Variable frequency drives (VFDs) have become very common in the industrial space and can improve your operations tremendously. However, they do not come without their own occasional challenges and potential downsides that can affect applications.
VFD Basics
VFDs control the rotational speed of alternating current electric motors by adjusting the frequency and voltage applied. 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 an efficient way to control varying flow rates and pressures.
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
- There are 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.
- Additional heat dissipation is required.
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.