High frequency analysis of an integrated planar transformer with common mode EMI suppression capability

High frequency transformers are one of the essential building blocks to provide galvanic isolation for power converters. Due to the switching nature of the converter, electromagnetic compatibility (EMC) of these converters is an essential requirement, to ensure not only its own operation but also the safe and secure operation of surrounding electrical equipment that are connected to same power distribution network. Thus, strict EMC standards such as CISPR 12 or SAEJ551/5 are imposed to provide safe and reliable operation of the power converters. Conventional passive filters used for EMI mitigation in power converters, comes at the expense of cost, size and weight, power losses and PCB real estate. In this paper, an integrated EMI filter embedded into the main high frequency planar transformer used in the DC/DC converter is proposed as a very cost-effective and efficient solution. The proposed structure is able to significantly suppress the Common-Mode (CM) EMI noise generated in the DC/DC converter. In order to evaluate the performance of the integrated transformer, a high frequency simulation through HFSS has been performed. Also, a prototype has been implemented to assess the feasibility of the proposed structure and confirm the HFSS simulation results. The results obtained from a 3KW prototype show that the proposed integrated EMI filter can effectively suppress the CM noise particularly for power converters operating at high switching frequency. The proposed structure can be a very simple and cost-effective EMI filtering solution for many applications such as future plug-in electric vehicle.