Resolving Siemens MM440 F0002 and A0910 on High-Inertia Fan Loads

The Siemens MICROMASTER 440 (MM440) is a robust sensorless vector drive, but on applications with high rotational inertia—industrial fans, large flywheels, rotary tables, centrifuges, and large-diameter machine-tool indexers—the drive will routinely trip on Fault F0002 (DC-link overvoltage) and report Alarm A0910 (Vdc-max controller de-activated). This reference explains the precise electromechanical mechanism behind both indications, the parameter set that controls the regenerative path, and the full resolution matrix from a software-only retune to a properly dimensioned dynamic braking resistor (DBR).

1. Problem Summary

2. Root Cause: Why a Fan Regenerates Energy

Any rotating mass stores kinetic energy. When the drive decelerates the motor (or the load back-drives the motor), that energy flows from the load through the motor (now acting as a generator), through the inverter IGBTs (acting as a passive diode bridge), and into the DC-link capacitor bank. The DC-link voltage rises until one of three things happens:

1. The Vdc-max controller (P1240) extends the ramp so kinetic energy dissipates as motor losses.
2. The dynamic brake chopper (P1237) switches the DBR across the bus and burns the energy as heat.
3. The DC-link voltage crosses the hardware trip threshold and the drive declares F0002.

For a fan application, the dominant energy term is rotational kinetic energy:

E_kin = 0.5 × J × ω²

where J is the total inertia referred to the motor shaft (kg·m²) and ω is the angular velocity (rad/s). The peak regenerative power the drive must absorb during a controlled stop is:

P_regen = E_kin / t_decel

Halving the deceleration time doubles the peak regen power. Tripling the load inertia triples the energy. This is why shorting the ramp on a 10 m-diameter rotary table is an electrical catastrophe even though the mechanical stop looks gentle.

2.1 DC-Link Nominal and Trip Levels

For a 3-phase uncontrolled rectifier front end, the average DC-link voltage is:

V_dc,nom = 1.35 × V_LL = 1.35 × 430 = 580.5 V DC

At no load, the capacitor peak charges to:

V_dc,peak = √2 × V_LL = 1.414 × 430 = 608 V DC

The MM440 trip threshold for F0002 on 400 V class units is approximately 820 V DC (factory-fixed, not user-adjustable on MM440 hardware). The brake-chopper turn-on threshold (P1237) is factory-set near 760 V DC for 400 V class. The user is reporting 785 V DC, which is already 25 V above the chopper threshold and within 35 V of the trip—operating on borrowed time.

3. Fault and Alarm Reference

3.1 F0002 — DC Link Overvoltage

F0002 is a latching trip. Once the DC-link voltage exceeds the hardware threshold, the IGBT gate drivers are inhibited, the output is removed, and the drive coasts the motor. The drive will not restart until the fault is acknowledged and the DC bus has discharged below the undervoltage lockout.

3.2 A0910 — Vdc-max Controller De-activated

A0910 is a status alarm, not a trip. It is raised when the firmware Vdc-max controller is configured (P1240 = 1 or 3) but has been forced off because the controller was unable to hold the bus at the requested level. The drive signals A0910 to tell the operator that the software clamp is no longer protecting the drive and a hardware brake is mandatory.

4. Parameter Map for the Overvoltage Path

The MM440 exposes the entire regen-energy path through a small set of parameters. Set these in the order shown during commissioning.

5. Diagnostic Procedure (Before Touching Parameters)

Capture the following readings before changing any parameter. Reproducibility matters; if you cannot reproduce the trip, you cannot verify the fix.

