Online SoC Balancing Strategy for Distributed Single-Stage MMC-Based BESS

Juan A. P. Garay; Pedro M. Almeida; Pedro G. Barbosa

doi:10.18618/REP.e202624

Authors

Juan A. P. Garay Federal University of Juiz de Fora https://orcid.org/0009-0003-0892-8831
Pedro M. Almeida Federal University of Juiz de Fora https://orcid.org/0000-0003-0979-0865
Pedro G. Barbosa Federal University of Juiz de Fora https://orcid.org/0000-0003-3838-2668

DOI:

https://doi.org/10.18618/REP.e202624

Keywords:

Modular multilevel converter, battery energy storage systems, SoC balancing algorithm, Circulating Current, ancillary services

Abstract

This paper proposes an online state-of-charge (SoC) balancing strategy for a distributed single-stage Modular Multilevel Converter-based Battery Energy Storage System (MMC-BESS). The main contribution is the development of a low-complexity sorting-based selection algorithm integrated into the smart-battery concept, enabling real-time energy redistribution among submodules without requiring additional auxiliary balancing circuits. The proposed method operates jointly with a phase-disposition pulse width modulation (PD-PWM) strategy and is coordinated with conventional grid current control in the synchronous reference frame and circulating current suppression control, thereby ensuring stable converter operation. The complete three-phase MMC-BESS, composed of 18 submodules per arm, was modeled and validated using PSCAD/EMTDC simulations. The performance of the proposed balancing algorithm was evaluated under multiple operating conditions, including active power injection, active power absorption, and reactive power support. Simulation results demonstrate effective SoC equalization across all submodules while maintaining high-quality AC voltage and current waveforms and while ensuring suppression of internal circulating currents. The simulation results confirm the robustness, scalability, and practical applicability of the proposed control strategy, highlighting its potential for improving reliability, extending battery lifetime, and enabling MMC-based BESS to provide ancillary services and support large-scale integration of renewable energy sources.

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Author Biographies

Juan A. P. Garay, Federal University of Juiz de Fora

received the B.S. and M.Sc. degrees in Electrical Engineering from the Federal University of Juiz de Fora (UFJF), Brazil, in 2023 and 2025, respectively. He is currently pursuing the Ph.D. degree in Electrical Engineering at the same institution.

Pedro M. Almeida, Federal University of Juiz de Fora

received the B.S., M.Sc., and Ph.D. degrees in electrical engineering from the Federal University of Juiz de Fora, Juiz de Fora, Brazil, in 2009, 2011, and 2013, respectively. Since 2014, he has been with the Department of Electrical Engineering at Federal University of Juiz de Fora, where he is currently an Associate Professor. His research interests include control of power electronics, three-phase grid-connected converters, and integration of renewable energy systems.

Pedro G. Barbosa, Federal University of Juiz de Fora

received the B.S. degree in electrical engineering from the Federal University of Juiz de Fora, Juiz de Fora, Brazil, in 1986 and the M.Sc. and Ph.D. degrees in electrical engineering from the Federal University of Rio de Janeiro, Rio de Janeiro, Brazil, in 1994 and 2000, respectively. From 1987 to 1992, he worked as an Engineer at the Rio de Janeiro Navy Arsenal, Rio de Janeiro, Brazil. Since 1999, he has been with the Department of Electrical Engineering at the Federal University of Juiz de Fora, where he is currently a Full Professor. His research interests include power electronics and its applications in electric power systems.

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