Magnetic Integration for a Dual Active Bridge Converter Planar Transformer with Accurate Leakage Inductances Estimation

Dual active bridge (DAB) converters are widely used in the on-board propulsion systems of transportation electrification applications. The tendency of decreasing volume consumption leads to the magnetic integration investigation of the planar transformers. For DABs, integration has been focused on integrating the series inductors and a high frequency transformer (HFT) into a single magnetic component by increasing the leakage inductance of the HFT. This brings a critical issue to the designers: whether structural modification is required for the selected core at the transformer design stage to achieve the aimed leakage inductance. Since equivalent series inductance in power characteristic is replaced by leakage inductance, e accurate leakage inductance estimation strategy is also required. This paper firstly proposed a reluctance based leakage inductance evaluation strategy for the accurate estimation with air-path leakage considered. As the common calculations of the winding-arrangement-dominated leakage inductance commonly ignores the air-path leakage fluxes. Based on the estimation of the threshold leakage inductance, an optimized magnetic integration procedure for planar transformer has been developed, which can help judge whether core modification is required and then provide winding arrangement coordination. 3D Finite Element Analysis (FEA) simulation and prototype experiments were conducted to validate the theoretical analyses.