Novel Concept of Universal AC/DC-DC Onboard Battery Charger for Electric Vehicles

In this paper, a universal bidirectional ac/dc-dc power electronic converter is introduced to enable power transfer between input and output in both directions. This converter is particularly suited for onboard battery charging systems, offering vehicle-to-grid and grid-to-vehicle functionality. The proposed system serves as a versatile and universal interface for connecting ac or dc grids and facilitating efficient power transfer. The system supports three-phase and single-phase ac, as well as two-wire and three-wire dc sources, without altering input wiring. Enhanced safety is provided through input-output isolation, and the use of active diodes at higher frequencies improves overall efficiency compared to traditional passive diodes. An 11 kW prototype was developed to validate the proposed converter. It operated successfully at up to 800 V battery voltage, with 100 kHz and 700 kHz switching frequencies for the rectifier and dc-dc stages. Proper functionality was demonstrated in both single-phase and threephase inverter modes under 5 kW testing.