SINAMICS G120C Standard vs Dynamic Drive Control: V/F to Vector

Overview of SINAMICS G120C Application Classes

The SINAMICS G120C is a compact, modular frequency inverter (catalog series 6SL3210-5) designed for low-voltage three-phase motors in the 0.55 kW to 132 kW range. The firmware family (FW V4.4 through V4.7 SP3 HF1) exposes three application classes that map directly to the underlying open-loop and closed-loop control strategies:

• Standard Drive Control — Voltage / Frequency (V/F) open-loop, the default commissioning path. Less sensitive to motor data inaccuracy and tolerant of poorly-characterized machines.
• Dynamic Drive Control — Sensorless Vector Control (SLVC). High dynamic response, accurate speed/load behavior, and the ability to deliver full torque at low speed without an encoder.
• Expert Drive Control — Vector Control with speed feedback, requires an HTL/TTL encoder at the G120C's interface module (not available on all frame sizes). Used for high-bandwidth positioning, winder, or hoisting applications.

The application class is selected during commissioning in STARTER, Startdrive (TIA Portal), the IOP-2 Intelligent Operator Panel, or the BOP-2 Basic Operator Panel. Internally, the choice writes parameter p1300 (open-loop/closed-loop control mode) and the surrounding parameter set. Once the application class is changed, the drive must re-initialize the motor model and the motor identification routine should be re-run.

Standard Drive Control — V/F Open-Loop Architecture

Standard Drive Control writes p1300 = 0 (V/f with linear characteristic) or p1300 = 2 (V/f with quadratic characteristic) at commissioning. The drive synthesizes an output voltage whose magnitude follows the setpoint frequency according to a programmable V/f profile, parameterized by:

• p1310 — Voltage boost, fixed (used to overcome stator resistance drop at low speed)
• p1311 — Voltage boost, acceleration-dependent
• p1312 — Voltage boost, startup-dependent
• p1320, p1321, p1322, p1323 — Four-point V/f profile (corner frequency / voltage pairs)
• p1335 — Slip compensation gain (active when p1300 = 0/2 and slip comp enabled)

Because the drive does not solve a motor flux model, V/F control is fundamentally a scalar control law. Speed accuracy at the shaft is governed by natural slip, which is load-dependent; a 1.5 kW four-pole induction motor at 50 Hz and full load can exhibit 5–8% slip, meaning the shaft runs at ~1450 rpm against a commanded 1500 rpm. Slip compensation (p1335) reduces but does not eliminate this error because the rotor time constant is approximated, not measured.

Advantages of Standard Drive Control for screw pump (oil) applications:

• Robust to imprecise motor nameplate data: a 10% error in stator resistance has minimal impact on speed stability.
• No rotating motor identification required; only the static resistance measurement is performed on first RUN enable (per SINAMICS G120 FW V4.7 SP3 HF1 Functions Overview).
• Lower CPU utilization on the Control Unit, leaving headroom for free function blocks (FFB) and trace recordings.

Disadvantages:

• No active current injection, so the drive cannot reliably detect a sudden mechanical stall within the first 200–400 ms. F07900 (Motor blocked) may be raised only after the mechanical event has progressed.
• Torque accuracy at low speed is poor; sustained operation below 3 Hz with high load can cause the drive to enter current limit and stall the motor thermally.
• Speed response to load steps is sluggish (typical 200–500 ms settling time on a 1.5 kW motor).

Dynamic Drive Control — Sensorless Vector Control Architecture

Dynamic Drive Control writes p1300 = 20 (sensorless vector control with speed estimator) and unlocks a closed-loop flux and torque model. The Control Unit uses a two-axis (d/q) reference frame, decoupled flux and torque control, and a Luenberger-style speed observer to estimate rotor speed from stator current and voltage without an encoder. The motor identification routine (p1900) measures the stator resistance, leakage inductance, and (if permitted) the moment of inertia.

