FAQ :: VFDs | How Does A Variable Frequency Drive Work?

An ACVariable Frequency Drive(VFD) is commonly referred to as an Inverter.This is because of the way aVFDworks. The following details the inner workings of aVFD:

  1. Alternating Current (AC) power is applied to the input of theVFDand feeds a bridge rectifier.
  2. The rectifier converts the Alternating Current (AC) voltage into Direct Current (DC) voltage.
  3. The Direct Current (DC) voltage then feeds the Direct Current (DC) buss capacitors on theVFDwhere it is stored for use by a transistor or Insulated-Gate Bipolar Transistor (IGBT).
  4. Direct Current (DC) from the capacitors feed the input of the transistor(s).
  5. The transistor(s) then continuously turns on and off at the appropriate frequency to build a new sine wave for use by the motor connected to the output of theVFD.

The process above is often referred to as inversion because it changes from one form to another then back again.

The voltage frequency, as distributed in the USA, is 60 cycles per second and the unit of measurement is Hertz (Hz).The output frequency and voltage of an ACVariable Frequency Drive(VFD) is variable and controlled by the speed at which the output transistor is continuously turned on and off.

The variable speedis controlled digitally in modernVFDs and changed by the operator through programming, an operator interface, or by changing an analog input to theVFDthat is programmed as speed reference input.