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

Vascular Studies for Nonvascular Surgeons

A patient’s therapeutic plan is guided by a combination of their medical history, vascular test results, and physical examination. Diagnostic tests play an essential role in the detection of vascular disease from both a venous and arterial standpoint. The sooner vascular disease can be identified in an individual, the sooner both physicians and patients can work toward integrating therapies that will prevent or mitigate ulcer formation. Knowledge regarding the proper indications and interpretations of the various vascular studies is critical to the successful management of each patient