Key parameters in SLVC mode:

• p0341 — Motor moment of inertia (kg·m²)
• p0342 — Ratio of total to motor moment of inertia
• p1470 — Speed controller proportional gain (Kp_n)
• p1472 — Speed controller integral time (Tn_n)
• p1610 — Torque setpoint static (open-loop boost for SLVC at low frequency)
• p1750 — Motor model configuration / changeover frequency between open-loop and closed-loop model

Speed accuracy in SLVC is typically < 0.5% of rated speed, and load-step settling is 20–50 ms — an order of magnitude faster than V/F. The current model is also far more sensitive to a stalled rotor: the drive detects the disagreement between the applied voltage vector and the observed current vector within ~50–100 ms, raising F07900 fast enough to actually protect the pump and motor from a mechanical jam.

The trade-off is that the model is sensitive to bad motor data. If the leakage inductance is off by 30% the speed observer becomes unstable, producing torque oscillations or worse, an overcurrent trip (F30001) on a moderate load step. This is why the firmware requires the motor identification routine to be completed before Dynamic Drive Control will operate in closed-loop at low speed.

Application Class Comparison

Parameter Mapping Reference

When commissioning transitions between application classes, the firmware rewrites a known subset of parameters. The most operationally significant are:

F07900 Motor Blocked — Root Cause Analysis

F07900 is raised by firmware when the following logical condition evaluates true for longer than p2177:

1. Absolute actual speed |n_act| < p2175 (default 7 rpm), AND
2. Speed setpoint |n_set| > p2175, AND
3. Magnitude of torque-generating current |I_q| > p2198 × p0305 (default 1.5 × rated motor current), AND
4. Acceleration / deceleration is complete (r1407.2 = 1, ramp-up completed).

For a 1.5 kW four-pole motor (rated current ~3.4 A on 400 V mains), condition 3 requires the drive to push >5.1 A of torque-producing current while the rotor sits below 7 rpm and the ramp has completed. This profile matches a screw pump attempting to move cold, viscous oil: the rotor is mechanically held by the load, the speed setpoint has reached the operating point, the ramp has finished, and the drive is delivering current at the limit.

The latency problem under V/F control is that slip compensation and voltage boost are both slow-acting. The drive is essentially "dumping" current into a stalled motor because the V/f profile commands rated voltage at rated frequency. Under SLVC, the speed estimator immediately recognizes that the rotor is not following the synchronous speed reference, the I_q controller saturates, and the firmware raises F07900 within a fraction of the time — which is precisely what is wanted for machine protection.

There are three legitimate remedies, in order of preference:

1. Migrate to Dynamic Drive Control (recommended when a stalled pump is the real failure mode). The vector controller's fast stall detection trips F07900 quickly and avoids thermal damage to the motor windings.
2. Loosen the blocked-detection thresholds if the F07900 is a nuisance trip during routine cold-start: increase p2177 to 5–8 s, or raise p2198 to 1.8–2.0. This does not fix the underlying stall sensitivity — it only delays the trip.
3. Add a soft-start pressure bypass or a clutch so the pump is unloaded during ramp-up. Mechanical solution, not a drive fix.

Prerequisites for Migrating to Dynamic Drive Control

Before switching the application class from Standard to Dynamic on a G120C, the following must be available:

1. Motor nameplate data with all of: rated voltage (p0304), rated current (p0305), rated power (p0307), rated power factor / cos φ (p0308), rated frequency (p0310), rated speed (p0311), motor cooling method (p0335), motor moment of inertia (p0341) if known. For the 1.5 kW oil-pump motor these are normally printed on the nameplate; if not, an OEM datasheet is required.
2. Uncoupled or unloaded pump for the rotating motor identification routine. The drive will run the motor up to a fraction of rated speed and apply test pulses; a fully loaded pump makes the inertia identification invalid. If a full uncouple is impossible, the static portion of motor ID (p1910 = 1) can be used, but p1960 (speed controller optimization) must be skipped.
3. Drive access via one of: IOP-2 with the application wizard, BOP-2 with the Setup menu, Startdrive in TIA Portal, or STARTER in legacy SINAMICS toolsets. The application class is not settable over the standard USS/Modbus fieldbus — it must be entered at the panel or through the engineering tool.
4. Recent parameter backup (commissioning archive, *.dsf for Startdrive or *.par for STARTER). The drive will be returned to factory defaults on application class change in some firmware versions; a backup makes recovery trivial if the new control mode is unstable.

