Modeling and Stability Analysis of Unified Immittance Network for AC/DC Hybrid System
Teng Zhiyuan, Chen Xin, Zhang Donghui
Jiangsu Key Laboratory of New Energy Generation and Power Conversion College of Automation Engineering Nanjing University of Aeronautics and Astronautics Nanjing 211106
Abstract：AC/DC hybrid system has become an effective solution for large-scale new energy consumption because of its characteristics of multiple power sources, multiple drop points, large capacity and cross-regional flexible transmission. However, the wide-frequency oscillation problem of AC/DC hybrid power system with high proportion of power electronics is prominent, which threatens the safe and stable operation of the system. At present, the stability analysis of hybrid system is mainly faced with the problem of how to take into account the AC and DC sections of the hybrid system at the same time and how to cover the system equipment with different impedance characteristics, so as to realize the unified analysis of the AC/DC hybrid network with multiple power electronic equipment. To address the above issues, this paper establishes a unified immittance network model for system-level stability assessment of hybrid systems. First, based on the voltage/current source type device characteristics of the network devices, the impedance/ admittance forms of each network module of the system are standardized to avoid the problem of solving for the right half-plane poles in the process of system stability analysis. Secondly, from the perspective of the AC and DC ports of the system equipment, the AC/DC hybrid system can be divided into mono immittance subsystem and hybrid immittance subsystem. Finally, based on the interaction relationship between system immittance networks, a unified immittance network model containing complete oscillation information of the hybrid system is established. Under the premise of covering the stability information at each AC and DC port of the hybrid system, the unified immittance network model reduces the dimension of the system network model, at the same time expands the system network matrix from a single AC or DC system to an AC/DC system. Furthermore, combined with the derivation and change process of the immittance network, and through the modularization of the system expansion, this paper makes the immittance network applicable to the analysis of objects with different topologies,and extends the unified immittance network to general AC/DC hybrid systems. In addition,in contrast to the matrix model that merely aggregates a single impedance feature or a single admittance feature, the unified immittance network encompasses the AC/DC systems with various impedance characteristics, accomplishing the mutual unification of the new energy unit with admittance properties and the load network with impedance properties. This facilitates the precise establishment of the network mathematical model when confronted with the AC/DC system that concurrently incorporates equipment with current/voltage source characteristics, and realizes the unified coverage of equipment models with dissimilar impedance characteristics. Based on the immittance network model, a unified immittance network stability criterion covering the interaction relationship of each AC/DC port of the hybrid system is derived. Combined with the expansion analysis of the immittance network, the criterion is extended to the general AC/DC hybrid system. The stability criterion comprehensively covers the stability problems of the AC/DC system, and avoids solving the problem of poles in the right half-plane, simplifying the analysis process. Furthermore, an oscillation traceability method for the hybrid system is given based on the immittance network model. Finally, based on the application examples of the AC/DC hybrid system, the immittance network model and its stability analysis method proposed in this paper are evaluated and verified.
