基于变流器输出阻抗的直流微电网下垂并联系统振荡机理与稳定边界分析

doi:10.19595/j.cnki.1000-6753.tces.220363

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Abstract DC microgrids are of great significance for fully using renewable energy and actively responding to the carbon peaking and carbon neutrality goals. In DC microgrids, power electronics converters are usually connected to the electrical power generation units and the DC bus. These converters interact with each other through parallel connections, which increases the instability risk of the system. However, existing research regarding the system stability of DC microgrids only focuses on the influence of the interaction between the source subsystem and the load subsystem. It does not consider the difference among parallel converters in the source subsystem and thus ignores the influence of the difference among the source converters on the system stability. The difference among the source converters will cause the difference in their output impedances, which will introduce the system oscillation. Therefore, this paper focuses on the influence of the interaction among the Buck converters on the system stability, analyzes the oscillation mechanism of the parallel converters, and proposes a solution for the stability boundary.
Firstly, the small-signal model of the output impedance of the single Buck converter under droop control is established in this paper, and the accuracy of the output impedance is verified by the frequency sweep in SABER. Secondly, the controller, main circuit, and parasitic parameters are analyzed to the output impedance model established, revealing the oscillation mechanism of the droop-controlled Buck converters in parallel. Thirdly, through qualitative analysis, the output impedance is further simplified. Fourthly, the stability boundary regarding the key parameters of the parallel converters is calculated by combining the oscillation mechanism revealed and the stability criterion. Finally, the experimental platform of parallel Buck converters is built to verify the correctness and effectiveness of the theoretical analysis.
The experimental results of the parallel converters show that when the proportional coefficient k_pi2 is less than 0.09, the time domain waveform of the parallel converters is stable. Then increase the proportional coefficient k_pi2 to 0.09 and 0.1, the output voltage oscillates, and the parallel system becomes unstable. The oscillation period is 1.3 ms, corresponding to the theoretical analysis of 781 Hz. Due to the slight difference between the parameters of the experimental platform and the theoretical analysis, the theoretical value of k_pi2 is also slightly different from the experimental value when it is critically stable. However, the error is within an acceptable range, and the oscillation frequency is consistent with the theoretical analysis, which verifies the effectiveness and correctness of the proposed oscillation mechanism and stability boundary.
The following conclusions can be drawn. This paper takes the parallel droop-controlled Buck converters as the research object, and the influence of the difference among Buck converters on the system stability is investigated. The output impedance of the Buck converter is characterized as follows. The amplitude-frequency curve has a resonance peak, and a phase mutation appears at the resonance peak frequency. The resonance peak frequency is mainly affected by key parameters such as the filter inductance L_f, the filter capacitor C_f and the current controller proportional coefficient k_pi. The mechanism of system oscillation is revealed when the key parameters, including filter inductances L_f and current controller parameters k_pi, of the converters are inconsistent and cause the phase difference between the output impedance of converters at the intersection frequency of amplitude-frequency curves exceeds 180 °. Finally, a segmented analytical formula of the output impedance and the stability boundary of the key parameters of the system is proposed. The experiments verify the correctness of the theoretical analysis.

Key words： Droop control output impedance parallel converters system stability boundary

Received: 14 March 2022

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	Wang Qing
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Wang Qing,Liu Zeng,Han Pengcheng等. Analysis of Oscillation Mechanism and Stability Boundary of Droop-Controlled Parallel Converters Based on Output Impedances of Individual Converters in DC Microgrids[J]. Transactions of China Electrotechnical Society, 2023, 38(8): 2148-2161.

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https://dgjsxb.ces-transaction.com/EN/10.19595/j.cnki.1000-6753.tces.220363 OR https://dgjsxb.ces-transaction.com/EN/Y2023/V38/I8/2148

