Variable frequency drive — basics and key parameters
How a VFD works, which parameters are set during commissioning, acceleration and deceleration, speed reference, and how parameters map across manufacturers.
What a VFD does
A variable frequency drive rectifies the mains voltage into a DC link, and an IGBT inverter turns it into a voltage of adjustable frequency and amplitude for an induction or synchronous motor. Motor speed is proportional to frequency, so the drive can accelerate, control and stop the machine smoothly.
Main control modes:
| Mode | Notes |
|---|---|
| V/f (scalar) | simple, suits pumps and fans, allows several motors on one drive |
| sensorless vector | holds speed and torque better at low frequency |
| vector with encoder | precise torque control and positioning |
Commissioning: what gets set
- Motor nameplate data: rated voltage, current, power, frequency, speed, cos φ. Protection and control quality depend on them.
- Motor identification (ID run, autotune) — the drive measures the equivalent-circuit parameters.
- Command source — terminals, keypad or network (see VFD control).
- Reference source — analog input, preset speeds, network.
- Limits: minimum and maximum frequency/speed, current limit.
- Acceleration and deceleration, stop mode.
Acceleration, deceleration, stopping
Acceleration time is usually defined from 0 to maximum (or reference) frequency, not to the current setpoint. If deceleration is too short, the machine's energy flows back into the DC link, the voltage rises and the drive trips on overvoltage. Remedies: longer deceleration, enable the Vdc_max controller, fit a braking resistor.
Stop modes: ramp stop, coast (voltage removed, the motor stops on its own), quick stop with a separate ramp.
The same parameters across manufacturers
| Purpose | Siemens G120 (CU240B/E-2) | ABB ACS580 | Rockwell PowerFlex 520 |
|---|---|---|---|
| Start/stop commands | p0840 (ON/OFF1) | 20.01 Ext1 commands | P046 Start Source 1 |
| Reference source | p1000 | 22.11 Ext1 speed ref1 / 28.11 | P047 Speed Reference1 |
| Acceleration time | p1120 | 23.12 / 28.72 | P041 Accel Time 1 |
| Deceleration time | p1121 | 23.13 / 28.73 | P042 Decel Time 1 |
| Min/max speed | p1080 / p1082 | 30.11 / 30.12 | P043 / P044 |
Parameter numbers depend on firmware version and model — check against the manual for the specific device.
Tools
- Diagnostic Database — fault and warning codes for Siemens, ABB, Danfoss, Rockwell, Schneider and ОВЕН drives.
- Analog Signal Calculator — convert a 4–20 mA / 0–10 V reference into frequency.
Connections
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Sources
Updated 2026-10-01