Abstract：The model predictive control (MPC) method for modular multilevel converter battery energy storage systems (MMC-BESS) faced challenges such as high computational burden, complex weighting factor tuning, and slow State-of-Charge (SOC) balancing. The conventional variable rounding level control (VRLC) method reduces computational complexity. Still, it failed to eliminate the dependency on weighting factors, resulting in a performance trade-off between output current tracking accuracy and circulating current suppression. Therefore, this paper proposes an improved fixed circulating current SOC equalization strategy based on weight-independent variable rounding level control (WI-VRLC). The strategy ensures low computational burden, eliminates weighting factors, enhances power quality, and achieves fast SOC balancing even under non-uniform inter-phase and inter-arm SOC differences. Two independent cost functions are employed for hierarchical control of output and circulating currents. First, in the output current MPC stage, the reference arm voltage is used to generate three candidate arm combinations through the variable rounding method, with the optimal combination subsequently selected based on evaluation of the output current cost function. In the subsequent circulating current MPC stage, the bridge arm reference voltages for circulating current control are processed through the variable rounding method, yielding two candidate submodule insertion numbers. These are then algebraically combined with the optimal bridge arm combination from the output current MPC stage to produce two new candidate bridge arm combinations. The circulating current cost function is used to evaluate these combinations and determine the optimal number of bridge arm insertions. Finally, the improved constant circulating current SOC balancing strategy calculates the circulating current reference value for SOC balancing, which is incorporated into the circulating current cost function to achieve closed-loop SOC control. Simulations and hardware-in-the-loop (HIL) experiments demonstrate the method's superiority. In simulation results, the steady-state output current total harmonic distortion (THD) decreases from 2.24% to 1.42% (at modulation index=0.9) and from 1.12% to 0.70% (at modulation index=0.45), while maintaining circulating current performance. Dynamic performance tests reveal that the proposed method exhibits slightly better circulating current response than traditional approaches. Both methods demonstrate excellent output current tracking capability. Regarding SOC balancing performance, the proposed method achieves SOC equalization under both non-uniform SOC distribution and extreme unbalanced conditions, while maintaining stable operation during varying grid-connected power levels and grid voltage sag. Experimental results show that the output current THD is reduced by 17% and 19.6% at modulation indices of 0.9 and 0.45, respectively, without compromising SOC balancing speed or circulating current performance. Three conclusions are as follows. (1) The hierarchical control architecture eliminates weighting factor requirements, reduces output current THD by ≥17%, and maintains superior circulating current suppression performance. (2) The method's computation remains fixed at five operations per control cycle, regardless of submodule count, thereby ensuring excellent scalability for high-submodule applications. (3) The enhanced fixed circulating current strategy achieves robust SOC balancing under non-uniform SOC distribution conditions.
刘战, 李全艮, 周桦, 付佳伟, 林志芳. 基于无权重变舍入电平控制的MMC-BESS改进定环流SOC均衡策略[J]. 电工技术学报, 2026, 41(8): 2718-2734.
Liu Zhan, Li Quangen, Zhou Hua, Fu Jiawei, Lin Zhifang. Improved Fixed Circulating Current SOC Equalization Strategy for MMC-BESS Based on Weight-Independent Variable Rounding Level Control. Transactions of China Electrotechnical Society, 2026, 41(8): 2718-2734.
