Conducted EMI characteristic and its implications to filter design in 3-phase diode front-end converters

EMI filter is becoming an essential part for modern power converter products, contributing to significant cost and sizes. Effective EMI filter design involves the identification and separation of common-mode (CM) and differential-mode (DM) conducted noises of the converter. In this paper, the impact by the diode conduction patterns on the EMI characteristics of a three-phase diode front-end converter is analyzed. There are classical two-line CM and DM noises similar to single phase cases corresponding to the two diode conducting case, the "mixed-mode" CM noise corresponding to no diodes conducting cases, and the three-line CM and DM noise corresponding to commutation cases. Though the present filter design based on single-phase approach seems to be adequate as a worst-case design, a more generic approach considering all three conditions together may provide opportunities for filter design optimization.