SINAMICS S120 PM340 Dynamic Braking with CU320-2 DP Setup

SINAMICS S120 PM340 Dynamic Braking with CU320-2 DP Setup

The SINAMICS S120 drive platform pairs a CU320-2 Control Unit with PM340 blocksize Power Modules to build high-performance multi-axis servo and vector systems. When the driven load is high-inertia, the application requires fast E-stop or OFF3 ramps, or an overhauling load is present, the regenerative energy pumped back into the DC link must be dissipated as heat through an external braking resistor switched by the PM340 internal chopper. This reference documents the wiring topology, the chopper parameter set, and the alarm diagnostics required to commission a PM340 chopper under a CU320-2 DP Control Unit via a CUA31 adapter, and to resolve the recurring F30002 DC-link overvoltage fault that fires when the resistor is wired but the chopper control is misconfigured or undersized.

System Architecture and Component Roles

The S120 with CU320-2 DP and PM340 is a hybrid topology: the higher-level control intelligence of a booksize Control Unit combined with the cost-effective blocksize Power Module. A typical dynamic-braking configuration uses the following components.

For a 75 kW PM340 with the matching 8.2 Ω resistor, this is a factory-approved stock combination. The chopper IGBT and the DC-link capacitor bank are integrated inside the PM340 housing; no external chopper module is required. A CUA31 (PM340 ≤ 22 kW frame FSA-FSC) or CUA32 (PM340 ≥ 30 kW frame FSD-FSG) is the only way to connect the PM340 PM-IF to the CU320-2 DRIVE-CLiQ ring.

The 821.5 V DC figure that the operator observed on a 22 kW PM340 application is the F30002 hardware trip threshold, not a software controller trip. A correctly wired and configured chopper will clamp the DC link at the 775 V chopper switch-in level, so a reading of 821.5 V at the moment of trip indicates the chopper never fired or fired too late.

Braking Resistor Hardware Integration

Before any parameter work, verify the wiring. The PM340 exposes a defined terminal block for the resistor and (where fitted) the thermal contact.

Terminal Assignments

On the lower terminal block of the PM340, the resistor wires to:

• DCP – positive DC-link rail; tied internally to the DC+ bus of the module.
• R1 – brake-chopper collector output; one side of the chopper IGBT inside the PM340.
• R2 – second chopper terminal; on smaller frames R1 and R2 are shorted internally inside the resistor housing and only DCP+R1 (or DCP+R2) is used. On larger frames (FSD-FSG) R1 and R2 are separate studs and the resistor's two leads land on DCP and R1 (or DCP and R2) with the second stud used for the thermal contact loop.

For a typical 75 kW frame FSD/FSE PM340 the wiring is: resistor lead 1 → DCP stud, resistor lead 2 → R1 stud. The thermal contact pairs to a digital input on the PM340 X122 strip or, if a CUA31 is used, to a digital input on the CUA31 X132/X142 connector.

Thermal Contact Integration

Most Siemens-approved braking resistors include a normally-closed thermal switch that opens at the resistor's rated maximum case temperature. The contact can be wired to:

• r722.x – raw digital-input status word; used to monitor the contact state.
• p0730, p0731, p0732 – binector input (BI) source for digital outputs DO 0/1/2; used to forward a fault to an external relay.
• p2100 / p2101 – fault configuration: assign the digital input to fault F30011 (brake resistor thermal overload) so the drive trips on a contact open.

Wiring the thermal contact is not strictly required for the chopper to operate. Without it, the resistor relies on the I²t thermal model of p0219. If p0219 is left at zero and the contact is unwired, sustained over-braking can destroy the resistor and present a fire risk.

Resistance Verification

With the drive de-energized, the line disconnected, and the DC link bled for at least five minutes, measure the resistance between DCP and R1 (or DCP and R2) using a four-wire ohmmeter. The reading should match the nameplate value within ±10 %:

• 8.2 Ω ± 0.8 Ω for the 75 kW / 80 kW reference design.
• 27 Ω ± 2.7 Ω for the 22 kW / 1.2 kW design.

If the reading is open-circuit, the resistor has tripped its internal thermal fuse (some 6SE70 series units have a one-shot thermal fuse) and must be replaced. A shorted reading indicates that the chopper IGBT has failed closed; remove and bench-test the PM340 before re-energizing the line.

Brake Chopper Threshold and DC-Link Behaviour

The PM340 chopper switch-in level is fixed by hardware and is not a configurable parameter. For a 400 V class PM340 the relevant operating points are:

The fixed 775 V chopper threshold means a properly wired and configured PM340 will begin dissipating regenerative current through the external resistor the moment the DC-link reaches that point. The VdcMax controller (p1240) is a software ramp-extender that engages slightly below the chopper threshold. If p1240 is set to engage below the chopper switch-in level, the controller and the chopper compete and the result is poor braking performance, chopper oscillation, or a direct overshoot to F30002.

