Influence of Output Terminations on Common-Mode Conducted Emissions Evaluation of Interface Converters

Current conducted emissions standards provide considerable flexibility in the handling of interface converters, which are of increasing importance for the design and implementation of microgrids. Of particular interest herein is the approach selected for terminating the output ports of such converters during conducted emissions qualification testing. This article provides a theoretical treatment of an interface converter consisting of a SiC-based single-phase inverter in a custom-built testbed for evaluating conducted emissions. The accompanying analysis demonstrates that the selection of output terminations plays a significant role in determining the resulting emissions, with a difference of up to 40 dB observed in the relevant emissions metrics. These predictions are validated with a set of empirical studies. The dependence on output termination selection is emphasized further in deployed systems, which are not influenced by the presence of compliance measurement equipment. In this configuration, the common-mode resonance of the system is shown to elevate peak emissions due to reduced damping. Overall, this paper highlights an opportunity to improve emissions standards with respect to interface converters by standardizing output terminations, particularly in view of the increased high-frequency emissions produced by systems implemented with wide band-gap technology.