Back-to-Back Cascaded Multilevel Converter for High Capacity Battery Energy Storage

This paper presents a cascaded transformer based multilevel converter (CTMLC) for high capacity battery energy storage (BES) plant. In this CTMC voltage source converter (VSC), each cell is configured with back-to-back connected fundamental switched H-bridges with transformer isolation. A conventional cascaded multilevel converter (MLC) configuration suffers a voltage balancing issue due to unequal energy contribution from different H bridge battery cells. The presented CTMLC and switching modulation strategy significantly minimize the H bridge battery cells voltage balancing issue. Moreover, battery utilization increased, and for the same DC battery capacity, the CTMC has higher power and energy capacity at the plant level as compared to conventional MLC. A 432MW/1728MWh (with four-hour backup) BES plant is modeled in MATLAB-Simulink to demonstrate its steady state, harmonics, and dynamic performance.