High power density isolated DC-DC converter for on-board charger applications

In recent years, there has been a growing demand for efficient converters in OBCs (On Board Chargers) for EVs (Electric Vehicles) . To meet new technological requirements, factors such as higher power densities, improved efficiencies, and reliability are critical considerations. Among various converter topologies, LLC resonant converters stand out due to their unique soft-switching capability, which helps mitigate switching losses. Specifically, LLC converters achieve ZVS (Zero Voltage Switching) for primary switches and ZCS (Zero Current Switching) for secondary-side rectifier diodes. In this study, the focus is on a three-phase LLC topology, comparing it to the conventional LLC converter. The three-phase LLC design evenly distributes losses across the circuit and it offers improved Electromagnetic Compatibility (EMC) performance. Additionally, the feasibility of using Planar transformers in this application is investigated. Planar transformers offer advantages such as a low profile and automated construction compared to traditional transformers. The investigation begins with a simulation to verify the structure’s behavior and ensure it meets system requirements. A market analysis evaluates the topology’s advantages and disadvantages. Finally, an 11 kW three-phase LLC prototype is built to validate theoretical results and estimate the proposed DC-DC converter’s performance.