Strict EMC standards are in place to ensure that electronic devices do not cause any unacceptable interference or are not themselves affected by electromagnetic influences. Industrial, scientific and household devices, for example, are subject to the requirements of CISPR 11/32, while EN 55022/55032 is relevant for IT and multimedia technology. In industrial environments, the standards EC 61000-6-1 to IEC 61000-6-4 regulate both the permissible emitted interference and the required immunity to external influences.

Devices that do not meet these standards must be extensively revised or may not be placed on the market at all. An essential component of any EMC strategy is therefore an effectively designed EMC filter that reduces unwanted conducted interference and ensures compliance with the standard.

Continue reading for a practical example:

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Asymmetrical interferences, also known as common mode interferences, occur when the same interference voltage with identical polarity spreads in both conductors of a line pair. This means that the interference flows in both conductors at the same time and in the same direction. A typical source of asymmetrical interference is external and internal electromagnetic field, which couple into the network capacitively and inductively, but also via radiation. For example, frequency converters that aer not sufficiently interference suppressed can generate such fields, which are transmitted to other devices as common mode interference via the power supply. As the interference affects both conductors in the same way, it can spread over large areas and affect several devices simultaneously. Another characteristic feature of common mode interference is that it is often coupled in via housings and earth connections and can lead to malfunctions in sensitive devices.

The use of protective earth chokes is subject to numerous legal requirements and standards that regulate the safety and interference immunity of electrical systems. Protective earth chokes are used to suppress common-mode interference caused by asymmetrical currents that are fed back via the protective earth conductor.

These interferences occur in particular in systems that operate at high switching frequencies, such as frequency converters, switching power supplies or inverters. The high impedance of the protective earth choke for high-frequency signals effectively interrupts the interference current path without impairing the low-frequency protective functions of the PE conductor.

There are many areas of application for protective earth chokes, but they are primarily used in devices and industrial applications where high electromagnetic compatibility requirements must be met. In frequency converters and drive systems, they help to minimize interference with other electrical devices and play a key role in complying with statutory interference limits. Their use is equally relevant in renewable energy systems, particularly in inverters for photovoltaic systems and wind power systems, where they prevent the spread of conducted interference to other network segments. A key benefit of protective earth chokes is that they improve the electromagnetic compatibility of installations and systems. According to the European EMC Directive 2014/30/EU [1], electrical devices and systems must be designed in such a way that they cause little electromagnetic interference and are themselves insensitive to such interference. Protective earth chokes support compliance with these requirements by increasing immunity to interference and at the same time ensuring that no impermissible interference is transmitted to the power grid or neighboring devices.

In addition, protective earth chokes reduce unwanted high-frequency residual currents, which can cause problems in industrial environments in particular, as they impair the tripping of residual current circuit breakers (RCDs) or trigger their unwanted activation. Protective earth chokes also help to increase the reliability of installations by protecting the PE conductor from potential thermal stress caused by high-frequency interference currents.

Due to their integration into the protective conductor structure, the use of protective earth chokes is subject to strict regulatory requirements, which are defined by legal guidelines and standards. According to DIN VDE 0100-540 [2], protective earth chokes must be designed in such a way that they dissipate low-frequency residual currents unhindered, while high-frequency interference is effectively blocked. Especially for powerful installations and systems this requires careful dimensioning of the chokes in order to meet the requirements. In accordance with DIN EN 60938-1 [3], minimum cross-sections for the cable cross-section of the protective earth choke are defined for different rated current ranges, whereby the protective earth choke itself must be dimensioned for the maximum residual current that can flow through the protective earth conductor. Furthermore, this standard describes both the permissible voltage that may occur at the choke and the resulting maximum permissible impedance. This results in an antiproportional relationship between the maximum rated current and the required inductance. The windings and the materials used in the protective earth choke must remain thermally and electrically stable, even in the event of brief high currents that may occur in the event of a fault.

Although protective earth chokes are indispensable in many applications, they also pose technical challenges. One of these is the thermal load that can occur with high fault currents. This can affectthe long-term stability and reliability of the component. In addition, it is essential that protective earth chokes are designed in such a way that they do not cause any impermissible voltage drops or delays in the protective current path so as not to impair the functionality of protective systems.

