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Common-Mode EMI Noise Reduction for Grid-Interface Converter in Low-Voltage DC Distribution System

Fig. 1. Single-phase full-bridge with proposed ac filter structure.
Special attention is given to the electromagnetic interference (EMI) issues that arise in grid-interface converter systems where the radio frequency (RF) conducted emissions have to be considered on both the dc and ac sides, such as in the application of photovoltaic (PV) system, dc distribution systems, and charging systems in electric vehicles (EVs). This paper presents a brief overview of the recent EMI research activities in such applications as well as EMI filter design and measurement considerations.

Common-mode (CM) conducted EMI noise poses particular challenges to filter design in the grid-interface converter systems because the noise propagation paths are coupled between the dc and ac sides through the grounding capacitors. As shown in Fig. 1, the ac filter strucure not only reduces the leakage current on the dc-side, but also highly reduces the ac-side CM noise propagated into the single-phase utility. Thus, the total passive filter volume could be reduced. In addition, this ac filter strucure can also decouple the impact of the dc-side CM capacitors to ac-side CM noise level, which reduce the filter design process where both dc and ac-side EMI noise has to be attenuated.

As shown in Fig. 2, the investigated ac filter achieves a strong ac CM noise reduction compared to the typical ac filter strucure.

Fig. 2. Ac-side CM noise measurement with (red) and without (blue) the floating filter when the heatsink is floated.
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