A Novel Hybrid Battery Based on a Bidirectional Four-Level Neutral-Point-Clamped DC-DC Power Converter Interfacing

Hybrid batteries combine cells of complementary chemistries, each offering distinct strengths, resulting in battery designs with intermediate features, tailored for each application. With the aim of contributing to the development of modular and scalable hybrid batteries, this paper proposes a novel hybrid battery configuration consisting of two different battery banks, each formed by three series-connected battery modules, and a four-level neutral-point-clamped dc-dc power converter to interface the two battery banks. A suitable operating principle, a modulation strategy, and a closed-loop control are conceived for the proposed system. The power converter enables bidirectional power flow between the battery banks, and it also enables a lossless battery module state of charge balancing, simply by regulating the contribution of each module to the total power transfer, as this is one of the degrees of freedom of the selected multilevel converter topology. Simulation and experimental results verify the feasibility and good performance of the proposed system, demonstrating a substantial regulation margin of battery module currents, even at high modulation index values.