Magnetic Integrated High Frequency Transformer Based Dual Active Bridge for Multifunctional Onboard EV Charger

A multifunctional onboard charger (MOC) is a two-stage converter, consisting of a front-end power factor correction circuit and a dual active bridge (DAB) circuit. This MOC charges the traction battery in grid-connected mode (GCM), and supplies power to low voltage bus in drive mode (DM). For the considered application, the DAB is required to handle 7.2 kW power at 360 V (nominal) in GCM, and 2.4 kW at 72 V in DM. For the efficient operation of the DAB at these voltage and power levels require different turns-ratio and interface inductances. To fulfill this, a magnetic integrated high-frequency transformer (MI-HFT) is proposed in this paper. This transformer has three limbs and three windings. Two windings are wound on the center limb, while the third winding is split equally and wound on the other two limbs. Depending on the mode of operation, the third winding is configured such that it acts as either an interface inductor or transformer. The use of the proposed MI-HFT improves the soft-switching range of DAB and eliminates the need for a discrete inductor. Detailed simulation studies are carried out to study the feasibility and operation of the proposed MI-HFT and the simulation results are experimentally validated.