When applying a Variable Frequency Drive (VFD) to a new or existing application there are many factors to consider prior to making a firm decision on what type of Variable Frequency Drive (VFD) should be used. If one already has an existing application where VFDs seem to consistently fail, they should look to using a different VFD type for potential success. For a new VFD application one should:

Research the motor and VFD specifications.
Research your application requirements.
Learn more about the VFD products that are available to you.
Understand the features of those VFD products to determine what is an appropriate solution for your application.

There are a several different types of Variable Frequency Drives (VFDs). Not all drive manufacturers offer every type of VFD available in the market. So if one has their heart set on a specific product line, one must first do research to ensure the desired manufacturer offers the type of VFD needed by the application. The following is a short summary of the three different types of VFDs that are available and when these types of drives should be considered in an application:

V/Hz (Volts per Hertz) Variable Frequency Drives (VFDs)

The most commonly used and most basic VFD available; this product is for a basic application in pumps, fans, conveyors, blowers and others. These applications do not require high starting torque, full motor torque at low rpm, and/or speed feedback. Most V/Hz VFDs have adequate programming features for manyapplications. Be certain adequate I/O and programming features are available to meet your applicationrequirements. This product is an inexpensive alternative to a phase converter since they will accept single phase input while providing three phase output.

Sensorless (Open Loop) Vector Variable Frequency Drives (VFDs)

The next VFD type that is commonly used in a lathe, mill or any application where full torque is require throughout the motor speed range. Sensorless Vector VFDs are are also referred to as open loop vector drives; these drives are more complex than V/Hz drives and should always be applied to applications where high starting torque and/or full torque operating at low RPM is required. If speed feedback and/or extremely complex programming must be considered in your application you CANNOT use a sensorless vector VFD. Sensorless vector/open-loop vector VFDs do offer complex programming to a certain degree, but when your application exceeds sensorless vector programming features, there is a third solution.

Closed Loop Vector Variable Frequency Drives (VFDs)

This next level of VFDs are more advanced. Applications that require accurate speed regulation and feedback from the motor and/or require complex programming will require a closed-loop vector drive. This type of VFD is often offered as a “three in one” and able to operate in all operating modes.

V / Hz (Volts per Hertz)
Sensorless (Open Loop) Vector and
Closed Loop Vector

These products are complex and extremely efficient when properly applied. Used in the most complex, advanced manufacturing facilities across the world, closed-loop vector technology has few limits in drive technology. The product features are phenominal. Applications where these products are utilized provide superior speed regulation and torque performance.

Before choosing a VFD for your application consult with a qualified integrator, distributor, or manufacturer who will ask all the right questions and make an appropriate recommendation. Be sure you will be able to get proper service and telephone support from them when you, or your qualified electrician, are setting up the drive for your application.