Research on a Modular High Performance Battery Equalizer
Liu Hongrui1, Li Hairui1, Wei Xiangyang1, Qian Jing2
1. Faculty of Electric Power Engineering Kunming University of Science and Technology Kunming 650500 China; 2. Faculty of Metallurgical and Energy Power Engineering Kunming University of Science and Technology Kunming 650093 China
Abstract At present, the performance of battery equalizer is uneven in balance speed, balance efficiency and scalability, and often attends one thing and loses another. Although the peak of the balance efficiency reached 94.5%, the value was obtained under certain experimental conditions. When the experimental conditions changed, the value would decrease. The balance speed slows down with the increase of the number of series batteries because it is seriously affected by the number of series batteries. In addition, the hardware and parameters of the equalizer are heavily dependent on the voltage level of the battery system. When the number of series batteries changes, the hardware and parameters need to be re selected and calculated, which limits the scope of application of the equalizer. In view of the problems existing in the current equalizer, a modular high-performance equalizer while taking into account the high balance efficiency and fast balance speed is proposed in this work. When the number of series batteries increases, only the number of equalizer modules needs to be increased, the hardware and parameters of the equalizer remain unchanged, and the equalizer still has high balance efficiency and fast balance speed. The following measures are taken to improve the balance efficiency: First, the shortest energy path is realized, that is, an energy path contains only one switching device, and the energy path is the shortest. Second, a new balance object with high voltage value is constructed, so that the proportion of the turn-on voltage drop of the switching device is reduced. To sum up, a layered balance strategy for different balance objects is proposed in this work. The first layer balance takes single battery as the balance object, and uses the shortest energy path. The second layer balance takes the battery unit as the new balance object, and uses the shortest energy path. In addition, the first layer balance adopts complementary PWM control with dead zone, which further improves the balance efficiency. A multi-objective parallel balancing strategy is proposed on the base of the layered balance in order to effectively improve the balance speed. The number of parallel balancing targets directly determines the balance speed. The number of parallel balance targets reaches the maximum, that is, the number of balance targets is equal to the number of series balance objects. The number of parallel balance targets in the first layer balance, reaches the number of single batteries in series. The number of parallel balance targets in the second layer reaches the number of battery units in series. The balance speed is fast and not affected by the number of series batteries because the number of parallel balance targets reaches the maximum. The equalizer adopts modular design, which determines the scalability of the equalizer and the stability of its performance parameters and hardware parameters after expansion. The performance parameters include balance efficiency and balance speed. The hardware parameters include all the hardware and parameters of the equalizer, among which the most important is the rated voltage parameters of the switching devices. Because of the same structure and independent equalization modules in each layer, the shortest energy path, and the maximum number of parallel balance targets, the equalizer has high balance efficiency and fast balance speed, and these superior performances are not affected by the number of series batteries. The selection of the rated voltage of the switching devices in the equalizer is independent of the voltage level of the entire battery system. Therefore, when the scale of the battery system increases, only the number of balance modules needs to be increased. Once the rated voltage parameters of the switching devices are determined, they will remain unchanged. The equalizer is easy to expand and has a wider application range because of the modular design. The experimental platform with eight series batteries is built for balance experiments, which can verify the advantages of the equalizer in the three aspects of balance efficiency, balance speed and modularity. In the balance experiment, the number of balance targets reaches the maximum, the balance efficiency reaches 97% and 95.1%, the rated voltages of the switching devices are 20 V and 40 V, and the rated voltage parameters are fixed and are independent of the battery system voltage level. The balance experiment proves that the balance efficiency is high and the numerical value is stable, the balance speed is fast and is not affected by the number of series batteries. The modular design makes the equalizer easy to expand. When the scale of the battery system becomes larger, only the number of balance modules needs to be increased, and the hardware and parameters of the equalizer remain unchanged. In the balance experiment, the number of balance targets is maximized, the balance efficiency is 97% and 95%, the rated voltage of the switching device is 20 V and 40 V, and the rated voltage parameters are fixed. The experimental result proves that the balance efficiency is high and the numerical value is stable, the balance speed is fast and is not affected by the number of series batteries. The modular design makes the equalizer easy to expand. When expanding the use, only the number of equalizer modules needs to be increased, and the hardware and parameters of the equalizer remain unchanged.
Liu Hongrui,Li Hairui,Wei Xiangyang等. Research on a Modular High Performance Battery Equalizer[J]. Transactions of China Electrotechnical Society, 2023, 38(17): 4574-4585.