[1] 吴向阳, 何梨梨, 李杨, 等. 弱电网下电网阻抗与PLL耦合效应对并网MMC系统稳定性的影响分析[J]. 电工技术学报, 2025, 40(4): 1236-1253. Wu Xiangyang, He Lili, Li Yang, et al.Analysis of the influence of grid impedance and PLL coupling effect on the stability of grid-connected MMC systems under weak grid[J]. Transactions of China Electro-technical Society, 2025, 40(4): 1236-1253. [2] 刘欣, 袁易, 王利桐, 等. 柔性直流输电系统三端口混合参数建模及其稳定性分析[J]. 电工技术学报, 2024, 39(16): 4968-4984. Liu Xin, Yuan Yi, Wang Litong, et al.Three-port hybrid parameter modeling and stability analysis of MMC-HVDC system[J]. Transactions of China Elec-trotechnical Society, 2024, 39(16): 4968-4984. [3] 吴丽丽, 茆美琴, 施永. 含主动限流控制的MMC-HVDC电网直流短路故障电流解析计算[J]. 电工技术学报, 2024, 39(3): 785-797. Wu Lili, Mao Meiqin Shi Yong. Analytical calcu-lation of DC short-circuit fault current of modular multi-level converter-HVDC grid with active current limiting control[J]. Transactions of China Electro-technical Society, 2024, 39(3): 785-797. [4] 王鹤, 郭家治, 边竞, 等. 基于故障安全域的混合级联直流输电系统后续换相失败抑制策略[J]. 电工技术学报, 2024, 39(5): 1352-1371. Wang He, Guo Jiazhi, Bian Jing, et al.Subsequent commutation failure suppression strategy for hybrid cascaded HVDC system based on fault security region[J]. Transactions of China Electrotechnical Society, 2024, 39(5): 1352-1371. [5] Huang Yanhui, Liu Fei, Zhuang Yizhan, et al.Bidirectional three-port converter for modular multilevel converter-based retired battery energy storage systems[J]. IEEE Transactions on Power Electronics, 2024, 39(9): 11148-11163. [6] 潘尧, 孙孝峰, 蔡瑶, 等. 一种拓展模块化多电平变换器的光伏系统稳定运行范围的谐波补偿调制策略[J]. 电工技术学报, 2024, 39(4): 1132-1146. Pan Yao, Sun Xiaofeng, Cai Yao, et al.A harmonic compensation modulation strategy for extending steady operation range of modular multilevel converter-based photovoltaic system[J]. Transactions of China Electrotechnical Society, 2024, 39(4): 1132-1146. [7] 潘尧, 孙孝峰, 蔡瑶, 等. 一种抑制模块化多电平变换器光伏系统共模电压的脉冲衔尾排布调制[J]. 电工技术学报, 2025, 40(4): 1221-1235. Pan Yao, Sun Xiaofeng, Cai Yao, et al.A nose-to-tail pulse arrangement modulation for suppressing common mode voltage of modular multilevel con-verter photovoltaic systems[J]. Transactions of China Electrotechnical Society, 2025, 40(4): 1221-1235. [8] 郑涛, 章若竹, 吕文轩, 等. 基于故障主动控制的海上风电交流汇集线路时域距离保护[J]. 电工技术学报, 2025, 40(1): 122-138. Zheng Tao, Zhang Ruozhu, Lü Wenxuan, et al.Time-domain distance protection of offshore AC transmission lines based on fault active control considering distributed capacitance’s impact[J]. Transactions of China Electrotechnical Society, 2025, 40(1): 122-138. [9] Kumar Y S, Poddar G.Medium-voltage vector control induction motor drive at zero frequency using modular multilevel converter[J]. IEEE Transactions on Industrial Electronics, 2018, 65(1): 125-132. [10] Vasiladiotis M, Rufer A.Analysis and control of modular multilevel converters with integrated battery energy storage[J]. IEEE Transactions on Power Electronics, 2015, 30(1): 163-175. [11] He Rongdong, Tian Kai, Ling Zhibin.Offline equalization control of modular multilevel converter-based battery energy storage system[J]. IEEE Transa-ctions on Industrial Electronics, 2024, 71(8): 9003-9012. [12] 陶海波, 杨晓峰, 李泽杰, 等. 电能路由器中基于MMC的超级电容储能系统及其改进SOC均衡控制策略[J]. 