6 and later, parameter structure documented in the SINAMICS G120 Parameter Manual).

3.1 Factory Reset (Optional but Recommended)

1. Set P0010 = 30 (commissioning parameter filter for factory reset).
2. Set P0970 = 1 to start the factory reset.
3. Wait until the drive returns to run-ready (no fault, P0010 reverts to 0 automatically). This typically takes 10–20 s.

3.2 Enter Quick Commissioning

1. Set P0010 = 1 (quick commissioning).
2. Set P0100 = 0 (SI units: kW, Hz, A — change to 1 for hp / °F if your region uses US units).
3. Set P0205 = 0 to use the Power Module default; only adjust if a specific application profile is loaded.

3.3 Enter Motor Data (Match the Nameplate Exactly)

3.4 Select the Control Mode

1. Set P1300 = 20 — speed control without encoder (SLVC). Value 21 is "with encoder" (requires CU250S-2 and connected encoder). Value 22 is torque control without encoder. See SINAMICS G120 List Manual, parameter P1300, for the complete options list.
2. Accept with OK / read the next prompt.

3.5 Set Application Limits, Reference Speed, Ramps

3.6 Configure PROFIBUS Communication

1. Set P0918 = <slave address> (e.g., 3, 4 — must match the PROFIBUS configuration in the PLC).
2. Set P0922 = 1 (Standard Telegram 1, PZD-2/2). Standard Telegram 1 provides STW1 (control word) and NSOLL (speed setpoint) from the PLC, and ZSW1 (status word) and NIST (actual speed) back. P0922 = 3 is Standard Telegram 3 (PZD-4/4) if your PLC uses it.
3. Confirm P2051[0] = r2050.0 (STW1) and P2051[1] = r2050.1 (NSOLL). These are the default interconnect points and do not normally need to be changed when using Standard Telegram 1.
4. Set P0010 = 0 (drive ready). The drive will leave commissioning mode at this point.

4. Motor Data Identification (Mandatory for SLVC)

V/f is self-commissioning once nameplate data is correct; SLVC is not. The flux model needs measured stator resistance, leakage inductance, rotor time constant, and (for the highest accuracy) the moment of inertia. SINAMICS provides two motor data identification routines:

4.1 Procedure (P1900 = 3)

1. Decouple the motor shaft from the gearbox / conveyor. Lock the uncoupled shaft if free rotation is a hazard.
2. Set P1900 = 3 and acknowledge the prompt on the IOP/BOP-2 (or with STARTER "Accept").
3. Issue ON command via PROFIBUS (STW1, bit 0 = 1) with NSOLL = 0.
4. The drive executes a stationary measurement (small impulses) followed by a controlled acceleration to about rated speed and back. This takes 30–120 s depending on motor inertia.
5. When the drive returns to ready and P1900 reads 0 (or 0.0), the identification is complete. The internal parameters P0356 (stator leakage inductance) and P0357 (rotor time constant) are now populated and the speed controller Kp/Tn are pre-tuned.
6. Re-couple the motor and load.

5. PROFIBUS Setpoint Normalization

The PLC sends a 16-bit speed setpoint to the drive. The relationship is:

• 100 % = 2¹⁴ = 4000_HEX = 16384_DEC
• 0 % = 0
• −100 % = C000_HEX = 16384_DEC (two's complement)

The 100 % point corresponds to P2000 (the reference speed). Example, with P2000 = 1500 rpm and a desired 150 rpm setpoint:

Setpoint = (150 rpm / 1500 rpm) × 16384 = 1638_DEC = 0666_HEX

5.1 Detailed Speed Setpoint (DWORD)

If the application needs a finer setpoint than ±0.006 % (16-bit resolution), use Standard Telegram 3 (4 PZD) or a free telegram with a 32-bit NSOLL_D. The 32-bit setpoint is normalized against P2000 using 2³⁰ = 4000 0000_HEX. The PLC then issues the raw 32-bit word directly — useful for ramps that need sub-rpm accuracy.

