Thermal Management Design of Transformers for Dual Active Bridge Power Converters

Abstract

A methodology for the design of compact transformers operating at high frequency is presented in this article. A particular emphasis is paid to the thermal management of the magnetic core and of the winding components. For a 7 kW dual active bridge dc–dc converter, the objective is to reduce the core volume (<80 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ), improve the power efficiency (>99%) and integrate the serial inductance (8.7 μH) as being the leakage inductance of the transformer. A parametric study shows that the heating in the copper winding is very sensitive to the anisotropic thermal conduction behavior of the wire. Due to this characteristic, a pot-core configuration is prone to a higher warming compared with the E-E core geometry, as the efficiency of the winding cooling is lower. In order to take part of the self-shielding ability of pot cores, we studied new configurations in which internal thermal drains are inserted into voids specially designed to shorten the distance between the external cooled walls and the hottest points of the winding. The heating of internal components of the transformer and resulting thermo-mechanical stress peak is reduced by 40% paving the way for robust transformers with a power density that could theoretically reach up to 200 kW/dm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .