Hybrid battery charging system combining OBC with LDC for electric vehicles

It presents a hybrid battery charging system unifying an on-board charger (OBC) with a low voltage dc-to-dc converter (LDC) for small and light design of EV charger. The proposed hybrid charger consists of three H-bridge converters including a selective switch, a high frequency transformer, and inductors. Front-end converter connected to the grid by a selective switch has two roles. One is to obtain unity power factor by ac-to-dc converting. It belongs to one of the behavior of OBC. The other is to charge an auxiliary battery by working a step-down converter. Back-end converter employs a transformer to ensure galvanic isolation between the grid and EV. It charges propulsion battery by phase-shift control, and as the occasion demands, energy stored in propulsion battery discharges to dc-link capacitor to supply power to the grid or auxiliary battery. To verify the validity of the proposed approach, we carry out computer-aided simulations and experiments.