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A Scalable Electronic-Embedded Transformer (EET), a New Concept toward Ultra-high-frequency High-power Transformer in DC-DC Converters

Year: 2023 | Author: Yuliang Cao | Paper: T1.1
Different solutions
Fig.1. (a) Parallel solution for high-power, high-frequency applications: (a) converter-level parallel, and (b) transformer-level parallel with EET units.
  The demand for high-power and high-density isolated DC-DC converters is driven by the fast development of energy-storage systems, data center power supplies, and transportation electrification. However, a high-power and high-frequency transformer design is very challenging because of the trade-off between thermal management, leakage inductance minimization, and insulation requirements. To negate this trade-off between power rating and operation frequency, a scalable electronic-embedded transformer (EET) is proposed, with a low-voltage bridge integrated into the transformer windings. Unlike the traditional converter-level parallel solution shown in Fig. 1(a), which benefit from simple open-loop control and natural current sharing, multiple EET units can be easily connected in parallel and scaled up to different power ratings, as shown in Fig. 1(b). According to this concept, an EET-based DC transformer (EET-DCX) is proposed to solve the issues of transformer-level paralleling and resonant point shifting in the traditional LLC-DCX. With the help of the embedded full bridge, the impedance of the leakage inductance can be cancelled completely, and thus the EET-DCX can work optimally at any frequency. In the meantime, the EET-DCX also retains the intrinsic merits of the LLC-DCX, such as load-independent voltage gain, simple open-loop control, full-load-range zero-voltage switching (ZVS), and low level of circulating current. Benefitting from these advantages, the proposed EET-DCX solution may push the transformer boundary to the MHz and tens or even hundreds of kW. Finally, as shown in Fig. 2, a 12kW 500kHz EET-DCX with four planar EET units was built to verify these aforementioned merits.

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