Pros and Cons of VFD Use

Schneider Electric VFDs

Variable frequency drives (VFDs) have become very common in the industrial space and can improve your operations tremendously. That being said, they do not come without their own occasional challenges, and I hope to make you aware of potential downsides that can affect your applications.

VFD Basics

VFDs control the rotational speed of alternating current electric motors by adjusting the frequency and voltage applied to their motors. This is done by switching IGBT output devices. VFDs can be used in fan, pump and air compressor applications, and account for more than half of the electricity consumed by U.S. industrial operations.

Although equipment can generally operate at less-than-maximum velocities of their connected motors without VFDs, this isn’t possible without employing the use of throttling devices such as valve, dampers or bypasses. A VFD provides a more efficient way to control varying flow rates and pressures.

It’s also important to note that variable frequency drives are also referred to as variable frequency inverters or frequency inverters.

Pros of Using Variable Frequency Drives

  • They provide substantial energy savings
  • Speed control is used to replace a valve or damper-type flow control
  • Smooth starting and stopping mechanisms reduce mechanical wear on loads
  • Integrated features allow for easy implementation of future modifications
  • They allow for increased power factors
  • They have regenerative braking
  • They control speeds up to 100 Hz

Cons of Using Variable Frequency Drives

  • Higher initial capital costs
  • Inverter duty motors should be used with VFDs to optimize motor life
  • Harmonics may occur if VFDs aren’t installed per manufacturer specifications
  • You will require additional heat dissipation

Alternatives to Variable Frequency Drives

If you don’t think that a VFD is the right choice for your application, there are alternatives that may be better suited for your environment. Across-the-line starting does not control speed, and allows for full-torque starting and stopping. Additionally, soft starting methods do not control speed but do allow for smooth starting and stopping.

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