Modeling and Optimization of Displacement Windings for Transformers in Dual Active Bridge Converters

The transformer in the dual active bridge converter (DAB) is the key element which provides galvanic insulation and voltage conversion. The parasitic parameters, including winding capacitance, ac resistance, and leakage inductance, are the primary considerations in its winding design. Without proper consideration of those parameters could result in issues on current ringing, high power loss, and overheating. In this paper, a comprehensive study is devoted to those parameters. A winding design method is presented by taking all those parameters into consideration. Special attention is paid to the impact of displacement winding, which is quite often in the manufacture and especially in prototype design phase. Both the normal and displacement winding will be studied and compared, with analytical, simulation, and experimental methods. Through comparison, additional coefficients are introduced to the simple analytical equations so that they could also be applied for displacement windings. Several considerations are given to control those parameters within a reasonable range in the design and manufacture phase. Finally, the analysis and design method are verified by finite element method and the experimental results on a 120 kHz prototype, and can be extended to other high-frequency magnetic designs.