Modular Equalization System Using Phase-Shift Switched Capacitor Converter and Tapped-Inductor-Based Resonant Voltage Multiplier for Energy Storage Systems

Large-scale energy storage systems consist of series-connected multiple energy storage modules, each comprising multiple cells connected in series and parallel, for the sake of manufacturing and assembling systems. Voltages of series-connected modules and cells, such as lithium-ion batteries and electric double-layer capacitors (EDLCs), gradually become imbalanced due to nonuniform individual characteristics, and the voltage imbalance needs to be eliminated in order to ensure years of safe operation. This paper proposes the modular equalization system integrating module-and cell-level voltage equalizers. Phase-shift switched capacitor converters (PS-SCCs) and tapped-inductor-based resonant voltage multiplier (TI-RVM) are employed as module-and cell-level equalizers, respectively. Since two kinds of equalizers are integrated with sharing active switches, the proposed system can halve the switch count compared to conventional modular systems, hence achieving the reduced circuit complexity and cost. An experimental equalization test was performed using the prototype for three EDLC modules, each containing six cells connected in series. Module and cell voltages were equalized at different rates, demonstrating the equalization performance of the proposed modular equalization system.