Battery Energy Storage Systems (BESS) offer scalable energy storage solutions, especially valuable for remote, off-grid applications. However, traditional battery packs with fixed series-parallel configurations lack reconfigurability and are limited by the weakest cell, hindering their application for second-life batteries. The Modular Multilevel Series-Parallel Converter (MMSPC) addresses these limitations by enabling dynamic reconfiguration, optimizing cell balancing, and enhancing energy control. This paper experimentally evaluates a single-phase BESS based on the MMSPC with an output power equivalent to 2 kW and two battery units (155V), demonstrating stable output and reduced internal losses across varied battery parameters.

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Modular multilevel series-parallel converters (MM-SPC) have become a suitable solution to provide higher operating voltages, fault tolerance operation, and reliability at a reduced cost, due to their ability to achieve a simpler internal voltage balance. Therefore, MMSPC is a promising solution for applications where the nominal operating conditions are high voltage levels on the DC side and high current ratings on the AC side of the system. To allow this operation, it is necessary to design the system with parallelization in each phase. Therefore, this article proposes a design that incorporates parallelization in each phases and analyzes the internal cross-circulating current generated due to parallelization. This current creates an unbalance and internal losses in the converter. In order to compensate for the cross-circulating current, two cases are compared: the first one with decoupled inductors in their phases, and the second one with coupled inductors. This way, a comparison is made to determine which case provides greater compensation of the circulating current, allowing for the delivery of a high current at the converter's output with the least possible imbalance and internal losses.@en