[1] 徐殿国, 刘瑜超, 武健. 多端直流输电系统控制研究综述[J]. 电工技术学报, 2015, 30(17): 1-12. Xu Dianguo, Liu Yuchao, Wu Jian.Review on control strategies of multi-terminal direct current transmission system[J]. Transactions of China Electrotechnical Society, 2015, 30(17): 1-12. [2] Ansari J A, Liu Chongru, Khan S A.MMC based MTDC grids: a detailed review on issues and challenges for operation, control and protection schemes[J]. IEEE Access, 2020, 8: 168154-168165. [3] 肖湘宁, 罗超, 廖坤玉. 新能源电力系统次同步振荡问题研究综述[J]. 电工技术学报, 2017, 32(6): 85-97. Xiao Xiangning, Luo Chao, Liao Kunyu.Review of the research on subsynchronous oscillation issues in electric power system with renewable energy sources[J]. Transactions of China Electrotechnical Society, 2017, 32(6): 85-97. [4] 马宁宁, 谢小荣, 贺静波, 等. 高比例新能源和电力电子设备电力系统的宽频振荡研究综述[J]. 中国电机工程学报, 2020, 40(15): 4719-4731. Ma Ningning, Xie Xiaorong, He Jingbo, et al.Review of wide-band oscillation in renewable and power electronics highly integrated power systems[J]. Proceedings of the CSEE, 2020, 40(15): 4719-4731. [5] 杜步阳, 邵德军, 朱建行, 等. 电压源型变流器并网系统多时间尺度间相互作用[J]. 电工技术学报, 2023, 38(20): 5547-5559. Du Buyang, Shao Dejun, Zhu Jianxing, et al.The interaction between multiple timescales of the grid-tied voltage source converter[J]. Transactions of China Electrotechnical Society, 2023, 38(20): 5547-5559. [6] Buchhagen C, Rauscher C, Menze A, et al.BorWin1- First Experiences with harmonic interactions in converter dominated grids[C]//International ETG Congress 2015; Die Energiewende - Blueprints for the new energy age, Bonn, Germany, 2015: 1-7. [7] 胡应宏, 李雨, 李阳, 等. 面向柔直换流站高频谐振问题的换流变压器建模与参数辨识[J]. 电工技术学报, 2024, 39(22): 7154-7166. Hu Yinghong, Li Yu, Li Yang, et al.Modeling and parameter identification of converter transformer for high-frequency resonance problem of flexible DC converter station[J]. Transactions of China Electro-technical Society, 2024, 39(22): 7154-7166. [8] 李云丰, 汤广福, 贺之渊, 等. MMC型直流输电系统阻尼控制策略研究[J]. 中国电机工程学报, 2016, 36(20): 5492-5503. Li Yunfeng, Tang Guangfu, He Zhiyuan, et al.Damping control strategy research for MMC based HVDC system[J]. Proceedings of the CSEE, 2016, 36(20): 5492-5503. [9] Sun Jian.Frequency-domain stability criteria for converter-based power systems[J]. IEEE Open Journal of Power Electronics, 2022, 3: 222-254. [10] 吴翔宇, 张晓红, 尚子轩, 等. 基于频域阻抗网络建模分析的交直流微电网振荡问题研究[J]. 电工技术学报, 2024, 39(8): 2294-2310. Wu Xiangyu, Zhang Xiaohong, Shang Zixuan, et al.Research on the oscillation problem of AC-DC microgrids based on frequency domain impedance network modeling and analysis[J]. Transactions of China Electrotechnical Society, 2024, 39(8): 2294-2310. [11] 刘津铭, 陈燕东, 伍文华, 等. 孤岛微电网序阻抗建模与高频振荡抑制[J]. 电工技术学报, 2020, 35(7): 1538-1552. Liu Jinming, Chen Yandong, Wu Wenhua, et al.Sequence impedance modeling and high-frequency oscillation suppression method for island microgrid[J]. Transactions of China Electrotechnical Society, 2020, 35(7): 1538-1552. [12] 刘欣, 郭志博, 贾焦心, 等. 基于单输入单输出等效序阻抗的微网VSG并网稳定性分析及虚拟阻抗设计[J]. 电工技术学报, 2023, 38(15): 4130-4146. Liu Xin, Guo Zhibo, Jia Jiaoxin, et al.Microgrid VSG grid-connection stability analysis and virtual impedance design based on single-input single-output equivalent sequence impedance[J]. Transactions of China Electrotechnical Society, 2023, 38(15): 4130-4146. [13] 吕敬, 董鹏, 施刚, 等. 大型双馈风电场经MMC-HVDC并网的次同步振荡及其抑制[J]. 