Design of a PQ Cores Magnetic Integrated Transformer for a 15 kW Three-Phase LLC Resonant Converter

In data center power systems, three-phase LLC resonant converters are widely adopted due to their advantages of electrical isolation and high power density. However, the conventional use of multiple discrete high-power transformers reduces both overall power density and efficiency. To address this issue, this paper proposes a novel three-phase magnetically integrated transformer design based on PQ cores. By optimizing the multi-layer winding structure, the proposed transformer ensures balanced current sharing among parallel windings under high-frequency conditions. Additionally, by sharing the side limbs between adjacent phases, the core volume and weight are further reduced. The feasibility of the proposed transformer is validated through magnetic circuit analysis, finite element simulation, and experimental testing. Compared with traditional magnetic integration methods, the proposed approach eliminates the need for custom magnetic cores, simplifying the manufacturing process. Furthermore, compared with the design using multiple discrete transformers, the proposed transformer achieves a 14.3% reduction in core volume and weight. To verify the performance of the proposed design, a two-stage 15 kW three-phase LLC resonant converter was built and tested.