A variable frequency drive (VFD) converts the fixed grid frequency (typically 50 or 60 Hz) into a variable output frequency. This allows the speed, torque, and power of electric drives to be precisely controlled. Variable frequency drives are also playing an increasingly important role in grid and railway power technology. Given the high levels of investment in drive technology and industrial facilities, variable frequency drives are becoming strategic components of energy efficiency strategies.
How does a variable frequency drive work?
In the first step, the incoming alternating current is converted into direct current via a rectifier. An inverter then generates a new alternating voltage from the direct current, adjustable in both frequency and amplitude. This allows, for example, asynchronous motors to be controlled steplessly, significantly reducing energy consumption in many industrial applications.
Key Characteristics at a Glance
- Energy savings through demand-based motor control
- Smooth start-up and controlled ramp-down of drives
- Reduction of load peaks and mechanical wear
- Integration into higher-level automation systems
- Used in pumps, fans, conveyor systems, compressors, and railway systems
- Active front-end drives with energy regeneration
- Medium-voltage drives for large motors up to several MW
Frequently Asked Questions
How much energy can be saved by using a variable frequency drive?
For variable-speed applications such as pumps and fans, savings of 30 to 50 percent are realistic, since power increases with the cube of speed. Over the service life of a drive, the frequency converter therefore often pays for itself within a few years.
What protective components are needed around a variable frequency drive?
Common components include line and motor reactors, filters to reduce harmonics, as well as fuses and, where applicable, separate isolating transformers. These components protect both the drive itself and the upstream and downstream grid.
What effect does a variable frequency drive have on grid power quality?
Variable frequency drives generate harmonics that can stress the grid. Line and motor reactors as well as passive or active filters reduce these effects. For larger installations, a power-quality-oriented design of the connection is essential.
What protective functions are integrated into modern drives?
Standard features include overcurrent, overload, over-temperature, earth-fault, under- and over-voltage protection, phase-failure protection, as well as extensive diagnostic and status messaging. Via fieldbus or Ethernet, this data can be integrated into higher-level control systems, enabling predictive maintenance.
We would be happy to advise you on the design of drive solutions with variable frequency drives and suitable filter components. Contact us for an individual concept.