Step-by-Step Conversion Procedure (IOP-2 / Startdrive)

1. Power down the drive and the motor section. Verify DC-link voltage is < 50 V on the Control Unit LEDs before opening the terminal cover. Lock-out / tag-out per local site rules.
2. Connect the commissioning tool — IOP-2 at the door-mounting kit, or USB-to-RJ45 at the G120C's service port. Launch Startdrive and perform a "Connect to target device" with the G120C's current IP (default 169.254.11.22).
3. Upload the existing project from the drive to the engineering PC. Save as a dated file (e.g., G120C_oilpump_StandardClass_backup_2024.dsf).
4. Open the Commissioning wizard. In Startdrive, this is Drive > Commissioning > Drive Wizard. The first question is the application class. Select Dynamic Drive Control.
5. Enter motor data from the nameplate: p0304, p0305, p0307, p0308, p0310, p0311, p0335. If the nameplate lists a specific motor series (e.g., 1LE1002-1AB42), the motor calculation routine can pre-fill leakage and magnetizing data; confirm each value.
6. Decide motor identification level:
   • p1900 = 1 — static ID only. The drive measures stator resistance and leakage inductance with the rotor at standstill. Safe to run with a coupled load; provides a usable but not optimal model.
   • p1900 = 2 — static + rotating ID. The drive additionally accelerates the motor with test pulses to identify the moment of inertia. Requires an uncoupled load.
7. Save the parameters to the drive (RAM > ROM). Power-cycle the Control Unit so the new p1300 = 20 takes effect on cold start.
8. Issue an ON command with no setpoint applied. The drive executes the motor identification routine. The motor may produce a brief audible tone and a slow rotation. The routine takes 20–60 s. Status is reflected in r0047 (motor ID status).
9. Verify successful completion: p1910 and p1960 should auto-reset to 0; r0047[0] should read 10400 (Identification successful). Any non-zero warning means a parameter was out of range; re-enter the nameplate data.
10. Issue a low-speed setpoint (5 Hz) and confirm the motor rotates smoothly with no audible cogging. Then ramp to 50 Hz under no load. The drive should reach 50 Hz with < 1% speed error per the keypad display.
11. Re-couple the pump and run the operating profile. Monitor r0027 (actual current) and r0029 (flux setpoint). Flux should be stable around the rated value; current should not oscillate.

Motor Identification — What Actually Happens

The static portion of the motor ID (always performed, even in Standard Drive Control, on first RUN) measures:

• Stator resistance (R_s) — by injecting a DC current and measuring the voltage drop.
• Leakage inductance (L_σ) — by injecting a stepped current and measuring the dI/dt response.

The rotating portion (only with p1900 = 2) additionally runs the motor to a fraction of rated speed with controlled torque pulses, identifying the moment of inertia (J) and the rotor time constant (T_r). These two values feed the SLVC speed observer, and their accuracy directly determines stability under load steps.

Per the SINAMICS G120 FW V4.7 SP3 HF1 Functions Overview, on first switch-on of Standard Drive Control the firmware executes a shortened motor identification routine automatically; in Dynamic Drive Control the routine is expanded and the rotating section is requested unless the operator explicitly suppresses it via p1900 = 0.

