Siemens SINAMICS Overspeed Fault: Speed Loop Tuning Guide

Problem Definition: Overspeed Trips on a SINAMICS Drive

An overspeed fault on a Siemens SINAMICS platform almost always originates in one of three layers: the speed setpoint channel has been commanded above the configured maximum, the speed controller has overshot the setpoint hard enough to trip the monitoring threshold, or the mechanical load is back-driving the motor (overshoot through stored kinetic energy) after a rapid deceleration. Before any P/I tuning is attempted, the engineer must determine which layer is firing the fault, because the remedy for each is fundamentally different.

The relevant SINAMICS fault identifiers are:

The most common field complaint is F07901 with the message text "Motor overspeed." When the drive is operating in sensorless vector control (SLVC) without an encoder, overspeed trips are typically produced by the controller winding up during a load-reject transient, not by a true motor runaway. Sensorless drives have no way to know the true rotor angle above a few Hz, so the controller integrates slip to estimate speed; a sudden load release causes the integral term to push the frequency up until the estimate trips the threshold.

Platform Identification: SINAMICS G vs SINAMICS S

Before changing any parameter, confirm the platform. The discussion often centers on a SINAMICS G120, G120C, G130, G150, S110, S120, or S150. The control structure differs in important ways:

The SINAMICS S/G List Manual is the canonical reference for every parameter mentioned in this article. Always confirm parameter numbers against the firmware version installed on the Control Unit (CU); indices in square brackets (e.g. p0300[0]) indicate the Motor Data Set (MDS), and motor data identification writes only into the active MDS.

Motor Equivalent Circuit Parameters (P350 to P360)

A SINAMICS overspeed fault that survives a fresh auto-tune almost always traces back to motor data that was either entered manually from the nameplate only, or carried over from a previous motor without a stationary identification. The motor equivalent circuit parameters below must be populated and sensible before speed-loop tuning begins:

The two most diagnostic values for an overspeed problem are:

• p0350 (stator resistance): too low and the drive believes the motor is faster than it is; too high and the field-weakening transition overshoots. Verify the cold value matches the nameplate Zs at 20 °C.
• p0360 (magnetizing inductance): miscalculated magnetizing inductance pushes the flux controller into saturation, which forces the speed controller to push the frequency higher to maintain torque, producing an apparent overspeed.

Running Motor Identification (p1910)

1. Set p1900 = 2 (motor identification all data, with rotating measurement) or p1900 = 1 (stationary only) when the motor cannot be uncoupled.
2. Set p1910 = 1 to accept the test sequence.
3. Set p1960 = 1 for speed controller optimization (rotating, requires no-load run).
4. Issue ON/OFF1 within 20 seconds.
5. Read back p0350, p0354, p0356, p0358, and p0360. Compare stator resistance with the value the motor manufacturer publishes.

Current and Flux Controller Parameters

Speed loop tuning on SINAMICS is performed on top of two inner loops: the flux controller (field-oriented) and the current controller (torque-producing). Both are normally auto-tuned by p1910, but they must be sanity-checked before the speed loop is touched.

A current controller with p1717 too low oscillates at the switching frequency harmonic (typically 2 to 4 kHz) and the resulting torque ripple is misread as speed ripple by the SLVC estimator, producing an overspeed trip. A flux controller with p1590 too high over-fluxes the motor on a step load change, which the speed controller interprets as extra speed and cancels by stepping the frequency down — the resulting cancellation transient can undershoot then overshoot.

Field sanity check: with the motor unloaded and stationary, command a 10% step in torque setpoint and trace r0079 (torque setpoint total) and r0080 (torque actual value). The torque actual should reach 95% of setpoint in less than three current-controller cycles. If it rings, raise p1717 by 25% and re-test.

Speed Controller Parameters: Encoder vs Sensorless

The two parameter pairs that consistently cause confusion in the field are:

• p1460: Speed controller P gain (with encoder)
• p1462: Speed controller integral-action time, s (with encoder)
• p1470: Speed controller P gain, sensorless
• p1472: Speed controller integral-action time, s, sensorless

The Siemens convention for the integral term is integral-action time in seconds: smaller = faster integrator = hotter tuning. This is the opposite of the proportional-band convention used on some older DC drives. Field engineers who are cross-trained on drives that use I-gain must convert mentally — a "hotter" I on a Siemens drive means a lower number.

Field-Proven P/I Speed Loop Tuning Procedure

The empirical approach described in the original field report — disable I, raise P until oscillation, back off 10%, then re-introduce I — works for the majority of non-servo applications. The expanded procedure below adds the safety checks that turn the heuristic into a reproducible commissioning recipe.

Prerequisites

• Motor identification completed and current/flux controller sanity-checked.
• Trace configured for r0060 (speed setpoint before filter), r0061 (actual speed unfiltered), r0079 (total torque setpoint), and r0080 (torque actual). Trigger on setpoint step.
• Mechanical load coupled and confirmed free (see Mechanical Diagnostics below).

Step-by-Step

1. Disable the integrator. Set p1472 = 10000 (effectively 10000 s) on SLVC, or p1462 = 10000 on VC/servo. The I-term is now out of the loop.
2. Start at 50% of expected P gain. The auto-tune value from p1960 is the starting point. Halve it.
3. Apply a small speed step. A 10% step around 30% rated speed is the standard test point — too low and friction dominates, too high and the speed controller is in field weakening.
4. Raise P gain in 25% increments. Watch r0080 (torque actual). The first sign of instability is oscillation in torque actual at a frequency below the speed-loop natural frequency (typically 2 to 8 Hz on a gear-coupled industrial load).
5. Back off 10% from the oscillating gain. This is the stable P ceiling.
6. Halve that value for the working point. Most process applications run at half the stable ceiling for headroom against load changes and supply transients.
7. Re-introduce the integrator. Start at p1472 = 1000 ms (or p1462) and step down in 25% increments while re-applying the speed step. Watch for low-frequency oscillation in r0061 (actual speed) below 2 Hz.
8. Back off 10% from the oscillating I-time. Record the final p1460, p1462, p1470, p1472 values.
9. Verify across the operating range. Repeat the step test at 25%, 50%, 75%, and 100% rated speed. Field-weakening reduces the effective torque per amp and the loop will be looser there.

