Research on differential mode conducted EMI in power converter

This paper researches differential mode (DM) conducted electromagnetic interference (EMI) in rectifier. The derivation and analysis of interference source generated by power electronic switches is given. Based on experimental and theoretical analysis, the conducted EMI of a three-phase rectifier is studied systematically. The study shows that conducted EMI are presented centrally at the integral times of its PWM controlling frequency and the conducted EMI decreases with the increase of frequency. By the experiment, DM EMI between 0kHz to 30MHz is studied. And the EMI spectrum in 0~500kHz, and 500kHz~30MHz are compared respectively. Furthermore, the rule of DM EMI with the change of the resistive loads is summarized. The study shows that it changes with resistive loads, and the DM EMI boosts up with the load drop, especially in low frequency bandwidth. In high frequency bandwidth, the effect of change of the resistive load on the DM EMI is not obvious because of the capacitance.