FAQ :: VFDs | How Do I Pick A Variable Frequency Drive for My Application?

When applying aVariable Frequency Drive (VFD) to a new or existingapplication there are many factors to consider prior to making a firm decision on what type ofVariable Frequency Drive (VFD)should be used. Ifone already has an existingapplication whereVFDs seem to consistently fail,they should look tousing a differentVFD typefor potential success. For a newVFD application one should:

  • Research the motor andVFD specifications.
  • Research yourapplication requirements.
  • Learn more abouttheVFD products that are available to you.
  • Understand thefeatures of thoseVFD products to determinewhatis an appropriate solutionfor yourapplication.

There are a several different types ofVariable Frequency Drives (VFDs). Not all drive manufacturers offer every type ofVFD availablein the market. So ifone has their heart set on a specific product line,one must first doresearch to ensure thedesired manufactureroffers the type ofVFD needed by theapplication. The following is a short summary ofthe three different types ofVFDsthat are availableand when these types of drives should be considered in anapplication:

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

The most commonly used and most basicVFD available; this product is for a basicapplication inpumps, fans, conveyors, blowers and others. Theseapplications do not require high starting torque, full motor torque at low rpm, and/or speed feedback. Most V/HzVFDs have adequate programming features for manyapplications. Be certain adequate I/O and programming features are available to meet yourapplicationrequirements. This product is an inexpensive alternative to a phase converter since they will acceptsingle phase input while providingthree phase output.

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

The nextVFD type that is commonly used in a lathe, mill or anyapplication where full torque is require throughout the motor speed range.Sensorless VectorVFDs areare also referred toas open loop vector drives; these drives are morecomplex than V/Hz drives and should always be applied toapplicationswhere high starting torque and/or full torque operating at lowRPM is required. If speed feedback and/or extremely complex programming must be considered in yourapplication youCANNOT use a sensorless vectorVFD. Sensorlessvector/open-loop vectorVFDsdo offer complex programming to a certain degree, but when your applicationexceeds sensorless vectorprogramming features, there is a third solution.

Closed Loop Vector Variable Frequency Drives (VFDs)

This next level ofVFDs 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. Thistype ofVFD 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, advancedmanufacturing facilitiesacrossthe world, closed-loop vector technology has few limitsin drive technology. The product features are phenominal.Applications where these products are utilized provide superior speed regulation and torque performance.

Before choosing aVFD for yourapplication 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 yourapplication.