EMC Issues in Motor Control Systems

As at 26 May 2026

Motor controllers are key components in modern automation systems. At the same time, they are among the most common sources of electromagnetic interference. Careful consideration of electromagnetic compatibility (EMC) is therefore crucial to ensuring that systems are reliable, compliant with standards and free from interference.

In this article, you will learn about the EMC effects that occur in motor control systems, the causes behind them, and the measures you can take to minimise them effectively.

What Does EMC Mean in Motor Control Systems?

Electromagnetic compatibility describes the ability of an electrical system:

  • - Not to emit any unauthorised electromagnetic interference
  • - To be sufficiently resistant to external interference

This is particularly relevant in motor control systems, as they generate strong electromagnetic fields due to rapid switching operations and high currents. At the same time, these systems are sensitive to external interference, which can lead to malfunctions or even system failures.

Common Sources of EMC Interference in Motor Control Systems

1. Power Electronics and Switching Operations

In frequency converters, servo controllers and stepper motor controllers, semiconductors are operated at high switching frequencies. These generate:

  • - Steep voltage transients (dV/dt)
  • - Rapid changes in current (dI/dt)
  • - Broadband interference spectra

These effects result in conducted and radiated interference.

2. Motor Cables

Motor cables often act as antennas. The following are particularly critical:

  • - Long cable runs
  • - Unshielded cables
  • - High clock speeds (PWM mode)

This results in radiated interference that can affect other systems.

3. Earthing and Potential Differences

Incorrect earthing is one of the most common causes of EMC problems:

  • - Ground loops
  • - Different reference potentials
  • - Inadequate shield connections

These can lead to unexpected interference currents.

4. Interference from External Sources

Motor control systems are often found in complex installations containing other sources of interference:

  • - Contactors and relays
  • - Switch-mode power supplies
  • - High-frequency sources (e.g. radio technology)

A robust design is therefore essential.

Effects of EMC Issues

A lack of EMC optimisation can have a wide range of consequences:

  • - Malfunctions in control systems
  • - Position errors in motors
  • - Communication faults (e.g. fieldbus, EtherCAT)
  • - Unexplained device stoppages
  • - Reduced service life of components

In safety-critical applications, EMC issues can even lead to significant risks.

Measures for EMC Optimisation

1. Correct Cabling

Well-planned cabling is the cornerstone of any EMC strategy:

  • - Use of shielded motor cables
  • - Separation of power and signal lines
  • - Short signal paths
  • - Avoiding loops

The cable shield should be connected over a large area and on both sides.

2. Fit Filters and Restrictors

Various components are used to reduce line-borne interference:

  • - Mains filter
  • - Output filter (dV/dt or sine wave filter)
  • - Ferrite cores

These effectively reduce high-frequency interference.

3. Optimised Earthing

A proper earthing system comprises:

  • - Star-shaped earthing or defined earthing configurations
  • - Large contact surfaces for shield connections
  • - Electrical isolation where required

Good earthing is often the key to ensuring system stability.

4. Enclosure and Control Cabinet Design

Mechanical factors also play a major role:

  • - Conductive control cabinet enclosures
  • - EMC-compliant cable glands
  • - Strategic placement of components
  • - Separation of the noise source and sensitive electronics

5. Selection of Suitable Motors and Control Systems

Modern motor solutions support EMC-optimised design:

  • - Built-in filter functions
  • - Reduced interference
  • - Optimised PWM technologies

A coordinated system comprising the motor and control unit significantly reduces the effort required.

Standards and Directives

There are clear requirements for EMC in the EU:

  • - EMC Directive 2014/30/EU
  • - EN 61800-3 (Drive systems)
  • - EN 61000 Series (Immunity and emissions)

Manufacturers and plant engineers are required to comply with these requirements and provide evidence of compliance.

Real-world Best Practices

Based on experience in drive technology, the following measures have proven effective:

  • - Take EMC into account right from the planning stage
  • - Carry out measurements at an early stage
  • - Check components systematically
  • - Consider the entire signal path, not just individual components

EMC problems rarely occur in isolation – they are usually the result of several factors.

Conclusion

EMC is a key factor in the success of motor control systems. With switching frequencies increasing and power densities rising, EMC requirements are becoming ever more demanding.

With a well-thought-out combination of:

  • - Appropriate cabling
  • - Correctly installed earthing
  • - The targeted use of filters
  • - and high-quality drive components

reliable and compliant systems can be implemented.