Differences Between VSD, VFD, VVVF Explained

One of the most perplexing questions in the electrical world revolves around VSD/VFD/VVVF devices.

Are there any differences between these devices, or are they essentially all the same thing?

AC/DC

The acronyms AC and DC describe two electrical currents which control different types of motors. Electrical motors use both AC and DC power.

AC is an alternating current and the normal mains power is 240 / 415 volts, referred to as low voltage.

DC, in contrast, is used mostly in extra low voltage circuits, solar applications or batteries because it’s a different current.

VSD

VSD is the acronym for variable speed drive. This all-encompassing term describes drives which are used for controlling both AC and DC motors, and technically, even mechanically control.

It’s commonly used in the context of AC or DC electric drives.

VFD

VFD is the term for a variable frequency drive. It refers explicitly to electronic drives which control the speed of AC motors through adjustment of voltage and the frequency delivered to motors.

The terms VFD and VSD are commonly interchanged.

VVVF

The acronym VVVF is used most often in the mining industry to refer to variable voltage variable frequency drives.

Both VVF and VFD describe the same AC drive. Any AC drive that works to automatically control voltage to adapt to the frequency which it is running at.

Inverter

To further add to confusion, identical devices in the mechanical services / HVAC industry are also regularly referred to as frequency inverters, or inverters.

Again, these terms refer predominantly to AC drives.

Which should I use?

Industrial control systems are most commonly AC-powered.

In this instance, the three acronyms are interchangeable because they refer to the same thing.

When it comes to a DC control system, VSD is most likely the correct term.

In the mechanical services and HVAC industries, AC can also be called inverters.

Same Same but Different!