Integrated capacitor for common-mode EMI mitigation applicable to high frequency planar transformers used in electric vehicles DC/DC converters

Currently, there is immense incentives-driven research, in the automotive industry to develop Plug-In Electric Vehicles (PIEVs) to reduce the green-house gas emissions and to comply with the Kyoto accord. Isolated High frequency AC-DC converters are a major component to transfer power from utility mains to the traction battery packs which store energy for the EV motors propulsion. The front-end AC/DC converters used in EVs are essentially made of two stages, the PFC stage at the input side and an isolated DC/DC converter at the battery side. Due to the switching frequency operation of these converters, electromagnetic compatibility (EMC) is required, to ensure a safe and secure operation of the electrical sub-system components in the vicinity. Thus, strict EMC standards of the on-board power converters must be met according to the CISPR 12 or SAEJ551/5 Conventional passive EMI filters comes at the expense of cost, size and weight, power losses and PCB real estate. In this paper, an EMI filter embedded into the main high frequency (HF) planar transformer used in the DC/DC converter is proposed as a cost-effective and efficient solution for EVs. The proposed structure is able to significantly suppress the Common-Mode (CM) EMI noise generated in the DC/DC converter by using different dielectric material to achieve the required capacitance and to reduce the numbers of the planar transformer PCB layers. Experimental results have been obtained from a 3KW prototype in order to prove the feasibility and performance of the proposed EMI solution. The results show that the proposed embedded EMI filter can effectively suppress the CM noise particularly for high switching frequency based power converters using a minimum number of PCB layers for the main HF transformer. The proposed structure is a simple and cost-effective EMI filtering solution for future PIEVs.