Some procedures in mitigating conducted electromagnetic interference

Abstract

In our opinion, the problem of conducted interference generated by power converters, represents not a simply mater of harmonics or even interharmonics, as usually is considered, but really a broader issue, which requires a careful treatment of a continuous spectrum of frequency, extending until 30MHZ. The following paper presents a conducted electromagnetic interference problem in the case of a power converter, included in one kinetic therapy equipment (actually a treadmill). Analysis is made, considering only conducted emissions at the mains supply port of the equipment. Tests carried out, outlined a few procedures in the analysis and mitigation of electromagnetic conducted interferences using electromagnetic interference mains filters. Virtually all products contain a power supply filter as the last circuit that noise currents pass through before they exit the product through the power cord. Sometimes, properly designed transformers can provide inherent filtering, and so can obviate the need for an intentional filter. In other cases, like the one presented in the paper, mains filters are not enough for mitigating conducted interferences and they must be replaced, or simpler retrofitted by an additional one, the filters’ cascade being able more often to mitigate perturbations. Mains passive EMI filters carry potentially high currents at dangerously high voltages, so the choice of these filters is an essential issue. From the paper it can be seen that the EMI filter issues should be considered with careful attention by designers, because they are not only ancillary devices, as they are more often treated.