1. Read the actual line-to-line voltage with a true-RMS meter at the drive input terminals, not at the transformer secondary. Look for swells above 430 V and imbalance > 2 %.
2. Connect a scopemeter or MM440 trace tool (Starter/StarterDrive, DriveMonitor) and capture DC-link voltage at the moment of the ON command and at every stop event. Plot V_dc vs. time.
3. Read r0026 (actual DC-link voltage) and r0031 (actual torque) into the trace.
4. Read the fault buffer: r0947[0..7] and the associated values r0949[0..7] for the trip context.
5. Read the alarm buffer: r2110[0..n] and the time stamp r2111[0..n]. Confirm the F0002 is preceded by A0910 within seconds.
6. Verify the brake chopper is enabled (P1237 = 1) and the chopper hardware is fitted. On MM440, the chopper is internal up to 75 kW; confirm the resistor is wired to the correct terminals (typically DC+ and B+ on the power terminal block).
7. Measure the DBR resistance cold and hot. A 10 % drift in resistance shifts the chopper duty cycle and the dissipation power.
8. Verify the motor data: P0304, P0305, P0307, P0310, P0311 match the nameplate. A motor rated 50 Hz/400 V can be over-fluxed if P0310 is 60 Hz; the slip becomes negative and the drive tries to brake continuously.
9. Compute J_total referred to the motor shaft using the load inertia divided by the gear ratio squared plus the motor rotor inertia. The MM440 cannot do this for you; you need the mechanical engineering input.

6. Step-by-Step Resolution

6.1 Immediate Workaround (No Hardware Change)

If the drive is required to run today and the DBR is on order, perform these steps in order.

1. Set P1240 = 1 (Vdc-max controller on). If the controller was set to 0, the user set it correctly to 1 already.
2. Increase P1121 (ramp-down) to 60–120 s. A 2.5 s ramp-down on a high-inertia load is a guaranteed trip. The ramp time must satisfy:
   t_decel >= 2 × E_kin × η / (T_motor × ω) with a comfortable 30 % margin.
3. Increase P1120 to 30–60 s only if the user is also tripping during the ON command. A 500 s ramp-up is excessive and will cause the drive to stall on the current limit; revert to a value consistent with the motor's thermal capability, typically 30–60 s for a fan.
4. Enable compound braking: P1236 = 50 %. This adds a controlled regen path through the motor's own stator copper loss; it does not eliminate the need for a DBR but it reduces the peak regen power seen at the bus.
5. Enable flying start: P1200 = 1. On a fan, residual airflow keeps the rotor turning after a stop command. When the operator issues the next ON command, the drive synchronizes to the actual rotor speed instead of injecting a hard step from 0 Hz. The transient that produces the 785 V DC spike during start is largely a flying-start problem, not a ramp problem.
6. Reduce P1243 (Vdc-max dynamic factor) only if A0910 still fires at the very end of the ramp—this is a sign the controller is overshooting and the ramp is shortening past the actual physical deceleration. Leave at 100 % unless you have a scope trace justifying a change.

6.2 Primary Fix: Dimension and Install a Braking Resistor

The MM440 internal brake chopper is rated to fire at ~760 V DC on 400 V class units. With the chopper enabled (P1237 = 1) and a properly sized DBR wired to the brake terminals, the bus is clamped at the chopper threshold during regen and the drive never sees 785 V DC.

6.2.1 Resistor Sizing

The required peak braking power equals the regen power calculated from the application:

P_peak = (J_total × ω²) / (2 × t_decel)

The continuous dissipation rating is the average regen power over the duty cycle:

P_cont = P_peak × (t_decel / t_cycle)

For the 10 m rotary table case with 15 kW motor and assumed J_total ≈ 4000 kg·m² referred to the motor shaft (typical for such a load through a 100:1 reducer):

• Motor rated speed ≈ 1500 rpm → ω ≈ 157 rad/s
• E_kin = 0.5 × 4000 × 157² ≈ 49.3 MJ at motor shaft, but referred to the table, the table itself stores E_kin = 0.5 × J_table × ω_table² where ω_table is the table's angular velocity, not the motor's. Through the reducer, the energy is the same, but the table's effective inertia seen by the motor is the table inertia divided by the gear ratio squared.
• For practical engineering, use the time-averaged dissipation. If the table cycles every 90 s and decelerates in 2.5 s, the duty ratio is ~2.8 %.

