Research on Current Sharing Optimization of Bidirectional LLC-DCX Multi-Module Parallel System Based on Resonant Network Optimization
Li Jiaming1,2, Ren Xiaoyong1, Zhou Zhicheng1, Zhang Zhiliang1, Chen Qianhong1
1. College of Automation Engineering Nanjing University of Aeronautics and Astronautics Nanjing 211106 China; 2. Nanjing Chenguang Group Co. Ltd Nanjing 210006 China
Abstract In recent years, bidirectional LLC DC transformers (DCX) have been widely applied in power supply systems. Multi-module parallel has become an important way to increase the power level of the system. However, the current sharing performance is the design difficulty of an LLC resonant converter parallel system. For LLC-DCX, if conventional current sharing methods are adopted, the fully decoupled modular parallel cannot be realized, and the current sharing control will reintroduce the control cost that has been saved. A current sharing method for a bidirectional LLC-DCX parallel system is proposed. By optimizing the resonant parameters, the natural current sharing performance of the converter can be improved, and the fully decoupled and modularized open-loop current sharing can be realized, which can simplify the control and reduce the cost to the maximum extent. Firstly, according to the equivalent circuit of the bidirectional LLC converter, the gain characteristics of the bidirectional operation are derived. Next, the forward parallel characteristics of bidirectional LLC-DCX are quantitatively analyzed. According to the forward equivalent circuit, the external characteristic curve equation is derived, and the expression of the current imbalance of each module in the forward parallel system is further derived. The current imbalance is composed of two parts. The first part is related to the no-load output voltage deviation of each module, and the second part is related to the internal resistance deviation of each module. According to the forward gain characteristics, the analysis shows that increasing the inductance ratio can optimize the impedance distribution of the resonant network, then reduce the first part of the current imbalance. Therefore, we can calculate the value range of the inductance ratio according to the requirement, then optimize the design of resonant parameters, to improve the current sharing performance of the forward parallel system. Next, the reverse parallel characteristics of bidirectional LLC-DCX are quantitatively analyzed. Similarly, the expression of the current imbalance of each module in the reverse parallel system is derived. Because the reverse no-load output voltage is constant, the current-sharing performance is only related to the internal resistance deviation. Therefore, the reverse parallel system naturally has a good current sharing performance without requiring to design of resonant parameters. Finally, a prototype of a three-module bidirectional LLC-DCX parallel system is built for the experiment. After optimizing resonant parameters, the current sharing performance of the forward parallel system is improved. Before and after the resonant parameter optimization, the reverse parallel system has good current sharing performance, and there is no noticeable difference. The forward parallel system and reverse parallel system have good dynamic current-sharing performance. The experimental results verify the feasibility and effectiveness of the proposed method. By optimizing the resonant parameters, the fully decoupled and modularized open-loop current sharing can be realized in a bidirectional LLC-DCX parallel system.
Li Jiaming,Ren Xiaoyong,Zhou Zhicheng等. Research on Current Sharing Optimization of Bidirectional LLC-DCX Multi-Module Parallel System Based on Resonant Network Optimization[J]. Transactions of China Electrotechnical Society, 2023, 38(10): 2720-2730.
