The use of power electronic converters to interface renewable sources and intelligent loads to electricity distribution systems is increasing at a rapid rate as they bring flexibility and control to the system. However, they also bring an increased level of conducted emissions (CE) to the system due to their switching behaviour -usually at a few tens of kilohertz. The increased emissions are seen particularly in the low-frequency range (2-150 kHz) and it may possibly impair the operation of information and communication technology (ICT) equipment connected to the same system. It is therefore essential to assure accurate measurement of low frequency emissions from a particular piece of equipment, to ensure it meets standards for electromagnetic compatibility (EMC). According to EMC standards, CE are usually measured by using a Line Impedance Stabilization Network (LISN). However, the standard LISN bandwidth does not fully cover this low-frequency range (2-150 kHz), resulting in inaccurate measurement and poor repeatability. This paper examines this issue, by investigating the limitations in using the CISPR 16-1-2 LISN topology for CE measurement at low frequency in a grid-tied inverter system, and by proposing a possible solution, which requires adding extra components to the LISN circuit.

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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 equivalentsource (linear) models for comparison. The dBµV values for the first spectral aggregate decrease as the augmenting DCside impedance becomes comparable with the smaller DC-link impedance, lowering the electromagnetic interference in the DC grid. This understanding may provide insights into the DClink capacitor design from an electromagnetic compatibility perspective, and towards developing a framework for DC power quality standards in the 2-150 kHz range.

DC Microgrid research has developed in the recent years following the increasing integration of power electronic based switching devices at the point of common coupling in DC grids. This has led to electromagnetic interference problems caused by the spectral aggregation of conducted emissions in the low-frequency range (2-150 kHz). To investigate this, a framework for understanding spectral aggregation resulting from the multiple switching harmonics from the interconnected DC grid devices is analysed. In this work, three modulation techniques are applied to identical & parallel connected DC/DC converters forming a lab-based DC grid. The harmonics are then analysed for spectral aggregation using an EMI receiver. This provides insights into the spectral aggregation of conducted emissions in the low-frequency range to promote electromagnetic compatibility and further facilitate a possible framework for standardisation of DC power quality.