Alternative: Symmetric Optimum

For process drives with a known inertia, the symmetrical optimum calculation provides a non-iterative starting point:

p1460 = (p0341 × 2π) / (p1112 × p1496 × 60 / (2π)) × 1/2

where p0341 is total inertia kg·m², p1112 is the speed controller sampling time (typically 1 ms), and p1496 is the scaling for the precontrol. Most engineers use the empirical method above because the inertia is rarely known accurately and the mechanical resonance frequencies of the load are not captured in any formula.

Reading the Speed and Torque Trace

A typical trace of an overspeed event shows three identifiable phases:

1. Command ramp: speed setpoint changes, torque spikes to overcome load and accelerate.
2. Recovery to setpoint: actual speed catches up, torque settles near steady-state.
3. Post-recovery transient: this is where the field report shows torque dropping below steady state, then jumping back up after several hundred milliseconds — and it is this phase that causes the F07901 trip.

The post-recovery signature is diagnostic. Two patterns are common:

Mechanical Causes of Speed Loop Oscillation

Many overspeed trips reported as tuning problems are mechanical problems that the controller has correctly detected. Before re-tuning, perform the mechanical checks below:

• Free rotation: turn the motor shaft by hand through one complete mechanical revolution. Listen and feel for bearing detents, rubbing, or endplay. A bent shaft or seized bearing presents as periodic torque disturbance.
• Coupling alignment: laser-align gear and direct couplings. Misalignment by more than 0.05 mm/m produces a once-per-revolution torque pulse that the speed controller integrates into a speed error.
• Backlash: gear trains with more than 0.5° of backlash show the "load disengage / re-engage" signature in r0080. Backlash can be quantified by commanding a small direction reversal with the motor unloaded and measuring the dead band.
• Chain drives: a chain climbing a sprocket tooth causes a sudden mechanical shock and a brief speed excursion. Check for proper tension — slightly slack is preferred to over-tight.
• Conveyor / roll systems: a free roll with a seized bearing drags the belt out of position. When the belt releases, the spring-back produces a transient the controller cannot distinguish from a motor runaway.
• Resonant structures: long conveyor spans and crane girders have torsional resonances in the 1 to 5 Hz range. A speed controller with bandwidth higher than the resonance amplifies the resonance. Identify the resonance by tapping the structure and watching r0080 decay.

Mechanical Verification Procedure

1. Lock out and tag out the drive. Confirm zero energy at the motor terminals.
2. Hand-rotate the load through at least two full revolutions. Document any binding, detent, or rubbing.
3. Inspect couplings for visible wear, missing hardware, or grease contamination.
4. Measure chain tension with the supplier's gauge; compare to specification.
5. Re-energize with the speed setpoint at 5% rated and observe r0080 on the trace. Any periodic torque component at the rotation frequency indicates a mechanical issue.

Commissioning with Starter and TIA Portal

SINAMICS G120 and S120 drives are commissioned through either the legacy STARTER tool (current builds maintained for service) or the integrated TIA Portal Startdrive environment. The tuning procedure is identical in both; the trace interface differs.

STARTER

1. Online → Select target device → Connect via PROFIBUS or PROFINET.
2. Project navigation → Drives → [Drive name] → Commissioning → Control structure.
3. Open the trace recorder (Trace → Function generator → Speed step).
4. Trigger: r0061 (actual speed) deviation from r0062 (speed setpoint after filter) > p2163.
5. Use the function generator's "step" signal type to generate the speed test pulse described in the tuning procedure above.

TIA Portal / Startdrive

1. Project tree → Devices & networks → [SINAMICS] → Online & diagnostics.
2. Commissioning → Control structure → Speed controller.
3. Trace viewer is integrated. Trigger setup is identical to STARTER.
4. Function generator is in the same panel.

For TIA Portal projects, the online parameter view respects the active Control Unit firmware version. The SINAMICS S/G List Manual is the canonical parameter reference and is published by Siemens Industry Online Support. The user list in the project should be backed up to the SD card of the Control Unit (p0977 = 1) after every tuning change.

Verification and Acceptance Test

After commissioning, capture the following acceptance record:

Save the trace recordings to the project folder. If a follow-up service call is required, the saved traces are the fastest path to a diagnosis.

Troubleshooting Matrix

Reading r0947 (fault value) and r2124 (alarm value) is mandatory before changing any parameter. The drive records the actual speed, torque, and current at the moment of fault; those values narrow the search space to a single layer.

Disarming or Raising the Overspeed Threshold

Disarming F07901 is rarely the correct response and should be considered only when the trip has been conclusively traced to a sensor noise or measurement artifact. The relevant parameters are:

• p2162: Threshold for overspeed detection (Hz). Default = p1082 + a small margin. Raise by 5% to add headroom for genuine overshoot.
• p2150: Hysteresis for "n > n_max" message.
• p2181: Load monitoring response enable. When load monitoring is configured, overspeed can be re-classified as a warning instead of a fault.

To convert the fault to a warning, set the corresponding response in p2100 / p2101 (fault / response mapping). The mapping depends on the firmware version; the SINAMICS S/G List Manual documents the current table.

FAQ