Analysis and Design of Novel High-Frequency Integrated Transformer with Adjusting Leakage Inductance for LLC Resonant Converter

Adjusting the leakage inductance to approximate the initial design value is important for obtaining the desired output voltage range for an LLC resonant converter with an integrated transformer. To date, various integrated transformer structures and design techniques have been explored to adjust leakage inductance; however, they often require additional devices or complex winding structures, making it difficult to apply them to normal winding-type transformers. This study presents a new integrated transformer structure based on a winding-type transformer that allows to adjust the leakage inductance without additional devices through segments where primary and secondary windings are completely separated or partially overlapped. The proposed integrated transformer structure is manufactured using design techniques that consider not only efficiency and power density, but also reliability factors such as magnetic flux and temperature. The proposed structure and design techniques are validated through finite element analysis simulations and experiments with a 10 kW LLC resonant converter, which confirms the exact design value of the leakage inductance and ensures resonant operation, resulting in a highly efficient resonant converter.