What is VFD and How does a VFD Works?

What is VFD?

A variable-frequency drive (VFD), also known as an adjustable-frequency drive (AFD), variable-voltage/variable-frequency (VVVF) drive, variable speed drive (VSD), AC drive, microdrive, or inverter drive, is a type of motor drive that controls AC motor speed and torque by varying motor input frequency and voltage.


How does a VFD works?

A VFD circuit consists of three parts.

1.The rectifier section

2.The filter section

3.The switching or inverter section

The Rectifier Section:

The rectifier section consists of six diodes D1 to D6. D1, D2 and D3 are connected to the positive rail, while D4, D5 and D6 are connected to the negative rail. These six diodes form a diode bridge, converting the three-phase AC signal into a single DC rail. Phases R, B, and Y are connected across the diode.

The Filter Section

As we all know, standard rectifier diodes only convert the AC signal to DC, but the output DC signal is not smooth enough due to frequency-dependent AC ripples. The use of ripple rejection filters is required to rectify the AC ripple and produce a smooth DC output.The standard part for the channel is to utilize distinctive kind of huge capacitors and inductors. In channel segment, predominantly the capacitor sift through the AC swell and gives smooth DC yield.

Sometimes, to decrease the information AC commotions and sounds, we use different sorts of channels

The switching or inverter section

The exchanging or inverter segment upsets the DC to AC. In this segment, various kinds of electronic switches are utilized, going from high force semiconductors, IGBT or MOSFETs. The switches are quickly turned on or off and the heap gets a throbbing voltage that is basically the same as AC. The yield recurrence is relative to the exchanging rate. A high exchanging rate gives a high-recurrence yield while a low exchanging rate gives a low-recurrence yield.

Construction of VFD


1.No clogging or jerking effect.

2.Wide speed and control range.

3.Consist of different types of protection circuits.

4.Constant power factor.


1.Complex to design.

2.Complex in respect of the implementation.

3.Requires additional hardware.