[1] 宋强, 赵彪, 刘文华, 等. 智能直流配电网研究综述[J]. 中国电机工程学报, 2013, 33(25): 9-19, 5.
Song Qiang, Zhao Biao, Liu Wenhua, et al.An overview of research on smart DC distribution power network[J]. Proceedings of the CSEE, 2013, 33(25): 9-19, 5.
[2] 杨新法, 苏剑, 吕志鹏, 等. 微电网技术综述[J]. 中国电机工程学报, 2014, 34(1): 57-70.
Yang Xinfa, Su Jian, Lü Zhipeng, et al.Overview on micro-grid technology[J]. Proceedings of the CSEE, 2014, 34(1): 57-70.
[3] 滕昌鹏, 王玉斌, 周博恺, 等. 含恒功率负载的直流微网大信号稳定性分析[J]. 电工技术学报, 2019, 34(5): 973-982.
Teng Changpeng, Wang Yubin, Zhou Bokai, et al.Large-signal stability analysis of DC microgrid with constant power loads[J]. Transactions of China Elec- trotechnical Society, 2019, 34(5): 973-982.
[4] 刘宿城, 李中鹏, 刘晓东, 等. 直流微网中下垂控制稳定性及灵敏度分析[J]. 电气自动化, 2019, 41(1): 16-18, 50.
Liu Sucheng, Li Zhongpeng, Liu Xiaodong, et al.Analysis of stability and sensitivity of droop control in the DC micro-grid[J]. Electrical Automation, 2019, 41(1): 16-18, 50.
[5] 支娜, 张辉, 肖曦, 等. 分布式控制的直流微网系统级稳定性分析[J]. 中国电机工程学报, 2016, 36(2): 368-378.
Zhi Na, Zhang Hui, Xiao Xi, et al.System-level stability analysis of DC microgrid with distributed control strategy[J]. Proceedings of the CSEE, 2016, 36(2): 368-378.
[6] 施婕, 郑漳华, 艾芊. 直流微电网建模与稳定性分析[J]. 电力自动化设备, 2010, 30(2): 86-90.
Shi Jie, Zheng Zhanghua, Ai Qian.Modeling of DC micro-grid and stability analysis[J]. Electric Power Automation Equipment, 2010, 30(2): 86-90.
[7] 朱晓荣, 李铮, 孟凡奇. 基于不同网架结构的直流微电网稳定性分析[J]. 电工技术学报, 2021, 36(1): 166-178.
Zhu Xiaorong, Li Zheng, Meng Fanqi.Stability analysis of DC microgrid based on different grid structures[J]. Transactions of China Electrotechnical Society, 2021, 36(1): 166-178.
[8] 杨道培, 丁志刚, 曹炜. 基于下垂控制的直流微电网小扰动稳定性分析[J]. 电气技术, 2015, 16(7): 20-26.
Yang Daopei, Ding Zhigang, Cao Wei.Small signal stability analysis of DC micro-grid based on droop control[J]. Electrical Engineering, 2015, 16(7): 20-26.
[9] 郭力, 冯怿彬, 李霞林, 等. 直流微电网稳定性分析及阻尼控制方法研究[J]. 中国电机工程学报, 2016, 36(4): 927-936.
Guo Li, Feng Yibin, Li Xialin, et al.Stability analysis and research of active damping method for DC microgrids[J]. Proceedings of the CSEE, 2016, 36(4): 927-936.
[10] Li Xialin, Guo Li, Zhang Shaohui, et al.Observer- based DC voltage droop and current feed-forward control of a DC microgrid[J]. IEEE Transactions on Smart Grid, 2018, 9(5): 5207-5216.
[11] 黄远胜, 刘和平, 苗轶如, 等. 基于并联虚拟电阻的级联DC-DC变换器稳定控制方法[J]. 电工技术学报, 2020, 35(18): 3927-3937.
Huang Yuansheng, Liu Heping, Miao Yiru, et al.Cascaded DC-DC converter stability control method based on paralleling virtual resistor[J]. Transactions of China Electrotechnical Society, 2020, 35(18): 3927-3937.
[12] 黄旭程, 刘亚丽, 陈燕东, 等. 直流电网阻抗建模与振荡机理及稳定控制方法[J]. 电力系统保护与控制, 2020, 48(7): 108-117.
Huang Xucheng, Liu Yali, Chen Yandong, et al.Impedance-based modeling, stability analysis and virtual damping approach in DC grid[J]. Power System Protection and Control, 2020, 48(7): 108-117.
[13] 彭方成, 范学鑫, 王瑞田, 等. 大容量DC-DC变流器输出阻抗特性分析及应用[J]. 电工技术学报, 2021, 36(16): 3422-3432.
Peng Fangcheng, Fan Xuexin, Wang Ruitian, et al.Analysis and application of output impedance characteristics of high-capacity DC-DC converter[J]. Transactions of China Electrotechnical Society, 2021, 36(16): 3422-3432.
[14] 姚雨迎, 张东来, 徐殿国. 级联式DC/DC变换器输出阻抗的优化设计与稳定性[J]. 电工技术学报, 2009, 24(3): 147-152.
Yao Yuying, Zhang Donglai, Xu Dianguo.Output impedance optimization and stability for cascade DC/DC converter[J]. Transactions of China Elec- trotechnical Society, 2009, 24(3): 147-152.
[15] Rashidirad N, Hamzeh M, Sheshyekani K, et al.High-frequency oscillations and their leading causes in DC microgrids[J]. IEEE Transactions on Energy Conversion, 2017, 32(4): 1479-1491.
[16] 李鹏飞, 郭力, 王洪达, 等. 直流微电网高频振荡稳定问题的降阶建模及分析[J]. 电力自动化设备, 2021, 41(5): 65-72.
Li Pengfei, Guo Li, Wang Hongda, et al.Reduced- order modeling and analysis of high-frequency oscillation stability in DC microgrid[J]. Electric Power Automation Equipment, 2021, 41(5): 65-72.
[17] 刘春喜, 陈鹏荣, 高姬, 等. 中频逆变器数字控制延时的线性化近似[J]. 电源学报, 2015, 13(3): 55-61.
Liu Chunxi, Chen Pengrong, Gao Ji, et al.An approximation method of digital control delay in inverter[J]. Journal of Power Supply, 2015, 13(3): 55-61.
[18] 沈传文, 肖国春, 于敏. 自动控制理论[M]. 西安: 西安交通大学出版社, 2007.
[19] 侯丹. 基于阻抗测量的多模块互联电力电子系统稳定性分析与判断[D]. 西安: 西安交通大学, 2010.
[20] 邵京一, 邵钟武. 波特图折线近似法的改进[J]. 华东石油学院学报, 1984, 81(1): 118-125.
Shao Jingyi, Shao Zhongwu.An improved broken- line approximation method of Bode diagram[J]. Journal of China University of Petroleum, 1984, 81(1): 118-125.