WHAT IS A VFD?

WHAT IS A VFD?



WHAT IS A VFD?

Today you will learn about VFD.  Specifically, what it is and when do we use it 

So what exactly is a VFD? Well, it stands for Variable Frequency Drive.

They are used for running an AC motor at variable speeds or let them ramp up 

Please watch this Video


VFDs work by adjusting the frequency of the motor to adjust the rpms.

To do this, a VFD will actually convert the voltage twice :
  1. First, it converts our three-phase AC to DC. This is accomplished with diodes.
  2. Then it cleans the DC with a capacitor.
  3. Next, it will convert the DC to AC. This is accomplished with transistors acting as switches.  
Utilizing these “switches” is what allows the VFD to adjust the frequency that the 




Now I know this is a lot of information to take in. Let me compare the internal 

First, let’s look at the diodes that convert the AC to DC. This operates like a 

A check valve, like a diode with electricity, only allows water to flow in one 

The capacitor acts as a water filter to keep everything clean and useable. 

The transistors act like valves. They turn the flow on and off when needed. This 




Now that we have an understanding of how a VFD works, let’s see what they are 

One very common use in industry is to control the speed of a water pump in a 

A water treatment plant typically has a constant flow of water coming in to the 

The operator can monitor water flow and manually adjust the VFD accordingly.

Another great thing about VFDs is the fact that they can be controlled with a PLC. 
PLCs can monitor and control motor speeds using the VFD.


This helps make a process like water treatment that much easier and more 



Let’s look back at what we now know. VFD stands for Variable Frequency Drive. 

They are also used for ramping up a motor for a smooth startup, or to prevent 

This is accomplished by adjusting the frequency delivered to the motor. A setup 

VFDs are used throughout industry. A common example is to regulate water 

There are many different brands and features available. If you are looking at 



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