For an 18.5 kW MM440 fan application, Siemens' recommended 6SE70 family and the MM440 400 V DBR selection chart gives a typical 4 Ω / 10 kW peak / 1.5 kW continuous resistor. Always cross-check against the drive's minimum allowed resistor value in the MM440 operating instructions; using a smaller resistance will exceed the chopper's peak current rating.

6.2.2 Resistor Wiring

Route the brake cables separately from signal cables; the chopper switching edge is a 50–200 V/µs transient that couples readily into analog harnesses.

6.3 Confirm the Chopper Is Firing

After wiring, force a controlled regen event and read r1239.0 (chopper active flag) on the BOP/AOP. If the flag does not toggle, the chopper is either not enabled (P1237 = 0) or the DBR is open-circuit. The MM440 will silently tolerate an open DBR—F0002 will still trip and you will assume the DBR is undersized when the actual fault is no DBR at all.

7. Software-Only Fixes (No DBR Available)

On a subset of high-inertia applications the regen energy is small enough that a DBR is not required. The following parameter combinations can stop the F0002/A0910 sequence without hardware. Confirm with a 24-hour scope trace before declaring victory.

7.1 Vdc-Max Controller + Long Ramp

This is the default recommendation for the user's case. Set P1240 = 1 and lengthen P1121 until the Vdc-max controller can absorb the regen by extending the ramp dynamically. The controller's authority is roughly:

ΔV_dc,max = P1243 × P1240_factor × (P_motor / I_dc,cap)

In practice, set P1121 to a value 30 % longer than the natural mechanical stop time of the load. Measure the natural stop by turning the drive off and timing the rotor with a tachometer.

7.2 Flying Start

On a fan, when the drive is told to start, the rotor is rarely stationary. The ON command against a 200-rpm turning rotor causes the drive to attempt an instantaneous step from 0 Hz to 50 Hz. The energy required to magnetize and accelerate the rotor in the first 50 ms can produce the exact 785 V spike the user is seeing. P1200 = 1 searches the actual rotor speed and synchronizes to it. The spike disappears within one or two start cycles.

7.3 Compound Braking

Set P1236 = 50 % to inject an additional DC component on top of the Vdc-max controller action. Compound braking forces a controlled regen current through the motor windings; the energy dissipates as I²R loss in the stator. This is not a substitute for a DBR on a 55 kW drive, but it will buy headroom for a 2–5 second ramp on a low-to-moderate inertia fan.

7.4 DC Braking at Standstill

Use P1232 and P1233 to apply a holding DC current once the ramp-down reaches zero speed. This is not regen clamping; it is a post-stop holding torque. It will not stop F0002 on its own but it will prevent back-rotation of the load that produces a different class of F0002 trip on the next start.

7.5 Kinetic Buffering (P1240 = 2 or 3)

The Vdc-min controller draws energy from the DC link during a brownout to keep the drive alive using the load's kinetic energy. P1240 = 3 enables both Vdc-max and Vdc-min. This does not fix F0002 directly, but it is a useful diagnostic: if the Vdc-min side fires on a controlled ramp-down, the load inertia is so high that the same energy is available for a controlled regen—and a DBR is definitely required.