Parameter Configuration

Default commissioning with STARTER or Startdrive does not always expose the chopper-relevant parameters on the standard parameter list. The expert list must be enabled to access p0219, p1240, p1280, and p1360. In STARTER, right-click the drive object (DO2) and select Expert list; in TIA Portal / Startdrive, check Show all parameters in the parameter editor view.

Essential Brake Parameters

Why p1240 = 0 Is Correct When a Chopper Is Wired

The VdcMax controller is a software extension of the ramp-function generator. It does not dissipate energy; it only reduces the deceleration rate so that the motor absorbs the regenerated energy as rotor loss. With a properly sized chopper and resistor, the hardware will clamp the DC link at ≈ 775 V and the VdcMax controller is unnecessary. More importantly, if p1240 is enabled and the controller engages below the chopper switch-in point, it will reduce the ramp slope before the chopper has a chance to fire, and the actual DC-link voltage may never reach the chopper threshold. The result is a slower-than-required stop with no resistor activity, and on a heavy regeneration event the controller saturates and the DC-link overshoots to F30002.

The correct commissioning sequence is therefore:

1. Wire the resistor and verify resistance as described in the previous section.
2. Set p0219 to the resistor's rated continuous power.
3. Set p1240 = 0 (VdcMax controller disabled).
4. Set p1280 = 0 (VdcMin controller disabled unless an Active Line Module is fitted).
5. Configure p1360 = 1 (chopper enabled).
6. Save the project and download to the CF card / non-volatile memory.
7. Perform a no-load commissioning run, then a loaded deceleration test at 50 % and 100 % of rated speed.

Parameter Reference Detail

p0219 – Braking Resistor Power Threshold. This value defines the average power the thermal model permits before tripping F30011. The parameter is in watts and is compared against an I²t integration of the resistor's instantaneous dissipation. For a 27 Ω, 1.2 kW continuous resistor, set p0219 = 1200. For the 8.2 Ω, 80 kW reference design, the resistor's continuous rating (not its peak rating) is the correct entry; for the standard 6SE7090 8.2 Ω / 80 kW unit this is typically 1.5 kW to 5 kW depending on the resistor's selected duty class. Entering the peak power instead of the continuous rating will defeat the I²t protection and allow the resistor to overheat.

p1240 / p1245 / p1247 – VdcMax Controller. These three parameters form a closed-loop controller with the ramp-function generator. p1240 enables the controller, p1245 sets the switch-in level (in V DC), and p1247 is the proportional gain factor. The default p1245 (≈ 757 V) is intentionally just below the chopper threshold so that the controller acts as a software fallback if the chopper is not fitted. If the chopper is fitted and p1240 is left at 1, the controller engages first and prevents the DC link from reaching the chopper threshold, so the chopper never fires. The correct setting with a fitted chopper is p1240 = 0.

p1280 / p1281 – VdcMin Controller. Mirror image of the VdcMax controller, used to extend the acceleration ramp if the DC link sags under a motoring surge. The PM340 does not need this controller for a passive-line-supply application; the line and DC-link capacitors provide sufficient energy. The VdcMin controller is used in systems with an Active Line Module (ALM) where regen transitions can pull the DC link below the motoring threshold.

p1360 / p1362 – Brake Chopper. p1360 enables the chopper IGBT and the I²t model; p1362 reports the actual switch-on threshold (read-only on the PM340). On firmware versions where p1360 was introduced, a factory-reset default of 0 has been observed; verify p1360 = 1 after any firmware upgrade or full restore.

Alarm and Fault Diagnostics

The most common alarm on a PM340 with a non-functional or undersized chopper is F30002 DC-link overvoltage. Other related events include F30011 Braking resistor thermal overload and A06800 Drive: DC-link voltage has reached warning threshold.

Fault F30002 – DC-Link Overvoltage

F30002 is a fault (OFF2 trip) that fires when the DC-link voltage exceeds the hardware cutoff threshold (≈ 820 V on a 400 V PM340). The alarm value r0949[0] reports the actual DC-link voltage in volts. When the operator reports 821.5 V DC on the bus at the moment of trip, the drive is at the F30002 cutoff, not at a software controller trip. The chopper, which should have clamped the DC link at ≈ 770 V, did not fire in time.

Root-cause analysis for F30002 on a system with a wired resistor:

1. Resistor open-circuit – measure resistance with the drive de-energized; replace if open.
2. Chopper IGBT failed open – the resistor measures correct but the chopper will not fire. Check r1361[0] (chopper IGBT duty cycle) during a controlled deceleration. If r1361 remains at 0 % while the DC link climbs past 770 V, the chopper is not gating.
3. p1240 enabled at a low switch-in level – the VdcMax controller is extending the ramp and keeping the DC link below the chopper threshold until the regenerated energy exceeds the ramped braking capability, at which point the DC link overshoots directly to F30002.
4. Resistor undersized for the cycle – the chopper is firing, but the I²t thermal model (if enabled) or the resistor's own thermal limit saturates the braking energy. Reduce the deceleration ramp time or fit a higher-rated resistor.
5. p0219 left at 0 – the chopper will still fire, but the I²t protection is disabled. This is not normally a root cause for F30002 but should be remediated before any production commissioning.

