VFDs: The Good, the Bad, and the Ugly

Variable frequency drives (VFDs) have changed the way many of us do business. Their design allows us to move away from larger, more expensive and cumbersome DC drives and instead use AC drives, which provide the same benefits. If you are considering this change, it’s worth looking at both the advantages and disadvantages of VFDs.

VFDs: the Good

First, let’s look at some of the advantages of using VFDs in your business. Many people find this short list of benefits is enough to convince them to consider switching to VFDs.

Control

The main advantage of VFDs is the control they provide to the user. Drives adjust the speed of the AC motor. The drive controls the motor on the fly and allows the user to switch the motor on and off or even reverse the operation of the motor. The drive communicates with the motor in different ways. These methods provide more control and increased options for both deceleration and acceleration.

Soft Start

Another benefit of using a drive is the soft start on the motor. The torque associated with the inrush of power strains the motor. Because a VFD provides a smooth and slow start for the motor, it reduces start-up torque and the related stress. Reducing that stress leads to a longer lifespan and less unexpected problems with your equipment.

Reduced Harmonics

Harmonics are a real issue in electrical power systems and electrical motors. Harmonics result in equipment overheating, torque pulsations, and VFD misfiring problems. These problems lead to the reduced lifespan of the motor. However, drives are a significant help to reduce harmonics.

Financial Savings

Another benefit of using VFDs is they save your business a considerable amount of money. These savings stem from reduced motor energy consumption. The lower the power consumption, the longer lifespan, and fewer problems associated with the motor.

VFDs: the Bad

Although there are more advantages to using VFDs than disadvantages, it is still important to consider their downsides. These include the following:

Initial Cost

The cost of purchasing a drive may be regarded as a disadvantage. However, that cost is often negated by the savings in reduced power consumption and reduced repair costs.

Bearing Currents

Another issue with drives is shaft currents that damage the bearings. However, there are ways to address and overcome this potential problem.

In Sum

This article briefly mentioned a few of the benefits associated with using VFDs, as well as possible disadvantages. Not all motor applications can use a VFD, but those that do provide significant advantages over those that don’t.

I know the article doesn’t list the Ugly, but I don’t want to be the person to refer to a VFD as ugly. VFDs have their own inner beauty. Who are we to judge?