Mechanism of Near-Field Coupling Between Noise Source and EMI Filter in Power Electronic Converter and Its Required Shielding

When designing a low electromagnetic interference (EMI) power electronic converter with high packaging density, its internal near-field coupling to an EMI filter is critical. In this paper, we investigated the near-field coupling between a noise source and a single-phase EMI filter. First, we measured the common-mode (CM) and differential-mode (DM) couplings separately using a four-port network analyzer. The DM coupling when the EMI filter was exposed to a magnetic field was larger than that when it was exposed to an electric field. On the other hand, the CM coupling when the EMI filter was exposed to an electric field was larger than that when it was exposed to a magnetic field. Second, we extracted parasitic coupling elements that determine the coupling magnitude of each mode of coupling. The coupling calculated by the extracted elements agreed with the measurement well. We identified the dominant coupling path between the noise source and the EMI filter. Finally, we studied the required shielding of the EMI filter to reduce the coupling efficiently. Consequently, we found that most of the coupling can be eliminated by shielding the dominant coupling path.