[1] 刘红锐, 张昭怀. 锂离子电池组充放电均衡器及均衡策略[J]. 电工技术学报, 2015, 30(8): 186-192. Liu Hongrui, Zhang Zhaohuai.The equalizer of charging and discharging and the balancing strategies for lithium-ion battery pack[J]. Transactions of China Electrotechnical Society, 2015, 30(8): 186-192. [2] 刘倩怡, 徐顺刚, 许建平, 等. 一种基于推挽变换器的模块化电池均衡电路[J]. 电工技术学报, 2018, 33(14): 3213-3221. Liu Qianyi, Xu Shungang, Xu Jianping, et al.A modularized equalizer for series-connected batteries based on push-pull converter[J]. Transactions of China Electrotechnical Society, 2018, 33(14): 3213-3221. [3] 李泉, 周云山, 王建德, 等. 基于双层准谐振开关电容的锂电池组均衡方法[J]. 电工技术学报, 2017, 32(21): 9-15. Li Quan, Zhou Yunshan, Wang Jiande, et al.Equalization method of lithium battery pack based on double-tiered quasi-resonant switched capacitor[J]. Transactions of China Electrotechnical Society, 2017, 32(21): 9-15. [4] Tashakor N, Farjah E, Ghanbari T.A bidirectional battery charger with modular integrated charge equalization circuit[J]. IEEE Transactions on Power Electronics, 2017, 32(3): 2133-2145. [5] Imtiaz A M, Khan F H.“Time shared flyback converter” based regenerative cell balancing technique for series connected Li-ion battery strings[J]. IEEE Transactions on Power Electronics, 2013, 28(12): 5960-5975. [6] Wei Y W, Liu G T, Xiong S N, et al.Research on power equalization using a low-loss DC-DC chopper for lithium-ion batteries in electric vehicle[C]//IOP Conference Series-Earth and Environmental Science, Sanya, China, 2017: 012038. [7] Shang Yunlong, Xia Bing, Yang Jufeng, et al.A delta-structured switched-capacitor equalizer for series-connected battery strings[C]//2017 IEEE Energy Conversion Congress and Exposition (ECCE), Cincinnati, OH, USA, 2017: 4493-4496. [8] Kim M Y, Kim C H, Kim J H, et al.A chain structure of switched capacitor for improved cell balancing speed of lithium-ion batteries[J]. IEEE Transactions on Industrial Electronics, 2014, 61(8): 3989-3999. [9] Dam S K, John V.A modular fast cell-to-cell battery voltage equalizer[J]. IEEE Transactions on Power Electronics, 2020, 35(9): 9443-9461. [10] Zheng Xinxin, Liu Xintian, He Yao, et al.Active vehicle battery equalization scheme in the condition of constant-voltage/current charging and discharging[J]. IEEE Transactions on Vehicular Technology, 2017, 66(5): 3714-3723. [11] Lu Junlong, Wang Yi, Li Xin.Isolated bidirectional DC-DC converter with quasi-resonant zero-voltage switching for battery charge equalization[J]. IEEE Transactions on Power Electronics, 2019, 34(5): 4388-4406. [12] 郭向伟, 耿佳豪, 刘震, 等. 基于反激变换器的双目标直接均衡方法[J]. 电工技术学报, 2021, 36(6): 1269-1278. Guo Xiangwei, Geng Jiahao, Liu Zhen, et al.The dual-objective direct balancing method based on flyback converter[J]. Transactions of China Electrotechnical Society, 2021, 36(6): 1269-1278. [13] Zhang Chenghui, Shang Yunlong, Li Zeyuan, et al.An interleaved equalization architecture with self-learning fuzzy logic control for series-connected battery strings[J]. IEEE Transactions on Vehicular Technology, 2017, 66(12): 10923-10934. [14] Tavakoli A, Ali Khajehoddin S, Salmon J.A modular battery voltage-balancing system using a series-connected topology[J]. IEEE Transactions on Power Electronics, 2020, 35(6): 5952-5964. [15] Chen Yang, Liu Xiaofang, Cui Yangyi, et al.A multiwinding transformer cell-to-cell active equalization method for lithium-ion batteries with reduced number of driving circuits[J]. IEEE Transactions on Power Electronics, 2016, 31(7): 4916-4929. [16] Yang Xiaoguang, Xi Ligen, Gao Zheng, et al.Analysis and design of a voltage equalizer based on boost full-bridge inverter and symmetrical voltage multiplier for series-connected batteries[J]. IEEE Transactions on Vehicular Technology, 2020, 69(4): 3828-3840. [17] McCurlie L, Preindl M, Emadi A. Fast model predictive control for redistributive lithium-ion battery balancing[J]. IEEE Transactions on Industrial Electronics, 2017, 64(2): 1350-1357. [18] Li Yu, Xu Jun, Mei Xuesong, et al.A unitized multiwinding transformer-based equalization method for series-connected battery strings[J]. IEEE Transactions on Power Electronics, 2019, 34(12): 11981-11989. [19] Wang Shubiao, Kang Longyun, Guo Xiangwei, et al.A novel layered bidirectional equalizer based on a Buck-Boost converter for series-connected battery strings[J]. Energies, 2017, 10(7): 1011. [20] Zhang Zhiliang, Gui Handong, Gu Dongjie, et al.A hierarchical active balancing architecture for lithium-ion batteries[J]. IEEE Transactions on Power Electronics, 2017, 32(4): 2757-2768. [21] Peng Faxiang, Wang Haoyu, Wei Zhengqi.An LLC-based highly efficient S2M and C2C hybrid hierarchical battery equalizer[J]. IEEE Transactions on Power Electronics, 2020, 35(6): 5928-5937. [22] Peng Faxiang, Wang Haoyu, Yu Liang.Analysis and design considerations of efficiency enhanced hierarchical battery equalizer based on bipolar CCM Buck-Boost units[J]. IEEE Transactions on Industry Applications, 2019, 55(4): 4053-4063.
2023, Vol. 38 
