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.
李加明, 任小永, 周治成, 张之梁, 陈乾宏. 基于谐振网络优化的双向LLC-DCX多模块并联系统均流优化研究[J]. 电工技术学报, 2023, 38(10): 2720-2730.
Li Jiaming, Ren Xiaoyong, Zhou Zhicheng, Zhang Zhiliang, Chen Qianhong. Research on Current Sharing Optimization of Bidirectional LLC-DCX Multi-Module Parallel System Based on Resonant Network Optimization. Transactions of China Electrotechnical Society, 2023, 38(10): 2720-2730.
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2023, Vol. 38 
