40‑kW isolated bidirectional DC/DC converter based on LLC/SRC and buck converters with ZVT for fast chargers

Jae-Hyuck Choi; Young-Joo Kim; So-Jeong Kong; Jin-Su Kim; Eui-Hoon Chung; Jun-Young Lee

40‑kW isolated bidirectional DC/DC converter based on LLC/SRC and buck converters with ZVT for fast chargers

Vol. 25, No. 5, pp. 814-825, May 2025

10.1007/s43236-025-01039-9

Zero-voltage transition

LLC/SRC converter

bidirectional DC/DC converter

Fast charger

Abstract

In this paper, a design method for a 40 kW DC/DC converter based on a two-stage structure that integrates an LLC/SRC converter and a zero-voltage transition (ZVT) buck converter is proposed to compensate for the shortcomings of the conventional DC/DC converters employed in bidirectional fast chargers, which necessitate a wide range of output voltages. During forward operation, the LLC/SRC converter functions in the LLC mode, effectively maintaining link voltage through narrow frequency control near the resonant frequency with low switch loss. In contrast, during reverse operation, the converter operates in the SRC mode, which facilitates stable reverse operation without the need for additional control. This is different from LLC operation since the maximum link voltage is determined at the maximum power input to the link voltage side, which can be limited by a proper SRC gain design. Furthermore, the buck converter achieves high efficiency across a wide range of output conditions by employing a half-resonant ZVT circuit. This configuration minimizes the loss in the auxiliary circuit while ensuring soft-switching operation. The validity of the proposed method was confirmed through a comparative analysis with previous studies, utilizing a prototype with specifications of Vin = 740 V, Vo = 150–850 V, and Po = 40 kW, where a maximum efficiency of 97.7% was achieved under Vo = 850 V.

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Cite this article

[IEEE Style]

J. Choi, Y. Kim, S. Kong, J. Kim, E. Chung, J. Lee, "40‑kW isolated bidirectional DC/DC converter based on LLC/SRC and buck converters with ZVT for fast chargers," Journal of Power Electronics, vol. 25, no. 5, pp. 814-825, 2025. DOI: 10.1007/s43236-025-01039-9.

[ACM Style]

Jae-Hyuck Choi, Young-Joo Kim, So-Jeong Kong, Jin-Su Kim, Eui-Hoon Chung, and Jun-Young Lee. 2025. 40‑kW isolated bidirectional DC/DC converter based on LLC/SRC and buck converters with ZVT for fast chargers. Journal of Power Electronics, 25, 5, (2025), 814-825. DOI: 10.1007/s43236-025-01039-9.