Buzz Words:

This “Did You Know” article is some random Buzz Words heard in the VFD marketplace.

Here goes:

  • VFD, VSD, ASD, VVVF, Drives:  All of them mean the same thing: a Variable Frequency Drive.
  • VFD-Variable Frequency Drive
  • VSD-Variable Speed Drive
  • ASD-Adjustable Speed Drive
  • VVVF-Variable Voltage Variable Frequency Drive
  • Freq Drive (Typically pronounced “Freak-Drive”)

IEEE519 or IEEE519-1992, IEEE519-2014.  In laymen’s terms, all the same thing.  This a “recommendation document” from IEEE that defines how clean the power must be supplied and consumed.  From our past history lessons, VFDs cause poor quality and TCI has correction products. 

Typical statement might be, “We need to meet IEEE519, do you have a product?”  Yes.

PWM- Pulse Width Modulation.  This is the method that VFDs use to supply power to the motor. 
V/Hz (Volts per Hertz) and V/F (Volts per Frequency) mean the same thing.

The voltage to the motor varies as the frequency varies.  The way all VFDs perform for the most part.
Closed Loop Vector control, Closed Loop control, and Encoder feedback control refer to the same thing.
In simplest terms, this means you have a “speedometer” (aka encoder) on the motor and it sends a feedback signal to the VFD to make corrections.  With encoder feedback, you get extreme precision on speed control. 

Open Loop Vector Control, Sensorless Vector Control, and Encoderless Vector Control are the same thing.
This means the VFD can “estimate” the speed of the motor and makes corrections to it. 

Special thanks to National Power Quality and
Consulting for providing these Did You Know articles.

For electrical consulting needs, NPQC can be contacted at