Resolving SINAMICS S120 F07411 Fault in Torque Control

Problem Overview

A SINAMICS S120 drive configured for closed-loop torque control with a Technology Controller (Dancer / tension PID) raises fault F07411 – Drive: Flux Controller Output Limited immediately after the standstill enables are set, before the winder spool has produced any web. The motor briefly rotates 10–20% of a mechanical revolution and stalls with the flux controller saturated at its maximum output. Reissuing the OFF1/Enable/Torque Enable bit sequence lets the drive run, but the first motion after every restart repeats the same stall and fault event.

The fault signature is specific:

• Fault occurs with the spool already at standstill (zero speed feedback, zero dancer setpoint deviation).
• Fault appears within 1–2 line cycles of the enable edges being set, not after a speed/position transition.
• Technology Controller is producing a torque command that is non-zero on the very first scan (residual setpoint, integral wind-up, or pre-loaded p1511).
• F07411 is reported with F07412, F07413, or F07414 as the secondary causes when the drive shuts down hard.

The root cause is almost never a damaged power module, a defective motor, or a wiring error. The flux controller is hitting its ceiling because the motor has not been magnetized, has not been identified, or is being asked to deliver flux and supplementary torque simultaneously at zero speed with encoderless or low-resolution feedback.

Understanding Fault F07411

F07411 is the standard SINAMICS S120 reaction when the field-weakening / flux model cannot produce the requested flux at the current operating point. It is raised by the closed-loop current control, not by the speed or torque controller. The detailed causes listed in the SINAMICS S120 List Manual are:

The fault value (r0949) typically shows a low-frequency value of 0002 0001 or 0000 0004, meaning the drive is in flux build-up with the flux controller saturated on I_max. The default Siemens S120 remediation text focuses on reducing the load or running motor identification. For a Technology-Controller-driven winder the issue is more subtle.

Root Cause Analysis

Four independent root causes combine to produce the symptom. They must be addressed in the order presented or the fault will reappear even after the first three are corrected.

1. Motor Data Identification Not Yet Performed

If p1910 = 1 (motor data identification, rotating) or p1960 = 1 (speed controller optimization) was not executed against the connected motor, the leakage inductance, magnetizing current, and rotor time constant used by the flux model are first-pass estimates. When a real load is applied at standstill, the flux controller demands more current than the model predicts, the current limit is hit, and F07411 is raised.

The standard commissioning sequence is mandatory before any torque control loop is closed:

1. Set p0341, p0342, p0640 to the actual motor data sheet values.
2. Set p1300 = 21 (torque control, with encoder) or p1300 = 22/23 (sensorless torque control).
3. Run p1900 = 2 (all measurements with parameter change) or p1900 = 1 and then p1910 / p1960 individually.
4. Acknowledge the alarm A07979 (internal rotor position identification) and let the pulse enable complete the standstill measurement.

2. Flux Build-Up Timing vs. Enable Sequence

SINAMICS S120 builds flux in the time window defined by:

• p1570 – Flux setpoint at field-weakening entry.
• p1571 – Time for flux build-up during magnetizing ramp.
• p1572 – Flux setpoint soft-start holding time.
• p1573 – Flux ramp-up time.
• p1574 – Dynamic load-angle limit.

If the Technology Controller is enabled simultaneously with OFF1 and torque enable, the supplementary torque is added to p1511 before the rotor flux has reached rated value. The current controller must simultaneously service the flux ramp and the torque demand. The flux controller saturates and the drive trips.

Correct sequence: pulses enabled → drive at standstill with speed setpoint = 0 → flux ramps to 100% over p1573 → Technology Controller is released last, with the integral component held at zero for the first 200–500 ms.

3. p1511 Preloaded With a Non-Zero Setpoint

p1511[0] is the source of Supplementary Torque 1 added to the active torque limit. On every power-up or re-initialization the parameter itself is zero, but the source connected to it is not. If the source is a PROFIdrive analog or a SIMATIC S7 word that retains its last value, the Technology Controller output (or a stale dancer PI component) is already requesting torque when the enable edges arrive. The drive tries to accelerate the spool against its own stiction and the rotor stalls. The flux controller sees the d-axis current command jump, saturates, and raises F07411.

Verify with r0079 (total torque setpoint) and r0080 (torque actual value) at the moment OFF1 is set. If r0079 is non-zero before the ramp-up, the supplementary setpoint is being written into p1511 from a non-volatile source.

4. Sensorless Operation at Standstill

Sensorless torque control (p1300 = 22 with no encoder) is unstable at exactly zero speed. The flux model loses its reference as soon as the EMF collapses, the observer needs a minimum slip frequency, and any sudden load step looks like a stalled rotor to the controller. F07411 with cause bit 2 is the textbook symptom.

For a winder/dancer application the right choice is closed-loop torque control with encoder (p1300 = 21) plus speed pre-control sourced from the line reference. A speed encoder (HTL, TTL, SSI on the SMCxx, or DRIVE-CLiQ from a Siemens motor) is required for stable standstill torque.

Pre-Checks Before Re-Commissioning

Before re-trying the start-up, capture the following with the drive in parameterization mode (no enable, no pulses). The values must be saved to a STARTER / StartDrive project for traceability.

Step-by-Step Resolution

Step 1 – Lock the PROFIdrive Telegram Before Enabling

The PROFIdrive telegram (typically Standard Telegram 105 with p0922 = 105 or Siemens Telegram 136) must be configured to receive a zero setpoint on the torque word when the PLC is in a controlled ramp-up. Implement this in the SIMATIC S7 logic with a "Drive Ready" handshake:

1. PLC sets STW1.0 = 0 (OFF1 low) on first scan.
2. PLC writes NSOLL_B = 0 (speed setpoint = 0).
3. PLC writes MOMRED or supplementary torque = 0.
4. PLC waits for ZSW1.0 = 1 (ready to switch on) and ZSW1.9 = 1 (control requested).
5. PLC waits an additional p1573 × 1.5 (flux ramp time × 1.5) before ramping torque.

