Small-Disturbance System Voltage Support Strength Assessment Method for Renewables VSC-HVDC Delivery System
Ma Fuyilong1, Xin Huanhai1, Liu Chenxi1, Li Shiyang2, Yuan Hui1, Dai Jiang3
1. College of Electrical Engineering Zhejiang University Hangzhou 310027 China; 2. Electric Power Research Institute China Southern Power Grid Guangzhou 510663 China; 3. Guizhou Electric Power Dispatching and Communication Bureau Guiyang 550002 China
Abstract：System voltage support strength (referred to as system strength) is used to describe the voltage response performance under a disturbance and rapidly quantify stability margin. The inverter-based resources in the system generally apply the grid-following control scheme and need to adapt to the current system strength; otherwise, sub-synchronous oscillations or even voltage collapse accidents are likely to occur. Therefore, it is necessary to accurately measure the system strength to ensure the safety and stability of the renewables system. The system strength indicated by short-circuit ratio (SCR) has provided an effective and intuitive reference for grid operators for a long time. However, the existing SCR-based methods rely on the premise that synchronous generators provide short-circuit capacity or voltage support. Due to this premise, these methods are unsuitable for renewables delivery systems with voltage source converter-based high voltage direct current (VSC-HVDC), where all apparatuses are power-electronic interfaces and no synchronous generators provide short-circuit capacity. It is a challenge to assess the system strength expediently and quantify the stability margin rapidly in the renewables VSC-HVDC delivery system (RVDS). As a result, this paper aims to respond this challenge and propose the system strength evaluation method in terms of small-disturbance analysis. Firstly, to describe the bus voltage response performance under a small disturbance, the sensitivity transfer function matrix of the bus voltage to the renewables multi-feed current is derived based on linearization analysis, and the closed-loop characteristic equation can be accordingly formed. With the bus voltage as output variable, the relationship between the voltage performance and static voltage stability/small-disturbance synchronous stability of RVDS can be described by the closed-loop characteristic equation. Secondly, the generalized short-circuit ratio (gSCR) is extended into the RVDS based on the voltage-source equivalent analysis of VSC-HVDC.Then, a source-grid separation method is presented to evaluate the system strength of RVDS by combining the apparatus critical SCR and the generalized short-circuit ratio. Finally, the proposed method is verified by simulation in multiple wind plants with VSC-HVDC. Simulation results show that the proposed system strength assessment is consistent with the trend of time-domain eigenvalues and electromagnetic transient analysis results; the stronger system strength indicates the lower instability risks. Furthermore, the voltage-supporting characteristics of VSC-HVDC can be analyzed from the perspective of system strength, and the influence of parameters variation of the voltage-current control loop of VSC-HVDC can be interpreted as the variation of gSCR. Improper parameter sets of VSC-HVDC that weaken the system should be avoided, which may trigger the subsynchronous oscillations. The following conclusions can be drawn: (1) The gSCR of RVDS essentially represents the sensitivity of power networks, reflecting the comprehensive electrical distance between the busbar and the equivalent voltage source for multiple renewable plants. It is independent of the short-circuit current analysis based on the existence of synchronize generators. Therefore, it can adapt to the renewable energy base without the traditional support from synchronous generators. (2) The gSCR can consider the dynamic voltage support characteristics of VSC-HVDC under different voltage control parameters and be suitable for static voltage stability and small-disturbance synchronous stability analysis. It is the extension of the generalized short-circuit ratio theory in RVDS. (3) The system strength of RVDS can be quantified by the relative difference value between the gSCR and apparatus critical SCR, which is convenient for collaborative implementation from both the resource and the network sides and helps to quickly screen and keep away from the system operations with high instability risks.
马富艺龙, 辛焕海, 刘晨曦, 李诗旸, 袁辉, 代江. 新能源基地柔性直流送出系统小扰动电压支撑强度评估[J]. 电工技术学报, 2023, 38(21): 5758-5770.
Ma Fuyilong, Xin Huanhai, Liu Chenxi, Li Shiyang, Yuan Hui, Dai Jiang. Small-Disturbance System Voltage Support Strength Assessment Method for Renewables VSC-HVDC Delivery System. Transactions of China Electrotechnical Society, 2023, 38(21): 5758-5770.
