A Scalable Matrix Integrated Transformer With Controllable Leakage Inductance for a Bi-Directional Resonant Converter

Integrated transformer with built-in leakage inductors is a good approach for simplifying the whole system, as it integrates discrete leakage inductors into the transformer with printed circuit board windings for a single-phase CLLC (1PCLLC) resonant converter. The EI-core-based integrated transformer can integrate adjustable leakage inductance into the transformer. Series or parallel connections of EI-core-based integrated transformers offer a possible solution for high-voltage and high-power applications: however, the penalty of more considerable core loss by the induced leakage flux is problematic. This article proposes a matrix integrated transformer with controllable leakage inductance for a 1PCLLC resonant converter. Three EI-core-based elemental integrated transformers can be integrated into one three-UI-core-based integrated transformer with built-in leakage inductance, and the benefits of evenly distributed flux inside the core and much-reduced core loss can be achieved. An asymmetrical winding structure and asymmetrical core structure were proposed to adjust the built-in leakage inductance for the proposed matrix integrated transformer. An 11-kW 1PCLLC resonant converter for 800-V onboard-charger application was built to verify the proposed novel matrix integrated transformer. The designed converter can achieve a power density of 250W/in(3) power density and 98.4% peak efficiency.