Design and Comparison of High-Power Bidirectional Isolated DC-DC Converters for Energy Storage Systems : Dual Active Bridge and CLLC Resonant Converter

Sammanfattning

As electric vehicles (EVs) and battery energy storage systems (BESS) scale in power and capacity, compact and efficient bidirectional power conversion systems are required to enable reliable and high-performance operation. Enabling functionalities such as vehicle-to-grid (V2G) and grid-to-vehicle (G2V) requires converters capable of both delivering and receiving energy with minimal losses and high power density. This thesis presents a comparative evaluation of two silicon carbide (SiC)-based bidirectional isolated DC-DC converter topologies: the Dual Active Bridge (DAB) and the CLLC resonant converter. The study is conducted under operating conditions of 600–900 V and 150–225 kW, with the converters acting as the essential DC-DC interface between the DC-link and the battery while ensuring galvanic isolation for safety. The methodology combines detailed PLECS simulations of conduction and switching behavior in SiC MOSFETs with analytical models for transformer core and winding losses, including skin and proximity effects. Transformer optimization, soft switching conditions and thermal performance are also investigated to ensure reliable operation under high-frequency, high-power conditions. The simulation results demonstrate that both converters achieve high efficiency through soft switching, with peak values of 98.83% for the DAB and 99.12% for the CLLC at 200 kW. Total losses were found to be 2.1–3.0 kW for the DAB and 1.8–2.9 kW for the CLLC across the studied battery operating range. Thermal analysis further confirmed that transformer temperatures remained below 42°C under full load, while the use of ferrite UU cores and litz wire windings resulted in low magnetic losses, enabling high power density. The comparative analysis highlights clear trade-offs: the DAB offers simpler control and scalability, making it attractive for practical high-power applications, whereas the CLLC achieves slightly higher efficiency at the cost of increased control complexity. These findings provide practical guidelines and insights for design of next-generation high-power bidirectional converters in EV and BESS applications.