Resolving Masterdrive MC Servomotor Vibration and F015 Fault

Resolving Masterdrive MC Servomotor Vibration and F015 Fault

When a Siemens Masterdrive MC (SIMOVERT Master Drives Motion Control, 6SE70 series) is commanded to enable a permanent-magnet synchronous servomotor in position-control mode, the drive normally ramps to zero speed and locks the rotor. If the rotor instead oscillates, hunts, or nods left-to-right even with a zero velocity setpoint, the root cause is almost always one of three conditions: (1) the power-cable phase sequence (U/V/W) does not match the encoder's electrical pole position, (2) the encoder-to-rotor zero is not aligned to the drive's model, or (3) the speed and position loop gains are too aggressive for the mechanical coupling. Each condition produces a characteristic symptom and a specific remedy, and getting the order wrong can lead to either a noisy, oscillating axis or, worse, an undetected over-speed event that destroys the inverter because of field-weakening collapse. The reference case documented in this guide produced both vibration and an F015 (motor blocked) trip, and was resolved by combining a phase-rotation correction with a careful retune of the speed and position controllers.

1. System Overview and Symptom Description

The reported configuration is a SIMOVERT Masterdrive MC controlling a brushless AC servomotor (a permanent-magnet synchronous machine, PMSM). The drive is set to position and speed regulation, and follows an absolute encoder mounted on a separate mechanical reference. The reference encoder is the master, the servomotor is the slave, and the drive is acting as a position follower. This master/follower topology is common in web-handling, indexing, and print-registration machinery, where one motor establishes the line speed and torque and a downstream motor must lock to a precise angle of product.

Observed symptoms:

• On enable with zero velocity setpoint, the motor shaft oscillates a small angle (a few electrical degrees) at a few hertz, producing audible chatter.
• Raising the speed setpoint eliminates the stall but the audible vibration remains at all speeds.
• No fault is present during the vibration, and the drive remains in operation (run state, not fault state).
• After swapping any two of the motor power leads, the noise changes character: the audible chatter at zero speed vanishes, but the shaft now nods from one side to the other and the drive trips with Fault F015 (motor blocked).

This combination — vibration at zero speed plus an F015 after a phase swap — is the diagnostic signature of a pole-position/encoder offset problem on a synchronous machine.

2. Why Phase Sequence Matters on a Synchronous Motor

For an induction motor, swapping two phases reverses rotation direction and the drive can be made to spin the other way simply by changing the sign of the speed setpoint. For a permanent-magnet synchronous motor the situation is fundamentally different: the rotor carries high-energy magnets that the drive must align to a rotating stator field at all times. The drive receives a rotor angle from the encoder (or resolver), and computes the voltage vector that should produce torque along the quadrature (q) axis. The angle used to transform stationary-frame currents into rotating-frame d/q components is the electrical angle:

θ_electrical = (pole_pairs) × θ_mechanical + θ_offset

If the three power leads U, V, W are connected in the wrong sequence relative to the encoder's count direction, the drive's model of the rotor position is offset from the actual magnetic axis of the rotor. The drive then commands a voltage vector that is rotated by ±120 electrical degrees from the correct torque-producing vector. The two consequences are:

1. Field-aligned output. The drive's voltage lands mostly on the d-axis. The result is no useful torque, full magnetic loading, and the rotor locks against a strong stator field that is not at the rotor's actual pole. The motor hums, draws high current, and does not rotate.
2. Field-weakening output. The drive's voltage lands mostly on the negative d-axis, weakening the permanent-magnet flux. With reduced back-EMF, the same DC-bus voltage accelerates the rotor far above rated speed. If OFF1 (ramp stop) or OFF3 (quick stop) is commanded, the drive briefly remains in regulation, but as soon as OFF2 (coast, pulse inhibit) is selected, the field collapses, the back-EMF rises sharply, and the DC-bus voltage can exceed the IGBT module's breakdown rating in a few milliseconds.

This is why an undetected phase-sequence error on a Masterdrive MC is more dangerous than the same error on a generic V/Hz drive: the field-orientation controller actively fights the mis-alignment by driving into field-weakening instead of tripping on a phase-loss or overcurrent detection.

3. Fault F015 (Motor Blocked) — Drive-Side Detection

F015 is raised by the drive's load-monitoring and stuck-rotor logic. The drive supervises the deviation between commanded and measured speed (or, in torque-mode, between torque and a speed threshold). On a Masterdrive MC the relevant parameters are:

F015 by itself is the least harmful reaction to a stuck rotor because the drive is already detecting that the rotor is not following the command. The dangerous case is a mis-phased synchronous machine that does not trip F015 but is in field-weakening — the controller thinks the rotor is moving, and the user thinks the drive is healthy. The combination of symptoms (low-speed oscillation + F015 after a phase swap) confirms that the initial wiring was field-weakening, and the corrected wiring produced a stalled but properly-fluxed rotor.

