Inserted-shunt Integrated Planar Transformer with Low Secondary Leakage Inductance for LLC Resonant Converters

The leakage inductance of an integrated transformer is usually utilised as the series inductor of an LLC topology. However, leakage inductance exists on both primary and secondary sides of an integrated transformer and secondary leakage inductance leads the control and design of the converter to difficulty. In this paper, a novel topology for inserted-shunt integrated transformers is proposed which has low secondary leakage inductance. The inserted shunt of the proposed topology is not segmental and can be located conveniently within the transformer. In addition, the inserted shunt does not require low permeability core material, simplifying its manufacture. The design and modelling of the proposed transformer topology are presented and verified by finite-element analysis and experimental implementation. The proposed topology is also compared with a recently published inserted-segmental-shunt integrated transformer. It is shown that the proposed transformer provides higher efficiency and lower AC resistance. Finally, an LLC resonant converter is implemented to examine the performance of the proposed integrated transformer in practice.