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EMI Filters for VFD Applications

What is EMI?

Electromagnetic Interference or EMI also commonly called Electrical Noise is the unwanted signal generated by electrical and electronic equipment.


  • Naturally occurring environmental events – ESD by touch, Lightning strikes, Solar flare.
  • Intentionally – High energy switching components.


EMI Problems in VFD

In Several motor applications today a variable frequency Drive (VFD) or adjustable frequency drive, AC Drive or Inverter Drive is commonly utilized.

EMI Problems in VFD range from corrupted Data transmission to Motor Drive Damage.

Abrupt voltage transitions on the output terminals of a variable-frequency drive (VFD) are an inherent source of radiated and conducted Electromagnetic Interference (EMI).

The operating function of VFDs causes high frequency electromagnetic and low frequency harmonic current noise. The high-speed switching of the inverter stage can emit significant radio frequency energy from its input and output wiring.

The Powerline noise emissions associated with variable frequency drives can cause disturbances in nearby equipment. Typical Disturbances include:

  • Dimmer and ballast instability
  • Lightning disturbances such as flashing
  • Flow metering fluctuation
  • Computer system failures
  • Nuisance faults PLC
  • Thermostat control problems
  • Encoder feedback errors


Mitigation on EMI Problems in VFD

EMI-related problems involve a source of noise, coupling of this noise by conduction or radiation, into circuits or equipment that are susceptible to this noise. The origin of noise from VFD operation is high dv/dt pulse-width modulated (PWM) output voltage which drive the motor and couple through stray capacitance to ground of cables and motors insulation resulting in high frequency ground currents

  • EMI mitigation levels are defined depending on whether the equipment is used in commercial or residential applications.
  • Depend on applicable Standard requirements

Without mitigation the emitted energy can interfere with other nearby electrical equipment.


Parameters required for Proper Selection of EMI filter for VFD

  • VFD Drive Power rating
  • Full load Current
  • Operating Voltage
  • Mounting Style : Chassis , Footprint and Bookshelf
  • Termination: Shockproof Connector, Stud, Circular connector and Cable.
  • EMC Category based on Requirements as per EN 61800-3 for Power Drive System
  • Application – ( Commercial or Residential Applications)


EMI Filters are used for various reasons

EMI filters are a combination of high frequency inductors and capacitors to reduce noise in the critical 150 KHz to 30MHz frequency range.

  • Firstly it protects the VFD from high-frequency noise that is being generated by other electrical loads on the power supply
  • Secondly it drains parasitic currents to ground instead of conducting them back onto the supply cable

The use of an EMI filter is the part of the CE mark that machinery gets.


EMC Standard EN/IEC 61800-3

EMC Standard EN/IEC 61800-3


Proper Installation of EMI filter

To ensure best possible EMC performance, correct installation and connection of the Drive, EMI filter and motor is essential.

Input filters reduce the conducted radio-frequency interference voltage. The input filter must be installed upstream on the mains side of the variable frequency drive. The EMI filter must be properly grounded.


Connection Diagram of EMI filter

EMI filter connection diagram