Abstract：For traditional buck converter, the duty cycle is narrow in high conversion ratio applications. This results in high losses and low efficiency of the converter. At the same time, the output current ripple of the converter becomes larger, and the stability will also deteriorate. In order to solve the above problems, scholars have proposed many methods to improve the voltage conversion ratio of converters. Among them, SC (Series Capacitor) Buck converter is a commonly used high voltage conversion ratio converter, and has the advantage of low voltage stress of switches in steady state. However, the voltage stress of the switches is high during converter start-up. This paper proposes an improved two-phase series-capacitor converter with high conversion ratio. While inheriting the advantages of the SC Buck converter, the converter has a higher voltage conversion ratio and lower output current ripple, and can effectively reduce the input filter capacitor value and the voltage stress of the switches during converter start-up. The proposed converter adds two capacitors and a switch to the SC Buck converter, which has the following advantages. First, compared to the SC Buck converter, the voltage distribution across the capacitor is changed, which results in a higher voltage conversion ratio and lower switching voltage stress in steady state. Second, the voltage across the inductor of the proposed converter is lower than that of the SC Buck converter, so the inductor current ripple and output current ripple of the proposed converter are smaller. Third, in the steady state, the voltage on the series capacitor satisfies the ampere-second balance, which provides a balanced loop between the two phases. This current sharing mechanism is inherent to the topology and acts like a damped harmonic oscillator. Fourth, the capacitor on the input side of the proposed converter is pre-charged before the converter starts, which reduces the voltage stress of the switches during start-up. Therefore, the proposed converter can use switches with lower voltage rating, which helps to reduce the loss of the switches and improve the efficiency of the converter. Fifth, compared to SC Buck converter, the input voltage ripple of the proposed converter is smaller when the input filter capacitance is the same, so when the input voltage ripple is the same, the input filter capacitance required by the proposed converter is smaller. A 110 W experimental prototype was built and the characteristics of the converter were verified. The experimental results show that when the converter achieves 48~5 V, the duty cycle is about 30%. In contrast, the SC Buck converter has a duty cycle of only about 20% when the same step-down ratio is reached, proving that the proposed converter has a higher voltage conversion ratio. In steady state, the voltage stress of two switches is 32 V, and the voltage stress of three switches is 16 V. The voltage stress of all switches is less than the input voltage. Before the converter starts, the voltage stress of two switches is 24 V, the voltage stress of three switches is 0 V. The maximum voltage stress of the switches before the converter starts is only half of the input voltage. And the maximum voltage stress of the switches during converter start-up is 32 V, which is less than the input voltage. The single-phase inductor current ripple is 3.5 A, and the current ripple after the superposition of the two phases is about 1.9 A. The two-phase interleaved parallel output structure greatly reduces the output current ripple. According to theoretical analysis and experimental verification, the following conclusions can be drawn: (1) Compared with SC Buck converter, the proposed converter has a higher voltage conversion ratio and lower output current ripple. (2) Compared with the SC Buck converter, the voltage stress of the switches of the proposed converter in the steady state is lower and the voltage stress of the switches during start-up is reduced. (3) The proposed converter has automatic phase current balancing capability. It can eliminate a control loop that requires high performance circuits to balance phase currents. (4) Compared with the SC Buck converter, when the voltage ripple of the input filter capacitor is the same, the required input filter capacitance is smaller.
刘桂花, 王博鑫, 王卫, 焦文渤. 一种改进型高转换比两相串联电容变换器[J]. 电工技术学报, 2023, 38(zk1): 114-123.
Liu Guihua, Wang Boxin, Wang We, Jiao Wenbo. An Improved Two-Phase Series-Capacitor Converter with High Conversion Ratio. Transactions of China Electrotechnical Society, 2023, 38(zk1): 114-123.