In practical applications, the protective earth choke is an important component for ensuring electromagnetic compatibility within industrial and energy contexts, and its use contributes significantly to compliance with legal requirements and maintaining the reliability of electrical systems. Nevertheless, their implementation requires a meticulous planning phase and careful adaptation to the specific requirements of the application. In view of the ongoing development of more powerful systems and the increasing importance of renewable energies, the targeted design of protective earth chokes will play an important role in the coming years.

Sources

For decades, passive EMC filters have been used, which operate on the basis of passive components such as inductors, capacitors and resistors. In view of new technologies such as active filters and digital signal processing, however, it seems reasonable to ask whether passive EMC filters are still up to date or whether they are gradually being superseded by more modern solutions.

Passive EMC filters are based on physical effects such as resonance and impedance matching to block unwanted frequencies. For this, no external power source is required. Typical topologies such as LC, RC or Pi filters have proven to be effective in suppressing conducted and radiated interference. Their advantages are their simplicity, robustness and reliability. They are particularly valued in applications with high power density and strict EMC requirements. However, they also face challenges due to technical progress and the miniaturization of modern systems.

A major disadvantage of passive EMC filters is their space requirement. Particularly inductors often have a large spatial footprint, which can make integration into compact designs challenging. Furthermore, passive filters are limited in their ability to suppress very broadband or high-frequency interference, which is an increasing problem, especially in modern electronic systems. In addition, the cost of high-quality components required in applications with high performance requirements must be considered [1].

In contrast, modern active EMC filters and digital solutions open up new perspectives. They use amplifiers and sensors to specifically eliminate interference. One method is to generate a counter-signal that compensates for the interference, similar to active noise suppression. These technologies prove to be efficient at low frequencies and enable a flexible response to variable sources of interference. Digital filters based on microcontrollers or FPGAs allow a real-time analysis and suppression of interference. They are used especially in systems that already have powerful digital controllers [2].

Despite these modern approaches, passive EMC filters are still indispensable in many applications. In the field of mains filtering, for example in switching power supplies, LC filters are still the most common solution. Their robustness and freedom from maintenance make them particularly attractive for use in industrial environments in which electronic systems are exposed to high loads. Due to their reliability, passive filters are also still preferred in the automotive industry, for example in control units or charging devices for electric vehicles. A study by Fischer et al. [3] shows that passive filters continue to be the preferred choice for variable frequency drives in industry, especially where high power requirements are involved.

The future will lie in hybrid approaches that combine the strenghts of passive and active technologies. One example of this is the integration of passive LC structures with digitally controlled active components, as described in reqports by Fraunhofer IISB [4]. Such systems enable targeted adaptation to the respective interference source, while at the same time utilizing the advantages of passive components.

EMC filters that only fulfil the function of passive filtering should therefore by no means be considered obsolete, even if they are becoming less important in certain areas of application. Their strengths – simplicity, robustness and cost efficiency – continue to guarantee them a firm place in the development of modern systems. Nevertheless, the specific requirements of the respective application must always be taken into account when selecting the filter technology. While active and digital filters are becoming increasingly important in dynamic and highly complex environments, passive EMC filters remain irreplaceable in applications with high demands on reliability and long-term stability.

In summary, it can be said that passive EMC filters are not obsolete but remain an essential component of modern EMC concepts. However, the future will increasingly be characterized by hybrid solutions that combine the best of both worlds. Ongoing research and development in this area promises exciting advances that will expand the boundaries of traditional EMC technologies.

Sources

• [1] Paul, C. R. (2018): “Introduction to Electromagnetic Compatibility”, Wiley.
  
• [2] Grasso, F., et al. (2021): “Active vs. Passive Filtering: A Comparative Study in Automotive Applications”, SAE International Journal of Passenger Cars.
  
• [3] Fischer, K., et al. (2023): “Advances in Electromagnetic Interference Filtering for Variable Speed Drives”, IEEE Transactions on Industrial Electronics.
  
• [4] Fraunhofer IISB (2022): “Hybrid Filtering Solutions for Electromagnetic Compatibility”, Fraunhofer Reports.