8. Mechanical-Side Solutions

The user's second case—10 m-diameter rotary table with 15 kW motor through a reducer—is a textbook case where the fault is electrical in name only; the cause is mechanical energy storage. Software alone will not solve this. Consider:

1. DBR sized for the worst-case inertia and shortest ramp time. Reuse the formula in §6.2.1 with the actual J_total from the mechanical datasheet.
2. Regenerative line-side converter (Active Line Module, AFE). If the user has multiple drives on the same bus, a shared regenerative front-end (e.g., Siemens SINAMICS Active Line Module) can sink the energy back to the line. This is the engineering solution for systems above 100 kW total regen.
3. Mechanical brake. A spring-applied, electrically-released brake on the motor or the table shaft clamps the load electrically instead of dissipating it in the drive. The drive no longer has to absorb the energy. This is the standard solution on machine-tool rotary tables.
4. Add a fluid coupling or torque limiter between the motor and the load. The inertia seen by the motor is reduced, the regen energy is reduced proportionally, and the existing drive may cope without a DBR. Verify that the process tolerates the slip.
5. Verify gear reducer backlash. A reversing load with backlash will momentarily motor, then regenerate, then motor again within a few hundred milliseconds. The MM440 sees the regen event as a separate stop and trips independently. Tighten the reducer or switch to P1240 = 3 with a fast-responding P1243 = 150 %.

9. Commissioning Verification

After applying any fix, run the following verification sequence. The drive is not considered commissioned until every step passes.

1. No-load test: Run the drive unloaded through three full accel/decel cycles at 60 s up, 120 s down. Monitor r0026 and confirm the DC link stays below 720 V DC throughout. No F0002, no A0910.
2. Loaded run-up: Apply the working load. Capture r0026, r0031, and r0052 on a 30 s trace. Confirm the DC link never crosses 760 V DC (the chopper threshold).
3. Loaded emergency stop: Trigger OFF3 (P1135). Confirm the drive decels within the configured time without F0002. The ramp profile should be smooth, not two-stepped.
4. Direction reversal under load: Issue a forward command, then a reverse command without a stop in between. This is the user's reported failure mode. Confirm the DC link does not spike. If it does, increase P1121 and P1135 by 50 % and re-test.
5. 24-hour endurance: Leave the drive on its normal duty cycle for 24 h. Check the fault buffer at the end. Zero F0002 events is the bar.
6. DBR thermal check: With the drive operating at the worst-case duty cycle, measure the DBR case temperature with a calibrated probe. Confirm it is below the resistor's rated surface temperature (typically 250 °C for wirewound, 350 °C for stainless-steel-grid).

10. Troubleshooting Matrix

11. Field-Proven Caveats

• The Vdc-max controller is a ramp stretcher, not a regen absorber. It can only slow the deceleration. It cannot dissipate energy that the load insists on delivering. On a 55 kW fan with a 4 MJ load, the controller will always give up and A0910 will fire.
• A0910 is the canary. If you see A0910 in the alarm buffer without an accompanying F0002, you are one or two stops away from a trip. Treat the alarm as a P1 service call, not a nuisance.
• DBR resistance is deceptively critical. Too low a resistance exceeds the chopper's peak current rating and destroys the IGBT; too high a resistance does not dissipate enough power and the bus still rises. Use the value specified in the MM440 operating instructions for the specific power rating. Do not improvise.
• Mechanical inspection matters. On the rotary table case, the user observed that the trip occurs only in one rotation direction. This is a hallmark of mechanical backlash or a one-direction brake fault. Replacing the drive or the DBR will not fix it. Open the reducer and inspect.
• Input voltage is high. 430 V AC at the input is at the upper end of the 400 V class tolerance (the MM440 tolerates 380–480 V +10 %). The DC-link nominal of 580 V DC is correspondingly high, leaving only ~240 V of headroom to the 820 V trip. Consider a 5 % input reactor to drop the no-load DC link by ~25 V and gain margin. This is a marginal, not primary, fix.
• The "I changed P1120 to 500 s and it still trips" observation is correct behavior. Ramp-up is not the cause of a regen trip on stop. The user conflated accel and decel. The 500 s ramp-up is also dangerously long for a fan that is being asked to start under load—it will exceed the motor's thermal limit before reaching speed.

12. Quick Reference: When to Use Each Solution

13. Related Faults and How to Tell Them Apart

14. FAQ