Resolving SINAMICS S120 F30002 Fault: Vdc Controller P1240 Setup

1. Overview of the F30002 Fault Condition

F30002 is the SINAMICS S120 / S110 drive-side fault code for DC link overvoltage. The intermediate-circuit (DC bus) voltage on the PM340 Power Module has crossed the upper hardware trip threshold, which for 400 V class hardware is approximately 800 V DC (peak rectified of a 480 V line-to-line supply, plus the energy stored in the motor and cable leakage inductance that the capacitors must absorb during a fast stop). The fault is raised by the Control Unit (in the application discussed, a 6SL3040-0LA01-0AA1 Control Unit, CU310-2 PN family) and is logged in the fault buffer with a fault value (r0949) that reports the actual DC link voltage at the moment the trip occurred.

The F30002 entry is one of the most common SINAMICS faults on horizontal-axes and vertical-axes machines that decelerate quickly, that have a high load inertia, or that are subject to an active overhauling load. The three field-proven remedies are:

1. Enable the Vdc_max controller (P1240) so the drive dynamically extends the deceleration ramp whenever the DC bus starts to climb.
2. Install (or verify) an external braking resistor sized to dissipate the peak regenerative energy.
3. Lengthen the OFF1 / OFF3 ramp-down times (P1121, P1135) so the motor cannot pump energy back faster than the chopper (or the Vdc controller) can absorb it.

This reference covers all three paths in detail for the PM340 Power Module 6SL3210-1SE14-1UA0 (1.6 kW, 380–480 V 3 AC) controlled by a 6SL3040-0LA01-0AA1 Control Unit, configured in STARTER V5.x or SINAMICS Startdrive (TIA Portal). The default Siemens documentation does not give a single click path for activating the Vdc controller - this is a known gap that this article fills.

2. Hardware Identification and Topology

Confirm the exact hardware stack before changing parameters. The MLFB numbers in the original post identify a SINAMICS S120 booksize configuration:

The PM340 FSA Power Module includes an integrated braking chopper (IGBT + freewheel diode) but ships without an internal braking resistor. The chopper IGBT activates when the DC link voltage crosses the chopper engagement threshold (typically 760 V DC on 400 V class hardware) and shorts the DCP / DCN terminals through the external resistor, converting regenerative energy to heat. The chopper engagement is fixed and is not the same as the Vdc_max controller - the chopper is a hard clamp, the Vdc controller is a software ramp manager.

If a braking resistor is physically present at the DCP and DCN (or R1 and R2 on the FSA terminal block), measure its resistance with the drive de-energised and confirmed discharged. For the FSA frame, the standard Siemens external braking resistor is rated 200 Ω continuous. A missing, open, or high-resistance resistor is the most common reason the chopper fails to arrest the F30002 trip. Refer to the SINAMICS S120 Power Modules PM340 manual for the terminal layout.

3. DC Link Voltage Thresholds and Fault Value Decoding

Use the diagnostic parameters, not the fault text, to size the fix. The relevant SINAMICS parameters are:

The F30002 trip threshold is not a single fixed value - it scales with p0210. For a 400 V AC line, the threshold is approximately 760 V DC (i.e., √2 × 400 × 1.34). For a 480 V AC line, the threshold rises to approximately 800 V DC. Always confirm p0210 matches the actual line voltage before changing any controller parameter; a mis-set p0210 is a frequent source of nuisance F30002 trips on machines that are moved between facilities.

For F30002 the fault value in r0949 holds the actual DC link voltage (in V DC) at the instant the trip occurred. A value near 800 V DC on a 400 V class line confirms that the bus reached the upper trip threshold. Lower values (e.g., 760 V) suggest the Vdc controller was not enabled (P1240 = 0) and the chopper did not engage, or the engage level is mis-set relative to p0210.

