Analytical method and suppression technique of conducted EMI noise in a multi-converter system

A method is proposed for the analysis of conducted electromagnetic interference (EMI) in multiple power converters connected to the same power line. This method is focused on the phase differences of the sub-harmonic modulation carrier signal for each power converter. It is confirmed that the phase difference among the power converters determines the EMI noise value in a multi-converter system by analyzing waveform of the common-mode current. In addition, EMI noise suppressions based on a novel phase-difference control technique are also proposed. In order to reduce volume of EMI filter effectively, phase difference θ should be set to 360/nN°, here n is high-order harmonic component near 150 kHz, and N is the number of power converters. On the other hand, in order to prevent radio disturbance, another phase-difference τ should be set to 180fc/fx° not depending on the number of converters (N), here fC is carrier frequency of the converters, and fX is center frequency of frequency band of AM radio. Therefore, Conducted EMI noise can be reduced effectively based on the proposed phase-control for any purpose.