Design and Implementation of Dual-Mode LLC Resonant Converter for Charging 400 V and 800 V Onboard Plug-in Electric Vehicles

Lithium-ion batteries used in electric vehicles (EVs) are generally rated at either 400 V or 800 V. Onboard chargers (OBCs) are evolving to support both voltage levels and high-power capabilities to enhance system efficiency. The plugin onboard EV chargers need to charge both voltage levels efficiently. Typically, this is achieved by regulating the output voltage through an additional DC-DC converter. However, this approach adds complexity to the circuit design. This article proposes a dual transformer based dual-mode LLC resonant (DM-LLCR) converter for charging 400 V and 800 V battery packs. The proposed converter can operate in voltage doubler mode to charge an 800 V battery or in current doubler mode to charge a 400 V battery. The proposed converter has a reduced switch count compared to the conventional dual transformerbased LLC resonant converter topologies. The operation of the proposed converter is validated in MATLAB/Simulink at a power rating of 10 kW. To further evaluate the feasibility of the proposed converter, a scaled-down 1 kW laboratory prototype was developed. The peak efficiency recorded is $96.4 \%$ for the voltage doubler mode and $96 \%$ for the current doubler mode.