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 dBμV 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.