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By 2030 around 12.5 million DC fast charging stations are expected to be in operation in the global electric vehicles market. However, without the right electromagnetic compatibility filters in place, there could be major issues with interference that have the potential to disrupt the power network.
Bloomberg’s Annual Electrical Vehicle Outlook 2022, there are already roughly 20 million passenger EVs on the roads globally. In addition, there are more than 280 million electric mopeds, motorbikes, scooters and three- wheelers as well as 1.3 million commercial EVs, including delivery vans, buses and trucks. These figures are expected to increase exponentially over the coming years and before we know it, polluting combustion engines will be consigned to the past. The market share of electric cars is expected to exceed 60 per cent by 2030 and autonomous, driverless vehicles will become a reality. However, there are factors that could hinder or slow down such rapid take-up of EVs, in particular the availability of EV charging stations. At present, the average small vehicle can be fully charged from a domestic mains supply within 24 to 36 hours using a one- or three-phase supply and a mains voltage of either 230 V or 400 V. Clearly, the faster a vehicle can be charged, the sooner it can be back on the road. Other important factors influencing growth in this market include battery technology which is also being developed to improve the amount of charge that can be held at any one time, enabling electric vehicles to travel further between charges. It has been calculated by Germany’s Bundesverband Freier Tankstellen (“the mouthpiece of free petrol stations”) that around 77,000 charging stations are needed for every one million EVs, including 7,000 DC rapid charging stations. BFT calculates that if 20 M EVs were sold every year, by 2030 there would need to be 140,000 DC fast charging stations in operation.
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THE CHALLENGES THAT EMC PRESENTS Apart from the considerable economical, technical and logistical issues this will raise, there is the significant problem of electromagnetic compatibility (EMC) in terms of the emission and immunity of any products that are connected to the mains supply. Without an appropriate EMC concept, EV charging stations are susceptible to interference that occurs during charging from a low-voltage network on the input side. This interference could have an impact on the local network. Likewise, on the output side it is important to ensure the safety of the operator
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here have been many debates and discussions about whether (or when) zero targets will be met around the world but the relentless move towards expanding the EV market cannot be denied. According to
while also achieving seamless interoperability between different stacked power modules and different types or models of vehicle. It must always be remembered that most charging stations will be used by members of the public and so safety is paramount.
STANDARDS DEFINE CHARGING STATION SAFETY
As would be expected, there are many standards in place that govern the use of EV charging stations and some of these relate to EMC. For example, there are specified limits to interference that can be emitted through semiconductor switching. If non-compliant products are used these will likely cause problems for other consumers who are connected to the same local power grid. The degree of a piece of equipment’s conformity can be verified by carrying out various tests, such conducted emission, but also surge, burst or flickr tests. The IEC61851-23 standard defines the various
safety-relevant aspects for DC fast charging stations. For EMC filters, the definition of the capacitors to protected earth (PE) is especially important: The maximum capacitor size is set to 1 µF. This means that with a filter in the system, there can be 500 nF capacitance on the positive and negative conductor towards ground (the capacitor size needs to be lower if several power modules are used in parallel). Also, all discharge resistors must be at least 1 MOhm to ensure insulation measurement in the system. Under the IEC61851-21-2 standard, the limit values and corresponding measurement set-ups are defined, so it is important to ensure the correct network simulations and limits are used. On the input (main grid) side, it is also important to define the environment in which the charging station will be used, for example whether it is industrial (Class A) or residential (Class B). The conductive power transfer (CPT) port must be terminated according to CISPR 25:2008 and the AC/DC input port terminated according to CISPR 16-1-2:2014. Similarly, limit lines for the AC/DC input port follow the specifications of IEC61000-6-3 and the limit values for the CPT port for conducted emission (between 150 kHz and 30 MHz) will apply. The size of filter used is often a crucial factor when designing EV charging stations, as are the overall filter costs. All too often, oversized filters are used unnecessarily in such applications.
PREVENTING DEVICES FROM BEING ADVERSELY AFFECTED For decades, Schaffner has designed and produced EMC filters that deliver compliance
By Dr. Guido Schlegelmilch, head of Products & Technologies, Schaffner
August 2023 Instrumentation Monthly
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