5.2 Status Word and Actual Speed

The drive returns ZSW1 and NIST in the receive buffer. Bit fields used by SINAMICS in ZSW1 (refer to the SINAMICS G120 List Manual for the full set):

6. Sending a Frequency (Hz) Setpoint Instead of RPM

Mitsubishi drives (FR-A800 / E700) accept a frequency setpoint over their bus. The SINAMICS G120 with PROFIBUS is a speed-controlled drive — the setpoint is normalized to P2000 in rpm, and the drive internally converts rpm → Hz via the motor pole pairs.

There are two practical ways to obtain a frequency-driven feel from the PLC:

1. Match P2000 to the 50 Hz equivalent speed. For a 4-pole induction motor at 50 Hz the synchronous speed is 1500 rpm. Set P2000 = 1500. Then a 1 % setpoint = 15 rpm = 0.5 Hz. This is the simplest approach and is what the customer on the conveyor line is using.
2. Use a free telegram with the frequency setpoint interconnect (NSetF). Configure a free telegram and route PZD3 / PZD4 to a connector that scales the raw value to Hz. This requires STARTER/Startdrive and is rarely needed for conveyors.

Do not change P2000 after PROFIBUS is configured without re-checking the PLC scaling block — the PLC's 100 % must match the new P2000 or the drive will run at the wrong speed.

7. Common Faults When Switching to SLVC and Their Causes

Full fault list is in chapter "Faults and alarms" of the SINAMICS G120 Operating Instructions.

8. Commissioning Procedure: Final Step-by-Step

1. Confirm hardware: CU240E-2 DP variant, correct Power Module, motor nameplate values recorded.
2. Issue a factory reset (P0010 = 30, P0970 = 1). Wait for run-ready.
3. Enter quick commissioning: P0010 = 1. Set P0100, P0205, then all P0300 series parameters to match the nameplate exactly.
4. Set P1300 = 20 (SLVC). Set application limits P1080, P1082, P2000, ramps P1120, P1121, P1500 = 6 (fieldbus).
5. Set PROFIBUS: P0918 = slave address, P0922 = 1 (Standard Telegram 1). Verify P2051[0/1] defaults.
6. Exit commissioning: P0010 = 0.
7. Mechanically decouple the motor from the conveyor. Set P1900 = 3. Issue ON via PROFIBUS. Wait for the drive to return to ready. P1900 should now be 0.
8. Re-couple the motor.
9. Run at low speed (10 % of P2000). Verify actual speed on the PLC or with the IOP — SLVC error should be within ±1 % of setpoint.
10. Run at rated speed. Verify the actual speed matches setpoint within ±1 %.
11. Apply a step load (e.g., place a test mass on the belt) and confirm the speed dip is within ±5 % and recovers in < 1 s.
12. Save the parameter set to the operator panel memory card or upload with STARTER / Startdrive for backup.

9. Verification Checklist

10. Field-Proven Caveats

• SLVC will not operate below ~2 % of rated speed with stability on most induction motors. If the conveyor must creep below that band, either accept V/f in that band, or move to encoder-based vector control (CU250S-2).
• Do not skip P1900. Nameplate values alone are not enough — the rotor time constant (P0357) is critical to the flux model and is not on the nameplate. Without P1900 the SLVC model is grossly inaccurate and the drive will fault within seconds of ON command.
• Cable length matters. For long motor cables (> 50 m), add the motor cable resistance to P0350 (line resistance) before P1900 = 3, or the model will overcompensate voltage drop.
• Star vs delta. A 230/400 V motor wired in star on a 400 V drive behaves differently than a 400/690 V motor in delta. P0335 must match the actual connection in the motor terminal box.
• Braking: with a conveyor, ramp-down regenerates. The PM240-2 has an integrated brake chopper; set P1231 to 1 to enable and dimension the brake resistor to the kinetic energy of the loaded belt.
• PROFIBUS integrity: for noisy industrial environments, the PROFIBUS connector's terminating resistor must be ON at the last physical node only, and shield continuity must be present on both ends of the bus cable.

11. FAQ