How to Mitigate Noise Produced by VFDs

 In Documentary

Variable frequency drives (VFDs) create electrical noise commonly referred to as electromagnetic interference (EMI). This noise can be caused by multiple sources including normal operation, abrupt voltage transitions on the output terminals, data transmission and motor drive damage. The EMI is often problematic because it causes disturbances in surrounding equipment, including dimmer and ballast instability, computer system failures, flow meter fluctuation, thermostat control problems, encoder feedback errors and many other issues.

Mitigating EMI involves a couple different strategies:

  • Troubleshooting to ensure noise is related to standard operation of the VFD.
  • Relying on EMI filtration to mitigate the noise and prevent damaging effects to surrounding electrical equipment.

Troubleshooting

Here are some of the most helpful issues to check with your VFD installation (taken from 7 Steps to Reducing EMI with VFDs)

  1. Ensure the VFD and other components are grounded correctly. Earth ground is a very important connection as it provides a path for EMI noise to drain. Consider the length (best to keep short) of the ground strap with wider surface area for connections and conductor gauge sized appropriately for the current.
  2. Verify the panel is grounded well to building power – especially if a regenerative drive is being used.
  3. Connect all ground connections to metal common ground block.
  4. Ensure adequate (greater than 8 in.) space between AC supply power, motor cable, high power DC voltage cables and control and data lines.

Filtration

An EMI filter is often critical to the success of VFD controlled applications. First, an EMI filter protects the VFD from high frequency noise generated by other electrical loads on the power supply. Secondly, the EMI filter helps drain currents back to ground (critical component mentioned above) instead of conducting them back to the supply cable.

In order to select the best EMI filter, consider the following (taken from EMI Filters for VFD Applications):

  • VFD Drive Power rating
  • Full load current
  • Operating voltage
  • Mounting style
  • Application

Proper installation of the EMI filter is also critical to success. The input filter must be installed upstream of the main side of the VFD and it must be properly grounded.

Elite Controls, Inc. is your available expert to help with specification of VFDs and filtration solutions for your application. Contact us today for further assistance.