4. Diagnostic Decision Tree

The following flow distinguishes the three most common causes of zero-speed oscillation on a Masterdrive MC synchronous axis.

5. Pre-Commissioning Verification

Before any parameter change, record the current parameter set to a DriveMonitor / Drive ES trace file so the original state can be restored. The Masterdrive MC parameter set is held in the EEPROM file and should be backed up via the serial or PROFIBUS interface using the SIMOVIS or DriveMonitor tool. Note that the Masterdrive MC platform was discontinued by Siemens, and the official commissioning tool is Drive ES Masterdrives. The legacy product page on the Siemens support site documents the basic toolchain.

5.1 Power wiring check

1. De-energize the drive and lock out the upstream disconnect. Wait five minutes for the DC-bus capacitors to discharge below 50 V (the drives's red DC-bus LED must be off).
2. Inspect the motor junction box. Verify the motor nameplate U/V/W against the cable conductors and against the drive's terminal block X2: U → X2:U, V → X2:V, W → X2:W.
3. Check the shield termination: the motor cable shield must be bonded to the drive's PE terminal at the drive end and to the motor frame at the motor end. A broken shield is the most common cause of encoder-angle-related instability.
4. Verify that the motor's protective-earth conductor is bonded to the drive's PE at the same point. Induced common-mode currents from a floating PE will appear as oscillation.

5.2 Encoder wiring check

1. Identify the encoder interface module installed in the drive: SBP (resolver), SBR (incremental sin/cos), or SBM (EnDat / SSI absolute).
2. Confirm the encoder pulses per revolution (P141) match the nameplate of the encoder — typical values are 2048, 4096, 8192 for incremental, or 13 to 25 bits for EnDat singleturn.
3. Confirm P142 (encoder type / signal evaluation) is set to match the connected module: 1 for resolver, 2 for TTL, 3 for sin/cos 1 Vpp, 4 for EnDat.
4. Confirm the encoder cable shield is bonded at the drive end only, with the motor-end shield left floating. This is the opposite of the power-cable practice and is the single most common wiring mistake on a Masterdrive MC.

6. Pole-Position Identification (P130 / P191)

The Masterdrive MC has built-in routines to identify the rotor's electrical pole position relative to the encoder's zero mark. The two are not the same thing — the encoder's zero is set at the factory, but the rotor's north pole is on the magnetic axis of the rotor and the two are offset by an unknown amount until the drive measures them. The commissioning routine captures this offset and stores it in the parameter P195 (encoder offset) so that on every subsequent enable the drive applies the offset before doing field orientation.

Procedure:

1. Disable the drive; do not allow any motion command during identification.
2. Set P130 = 1 (motor type = permanent-magnet synchronous).
3. Set P191 = 1 (start pole-position identification on next enable). The drive applies a low-frequency rotating field, measures the current signature, and computes the angle. The motor must be free to rotate a few electrical degrees during this step; clamp the load if necessary to prevent mechanical excursion.
4. Enable the drive. The routine takes 0.5 – 3 s, during which r0029 (drive status word) shows identification active.
5. When identification completes, save the result to EEPROM (P971 = 1).
6. Cycle the enable. The drive now uses the stored offset and the motor should hold zero speed without oscillation.

If oscillation persists, the most likely cause is that the encoder's count direction is reversed relative to the motor. The motor's mechanical rotation direction must increase the encoder count. If not, swap the encoder's A and A/ signals in the drive's encoder module, or invert the sign with the parameter P143 (encoder direction).

7. Speed and Position Loop Tuning

If the wiring and the pole-position identification are correct and the axis still hunts, the loop gains are too high for the mechanical inertia and coupling. The Masterdrive MC separates the speed and position controllers, and the cascade must be tuned outer to inner: current first, then speed, then position.

7.1 Tuning procedure

1. Start conservative. Set P235 = 0.2, P240 = 200 ms, P204 = 5, P195 = 4 ms. The axis should be sluggish but stable. If it still oscillates, the problem is mechanical or wiring, not tuning.
2. Step the speed setpoint. Command a small step in speed (e.g. 5 % of rated) and observe the response. With DriveMonitor's trace function, log r021 (actual speed), r023 (speed controller output), and r015 (current iq).
3. Raise P235 until you see a single overshoot of 5 – 10 % at the step. Each raise of P235 tightens the speed response.
4. Lower P240 in small steps (e.g. 200 → 100 → 50 ms) until the overshoot increases. The P240 that gives a clean step response is your speed-loop integral time.
5. Add P195 in 2 ms increments. Each increase attenuates the resolver feedback noise by a first-order filter. Too much P195 makes the response sluggish; too little lets the noise excite the loop.
6. Raise P204 for position-loop performance. A good initial target is P204 ≈ 0.5 × P235 / J_mech, where J_mech is the total inertia at the motor in kg·m².
7. Verify under load. Re-test with the actual load. Coupled inertia in a Masterdrive / servomotor / gearbox / load chain can be 10× the motor's own rotor inertia, and the position loop Kv must be scaled accordingly.

