Main Parts of VFD
Their Functions and Applications.


  1. VFD- variable frequency drive.
  2. Section or Parts of VFD.
  3. VFD function.

1 - VFD- variable frequency drive :

A VFD- Variable frequency drive is electronic device which is used for controlling the speed of AC induction motor. It has two main functions that one is speed controller and second is energy savings. Motor speed is controlled according frequency control which is controlled by VFD. It is mostly used in water pump motor, air blower motor, fans etc.

  • Motor start and stop controlling.
  • Motor speed control according load capacity.
    • Air blower or AHU is controlled according temp.
    • Water pump is controlled water pressure and water temp.
Parts of variable frequency drive(VFD) and their functions

2 - Section or parts of VFD:

The VFD is the main function of frequency controlling which is processed in digitally. The frequency controlling process is the pats of some section which below mentioned.

1- Rectifier Section:

In this sections The diodes are used for AC to DC form through brig rectifier process. Here the 6 diode are used for power conversion like as three numbers diode are connected for positive and three others are connected as negative. Three phase R,Y and B are connected to across the diode. For getting output in sine wave form the diodes works in reverse and forwarding condition.

2- Filter Section:

We know very well that the output of rectifier is not a pure DC which is effected of AC ripples and harmonic rays. For getting pure DC the power capacitors are used which is connected with parallel to the rectifier output.

3- Invertor or Switching Section:

Invertor is a convertor which converts DC supply into AC supply. In this section many electronic components are used for converting AC to DC. Its works as apposite in comparison of diode. For this process many high power electronic switches are used like as IGBT or MOSFET.

These switches are operated as ON or Off rapidly and output is received as pulsating. For getting high frequency output, the switching device works as rapidly and for low frequency the switching device works as slow./P>

4- Controller:

Control unit is a microprocessor based electronic device which monitors and controls to the rectifier and invertor section. Some important features are below mentioned.

  • Speed is controlled through speed sensor in auto mode.
  • Speed is also controlled through user interface in manual mode.
  • It provides necessary data.
  • Any fault condition is also monitored and fault data is stored in history.

3 - Function of VFD:

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