Step 2 – Run Motor Identification

Execute motor data identification end-to-end. From StartDrive V16 or higher:

1. Set p1900 = 2 to start all static and rotating measurements.
2. Enable the drive (OFF1 = 1, enable = 1) with no load attached if possible. The motor will run through controlled acceleration / deceleration cycles defined by p1958 and p1959.
3. Wait for completion. The drive de-energizes automatically when r0046.29 = 0 (motor data identification complete).
4. Save to RAM-to-ROM (Copy RAM to ROM button in StartDrive, or p0977 = 1 via BOP).

If rotating measurement is not permissible in a wound spool (danger of web breakage), run p1910 = 1 (static measurement only) and accept the limited flux-model accuracy. The application will still work, but the dynamic response of the technology controller at low speeds will be reduced.

Step 3 – Configure Flux Ramp Parameters

Tune the magnetizing ramp so that flux is fully built before any torque is requested:

p1570 = 100% (rated flux)
p1571 = 0.05 s (flux build-up smoothing)
p1572 = 0.10 s (soft-start hold time)
p1573 = 0.30 s (ramp-up time)
p1574 = 80° (dynamic load-angle limit)
p1603 = 130% of p0305 (magnetizing current ceiling)

After tuning, monitor r0083[0] (flux actual value) during the enable sequence. It must reach 95% of rated flux within 500 ms of OFF1 going high. If it does not, increase p1603 in 5% steps until it does, but do not exceed the inverter rated current (r0207).

Step 4 – Wire the Technology Controller Correctly

The Technology Controller is enabled via p2200 = 1 (technology controller enable) and the output is wired to p1511[0] (Supplementary Torque 1). A typical tension-controller setup:

p2200 = 1
p2251 = B#0 (tech controller enable = drive status bit)
p2253[0] = r2260 (setpoint from PLC, scaled in %)
p2254[0] = r2261 (actual value, dancer position feedback)
p2255 = 1.0 (Kp – proportional gain)
p2256 = 0.5 s (Tn – integral action time)
p2257 = 0.0 s (Tv – derivative action time)
p2258 = 0.0 (Td delay)
p2260 = ... (setpoint source – from PLC or fixed)
p2261 = ... (actual source – from dancer transducer)
p2263 = r2250 (setpoint after ramp generator)
p2264 = r2251 (feedback signal source)
p2280 = 0.0 s (integral component hold time)
p2285 = 0.0 s (derivative component delay)
p1511[0] = r2294 (tech controller output as supplementary torque)

Critical: at power-up, p2280 (integral hold) must be greater than zero so the I-component is held at zero until the first valid feedback sample arrives. Setting p2280 = 1.0 s is a common safe value for winder applications.

Step 5 – Set Torque Limits

Apply a torque limit that is well within the motor rating during commissioning. Use the SIMATIC S7 Motion Control instruction MC_TorqueLimiting per the Siemens Application Note (109795023) to cap the torque requested by the technology controller. Reference the S7-1500 / S120 torque-limiting PDF for BICO and function block usage:

SIMATIC S7-1500 with SINAMICS S120: Torque limiting (Application Note 109795023)

MC_TorqueLimiting(Axis := winderAxis,
                    Enable := TRUE,
                    Limit := 60.0,    // 60% of rated torque
                    Mode := 1,        // symmetric limit
                    ...);

Verification

After the changes, the verification sequence proves the fix without putting the line at risk:

1. Disable the web pull (line speed reference set to 0).
2. Set the dancer setpoint to a small value (5% of full scale) so the technology controller has a non-zero demand.
3. Apply OFF1 = 1, enable = 1, torque enable = 1 in the proper sequence.
4. Monitor r0046 (status word), r0080 (torque actual), and r0947 (fault code) for at least 5 minutes.
5. Confirm F07411 is NOT raised and that r0079 stabilizes within 2% of r0077 (torque actual).
6. Slowly raise the dancer setpoint to 100% and verify torque response follows the PID output without overshoot > 5%.
7. Issue a controlled OFF1 / OFF2 / OFF3 sequence to verify clean shutdown with no post-disable fault.

Run this loop three times back-to-back. If F07411 does not return, perform a power-cycle and repeat once more.

Field-Ready Parameter Recipe

For a typical 7.5 kW SINAMICS S120 / 1PH8 motor in a winder at 1500 rpm, the following values have been proven in production environments:

Related Faults and Cross-Reference

If F07412 follows F07411, the encoder wiring is suspect. If F07902 follows, the load is too high. If A07965 follows, you are operating in sensorless mode without an encoder – change p1300 = 21 and install a real encoder.

Why the Fault Disappears on the Second Try

When OFF1 is released and re-asserted, the SINAMICS S120 saves the last successful flux model to p1590 and p1592. The first attempt primes the flux model. On the second attempt the controller already knows the rotor position (p0431) and the flux ramp starts from a valid reference, not from a cold start. The user perceives this as "the drive needed a higher initial set point to start rotation" – in reality, the flux model simply needed one enable cycle to learn.

This is why pre-loading the drive by toggling OFF1 once before the production run is a recommended commissioning practice. The first cycle raises the fault and clears it; the second cycle runs clean. Always run a clean cycle at the end of commissioning and verify that no faults are raised.

State Machine for Commissioning

FAQ