中国电机工程学报, 2015, 35(19): 4852-4860. Lü Jing, Dong Peng, Shi Gang, et al.Subsynchronous oscillation and its mitigation of MMC-based HVDC with large doubly-fed induction generator-based wind farm integration[J]. Proceedings of the CSEE, 2015, 35(19): 4852-4860. [14] 郭贤珊, 刘泽洪, 李云丰, 等. 柔性直流输电系统高频振荡特性分析及抑制策略研究[J]. 中国电机工程学报, 2020, 40(1): 19-29. Guo Xianshan, Liu Zehong, Li Yunfeng, et al.Characteristic analysis of high-frequency resonance of flexible high voltage direct current and research on its damping control strategy[J]. Proceedings of the CSEE, 2020, 40(1): 19-29. [15] Liu Jianing, Tao Xin, Yu Miao, et al.Impedance modeling and analysis of three-phase voltage-source converters viewing from DC side[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020, 8(4): 3906-3916. [16] 李国庆, 孙银锋, 吴学光. 柔性直流输电稳定性分析及控制参数整定[J]. 电工技术学报, 2017, 32(6): 231-239. Li Guoqing, Sun Yinfeng, Wu Xueguang.VSC-HVDC stability analysis and control parameter setting[J]. Transactions of China Electrotechnical Society, 2017, 32(6): 231-239. [17] Ji Ke, Tang Guangfu, Yang Jie, et al.Harmonic stability analysis of MMC-based DC system using DC impedance model[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020, 8(2): 1152-1163. [18] Li Yang, Shuai Zhikang, Fang Junbin, et al.Small-signal stability analysis method for hybrid AC-DC systems with multiple DC buses[J]. IEEE Journal on Emerging and Selected Topics in Circuits and Systems, 2021, 11(1): 17-27. [19] 吴天昊, 谢小荣, 姜齐荣, 等. 考虑频率耦合及交直流端口耦合效应的并网变流器三端口导纳模型[J]. 中国电机工程学报, 2022, 42(1): 248-259. Wu Tianhao, Xie Xiaorong, Jiang Qirong, et al.Three-port admittance modeling of grid-connected converters considering frequency-coupling and AC/DC coupling effects[J]. Proceedings of the CSEE, 2022, 42(1): 248-259. [20] Zhang Haitao, Mehrabankhomartash M, Saeedifard M, et al.Stability analysis of a grid-tied interlinking converter system with the hybrid AC/DC admittance model and determinant-based GNC[J]. IEEE Transactions on Power Delivery, 2022, 37(2): 798-812. [21] Zhang Haitao, Wang Xiuli, Mehrabankhomartash M, et al.Harmonic stability assessment of multiterminal DC (MTDC) systems based on the hybrid AC/DC admittance model and determinant-based GNC[J]. IEEE Transactions on Power Electronics, 2022, 37(2): 1653-1665. [22] Sun Jian.Two-port characterization and transfer immittances of AC-DC converters-part II: applications[J]. IEEE Open Journal of Power Electronics, 2021, 2: 483-510. [23] 李光辉, 王伟胜, 张兴, 等. 考虑机侧模型的直驱风电机组序阻抗建模及分析[J]. 中国电机工程学报, 2019, 39(21): 6200-6211. Li Guanghui, Wang Weisheng, Zhang Xing, et al.Sequence impedance modeling and analysis of permanent magnet synchronous generator considering machine side model[J]. Proceedings of the CSEE, 2019, 39(21): 6200-6211. [24] Sun Jian.Impedance-based stability criterion for grid-connected inverters[J]. IEEE Transactions on Power Electronics, 2011, 26(11): 3075-3078. [25] 张东辉, 陈新, 张旸, 等. 基于有源节点序阻抗模型的风电场稳定性分析及其振荡参与风险评估方法[J]. 中国电机工程学报, 2023, 43(10): 3832-3843. Zhang Donghui, Chen Xin, Zhang Yang, et al.Stability analysis and resonance participation risk assessment of wind farm based on active node sequence impedance model[J]. Proceedings of the CSEE, 2023, 43(10): 3832-3843. [26] 汤广福, 王高勇, 贺之渊, 等. 张北500kV直流电网关键技术与设备研究[J]. 高电压技术, 2018, 44(7): 2097-2106. Tang Guangfu, Wang Gaoyong, He Zhiyuan, et al.Research on key technology and equipment for Zhangbei 500 kV DC grid[J]. High Voltage Engineering, 2018, 44(7): 2097-2106.
2025, Vol. 40 