8. Setpoint Smoothing and the Role of P195

P195 is a first-order low-pass filter applied to the speed setpoint before it is compared to the measured speed. The filter's purpose is not to clean the encoder — the encoder is hardware-filtered at the SBR/SBM module — but to remove the quantisation steps that appear when the position setpoint is generated by a PLC at a low update rate (typically 4 – 20 ms). On a Masterdrive MC, the position setpoint is interpolated internally, and the residual step at each interpolation point excites the speed loop as a torque impulse. P195 attenuates these impulses before they reach the current controller.

The default is 0 ms, which is correct for drives that receive a smoothly interpolated setpoint from a SIMOTION or SIMATIC controller over PROFIBUS at 1 ms cycle. For drives that receive setpoints from a slower controller, or from a master encoder via the drive's pulse-input or master/slave interface, P195 should be set to 2 – 4 × the controller's cycle time. A value of 4 – 8 ms is typical for a Masterdrive MC following an absolute encoder over the SIMOLINK fiber ring.

9. Verification Procedure

Once the wiring, pole-position identification, and tuning are complete, run a structured verification before returning the axis to production.

1. Standstill current. With the drive enabled and zero setpoint, record r015 (torque-producing current) and r016 (flux-producing current). On a properly-tuned synchronous axis, both should be less than 5 % of rated.
2. Step response. Apply a 5 % step in speed setpoint. Record r021 (actual speed) and the time to reach 95 % of setpoint. The expected value is 30 – 100 ms depending on the loop tuning.
3. Position following error. Apply a small position step and record r040 (following error). The error should peak at 1 – 5 % of the step size and decay to zero within 50 – 200 ms. A persistent oscillation in the following error means P204 is too high.
4. Direction reversal. Command a square-wave position setpoint. Listen for mechanical chatter; an audible clack at the reversal is a sign of backlash, not oscillation, and is a separate concern from this guide.
5. Thermal check. Run the axis at 50 % rated speed for 15 minutes. The motor case temperature should stabilise below the motor's class rating (typically 130 °C for class B, 155 °C for class F). Sustained elevated temperature after a wiring change can indicate that the drive is still in field-weakening.
6. F015 regression test. With the load applied, command a stall (mechanically lock the shaft) and verify the drive trips F015 within the time set in P216.

10. Edge Cases and Field-Proven Caveats

• Long motor cables. If the motor cable exceeds 50 m, the cable capacitance loads the drive's output filter and the controller's model of the electrical plant is wrong. The result is a 1 – 3 Hz hunting at low speed. Solutions: a sine-wave filter at the drive output, or use a drive with a higher switching frequency (raise P110 in the Masterdrive MC).
• Encoder cable near power cables. Routing the encoder cable in the same tray as the motor power cable couples switching transients into the encoder lines. The SBR and SBM modules have differential receivers that reject common-mode noise, but the 80 kHz – 1 MHz spectrum of the IGBT edges is hard to reject. Move the encoder cable to a separate tray with at least 200 mm of separation.
• Resolver-to-encoder retrofit. Replacing a resolver with an absolute encoder without re-running P191 leaves the old offset in the parameter set. The result is an F015 at first enable. Always re-run pole-position identification after any encoder change.
• Mechanical wear. The Masterdrive MC is a long-life platform and the typical field-failure on a multi-year-old machine is a worn coupling or a stretched belt, not an electronic fault. Before changing parameters, inspect the mechanical chain: key the pulley to the shaft, check the belt tension, and verify the coupling alignment.
• Stator on a servomotor. Servomotors with a stalled rotor that has been powered in field-weakening for an extended time can be permanently demagnetised. After the corrective wiring change, verify the no-load back-EMF constant (Ke) at a known speed. A Ke that is more than 10 % below the nameplate indicates irreversible demagnetisation and the motor must be replaced.

11. Safety and Discontinuation Notice

The SIMOVERT Master Drive (6SE70) and Master Drive Motion Control (6SE70 MC) product families were officially discontinued by Siemens AG. New units are no longer manufactured, and spare-parts availability is limited. Existing installations must be maintained on the legacy toolchain (DriveMonitor, Drive ES Masterdrives, SIMOVIS), and field service is provided by Siemens Industrial Customer Support on a best-effort basis. When upgrading an installation, the modern successor platform is the SINAMICS S120 family, which retains the same field-oriented control architecture with a different parameter set.

12. Frequently Asked Questions