Investigation on the mode conversion between common-mode and differential-mode noises in EMI filters for power electronics circuits

The noise mode conversion between common-mode and differential-mode can occur in power electronics circuits because of the unbalance in the circuits. In this study, an equivalent circuit of an electromagnetic interference (EMI) filter was built, in which the leakage of the magnet flux of the common-mode choke was taken into account. Using the equivalent circuit, the mode conversion between common-mode and differentialmode in the filter was analyzed. The mode conversion was measured using a 2-port network analyzer and a differential probe in practical filter implementation. With the measurement system, the mode conversion between common-mode and differential mode can be measured regardless of the impedance of an equipment under test. The measurement results agree with simulated results within a difference of around 3 dB. The resonant frequencies shown in the mode conversion were explained using the equivalent circuit.