4. Root Cause Analysis: Why the DC Bus Overcharges

The DC bus is a stiff capacitor bank. When the motor regenerates energy (which it does whenever it acts as a generator - i.e., whenever the electromagnetic torque is opposite to the rotation direction), the energy has to go somewhere. The possible sinks are:

1. Losses in the motor (iron + copper + friction).
2. Losses in the cables and the line filter.
3. The line itself (only possible if a line-side Active Line Module is feeding energy back to the grid - the PM340 has a Basic Line Module or unregulated supply, so this path is not available in the standard PM340 stack).
4. The external braking resistor (if fitted and the chopper is enabled).

If the regenerated power exceeds the sum of the first three sinks, and no resistor is present, the DC bus voltage will rise until the chopper engages (if a resistor is present) or until the F30002 trip threshold is reached. The classic scenarios that cause F30002 are:

5. Solution Path 1: Activating the Vdc_max Controller (P1240)

The Vdc_max controller is the software mechanism that prevents F30002 by extending the effective ramp-down time as soon as the DC bus approaches the trip level. The parameter is P1240, "Configuration of the Vdc controller." The Siemens SINAMICS S120/S150 List Manual lists the four valid values:

For a horizontal-axes or general-purpose application where F30002 is the reported fault, set P1240[0] = 1. This is the single most common corrective action for F30002 on a PM340 with a normal-cycle duty.

After enabling, the drive dynamically extends the frequency setpoint ramp during deceleration whenever the actual DC link voltage (r0026) approaches the engage level (r1242). This is not a "brake" - the motor still decelerates, but at a variable rate that adapts to the available dissipation. The result is no F30002 trip but a slightly longer stop time under heavy regenerative loading. The overshoot the original poster observed (overshoot of the actual speed) is a normal artefact of the Vdc controller engaging late - tighten the ramp by reducing P1252 (pre-control factor) or by raising the engage window r1242 (closer to the trip level, but never above it).

Working parameter set for a PM340 with Vdc_max enabled, suitable as a starting point:

p1240[0] = 1          ; Vdc_max controller enabled
p1250[0] = 1.0        ; Proportional gain (default)
p1251[0] = 0.0        ; Integral time = 0 (P-only controller, factory default)
p1252[0] = 1.0        ; Pre-control factor (reduce to 0.5 if overshoot is excessive)
p1253[0] = 0.0        ; Output limit additional (default 0)
p1254[0] = 0          ; Automatic sensing of Vdc engage levels (0 = use calculated values)

If P1240 was already 1 or 3 and the F30002 trip is still occurring, the engage level itself is too close to the trip level - the controller cannot react fast enough. In that case either install a braking resistor (path 2) or lengthen the ramp (path 3), or both. The original poster's experience (overshoot after enabling P1240) is consistent with a load that needs the resistor as well - the Vdc controller alone is not enough at that inertia ratio.

6. Solution Path 2: External Braking Resistor Sizing

The braking resistor is sized from the peak regenerative power, which comes from the kinetic energy of the load divided by the deceleration time. The applicable formulas are:

For a horizontal axis decelerating from ω1 to ω2 in time t_brake, the peak regenerative power is:

P_peak (W) = (1/2) × J_total (kg·m²) × (ω1² − ω2²) (rad²/s²) / t_brake (s)

where J_total is the sum of motor rotor inertia and load inertia reflected to the motor shaft. For a triangular stop profile (most stops in practice), the average power is roughly P_peak / 2.

For an overhauling vertical axis, the regenerative power is continuous:

P_cont (W) = T_load (N·m) × ω (rad/s)

Select a resistor whose continuous power rating is ≥ P_cont and whose peak (short-term, typically 5 s) rating is ≥ 1.5 × P_peak. For the PM340 FSA (1.6 kW), the standard Siemens external braking resistor family in the SINAMICS S120 PM340 catalog is the 6SE7090-0XX84 series (200 Ω class). Use only resistors that are listed as compatible with the FSA frame in the SINAMICS S120 PM340 Power Modules manual. Wire the resistor between DCP and DCN (or the R1 / R2 terminals on the FSA frame) with the conductors sized for the peak current:

I_peak (A) = V_chopper (V DC) / R_brake (Ω)

For a 760 V chopper voltage and 200 Ω resistor, I_peak ≈ 3.8 A, which is well within the chopper rating of the PM340 FSA. Verify the wiring by monitoring r0026 during a controlled stop - the DC bus voltage should peak at r1242 (engage level) and then decay, never reaching r0949 at the trip point.

