What is a Variable Frequency Drive?

Variable frequency drives (VFD) are also known as variable speed drives (VSD), and inverters. Variable frequency drives are solid state motor control systems used in manufacturing facilities across the globe. Variable frequency drives are designed to control the speed of an alternating current (AC) electric motor. Variable frequency drives can reduce energy costs up to 50% by speed reduction on applications where the full speed (RPM) of the electric motor is not required.

This energy savings is often significant enough to pay for the variable frequency drive within a couple of months. Variable frequency drives are commonly used on pump, fan, and air compressor applications, and are often used in manufacturing facilities to increase or decrease the start up time on alternating current (AC) motors.

Increasing and/or decreasing the start up time on an AC motor can add years to the overall lifespan of an AC motor, and can also improve efficiency on production demands. Variable frequency drives provide the ability to control the frequency of starting and stopping an AC motor.This ability provides a means by which an AC electric motor is only operating when needed. AC electric motors have a longer lifespan if they are not continuously operating when they do not need to be.

There are a few different types of variable frequency drives. The most common type of variable frequency drive is known as a V/Hz (volts per hertz), and are applied to applications such as fans, pumps, air compressors, and other related applications where high starting torque is not required. V/Hz variable frequency drive applications typically do not require full torque when the AC motor is operating at less than the base speed (RPM) of the electric motor.

Another type of variable frequency drive is known as a vector control. Vector control is used on variable frequency drives where high starting torque and full torque at low speed (RPM) is present. Vector control variable frequency drives are usually more expensive than a V/Hz drives.

There are other types of variable frequency drives that are more complex than V/Hz and vector control. These more complex variable frequency drives are typically used for precise speed regulation of an AC motor as well as complex programming to regulate starting and stopping of an AC motor.