[1] Liu Xinjian, Calhoun B H, Li Shuo.A sub-nW 93% peak efficiency Buck converter with wide dynamic range, fast DVFS, and asynchronous load-transient control[J]. IEEE Journal of Solid-State Circuits, 2022, 57(7): 2054-2067. [2] Do H-L.Zero-voltage-switching synchronous buck converter with a coupled inductor[J]. IEEE Transactions on Industrial Electronics, 2011, 58(8): 3440-3447. [3] Lee S S.Step-down converter with efficient ZVS operation with load variation[J]. IEEE Transactions on Industrial Electronics, 2014, 61(1): 591-597. [4] Yau Y T, Jiang W Z, Hwu K I.Ultrahigh step-down converter with wide input voltage range based on topology exchange[J]. IEEE Transactions on Power Electronics, 2017, 32(7): 5341-5364. [5] 肖思昌, 陈洪胜, 陈锦立, 等. 分布式储能中大降压比Buck变换器的优化设计[J]. 电源学报, 2023, 21(3): 20-26. Xiao Sichang, Chen Hongsheng, Chen Jinli, et al.Optimal design of Buck converter with large step-down ratio for distributed energy storage[J]. Journal of Power Supply, 2023, 21(3): 20-26. [6] He Liangzong, Chen Jiazhe, Xu Xinyong, et al.Soft-switching voltage-demultiplier-cell-based high step-down DC-DC converter[J]. IEEE Transactions on Power Electronics, 2019, 34(10): 9828-9843. [7] 刘俊峰, 胡仁俊, 曾君. 一种非隔离交错工作的高降压比DC-DC功率变换器[J]. 电工技术学报, 2018, 33(20): 4763-4770. Liu Junfeng, Hu Renjun, Zeng Jun.A non-isolated interleaved step-down DC-DC power converter with high ratio[J]. Transactions of China Electrotechnical Society, 2018, 33(20): 4763-4770. [8] Marvi F, Adib E, Farzanehfard H.Efficient ZVS synchronous Buck converter with extended duty cycle and low-current ripple[J]. IEEE Transactions on Industrial Electronics, 2016, 63(9): 5403-5409. [9] Liu Jianhong, Tseng C W, Chu C-C.High step-down conversion ratios of DC-DC converters under triple PWM control schemes[C]//IEEE Industry Applications Society Annual Meeting, Vancouver, BC, Canada, 2022: 1-8. [10] Xie Xiaogao, Qian Zhaoming.A new two-stage Buck converter for voltage regulators[C]//IEEE Power Electronics Specialists Conference, Rhodes, Greece, 2008: 1580-1584. [11] 梅杨, 陈丽莎, 黄伟超, 等. 级联式双向DC-DC变换器的优化控制方法[J]. 电工技术学报, 2017, 32(19): 153-159. Mei Yang, Chen Lisha, Huang Weichao, et al.Optimized control method of cascaded Bi-directional DC-DC converters[J]. Transactions of China Electrotechnical Society, 2017, 32(19): 153-159. [12] Hwu K I, Jiang W Z, Wu P Y.An expandable two-phase interleaved ultrahigh step-down converter with automatic current balance[J]. IEEE Transactions on Power Electronics, 2017, 32(12): 9223-9237. [13] Grant D A, Darroman Y, Suter J.Synthesis of tapped-inductor switched-mode converters[J]. IEEE Transactions on Power Electronics, 2007, 22(5): 1964-1969. [14] Yao Kaiwei, Ye Mao, Xu Ming, et al.Tapped-inductor buck converter for high-step-down DC-DC conversion[J]. IEEE Transactions on Power Electronics, 2005, 20(4): 775-780. [15] Modeer T, Norrga S, Nee H P.High-voltage tapped-inductor Buck converter utilizing an autonomous high-side switch[J]. IEEE Transactions on Industrial Electronics, 2015, 62(5): 2868-2878. [16] Hajiheidari M, Farzanehfard H, Adib E.High-step-down DC-DC converter with continuous output current using coupled-inductors[J] IEEE Transactions on Power Electronics, 2019, 34(11): 10936-10944. [17] Xu Peng, Wei Jia, Lee F C.The active-clamp couple-buck converter-a novel high efficiency voltage regulator modules[C]//Sixteenth Annual IEEE Applied Power Electronics Conference and Exposition, Anaheim, CA, USA,2002: 252-257. [18] Esteki M, Poorali B, Adib E, et al.Interleaved Buck converter with continuous input current, extremely low output current ripple, low switching losses, and improved step-down conversion ratio[J]. IEEE Transactions on Industrial Electronics, 2015, 62(8): 4769-4776. [19] Shenoy P S, Lazaro O, Ramani R, et al.A 5 MHz, 12 V, 10 A, monolithically integrated two-phase series capacitor Buck converter[C]// IEEE Applied Power Electronics Conference and Exposition, Long Beach, CA, USA, 2016: 66-72. [20] Shenoy P S, Amaro M, Morroni J, et al.Comparison of a Buck converter and a series capacitor Buck converter for high-frequency, high-conversion-ratio voltage regulators[J]. IEEE Transactions on Power Electronics, 2016, 31(10): 7006-7015. [21] Lee I O, Cho S Y, Moon G W.Interleaved Buck converter having low switching losses and improved step-down conversion ratio[J]. IEEE Transactions on Power Electronics, 2012, 27(8): 3664-3675. [22] Shenoy P S, Lazaro O, Amaro Mi, et al.Automatic current sharing mechanism in the series capacitor Buck converter[C]//IEEE Energy Conversion Congress and Exposition, Montreal, QC, Canada, 2015: 2003-2009. [23] Kirshenboim O, Peretz M M.High-efficiency nonisolated converter with very high step-down conversion ratio[J]. IEEE Transactions on Power Electronics, 2017, 32(5): 3683-3690. [24] Kim K, Cha H, Park S, et al.A modified series-capacitor high conversion ratio DC-DC converter eliminating start-up voltage stress problem[J]. IEEE Transactions on Power Electronics, 2018, 33(1): 8-12. [25] Wang Yijie, Zhang Jinfeng, Guan Yueshi, et al.Analysis and design of a two-phase series capacitor dual-path hybrid DC-DC converter[J]. IEEE Transactions on Power Electronics, 2022, 37(8): 9492-9502.
2023, Vol. 38 
