T-shaped hybrid alternate arm converter with arm energy balancing control for battery energy storage systems

Multilevel voltage source converters (VSCs), such as modular multilevel converter (MMC), cascaded H-Bridge (CHB) and alternate arm converter (AAC), are competent topologies for battery energy storage systems (BESSs) due to modularity, scalability and low harmonic distortion. However, there is a lack of studies about interfacing AAC with a BESS due to the arm energy balancing issue. Redundant sub-modules (SMs) are inserted passively into MMC, CHB and AAC to achieve high reliability; consequently, some of them are constantly idling, resulting in low SM utilization. We propose a novel topology -T-shaped hybrid alternate arm converter (TSHAAC) for BESS applications. In addition to the aforementioned features, the proposed TSHAAC requires lower number of SMs than MMC and AAC, along with lower number of switches than CHB. Moreover, an adapted arm energy balancing control is proposed to take advantage of the redundant SMs that are idling to achieve faster balancing than in conventional AAC configuration. The simulation results validate the integration of TSHAAC configuration in a BESS; the adapted arm energy balancing control is able to improve the balancing duration by 27 %.