Influence of Impedance Interaction & Comparability on Spectral Aggregation (2-150 kHz) in DC Grids

The reported higher levels of conducted emissions in DC grids in the 2-150 kHz range are caused by the spectral aggregations resulting from the converter's switching harmonics. The dominant influence for these spectral aggregates is the impedance correlation between the DC-link capacitor and the converters. This paper analyses the impedance interaction & comparability between the DC-link and the DC/DC converters at the point of common coupling in the DC grid. Simulations with four DC-link capacitors and forty parallel DC/DC converters are conducted, with full (non-linear) and equivalent-source (linear) models for comparison. The dB/JV values for the first spectral aggregate decrease as the augmenting DC-side impedance becomes comparable with the smaller DC-link impedance, lowering the electromagnetic interference in the DC grid. This understanding may provide insights into the DC-link capacitor design from an electromagnetic compatibility perspective, and towards developing a framework for DC power quality standards in the 2-150 kHz range.