Delta VFD

“Before Learning about AC VFD Work. We need to understand What is AC VFD Systems.” 

In this blog, we will cover the Internal Electronics of the AC VFD systems and how each electronics work in AC VFD. 

What is AC VFD?

VFD stands for Variable Frequency Drive. VFD is used to run an AC motor at a variable speed & time. VFD Drives are also called “Motor Controllers”. 

These electronics systems are now becoming the major component in the Industrial Field. As they are not only controlling the Motor but also reducing the Power Consumption in the whole Industry. 

Major Application of VFD System

& many more…

Circuits Helping AC VFD Work : 

  1. Rectifier Circuit
  2. Capacitor Bank
  3. IGBT
  4. Precharge Resistor
  5. Dynamic Breaking Resistor
  6. SMPS Circuit of VFD


Power Card of AC VFD


Circuit Diagram of AC VFD System


Rectifier Circuit

The rectifier converts AC to DC, here the rectifier will do the same as a normal rectifier Circuit.

In the above diagram, we can see two sections one is R, S, T & the second one is U, V, W where R, S, T are inputs for the VFD System. So the Input supply of VFD is AC which is then converted into DC using Rectifier Circuit. 

So the Initial sector of VFD is a Rectifier Circuit that distributes the power to the whole other area of VFD (Control Card, IGBT, Capacitor bank, etc. )

In conclusion, we can say that Rectifier is the Power Source for the working of the VFD System.

2) Capacitor Bank

AC VFD Capacitor Bank
Hardware AC VFD Capacitor Bank
Capacitor Bank Circuit
Capacitor Bank Circuit of AC VFD

The DC output in the rectifier is not pure DC. To convert the pure DC we have to use Capacitor Bank. The portion you are looking at in the given diagram is known as Capacitor Bank.


IGBT of AC VFD Drive

IGBT is an Insulated -Gate Bipolar Transistor. Most commonly IGBT Systems are used where the application is needing HIGH POWER i.e., voltage and current

In an IGBT there are different combination of Gates that operates as per the requirement of power in a circuit.  As it is designed to Turn on and Off very rapidly, this is the reason it is vastly used in Switching amplifiers & Industrial Control Systems like AC VFD.

4) Pre Recharge Resistor

Pre-Recharge resistor

If we give the output of the rectifier directly to the capacitor, then the capacitor will take its maximum current, by taking the maximum current, MCB installed for the supply will trip again and again.

To overcome this problem we use a Pre-recharge resistor on it.

5) Dynamic Breaking Resistor.

Dynamic Breaking Resistor

Dynamic Breaking Resistor (DBR) helps AC VFD Systems to dissipate the extra power generated in AC Motors.

DBR is most commonly used in Heavy-Duty Applications. The reason is that the Low Power consumption application of the AC VFD System is itself capable of removing extra power. 

But it is best practice to use DBR in your Application.

6) SMPS (Switch Mode Power Supply)

In a VFD System, there is a requirement for multiple DC Power sources for executing multiple applications. 

For Example, a VFD system has its own Display Unit, Control Units. So Power supply consumption for each unit is different. 

Major Power supplies needed in AC VFD are 5Volts, 24 Volts & 10 Volts. So the SMPS Section provides.

  • AC to DC Conversion.
  • Step Up & Step Down the Power Supply.
  • Filter the Power Supply.

Video Description of All the AC VFD Parts

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