Goseeko blog

What is a Variable Frequency Drive?

by Sonali

A controller which controls the motor is called Variable Frequency Drive. By varying the frequency and voltage of supply it controls the motor. As it is known that frequency and speed of motors are directly related to each other. The variable frequency drive can also control the speed of the motor by varying frequency of supply. 


The converter is the first stage of voltage frequency drive. This converter is made of six diodes which helps the current to flow in only one direction. The converter has a three phase supply. Then for instance if phase voltage of L1 is more compared to other two phase voltages then the diode connected to phase L1 will be forward biased and allow all the current to flow through it. Similarly, diodes are forward biased when phase L2 and L3 are more in their respective cycles.

The ripples on the DC bus can be removed by using a capacitor (C in above figure). The capacitor absorbs AC ripples and also supplies dc voltage.


  • It reduces the energy consumption.
  • It also reduces the energy costs as well.
  • Due to proper process control it increases the production.
  • The life of equipment increases as VFD provides proper control of the motor. Due to this the life span of equipment increases.
  • SInce, the life of equipment increases this in turn reduces the maintenance cost of the equipment. 

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