A Current Sharing Method Utilizing Single Balancing Transformer for a Multiphase LLC Resonant Converter with Integrated Magnetics

Mostafa Noah, Shun Endo, Hiroki Ishibashi, Kimihiro Nanamori, Jun Imaoka, Kazuhiro Umetani, Masayoshi Yamamoto

Research output: Contribution to journalArticle

11 Citations (Scopus)


Integrated magnetics is applied to replace the threediscrete transformers by a single core transformer in a threephase LLC resonant converter. The magnetic circuit of the integrated transformer is analyzed to derive coupling factors between the phases; these coupling factors are intentionally minimized to realize the magnetic behavior of the three discrete transformers, with the benefit of eliminating the dead space between them. However, in a practical design, the transformer parameters in a multi-phase LLC resonant converter are never exactly identical among the phases, leading to unbalanced current sharing between the paralleled modules. In this regard, a current balancing method is proposed in this paper. The proposed method can improve the current sharing between the paralleled phases relying on a single balancing transformer, and its theory is based on Ampere’s law, by forcing the sum of the three resonant currents to zero. Theoretically, if an ideal balancing transformer has been utilized, it would impose the same effect of connecting the integrated transformer in a solid star connection. However, as the core permeability of the balancing transformer is finite, the unbalanced current can’t be completely suppressed. Nonetheless, utilizing a single balancing transformer has an advantage over the star connection, as it keeps the interleaving structure simple which allows for traditional phase-shedding techniques, and it can be a solution for the other multi-phase topologies where realizing a star connection is not feasible. Along with the theoretical discussion, simulation and experimental results are also presented to evaluate the proposed method considering various sources of the unbalance such as a mismatch in: 1) Resonant and magnetizing inductances 2) Resonant capacitors. 3) Transistor on-resistances of the Mosfets. 4) Propagation Delay of the gate drivers.

Original languageEnglish
JournalIEEE Journal of Emerging and Selected Topics in Power Electronics
Publication statusAccepted/In press - Nov 23 2017


  • Capacitors
  • Control systems
  • current balance
  • imbalanced current
  • Inductance
  • isolated dc/dc converters
  • multi-phase LLC resonant converter
  • resonant converter
  • three-phase
  • Topology
  • Transformer cores

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Electrical and Electronic Engineering

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