Variable frequency drives: A variable frequency drive (VFD) controls motor speed by varying the frequency and voltage supplied to the motor.
How it works
A drive converts the incoming AC supply to DC and then creates a new AC output with the frequency and voltage it needs. By changing the output frequency, it changes the motor speed.
The drive controller can also limit current, ramp the speed up and down, and protect the motor. Control inputs come from a controller, a panel or a network.
Types
Drives are grouped by control method, such as scalar (V/Hz) and vector control. They are also grouped by voltage class, power range and enclosure, and by whether they can feed energy back to the supply.
Key specifications
| Parameter | What it affects | Value or range | Source and conditions |
|---|---|---|---|
| Rated output current | Sets the largest motor the drive can supply | Demo range: 2 to 300 | Demo data, not from a datasheet |
| Supply voltage | Must match the installation | Demo: 400 | Demo data, not from a datasheet |
| Control mode (type) | Affects speed accuracy and torque at low speed | Scalar and vector (demo) | Demo data, not from a datasheet |
| Overload capacity (%) | Sets how much extra current is allowed for a short time | Demo: 150 for 60 s | Demo data, not from a datasheet |
| Enclosure rating (IP code) | Sets protection in the installation environment | Demo: IP20 or IP55 | Demo data, not from a datasheet |
Selection criteria
- Motor: rated current and suitability for drive operation
- Load type: constant torque or variable torque
- Speed range, accuracy and braking needs
- Supply: voltage, harmonics and cable length
- Environment and cooling
- Network connection and support for programming
Sources and review
- References
- Demo reference: manufacturer datasheet (placeholder) (checked 2026-11-07)
- Demo reference: relevant standard (placeholder) (checked 2026-11-07)
- Last reviewed
- Not yet reviewed
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FAQ
Why use a drive instead of a fixed-speed starter?
A drive lets the speed follow the process, which can reduce energy use on loads such as pumps and fans. It also gives a soft start. Check the saving with your real operating profile.
What is the difference between scalar and vector control?
Scalar control sets the output voltage in proportion to frequency and is simple. Vector control regulates the motor’s torque and speed more closely, especially at low speed.
Do I need a line or output filter?
Long motor cables, harmonic limits and sensitive equipment on the same supply may call for filters. Ask the drive supplier to confirm for your installation.
What should I ask a supplier before I decide?
Ask which model and revision the figures describe, the conditions they were measured under, which standards apply and for what scope, and what local support and spares are available.