By Holger Urban, head of product management, Schaffner

growth in the coming years. In 2018, the market share of electric cars reached approximately 2.5%, and the number of electric cars built worldwide rose to more than two million units for the first time. By 2030, the number is expected to increase tenfold, up to 60%, which will correspond to twenty million cars sold per year worldwide. It is notable that around 80 % of electric vehicle sales today are for purely electric vehicles (BEVs).


The charging infrastructure currently seems to be receiving little consideration in the rush to design and develop new electric car models. However, this is at least as important as the cars themselves in order to successfully implement the eMobility rollout in prospect. Approximately 77,000 charging stations are

required for 1 million electric vehicles, including 7,000 DC rapid charging stations (source: Bundesverband Freier Tankstellen -bft). With 20 million cars sold per year, 140,000 DC fast charging stations would have to be installed by 2030. This is a challenge not only from an economic point of view, but also from a technical point of view. Electromagnetic compatibility (EMC) plays a key role in products designed for charging BEV (Battery Electric Vehicles) and HEV (hybrid electric vehicles). Electromagnetic compatibility (EMC) is concerned

with the emission and immunity of products connected to the mains supply. The emitted interference or emission generated by lossy switching operations must not exceed specified limits. If noncompliant products are brought onto the market, problems may arise in operation with other consumers connected to the main power grid. Immunity to interference describes the ability of products to withstand external influences without error. The immunity of products can be verified by various tests, for example by means of the surge, burst or flicker test. EMC filters, as developed by Schaffner, are

available to enable compliance with emission limit standards. These filters are designed to operate in the frequency range between 9 kHz and 30 MHz in order to suppress conducted interference. This prevents other devices in the environment from being negatively affected. All standard filters should be designed in accordance with the IEC 60939-3 standard (“Passive filter units for electromagnetic interference suppression”) and other international standards and are therefore readily available for use in a potential customer system. In the case of EV charging stations,

electromagnetic compatibility is particularly important, because, without filters any interference that occurs during rectification in charging stations operated directly from a low-voltage network on the

input side could have an effect on the entire network. On the output side, i.e., on the side where the car is charged, the safety of the operator and the interoperability between different charging stations and car manufacturers are of primary importance. Both factors must therefore also be taken into account in the design of the EMC filters.


The “Norms” on the subject of EMC are completely defined in the area of charging stations. The IEC 61851-23 standard defines the safety-relevant aspects for DC charging stations (fast charging stations). For EMC filters, the definition of the capacitors on the DC side (output side) is particularly important. The maximum capacitor size is set to 1 uF at the DC output, i.e., with a filter in the system, the filter can be provided with 500 nF capacitance on positive and negative conductor If several filters are used in parallel, the size must be reduced accordingly. In addition, the discharge resistors must be at least 1 MOhm to enable insulation measurement in the system. The design of Schaffner standard filters provide the opportunity to modify the components used to meet customer specifications within the scope of the existing safety certificates. DC filters about to be launched to the market are the models FN2220 or FN2230, which can be adapted as required and identified with a unique suffix. Customer specific modifications are also possible

for standard AC filters, but there are different requirements for the design of these filters (>1 MOhm leakage resistors remain). The great advantage of modification of a standard filter is that it has already been certified. This means that even after modification, all certifications remain in place, which considerably reduces the time to-market. If the mechanics remain the same, samples ready for series production can be rapidly made available and initial delivery can take place quickly. Schaffner works on the premise of “first time right“ saving valuable waiting time for our customers before series production can take place.

ew electric car models are being introduced almost daily. The market forecast for the BEV (Battery Electric Vehicle) predicts very strong


A part of the IEC61851-21-2 standard defines the limit values and the corresponding measurement setups. It is important to ensure that the correct network simulations and limits are used. On the input side (main power grid side) it must also be defined in which environment the charging point will be used, i.e., whether it is an industrial (Class A) or residential environment (Class B). The “CPT” port (conductive power transfer) must be terminated according to CISPR 25:2008 and the AC/DC input port terminated according to CISPR 16-1-2:2014. The limit lines for the AC/DC input port follow the specifications of IEC 61000-6-3, for the CPT port the limit values shown in the following diagram for conducted emission (between 150 kHz and 30 MHz) apply. Since not only the functionality but also the design

of the charging stations is important, the size of the filters is often also decisive. Furthermore, the cost factor is playing an increasingly important role. The life cycle of products is similar to that of the start of photovoltaic industry, all manufacturers initially grow very fast and have few resources available to deal with the EMC filter topic. This often results in oversized filters. The first major wave of industrialisation is typically followed by a consolidation of manufacturers, and thus also by an increase in production capacity. At this time, cost factors also play an important role. At the time of consolidation an application-specific solution must be available so customers can continue to be satisfactorily served in the future. This application- specific solution must also be optimized in terms of cost and size. FN2220 and FN2230 will be application specific filters designed for EV charging purposes. To ensure the safe operation of EV charging stations, a galvanic separation between the input and output side is required in addition to compliance with EMC requirements and standards. The use of medium-frequency transformers is particularly beneficial for DC fast charging stations, where inverter technology is anyway required for rectifying the AC mains voltage. Compared to conventional main grid transformers, they can be designed much more compact with the same performance. This means that they can also be placed in constricted charging stations. Schaffner offers a broad portfolio that can meet almost all customer needs. Depending on requirements cooling can be natural or forced convection or even water cooling can be applied. Power in the two to three-digit kVA range can be generated. Within the framework of a research project in operation with RWTH Aachen University, even a 5,000 kVA medium-frequency transformer for coupling DC networks was successfully delivered and tested.


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