Verifying Chopper Operation

To confirm the chopper is firing during a deceleration:

1. Place the drive in local jog or use STARTER trace to record a 5-second trace.
2. Open the STARTER trace and record r0070 (DC-link voltage) and r1361.0 (chopper IGBT duty cycle) at 1 ms sample time.
3. Command an OFF1 ramp from rated speed to zero with the motor unloaded.
4. Observe r0070: the DC link should rise to ≈ 770 V, then the chopper should clamp it at 770 – 780 V throughout the ramp.
5. Observe r1361.0: the duty cycle should pulse from 0 % to 50 – 90 % during the regeneration interval.
6. If r0070 climbs above 800 V and r1361.0 stays at 0 %, the chopper is not firing – confirm wiring, then check p1360 setting.

Fault F30011 – Braking Resistor Thermal Overload

F30011 is reported when the I²t integral of the resistor's absorbed energy exceeds the threshold set in p0219. The default response is OFF2, but p2102[0..n] / p2103[0..n] can reconfigure the response. For a 27 Ω, 1.2 kW continuous resistor, set p0219 = 1200. For the 75 kW / 8.2 Ω reference design, p0219 is typically 1500 to 20000 W depending on the application duty cycle (consult the resistor data sheet for the cyclic load curve).

Note: if p0219 is set to 0, the I²t model is disabled and the drive will not trip F30011 even if the resistor is melting. Always set p0219 to a non-zero value before commissioning.

Alarm A06800 – DC-Link Warning Threshold

A06800 is a warning that fires when the DC-link voltage reaches the warning threshold (r0296 default ≈ 750 V). It is informational and will not trip the drive. If A06800 is reported during normal acceleration, the line supply may be sagging or the line reactor is undersized. If it appears only on deceleration, the chopper is firing correctly and the warning is the leading edge of the chopper switch-in event.

Resistor Sizing Worked Example

For a 22 kW PM340 with a 27 Ω, 1.2 kW continuous external resistor, the design peak braking power at the chopper switch-in level is:

P_peak = V² / R = 770² / 27 = 21.96 kW peak

With p0219 = 1200 W, the chopper thermal model allows the resistor to absorb up to 1.2 kW of average energy indefinitely. Above this average, the model accumulates I²t and trips F30011. A 1.2 kW resistor with a typical 100× peak overload rating (≈ 120 kW for 100 ms) can handle the worst-case 22 kW / 1 s regeneration event from rated speed without damage. If the application requires more than 1 s of continuous regeneration at 22 kW, a higher-rated resistor or a regenerative line supply (Active Line Module) must be used.

For the 75 kW PM340 with 8.2 Ω, 80 kW resistor:

P_peak = V² / R = 770² / 8.2 = 72.3 kW peak

This is consistent with the 80 kW peak rating of the resistor. The continuous rating of a stock 6SE70 8.2 Ω unit is 1.5 kW to 5 kW, so set p0219 to the resistor's continuous rating. The thermal model will then limit the average dissipated power to the continuous rating and prevent resistor failure on cyclic overloads.

Commissioning Procedure

Use the following sequence when commissioning a fresh S120 + CU320-2 + PM340 + external resistor system.

Prerequisites

• STARTER V5.4 or later, or TIA Portal / Startdrive V16+ with the SINAMICS support package installed.
• CU320-2 DP firmware appropriate for the PM340 hardware (consult the Siemens Industry Online Support compatibility list for the exact pairing).
• DRIVE-CLiQ cables between the CU320-2, CUA31, and any SMC/SME sensor modules.
• PROFIBUS DP connection (or PROFINET for the CU320-2 PN variant) to the higher-level controller.
• Motor data sheet for the driven motor: rated current, voltage, speed, encoder type.
• The SINAMICS S120 List Manual and Operating Instructions for the firmware version installed.

