An Accurate Leakage Inductance Model for Magnetic Integrated Planar Transformers in LLC Resonant Converters

Magnetic integration effectively enhances the power density of LLC resonant converter through the integration of the resonant inductor and main transformer. Following the technical approach of utilizing inherent leakage inductance of the transformer, precise leakage inductance control becomes critical. In this paper, an accurate leakage inductance model for magnetic integrated planar transformers is proposed. A revised leakage inductance calculation formula is derived, enabling precise computation of air-gapped transformers. Based on the proposed model, a design flow of transformers with customized leakage inductance is proposed and applied to an LLC resonant converter. The resonant frequency accuracy reaches over 99%, demonstrating the precision of the proposed model as well as the feasibility of the design flow.