Conducted Emission and Power Line Filter Design of a Three-phase Grid-connected Battery Charger for Automotive Application

The growing diffusion of off-board battery chargers for electric vehicles leads to a severe increase in electromagnetic interference (EMI) in power grids, and in particular of conducted disturbances. The battery chargers must therefore be equipped with suitable power line filters to reduce conducted emission (CE). In order to efficiently design the three-phase filter, the modal decomposition of the disturbance is exploited. In three-phase systems both the differential mode (DM) and common mode (CM) components of the specific phase disturbances generally contribute differently to the overall CE. This paper shows a simple methodology for the design of a three-phase EMI filter using a setup capable of simultaneously measuring the conducted disturbances on each phase and directly calculating the modal components. The method is applied to a 25 kW three-phase off-board battery charger.