Control Improvement and Efficiency Optimization of Four Switch Three-Level Half-Bridge LLC Converter
Chen Jie, Liu Changyong, Deng Wenming, Gao Yu, Ruan Xinbo
Ministry of Industry And Information Key Laboratory of More-Electric Power System Nanjing University of Aeronautics & Astronautics Nanjing 211106 China
Abstract The ram air turbine (RAT) is an emergency power supply for aircraft when the engine and the auxiliary power system fail. It is the final guarantee to ensure the safe landing of the aircraft. The output voltage amplitude and frequency of permanent magnet synchronous generators vary widely due to the wide speed range of the RAT. Since most onboard emergency electronic devices or loads are powered by DC voltage, it is necessary to rectify the AC voltage to an uncontrolled DC voltage and then convert it to a desired DC voltage by a cascaded DC-DC converter. Therefore, the input voltage range becomes very wide for the DC-DC converter. Similarly, such a wide input voltage range also exists in spacecraft solar arrays and photovoltaic power generation. Thus, converters operating with an extensive wide range of input voltage are necessary. Currently, various topologies and control strategies are suitable for wide input voltage ranges. Among them, the three-level half-bridge (TLHB) LLC resonant converter has a relatively simple topology and low voltage stress. Consequently, this paper analyzes the operational principle, control strategy, and parameter optimization of the TLHB LLC resonant converter. Firstly, the paper compares different structures of LLC resonant converters suitable for wide input voltage ranges and the commonly used control strategies, analyzes the merits and drawbacks of various topologies and control strategies, and gives the selection consideration of the topology. Considering the broad input voltage range, the two-stage topology is adopted. The four-switch TLHB resonant LLC topology is employed as the front-end converter. It operates in an open-loop state with a fixed resonant cavity input voltage frequency, with the advantage of easy parameter optimization and loss reduction. The second stage uses the synchronous rectification Buck circuit. Secondly, the operating mode of the LLC converter is analyzed using the constant switching frequency dual mode control strategy. The mathematical model of the TLHB LLC resonant converter is obtained based on the first harmonic approximation (FHA) method, and the relationship between the main parameters and output gain of the resonant converter is analyzed. The impact of switching frequency on the over current phenomenon is revealed, and a soft switching control strategy is proposed for a smooth transition between the two control modes. Additionally, the voltage imbalance mechanism of input bus capacitors is analyzed, the influence of the duty cycle on the capacitor voltage balancing is investigated, and an input bus capacitor voltage balancing control strategy is proposed. The loss distribution of the TLHB LLC resonant converter is analyzed, and the expressions of power losses and several key currents are quantitatively derived. The optimized parameters of the converter are solved using the cuckoo search algorithm regarding the relative loss rate of the converter as its objective function. The optimized parameters significantly improve the converter’s efficiency. Finally, a 500 W four-switch TLHB LLC resonant converter is developed. Experimental results validate the correctness and effectiveness of the proposed control strategies and the parameter optimization design.
Chen Jie,Liu Changyong,Deng Wenming等. Control Improvement and Efficiency Optimization of Four Switch Three-Level Half-Bridge LLC Converter[J]. Transactions of China Electrotechnical Society, 2024, 39(24): 7833-7845.
