EMI filter optimization by adjusting common mode noise impedance of a balanced boost converter

This paper introduces a novel method to adjust the common mode (CM) noise impedance by adding a balanced winding in series with a balanced resistance. The balanced winding is wound in an E-E core with two inductors of a balanced boost converter. Two kinds of electromagnetic interference (EMI) filters and a three-port network, which comprises the power inductors, balanced winding and balanced resistance, are characterized using Scattering parameters (S-parameters), respectively. Based on the measured S-parameters, designers can make the selection of an appropriate balanced resistance. Experiments are then carried out to verify this method. The proposed method could widen the impedance mismatch on the noise source side and, in turn, significantly boost the CM insertion loss of an EMI filter. Following this method, researchers will optimize the performance of an EMI filter even if its structure is fixed. Thus, a design gap among impedance measurement, EMI filter characterization and EMI filter design can be bridged. At the same time, the over design of an EMI filter is avoided.