Step-by-Step Commissioning

1. Power up the CU320-2 with 24 V at X124. Verify that all DRIVE-CLiQ nodes come up green on the diagnostic LEDs (the CUA31 port LEDs and any sensor module port LEDs).
2. Open STARTER (or Startdrive) and connect to the CU320-2 over PROFIBUS or Ethernet. The drive objects should appear: CU320-2, PM340 (drive object DO2), and any sensor modules.
3. Run the configuration wizard. Select the PM340 power module from the catalog and assign the motor. The wizard will set p0210 (line voltage) and p0300 / p0301 (motor data).
4. Enable the expert list: right-click DO2 in the project tree and select Show expert parameters. Confirm that p0219, p1240, p1280, p1360, and p1362 are now visible.
5. Configure the chopper parameters:

   p0219 = 1200   ; Braking resistor power threshold (W)
   p1240 = 0      ; VdcMax controller disabled
   p1280 = 0      ; VdcMin controller disabled (no ALM fitted)
   p1360 = 1      ; Brake chopper enabled

6. Wire the thermal contact (if fitted) to a free digital input and parameterize the response via p2100 / p2101 fault configuration.
7. Save the project and download to the CF card or directly to the drive's non-volatile memory (RAM-to-ROM with Copy RAM to ROM).
8. Perform a motor identification run (p1910 for stationary identification, p1960 for rotating identification if the motor can be decoupled from the load).
9. Test the chopper: command a controlled deceleration from rated speed with the motor unloaded. Use a STARTER trace to capture r0070 (DC link) and r1361.0 (chopper duty). Verify the clamp at 770 – 780 V.
10. Load test: with the motor coupled to its load, command OFF1 and OFF3 ramps at 25 %, 50 %, and 100 % of rated speed. The DC link should stay below 790 V at all times, and the drive should not report F30002 or F30011.
11. Thermal soak: run the production cycle for at least one hour under the worst-case load profile; verify that the resistor's surface temperature stabilizes below the resistor's rated case temperature.

Verification Checklist

Troubleshooting Matrix

Edge Cases and Field Notes

CUA32 versus CUA31. The CUA32 adapter is the PROFINET / Ethernet variant of the CUA31; it is functionally equivalent for chopper purposes. The chopper wiring on the PM340 side is identical regardless of which CUA is used.

Firmware compatibility. On older CU320-2 firmware where p1360 was not an exposed parameter, the chopper was always enabled by default. After a firmware upgrade, p1360 may default to 0 on a fresh restore. Re-verify p1360 = 1 after any firmware upgrade or full parameter reset.

PM340 with Active Line Module (ALM). If the S120 is supplied from an ALM (booksize Active Line Module) rather than a passive line, the ALM can regenerate energy back to the line. The PM340 chopper is still functional and should be retained as a hardware safety; the ALM and the chopper can coexist. In this case, p1280 (VdcMin controller) is typically set to 1 with the appropriate switch-in level, because the ALM can pull the DC link below the motoring threshold during regen transitions.

PM340 with Basic Line Module (BLM). The BLM cannot regenerate. The PM340 chopper is mandatory whenever the BLM is the supply and overhauling loads or fast ramps are present.

Multiple PM340 on a common DC bus. When several PM340 modules share a common DC bus (permitted only with an Active Line Module supply and a DC bus link), each PM340 must have its own braking resistor; one central chopper cannot be shared.

Resistor in parallel. Two identical braking resistors can be wired in parallel only if the resulting resistance is above the PM340 chopper's minimum permitted value. On the 400 V class PM340 the chopper IGBT is sized for a minimum resistance (typically 3.1 Ω for frames FSA-FSC, 2.0 Ω for FSD-FSG). Two 8.2 Ω resistors in parallel produce 4.1 Ω, which is within the FSA-FSC minimum and is acceptable. Verify the PM340 manual for the exact minimum resistance for the specific frame size.

PM340 with Smart Line Module (SLM). The SLM is a borderline-regenerative line supply; it can accept regeneration for a limited time window (typically 5 s) and then closes the line thyristors and waits. The PM340 chopper is required as a safety to clamp the DC link during the SLM's non-regenerative intervals.

Operation on a generator supply or UPS. When the PM340 is fed from a generator or a large UPS with a high source impedance, the line voltage can rise under regenerative load. The chopper clamps the DC link at 770 V regardless of line behaviour, but the line-side overvoltage can trigger a different alarm (F30009 on the line side). Coordinate the chopper and the line-side protection.

Encoderless operation. Sensorless vector control (SLVC) on the PM340 will still operate the chopper correctly, because the chopper is purely a DC-link function. Encoder loss only affects the motor's torque and speed control loops, not the chopper.

Hot swap of the CU320-2 or CUA31. The chopper parameters are stored on the CU320-2 and on the CF card (if fitted). After a hot swap, verify p0219, p1240, p1280, and p1360 are still set as expected; a parameter restore from a non-matching project file can overwrite the chopper settings.

Troubleshooting checklist for p0219 not visible. If p0219 does not appear in the parameter list, the most common reasons are: (1) the expert list is not enabled, (2) the drive object is not the PM340 (verify the correct DO is being edited), (3) the commissioning tool is filtering parameters by access level, or (4) the firmware version does not support p0219. Address these in order; the expert list toggle resolves 90 % of the "missing parameter" reports.

Frequently Asked Questions