Identification and Model of Near Field Magnetic Coupling in a PFC Converter

The attenuation characteristic of on board EMI filter may be deteriorated greatly by the stray magnetic field produced by main circuit of switched mode power supply. In this paper, the magnetic coupling effect between a PFC inductor and an EMI common mode inductor is studied by experiments after analyzing the stray magnetic field distribution characteristic of PFC inductor and the sensitivity of common mode inductor. A differential mode EMI model of this PFC converter is built up, which includes the magnetic coupling effect. Based on this model, the coupling EMI component is distinguished. The unequal EMI emission phenomenon on L and N line is explained too. In the end, several measures are proposed to decrease DM emission and verified by experiments