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  • How to select a variable frequency drive: The top 8 considerations

What is a variable frequency drive?

The top 8 considerations when selecting a variable frequency drive


Harmonic mitigation.


These are just some of many variables that impact the selection of the right variable frequency drive (VFD) for your application.

The vastness of the options for the technology can be daunting at best and selecting the wrong VFD can create more problems than the ones that you are attempting to solve.

The following is a list of 8 considerations for selecting a variable frequency drive for your specific application:


1. Environment

The environment in which the motor and power conversion equipment operates is of prime concern. Conditions such as ambient temperature, cooling air supply and the presence of gas, moisture and dust should all be considered when choosing a drive, its enclosures and protective features.

2. Speed range

The minimum and maximum motor speeds for the application will determine the drive’s base speed.

3. Speed regulation

The allowable amount of speed variation should be considered. Does the application require unvarying speed at all torque values or will variations be tolerated?

4. Torque requirements

The starting, peak and running torques should be considered when selecting a drive. Starting torque requirements can vary from a small percentage of the full load to a value several times full load torque. The peak torque varies because of a change in load conditions or mechanical nature of the machine. The motor torque available to the driven machine must be more than that required by the machine from start to full speed. The greater the excess torque, the more

5. Acceleration

The necessary acceleration time should be considered. Acceleration time is directly proportional to the total inertia and inversely proportional to the torque available.

6. Duty cycle

Selecting the proper drive depends on whether the load is steady, varies, follows a repetitive cycle of variation or has pulsating torques. The duty cycle, which is defined as a fixed repetitive load pattern over a given period of time, is expressed as the ratio of on-time to the cycle period. When the operating cycle is such that the drive operates at idle, or a reduced load for more than 25% of the time, the duty cycle becomes a factor in selecting the proper drive

7. Heating

The temperature of a motor or controller is a function of ventilation and losses. Operating self-ventilated motors at reduced speeds may cause above normal temperature rises. Derating or forced ventilation may be necessary to achieve the rated mot

8. Drive type

Does the application require performance elements such as quick speed response or torque control? These may require the use of a flux vector or closed loop vector drive, instead of a volts per hertz drive.