电网技术, 2019, 43(11): 3970-3978. Tao Haibo, Yang Xiaofeng, Li Zejie, et al.A modified SOC equalization control strategy of MMC based super capacitor energy storage system in electrical energy router application[J]. Power System Tech-nology, 2019, 43(11): 3970-3978. [13] 汪晋安, 许建中. 分布式储能型MMC电池荷电状态均衡优化控制策略[J]. 电力自动化设备, 2023, 43(7): 44-50. Wang Jin’an, Xu Jianzhong.SOC balancing optimal control strategy amongst batteries in MMC-DES[J]. Electric Power Automation Equipment, 2023, 43(7): 44-50. [14] 马文忠, 孙伟, 王玉生, 等. 基于MMC的分布式储能系统及其快速SOC均衡控制策略[J]. 电力系统保护与控制, 2024, 52(16): 1-11. Ma Wenzhong, Sun Wei, Wang Yusheng, et al.Distributed energy storage system based on MMC and rapid SOC balancing control strategy[J]. Power System Protection and Control, 2024, 52(16): 1-11. [15] 肖迁, 于浩霖, 金昱, 等. 面向中压直流配电网的模块化多电平电池储能系统电荷吞吐量抑制策略[J]. 中国电机工程学报, 2024, 44(16): 6482-6494. Xiao Qian, Yu Haolin, Jin Yu, et al.Charge throughput suppression strategy of the modular multilevel converter-battery energy storage system for the medium-voltage DC distribution network[J]. Proceedings of the CSEE, 2024, 44(16): 6482-6494. [16] Liu Zhan, Li Quangen, Zhou Hua, et al.An improved SOC balancing strategy based on reduced com-putational burden voltage level model predictive control for modular multilevel converter-battery energy storage system[J]. Electrical Engineering, 2025, 107: 10303-10316. [17] 曾武, 李睿, 蔡旭. 基于复用桥臂的储能型模块化多电平换流器[J]. 电力系统自动化, 2023, 47(3): 177-186. Zeng Wu, Li Rui, Cai Xu.Multiplexing arm based modular multilevel converter with energy storage[J]. Automation of Electric Power Systems, 2023, 47(3): 177-186. [18] Böcker J, Freudenberg B, The A, et al.Experimental comparison of model predictive control and cascaded control of the modular multilevel converter[J]. IEEE Transactions on Power Electronics, 2015, 30(1): 422-430. [19] Moon J W, Gwon J S, Park J W, et al.Model predictive control with a reduced number of con-sidered states in a modular multilevel converter for HVDC system[J]. IEEE Transactions on Power Delivery, 2015, 30(2): 608-617. [20] Huang Jingjing, Yang Bo, Guo Fanghong, et al.Priority sorting approach for modular multilevel converter based on simplified model predictive control[J]. IEEE Transactions on Industrial Elec-tronics, 2017, 65(6): 4819-4830. [21] Chen Xingxing, Liu Jinjun, Song Shuguang, et al.Modified increased-level model predictive control methods with reduced computation load for modular multilevel converter[J]. IEEE Transactions on Power Electronics, 2018, 34(8): 7310-7325. [22] Wang Jinyu, Liu Xiong, Xiao Qian, et al.Modulated model predictive control for modular multilevel converters with easy implementation and enhanced steady-state performance[J]. IEEE Transactions on Power Electronics, 2020, 35(9): 9107-9118. [23] Yin Jiapeng, Leon J I, Perez M A, et al.Variable rounding level control method for modular multilevel converters[J]. IEEE Transactions on Power Elec-tronics, 2021, 36(4): 4791-4801. [24] 杨晓峰, 郑琼林. 基于MMC环流模型的通用环流抑制策略[J]. 中国电机工程学报, 2012, 32(18): 59-65, 178. Yang Xiaofeng, Zheng Trillion Q.A novel universal circulating current suppressing strategy based on the MMC circulating current model[J]. Proceedings of the CSEE, 2012, 32(18): 59-65, 178.
2026, Vol. 41 