7. Solution Path 3: Ramp-Down Time Tuning (P1121, P1135)

If the Vdc controller and the braking resistor together cannot prevent the F30002 trip, the final software knob is to slow the deceleration. The relevant parameters are:

The original poster reported success extending P1135 from 1.0 s to 2.4 s and seeing fewer F30002 trips but not eliminating them. This is the expected outcome when the inertia is too high to be controlled by ramp time alone - the Vdc controller (path 1) and / or the resistor (path 2) must also be applied. As a rule of thumb, if the Vdc controller engages for more than 25 % of the deceleration time, the system is too close to the trip level and a resistor is required.

8. STARTER and Startdrive Commissioning Procedure

Use STARTER (legacy offline-online parameterisation) or SINAMICS Startdrive in TIA Portal (the current Siemens commissioning environment, which replaces STARTER for new projects). The procedure below applies to both, with the path adjusted.

STARTER path (legacy)

1. Open STARTER V5.x and connect to the drive. The default connection is PROFINET to the CU310-2 PN (6SL3040-0LA01-0AA1) on IP 192.168.0.2, or RS232 to the X127 port if your drive is older.
2. Right-click the drive object (DO) and select Connect to target system → Online.
3. Navigate to the expert list: Drive → Commissioning → Parameter list, then enable the expert view via Tools → Expert list.
4. Filter for P1240. The parameter appears in function group "DC link voltage monitoring".
5. Set P1240[0] = 1 (or 3 if you also want kinetic buffering).
6. Set P1250[0] = 1.0 and P1251[0] = 0.0 (factory defaults for a horizontal-axes application).
7. Click RAM to ROM (or the icon that writes the parameters to the CF card / persistent memory).
8. Power-cycle the drive (Control Unit + Power Module) so the new values are loaded as the active run-time set.

Startdrive in TIA Portal path (current)

1. Open TIA Portal V17 or later. Open the project that contains the SINAMICS S120 device.
2. Right-click the drive in the project tree and select Go online.
3. Open the parameter view: Drive → Parameters → enable the Expert list via the toolbar icon.
4. Set P1240[0] = 1.
5. If the drive is in the Run state, click Copy RAM to ROM in the toolbar.
6. Execute Commissioning → RESTORE → save RAM to ROM if you want the new value to survive a CU swap.

9. Parameter Reference Table

The complete parameter set for F30002 remediation on a PM340 with Vdc controller enabled and a braking resistor fitted:

10. Commissioning Verification Checklist

After enabling the Vdc controller, the verification sequence below confirms that the fix is in place and that the system can survive the worst-case stop:

1. Read r0947[0] and confirm it is 0 (no active fault).
2. Confirm P1240[0] reads back as 1 in the expert list.
3. Trigger a controlled stop (OFF1) and watch r0026 in trace - it should peak at r1242 (engage level) and settle to the nominal line-rectified value without reaching the F30002 trip level.
4. Trigger a fast stop (OFF3) and watch the same trace. P1135 sets the nominal ramp; the Vdc controller should engage visibly (r1242) and extend the stop time beyond P1135.
5. Power-cycle and confirm the P1240 setting persists in the offline project (Startdrive) and on the drive's persistent memory (CF card / RAM to ROM).
6. Run a full load-inertia worst-case stop (e.g., the load at rated speed, OFF3, no warning) and verify r0026 never crosses the F30002 trip level. Capture a STARTER trace of r0026, r0070, and the speed actual r0063 if overshoot is suspected.
7. Re-check the braking resistor body temperature after 10 consecutive worst-case stops - it should be below the resistor's rated temperature (typically 115 °C for the standard Siemens 6SE7090 series).

11. Troubleshooting Matrix

Symptom → cause → action. Use this when the F30002 trip persists after the standard remediation.

12. Frequently Asked Questions