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Design of Integrated Transformer and Inductor for High Frequency Dual Active Bridge GaN Charger for PHEV

Fig. 1 Transformer and inductor in one component.
We propose a design of a high-power-density-transformer and inductor for a high-frequency dual active bridge (DAB) GaN charger. Because the charger operates at 500 kHz, the inductance needed to achieve ZVS for the DAB converter is reduced to as low as 3uH. As a result, it is possible to utilize the leakage inductor as the resonant inductor of the DAB converter. To create this amount of leakage inductance, a certain amount of space between the primary and secondary winding is allocated to store the leakage flux energy. The designed transformer is 99.2% efficient while delivering 3.3kW. Its volume is 40% smaller than the nearest published equivalent counterpart, and over 63% smaller than the lump transformer and inductor in a 50kHz Si charger.

Fig. 2. Space between primary and secondary windings.
Fig. 3. Litz wire selection to reduce winding loss.
Fig. 4. Thermal management.