Multimodule isolated converters incorporating excellent features of galvanic isolation, bidirectional power flow, and simple control are widely adopted in medium-voltage (MV) high-power dc–dc applications. However, the converter size and dc-link capacitor voltage balancing are significant concerns in galvanically isolated cascaded dc–dc converters. This article proposes a new design of an integrated transformer implementing toroidal cores named toroidal core multilimb transformer (TCMLT), employed in a dc–dc modular isolated bidirectional dual-active-bridge (IB-DAB) resonant converter topology. The modular design structure of the proposed transformer can be conveniently constructed and implemented for more number of participating modules conforming the compactness constraint. Moreover, an external coupling winding is implemented in the TCMLT structure to resolve the dc-link voltage balancing issue. This coupling winding method substitutes the expensive complex control circuits, which consequently results in cost reduction and reliability enhancement. Besides, the reluctance model of the proposed structure is analyzed. Based on the reluctance model, a common mode–difference mode (CM-DM) electrical circuit is realized for the proposed scheme. Furthermore, unlike the conventional approach of implementing U, UI, and EI cores for multilimb transformer (MLT) structure with separate limbs, a synthesis method of TCMLT in toroidal form is proposed. The comparative study of the proposed design with the conventional U-core MLT confirms that the proposed TCMLT offers less leakage inductance with significant size reduction. Finally, to validate the efficacy of TCMLT, a three-limb laboratory-scale prototype is employed in a 6-kW cascaded IB-DAB resonant converter topology.

中文翻译：

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用于大功率直流应用的环形铁芯多臂变压器 (TCMLT) 的研究

具有电流隔离、双向功率流和简单控制等优异特性的多模块隔离转换器被广泛用于中压 (MV) 大功率 DC-DC 应用。然而，转换器尺寸和直流链路电容器电压平衡是电流隔离级联直流-直流转换器中的重要问题。本文提出了一种实现环形磁芯的集成变压器的新设计，称为环形磁芯多臂变压器 (TCMLT)，用于 DC-DC 模块化隔离双向双有源桥 (IB-DAB) 谐振转换器拓扑结构。所提出的变压器的模块化设计结构可以方便地构建和实现更多数量的符合紧凑性约束的参与模块。而且，在 TCMLT 结构中实现了一个外部耦合绕组，以解决直流链路电压平衡问题。这种耦合绕组方式替代了昂贵的复杂控制电路，从而降低了成本并提高了可靠性。此外，分析了所提出结构的磁阻模型。基于磁阻模型，为所提出的方案实现了共模-差模（CM-DM）电路。此外，与实现 U、UI 和 EI 磁芯的传统方法不同，多臂变压器 (MLT) 结构具有独立的臂，提出了一种环形形式的 TCMLT 合成方法。所提议的设计与传统 U 型芯 MLT 的比较研究证实，所提议的 TCMLT 提供更少的漏电感，并显着减小了尺寸。最后，