Abstract: In order to suppress the injection of three-phase Electromagnetic Interference (EMI) of switching power supply into the power grid, a design method of three-phase EMI filter is proposed. By modeling and analyzing the three-phase common-mode inductance, the ideal equivalent circuits of common-mode and differential-mode filters are built. The effect of high frequency on ideal equivalent circuits is analyzed. The insertion loss expression based on parameter matrix is determined. Parameter matrixes of common-mode and differential-mode filters are derived under ideal and high frequency conditions. According to the characteristics of load impedance in the power grid side and source impedance in the switching power supply side, the relationship between insertion loss and frequency is analyzed. Because that high conductivity of soft magnetic ferrite has gyromagnetic frequency limit and nonlinear hysteresis loop, their inhibitory effect on common-mode inductance and their influence on common-mode insertion loss are analyzed. The filter's parameters are determined based on the related suppress standards and requirements. Experiment results show that using three-phase EMI filter the noise peak of the switching power supply can be suppressed by about 21dB.

Key words: electrical engineering, electromagnetic compatibility, three-phase EMI filter, switching power supply, common-modeinductor