[1] 缪哲语, 仝昊, 姚文熙, 等. 一种柔性多模态宽范围全桥LLC变换器控制方法[J]. 中国电机工程学报, 2022, 42(2): 747-760. Miao Zheyu, Tong Hao, Yao Wenxi, et al.A flexible variable-mode control method for wide-range full-bridge LLC converter[J]. Proceedings of the CSEE, 2022, 42(2): 747-760. [2] Ta L A D, Dao N D, Lee D C. High-efficiency hybrid LLC resonant converter for on-board chargers of plug-in electric vehicles[J]. IEEE Transactions on Power Electronics, 2020, 35(8): 8324-8334. [3] 刘硕. 高效率LLC变换器若干关键问题的研究[D]. 南京: 南京航空航天大学, 2019. Liu Shuo.Research on some key problems of high efficiency LLC converter[D]. Nanjing: Nanjing University of Aeronautics and Astronautics, 2019. [4] Tang Xinxi, Xing Yan, Wu Hongfei, et al.An improved LLC resonant converter with reconfigurable hybrid voltage multiplier and PWM-plus-PFM hybrid control for wide output range applications[J]. IEEE Transactions on Power Electronics, 2020, 35(1): 185-197. [5] Khan S, Sha Deshang, Jia Xiangshuai, et al.Resonant LLC DC-DC converter employing fixed switching frequency based on dual-transformer with wide input-voltage range[J]. IEEE Transactions on Power Electronics, 2021, 36(1): 607-616. [6] Sun Wenjin, Xing Yan, Wu Hongfei, et al.Modified high-efficiency LLC converters with two split resonant branches for wide input-voltage range applications[J]. IEEE Transactions on Power Elec-tronics, 2018, 33(9): 7867-7879. [7] 周国华,邱森林,张小兵. 宽增益高效率级联式四开关Buck-Boost LLC变换器[J]. 电工技术学报, 2024, 39(4): 1103-1115. Zhou Guohua, Qiu Senlin, Zhang Xiaobing.Cascaded four-switch Buck-Boost LLC converter with wide gain range and high efficiency[J]. Transactions of China Electrotechnical Society, 2024, 39(4): 1103-1115. [8] Zhao Qinglin, Zhang Jianmeng, Gao Yuxia, et al.Hybrid variable frequency LLC resonant converter with wide output voltage range[J]. IEEE Transactions on Power Electronics, 2023, 38(9): 11038-11049. [9] Awasthi A, Bagawade S, Jain P K.Analysis of a hybrid variable-frequency-duty-cycle-modulated low-Q LLC resonant converter for improving the light-load efficiency for a wide input voltage range[J]. IEEE Transactions on Power Electronics, 2021, 36(7): 8476-8493. [10] 袁义生, 赖立. 一种适用于宽范围输出的复合谐振型全桥变换器[J]. 中国电机工程学报, 2020, 40(20): 6694-6703. Yuan Yisheng, Lai Li.A compound resonant full-bridge converter suitable for wide range output[J]. Proceedings of the CSEE, 2020, 40(20): 6694-6703. [11] Hu Haibing, Fang Xiang, Chen F, et al.A modified high-efficiency LLC converter with two transformers for wide input-voltage range applications[J]. IEEE Transactions on Power Electronics, 2013, 28(4): 1946-1960. [12] 张之梁. 零电压开关 PWM全桥三电平变换器[D]. 南京: 南京航空航天大学, 2005. Zhang Zhiliang.Zero-voltage switching PWM full-bridge three-level converter[D]. Nanjing: Nanjing University of Aeronautics and Astronautics, 2005. [13] 胡海兵, 王万宝, 孙文进, 等. LLC谐振变换器效率优化设计[J]. 中国电机工程学报, 2013, 33(18): 48-56. Hu Haibing, Wang Wanbao, Sun Wenjin, et al.Optimal efficiency design of LLC resonant converters[J]. Proceedings of the CSEE, 2013, 33(18): 48-56. [14] 任仁, 张方华, 刘硕. 基于LLC直流变压器 (LLC-DCT) 效率优化的死区时间与励磁电感设计[J]. 电工技术学报, 2014, 29(10): 141-146. Ren Ren, Zhang Fanghua, Liu Shuo.Optimal design for efficiency based on the dead time and magnetizing inductance of LLC DC transformer[J]. Transactions of China Electrotechnical Society, 2014, 29(10): 141-146. [15] 袁义生, 张钟艺, 梅相龙, 等. 三电平LLC谐振变换器关断损耗的优化设计[J]. 电力自动化设备, 2020, 40(2): 28-34. Yuan Yisheng, Zhang Zhongyi, Mei Xianglong, et al.Optimal design of switching-off loss in three-level LLC resonant converters[J]. Electric Power Auto-mation Equipment, 2020, 40(2): 28-34. [16] 周子航, 高祎韩, 刘懿静, 等. 基于平面磁元件的LLC变换器相关参数的整体优化设计方法[J]. 电工技术学报, 2024, 39(15): 4820-4829, 4895. Zhou Zihang, Gao Weihan, Liu Yijing, et al.Para-meters global optimization design method for LLC converter with planar magnetic[J]. Transactions of China Electrotechnical Society, 2024, 39(15): 4820-4829, 4895. [17] Yang Xinshe, Deb S.Engineering optimisation by cuckoo search[J]. International Journal of Mathematical Modelling and Numerical Optimisation, 2010, 1(4): 330. [18] 张晓凤, 王秀英. 布谷鸟搜索算法综述[J]. 计算机工程与应用, 2018, 54(18): 8-16. Zhang Xiaofeng, Wang Xiuying.Survey of cuckoo search algorithm[J]. Computer Engineering and Applications, 2018, 54(18): 8-16. [19] 黄敏丽, 于艾清. 基于改进布谷鸟算法的电动汽车换电站有序充电策略研究[J]. 中国电机工程学报, 2018, 38(4): 1075-1083. Huang Minli, Yu Aiqing.Study on coordinated charging strategy for battery swapping station based on improved Cuckoo search algorithm[J]. Proceedings of the CSEE, 2018, 38(4): 1075-1083. [20] Wang Likun, Guo Hai, Marignetti F, et al.Cuckoo search algorithm for multi-objective optimization of transient starting characteristics of a self-starting HVPMSM[J]. IEEE Transactions on Energy Con-version, 2021, 36(3): 1861-1872.
2024, Vol. 39 
