フライングキャパシタにより無制御での電流バランスを実現する対称共振3相LLCコンバータ

抄録

To meet the increasing demand for high-power isolated converters, interleaved LLC converters are being extensively studied. However, traditional interleaved LLC converters need auxiliary circuits or bulky magnetic components to achieve current balancing among parallel-connected phases, resulting in increased circuit complexity and volume. The automatic current balancing three-phase LLC asymmetric resonant converter was proposed in a previous work. Although phase currents can be balanced automatically by flying capacitors, the conventional asymmetric resonant operation with an asymmetric duty cycle of d ≠ 0.5 has various limitations, such as the increased difficulty in circuit design and analysis, impaired extendibility, and the need of dc blocking capacitors on the transformers' secondary side. This paper proposes a three-phase LLC symmetric resonant converter using flying capacitors. In addition to the automatic current balancing capability, the symmetric resonant operation with d =0.5 simplifies the circuit design and allows the traditional fundamental harmonics approximation to be used for analysis. The experimental verification tests using a 1-kW prototype demonstrated the automatic current balancing performance, regardless of the significant mismatch in the transformers' parameters.