Variability of Conducted Emissions of EV Chargers due to Mutual Effects on a DC Grid

DC grids are becoming a popular choice to cope with highly dynamic and distorting loads, such as electric vehicle chargers that feature significant conducted emissions in the supraharmonic range, on/off load profiles and large power levels (especially for fast charging mode, enabled by connection to a DC grid). One major factor affecting the reliable assessment of emissions in the supraharmonic frequency interval (2 kHz to 150 kHz) is the definition of the supply conditions namely the feeding impedance; in addition, emissions in this frequency range are a mix of differential- and common-mode emissions, with prevalence of the former. It is demonstrated that supply impedance values at the EV charger connection may be highly variable depending on network loading and location of the other connected EV chargers: some scenarios of small and medium extension of the DC network are evaluated, showing peculiar frequency intervals where emissions could vary by as much as 20 dB simply as the consequence of connection and disconnection of other EVs.