电工技术学报  2024, Vol. 39 Issue (4): 1103-1115    DOI: 10.19595/j.cnki.1000-6753.tces.222252
电力电子 |
宽增益高效率级联式四开关Buck-Boost LLC变换器
周国华, 邱森林, 张小兵
西南交通大学电气工程学院 成都 611756
Cascaded Four-Switch Buck-Boost LLC Converter with Wide Gain Range and High Efficiency
Zhou Guohua, Qiu Senlin, Zhang Xiaobing
School of Electrical Engineering Southwest Jiaotong University Chengdu 611756 China
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摘要 为了解决变频控制的桥臂共用型四开关Buck-Boost LLC级联变换器磁性元件设计和优化困难的问题,提出一种二次侧为特殊全桥整流结构的级联式四开关Buck-Boost LLC变换器。通过控制二次侧开关管的交叠导通时间以拓宽变换器的电压增益。该变换器可根据不同的输入电压范围工作在交叠模式和整流模式;在不改变变换器参数的条件下将增益显著提高,能够适应更宽范围的输入电压,同时保持了变换器较高的工作效率。在两种工作模式的基础上,采用移相控制使变换器所有开关管实现零电压导通(ZVS),二极管实现零电流关断(ZCS)。结合状态平面轨迹分析法,对定频控制的级联式四开关Buck-Boost LLC变换器进行模态分析,并推导两种工作模式下的输入-输出表达式和开关管的软开关实现条件。最后,通过研制一台70~280 V输入、240 W/28 V输出的实验样机,验证了理论分析的正确性。
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关键词 宽输入电压范围四开关Buck-BoostLLC变换器移相控制软开关    
Abstract:In new energy resource and electric vehicle fields, DC-DC converters are required to have more advantages, such as wide gain range, isolation, and high efficiency. Therefore, a cascaded four-switch Buck- Boost LLC converter with power switch integration is selected by discussing the advantages and disadvantages of various DC-DC converters. The cascaded converter has a four-switch Buck-Boost converter in the pre-stage and a half-bridge LLC resonant converter in the post-stage. Since designing and optimizing the magnetic components of the cascaded converter controlled by variable frequency is difficult, a special full bridge rectifier structure on the transformer’s secondary side is proposed. The cascaded converter with a special full bridge rectifier structure can widen the input voltage range under fixed frequency control and realize the wide gain range, isolation, high efficiency, and parameter optimization.
The low-side switching devices of the special full bridge rectifier structure on the transformer’s secondary side are switches. The simultaneous on-time of the low-side switches is called the overlapping turn-on time. The gain of the cascaded converter can be improved by controlling the overlapping turn-on time. Therefore, the gain range can be widened, and the efficiency is optimized under fixed frequency control. The gain of the converter that the parameters are unchanged is increased significantly so that the cascaded converter could be adapted to a wider input voltage range and maintain higher efficiency simultaneously. When the input voltage is less than or equal to the threshold input voltage, the cascaded converter adjusts the overlapping turn-on time to stabilize the output voltage. This mode is called overlapping mode. When the input voltage exceeds the threshold input voltage, the overlapping turn-on time is zero, and the cascaded converter performs pulse width modulation on the input leg on the primary side to stabilize the output voltage. This mode is called rectification mode. Based on the two modes, the phase shift control technique is applied to the two-leg on the primary side of the cascaded converter. The waveform shape of the middle inductor current of the pre-stage four-switch Buck-Boost converter is changed by the phase shift control technique, which can achieve zero voltage switching (ZVS) of switches and zero current switching (ZCS) of diodes. The modal analysis of the cascaded four-switch Buck-Boost LLC converter with fixed frequency control was carried out using the state plane trajectory analysis method, and the input-output expressions and the soft switching conditions of the switches in two modes were derived.
In order to verify the correctness of the theoretical analysis, an experimental prototype with 70~280 V input voltage and 240 W/28 V output was designed. The experimental tests included the wide input range, operating mode, phase shift control technique, soft switching, and efficiency of the converter. The peak efficiency was 93.6% in overlapping mode and 94.4% in rectification mode. In addition, it was experimentally verified that both operating modes could achieve soft switching, and there was a large soft switching time margin in the overlapping mode. The cascaded four-switch Buck-Boost LLC converter with a special full bridge rectifier structure on the secondary side had wide gain and high efficiency compared with the same type of converter.
The following conclusions can be drawn from the theoretical analysis and experiments. The proposed cascaded converter works under fixed frequency control, solving the difficulty of designing and optimizing the magnetic components controlled by variable frequency. The cascaded converter has a wide gain range and high efficiency, and can realize soft switching of all switches and diodes. In addition, the converter can be designed for more than four times of input voltage multiplier. In future work, the phase shift control technique of the converter will be optimized to make it smoother and simpler.
Key wordsWide input voltage range    four-switch Buck-Boost    LLC converter    phase shift    soft switching   
收稿日期: 2022-12-05     
PACS: TM46  
基金资助:国家自然科学基金资助项目(62271417, 61771405)
通讯作者: 周国华 男,1983年生,教授,博士生导师,研究方向为电力电子调制与控制技术、数字控制技术、建模与稳定性分析,电力电子技术在新能源发电系统中的应用等。E-mail: ghzhou-swjtu@163.com   
作者简介: 邱森林 男,1996年生,硕士研究生,研究方向为开关变换器拓扑及其控制技术。E-mail: slqiu_pece@163.com
引用本文:   
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. Transactions of China Electrotechnical Society, 2024, 39(4): 1103-1115.
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