Verification and Acceptance Testing

After conversion, perform a structured verification before handing the drive back to operations:

1. No-load speed accuracy: command 25, 50, 75 % of rated speed; confirm actual speed at each point is within 0.5% of setpoint (read via r0021 or keypad).
2. Load step response: apply a step load (e.g., briefly close a downstream valve) and capture r0021 and r0027 via the trace function. The speed should dip < 5% and recover within 200 ms. If the dip exceeds 10% or oscillation persists, re-tune p1470 / p1472 using the Startdrive controller-tuning dialog.
3. F07900 sensitivity check: deliberately stall the pump mechanically (e.g., close the suction valve) and verify the drive trips within ~500 ms. If the trip takes >2 s, F07900 detection is still behaving as in V/F mode and the SLVC observer is not active — check p1300 = 20 in the live parameters.
4. Thermal monitoring: run at full load for 30 min, capture r0035[0] (motor temperature model). It should stabilize < 80% of p0605 trip threshold. A rising trend toward 100% indicates the motor is being driven above its nameplate rating — re-check p0307.
5. Regenerative behavior: for a screw pump, the load is rarely overhauling, but verify by commanding a fast deceleration that the drive does not raise F30001 (overcurrent) or F30002 (DC-link overvoltage). A brake resistor is not normally required on a pump, but the deceleration ramp p1121 may need to be lengthened to 15–20 s for a 1.5 kW motor with a high-inertia load.

Field Commissioning Notes and Edge Cases

Several field-proven caveats from real commissioning experience with G120C on viscous-pump and mixer applications:

• Nameplate cos φ is critical. If the motor's p0308 is entered as 1.0 (default) instead of the actual 0.78–0.85, the SLVC flux model will under-flux the motor. The drive appears to work, but torque is limited and the motor runs hot. Always enter the real cos φ.
• Motor connection star vs delta. A 230/400 V motor wired in delta on a 400 V supply will draw 3× the rated current at the same torque, and the SLVC model will be unstable. Verify p0304 matches the supply configuration before starting the motor ID.
• Long motor cables. If the cable between the G120C and the motor exceeds 25 m, the cable capacitance can interact with the SLVC current model. The default G120C output filter is a basic dV/dt filter; for > 50 m of cable, an external sine filter (e.g., 6SL3202-0AE31-1SA0) is required to maintain SLVC stability.
• Parallel motors. SLVC does not support multiple motors on a single drive. If the pump skid has two 0.75 kW motors, either run each from its own G120C or use Standard Drive Control (V/F) on the single drive with a slightly larger kVA rating.
• Stator resistance drift. If the motor is a 5+ year old wound induction motor, the stator resistance can have drifted upward by 10–15% from its nameplate-calculated value. The static motor ID will catch this; do not skip it even if "the drive worked before".

Troubleshooting Matrix

Switching Back to Standard Drive Control

If the SLVC migration proves unstable — for example, the rotating motor ID cannot be run on a fully-coupled pump, and static ID alone is not giving acceptable performance — reverting to Standard Drive Control is fully supported. The procedure is the same as the forward migration: enter the commissioning wizard, select Standard Drive Control, save, and power cycle. The drive resets p1300 = 0 and disables p1960 (rotating optimization). The previously-identified motor equivalent-circuit parameters are retained in p0350–p0360 and provide a faster cold-start of the V/F profile.

For an oil screw pump where F07900 is a documented nuisance trip, the most robust path is to remain on Standard Drive Control but apply a single change: raise p2177 (motor blocked delay time) from 3.0 s to 5.0 s, and add a 2-second pre-lubrication output (digital output DO0) that holds the pump at 5 Hz for 2 s before ramping to operating speed. This mechanical-preconditioning approach avoids the SLVC migration complexity while still protecting the motor thermally.

Summary Recommendation for 1.5 kW Oil Screw Pump

Migrating to Dynamic Drive Control is the right call when F07900 is a true stall trip and the pump can be uncoupled for the rotating motor ID. The vector controller's fast stall detection will catch a real jam in < 100 ms and protect the motor windings — a job V/F control cannot do reliably. When a full uncouple is impossible, the static-only ID (p1900 = 1) gives a usable SLVC model, and F07900 detection still operates from the current model. In either case, do not bypass the F07900 threshold as a substitute for either vector control or a mechanical preconditioning sequence.