[1] 杨东江, 段彬, 丁文龙, 等. 一种带辅助双向开关单元的宽输入电压范围LLC谐振变换器[J]. 电工技术学报, 2020, 35(4): 775-785. Yang Dongjiang, Duan Bin, Ding Wenlong, et al.An improved LLC resonant converter with auxiliary bi-directional switch for wide-input-voltage range applications[J]. Transactions of China Electro- technical Society, 2020, 35(4): 775-785. [2] Tan D F D. A review of immediate bus architecture: a system perspective[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2014, 2(3): 363-373. [3] Ren Ren, Liu Shuo, Wang Jinlong, et al.High frequency LLC DC-transformer based on GaN devices and the dead time optimization[C]//International Power Electronics and Application Conference and Exposition, Shanghai, China, 2015: 462-467. [4] Jean-Pierre G, El Shafei A, Altin N, et al.A multiport bidirectional LLC resonant converter for grid-tied photovoltaic-battery hybrid system[C]//International Conference on Renewable Energy Research and Applications (ICRERA), Brasov, 2020: 755-760. [5] Li Haoran, Zhang Zhiliang, Wang Shengdong, et al.A 300-kHz 6.6-kW SiC bidirectional LLC onboard charger[J]. IEEE Transactions on Industrial Electro- nics, 2020, 67(2): 1435-1445. [6] 林霖, 裴忠晨, 蔡国伟, 等. 混合式隔离型模块化多电平变换器[J]. 电工技术学报, 2021, 36(16): 3319-3330. Lin Lin, Pei Zhongchen, Cai Guowei, et al.Hybrid isolated modular multilevel converter[J]. Transactions of China Electrotechnical Society, 2021, 36(16): 3319-3330. [7] 任小永, 张强, 庞振进, 等. 输入串联输出准并联的多路输出变换器[J]. 中国电机工程学报, 2016, 36(13): 3582-3589, 3377. Ren Xiaoyong, Zhang Qiang, Pang Zhenjin, et al.Input-series output-quasi-parallel multiple output converter[J]. Proceedings of the CSEE, 2016, 36(13): 3582-3589, 3377. [8] Jang J, Choi S, Choi B, et al.Average current mode control to improve current distributions in multi- module esonant DC-to-DC converters[C]//International Conference on Power Electronics-ECCE Asia, Jeju, 2011: 2312-2319. [9] Wang Hongliang, Chen Yang, Qiu Yajie, et al.Common capacitor mutiphase LLC converter with passive current sharing ability[J]. IEEE Transactions on Power Electronics, 2018, 33(1): 370-387. [10] Wang Hongliang, Chen Yang, Liu Yanfei, et al.A passive current sharing method with common inductor multiphase LLC resonant converter[J]. IEEE Transa- ctions on Power Electronics, 2017, 32(9): 6994-7010. [11] 杨玉岗, 吴晗, 关婷婷. 交错并联LLC谐振变换器的磁集成均流特性[J]. 电工技术学报, 2019, 34(12): 2529-2538. Yang Yugang, Wu Han, Guan Tingting.Magnetic integrated current sharing characteristics of inter- leaved LLC resonant converter[J]. Transactions of China Electrotechnical Society, 2019, 34(12): 2529-2538. [12] Yang Gang, Dubus P, Sadarnac D.Double-phase high-efficiency, wide load range high-voltage/low- voltage LLC DC/DC converter for electric/hybrid vehicles[J]. IEEE Transactions on Power Electronics, 2015, 30(4): 1876-1886. [13] 任小永, 王亚坤, 陈宇, 等. 基于虚拟阻抗的LLC谐振变换器并联均流控制[J]. 电工技术学报, 2019, 34(21): 4540-4550. Ren Xiaoyong, Wang Yakun, Chen Yu, et al.Parallel current sharing control of LLC resonant converter based on virtual impedance[J]. Transactions of China Electrotechnical Society, 2019, 34(21): 4540-4550. [14] 刘硕, 苏建徽, 赖纪东, 等. LLC谐振变换器PO模式增益公式与模式边界条件分析[J]. 电力系统自动化, 2020, 44(6): 164-170. Liu Shuo, Su Jianhui, Lai Jidong, et al.Analysis on gain formula and mode boundary condition for LLC resonant converter in PO mode[J]. Automation of Electric Power Systems, 2020, 44(6): 164-170. [15] Pledl G, Tauer M, Buecherl D.Theory of operation, design procedure and simulation of a bidirectional LLC resonant converter for vehicular applications[C]// IEEE Vehicle Power and Propulsion Conference, Lille, France, 2011: 1-5.
2023, Vol. 38 
