Feature: EVs
Because the top end of the scale is
marked at 600A and 1000V, fast charging to 600kW can be achieved with just one EMC filter
of conformity of the equipment can be verified with tests, for conducted emissions, surge, burst and flicker, among other parameters. Te IEC61851-23 standard defines the
various safety-relevant design aspects for DC fast-charging stations. For EMC filters, the definition of the capacitors to protected earth (PE) is especially important: Te maximum capacitor size is set to 1µF. Tis means that with a filter in the system, there can be 500nF capacitance each on the positive and negative conductors towards ground, with lower capacitor size if several power modules are used in parallel. Also, all discharge resistors must be at least 1MΩ to ensure the system’s insulation. Te limit values and corresponding
measurement setups are defined by the IEC61851-21-2 standard, and it’s important to ensure that the correct network simulations and limits are used. On the input (main grid) side, it’s 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). Te 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 emissions (between 150kHz and 30MHz) will apply. Te size of the filter used is oſten a
crucial factor when designing EV charging stations, as are the overall filter costs. All too oſten, oversized filters are used unnecessarily in these applications.
Domestic charging We are also seeing an exponential growth in the demand for domestic charging ports. However, these bring a whole new set of challenges for designers. Here, too, EMC is a problem and must be addressed as early as possible in the design process. Residential charging brings its own particular EMC challenges, mainly because the process is interacting with a consumer- based system as well as the main power grid. Indeed, a great deal of time can be
saved and costs reduced during the certification process if designers can be certain they are complying with all the relevant specifications and standards. For obvious reasons, electromagnetic interference (EMI) – electrical ‘noise’ – must be avoided in a motor vehicle if it is to run efficiently, reliably and safely and the reality is that most power electronics engineers leave it to the experts when it comes to achieving full EMC certification.
www.electronicsworld.co.uk March 2024 29
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