Highly Extendable Modular Voltage Equalizer Integrating Cell and Module Voltage Equalizers for Series-Connected Electric Double-Layer Capacitors

Large-scale energy storage systems comprise numerous series-connected modules, each containing several cells connected in series. Such systems require not only cell-but also module-level voltage equalizers, increasing system complexity and cost. Both cell-and module-level equalizers are desirable to exhibit constant current characteristics to prevent excessive current. Additionally, equalizers should be flexibly extendable as the number of series-connected modules varies depending on applications. This paper proposes a highly extendable modular voltage equalizer. The proposed equalizer achieves a simplified system and low-cost by integrating cell-and module-level equalizers. Cell-and module-level equalizers are based on series-resonant converters that realize inherent constant current characteristics. The proposed equalizer is capable of module-level extension, allowing the system to be flexibly scaled up. An equalization test was performed for three six-cell modules, and the proposed equalizer eliminated both cell and module voltage imbalance.