Enhancement of Performance, Availability, and Flexibility of a Battery Energy Storage System Based on a Modular Multilevel Cascaded Converter (MMCC-SSBC)

This paper provides a theoretical and experimental discussion about the performance, availability, and flexibility of a battery energy storage system (BESS) using a modular multi-level cascaded converter based on single-star bridge cells (MMCC-SSBC). The SSBC-based BESS produces three-phase multilevel voltage waveforms, and eliminates both harmonic filters and a complicated zig-zag transformer from the ac side. The circuit modularity of the SSBC enables the usage of multiple individual low-voltage battery modules. Along with control strategy based on zero-sequence-voltage injection, this modularity enhances the availability and flexibility of the BESS. A three-phase laboratory downscaled system rated at 140 V, 10 kW, and 21 kW.h is designed, constructed, and tested to verify the operating principles and performance. The tested BESS produces a current total harmonic distortion (THD) of 3.0% even when it operates with different active-power commands for individual bridge cells. In addition, zero-voltage ride-through capability is verified for the severest single-phase, two-phase, and three-phase voltage sags. Mathematical analysis and experimental verification validate the downscaled system and performance, making the BESS prospective.