What is a Variable Frequency Drive?
A Variable Frequency Drive (also referred to as a VFD – Variable Frequency Drive) is a device that controls the speed of an electric motor by adjusting the frequency and voltage of its supply.
Variable frequency drives are widely used in industrial installations to save energy, improve process control and reduce mechanical wear.
🧠 How does a VFD work?
- The mains voltage (AC) is converted to DC voltage via a rectifier.
- This DC is then converted back via an inverter into an AC voltage with controllable frequency and voltage.
- By varying the frequency, the rotational speed of the motor changes.
Many modern drives also include feedback via Encoder or current measurement, for precise speed control or Closed-loop regulation.
🏭 Application of VFDs in industry
- Pumps and fans: energy savings through speed adjustment
- Conveyors: controlled start/stop and speed
- Centrifuges: variable speed for different phases
- Compressors: reduction of peak demand and wear
- Hoisting installations: controlled acceleration and positioning
VFDs are commonly applied in processes where variable speed is needed or where soft start/stop is important for machine safety and maintenance.
🔍 VFD vs. Soft Starter
| Aspect | Variable Frequency Drive (VFD) | Soft Starter |
|---|---|---|
| Speed control | Yes, across the full range | No, only during start/stop phase |
| Application | Variable speed required | Only soft start needed |
| Complexity | More advanced, more parameters | Simpler, less tuning |
| Energy savings | Yes, under partial load | Limited to startup |
| Cost | Higher | Lower |
🔐 Security aspects
- VFDs may include built-in protections against overload, overtemperature, phase loss
- Drive parameters must be set correctly so as not to exceed motor and cable limits
- In OT networks, VFDs may be connected via Ethernet IP, ProfiNET or Modbus TCP – and therefore present cyber risks
- Secure communication via VLAN, Firewall and segmentation in line with the Purdue Model
📌 In summary
A variable frequency drive is a critical component in modern drive technology. It delivers energy efficiency, better process control and extended service life of motors and mechanics.