[1] 舒印彪, 陈国平, 贺静波, 等. 构建以新能源为主体的新型电力系统框架研究[J]. 中国工程科学, 2021, 23(6): 61-69. Shu Yinbiao, Chen Guoping, He Jingbo, et al.Building a new electric power system based on new energy sources[J]. Strategic Study of CAE, 2021, 23(6): 61-69. [2] 樊肖杰, 迟永宁, 马士聪, 等. 大规模海上风电接入电网关键技术与技术标准的研究及应用[J]. 电网技术, 2022, 46(8): 2859-2870. Fan Xiaojie, Chi Yongning, Ma Shicong, et al.Research and application of key technologies and technical standards for large-scale offshore wind farms connecting to power grid[J]. Power System Technology, 2022, 46(8): 2859-2870. [3] Wang Weisheng, Li Guanghui, Guo Jianbo.Large-scale renewable energy transmission by HVDC: challenges and proposals[J]. Engineering, 2022, 19: 252-267. [4] 董文凯, 杜文娟, 王海风. 弱连接条件下锁相环动态主导的并网直驱风电场小干扰稳定性研究[J]. 电工技术学报, 2021, 36(3): 609-622. Dong Wenkai, Du Wenjuan, Wang Haifeng.Small-signal stability of a grid-connected PMSG wind farm dominated by dynamics of PLLs under weak grid connection[J]. Transactions of China Electrotechnical Society, 2021, 36(3): 609-622. [5] 邵冰冰, 赵峥, 肖琪, 等. 多直驱风机经柔直并网系统相近次同步振荡模式参与因子的弱鲁棒性分析[J]. 电工技术学报, 2023, 38(3): 754-769. Shao Bingbing, Zhao Zheng, Xiao Qi, et al.Weak robustness analysis of close subsynchronous oscillation modes’ participation factors in multiple direct-drive wind turbines with the VSC-HVDC system[J]. Transactions of China Electrotechnical Society, 2023, 38(3): 754-769. [6] 王一凡, 赵成勇, 郭春义. 双馈风电场孤岛经模块化多电平换流器直流输电并网系统小信号稳定性分析与振荡抑制方法[J]. 电工技术学报, 2019, 34(10): 2116-2129. Wang Yifan, Zhao Chengyong, Guo Chunyi.Small signal stability and oscillation suppression method for islanded double fed induction generator-based wind farm integrated by modular multilevel converter based HVDC system[J]. Transactions of China Electrotechnical Society, 2019, 34(10): 2116-2129. [7] 李光辉, 王伟胜, 郭剑波, 等. 风电场经MMC-HVDC送出系统宽频带振荡机理与分析方法[J]. 中国电机工程学报, 2019, 39(18): 5281-5297, 5575. Li Guanghui, Wang Weisheng, Guo Jianbo, et al.Broadband oscillation mechanism and analysis for wind farm integration through MMC-HVDC system[J]. Proceedings of the CSEE, 2019, 39(18): 5281-5297, 5575. [8] 马秀达, 卢宇, 田杰, 等. 柔性直流输电系统的构网型控制关键技术与挑战[J]. 电力系统自动化, 2023, 47(3): 1-11. Ma Xiuda, Lu Yu, Tian Jie, et al.Key technologies and challenges of grid-forming control for flexible DC transmission system[J]. Automation of Electric Power Systems, 2023, 47(3): 1-11. [9] 于琳, 孙华东, 赵兵, 等. 新能源并网系统短路比指标分析及临界短路比计算方法[J]. 中国电机工程学报, 2022, 42(3): 919-929. Yu Lin, Sun Huadong, Zhao Bing, et al.Short circuit ratio index analysis and critical short circuit ratio calculation of renewable energy grid-connected system[J]. Proceedings of the CSEE, 2022, 42(3): 919-929. [10] 徐政. 新型电力系统背景下电网强度的合理定义及其计算方法[J]. 高电压技术, 2022, 48(10): 3805-3819. Xu Zheng.Reasonable definition and calculation method of power grid strength under the background of new type power systems[J]. High Voltage Engineering, 2022, 48(10): 3805-3819. [11] 辛焕海, 董炜, 袁小明, 等. 电力电子多馈入电力系统的广义短路比[J]. 中国电机工程学报, 2016, 36(22): 6013-6027. Xin Huanhai, Dong Wei, Yuan Xiaoming, et al.Generalized short circuit ratio for multi power electronic based devices infeed to power systems[J]. Proceedings of the CSEE, 2016, 36(22): 6013-6027. [12] 吴林林, 李蕴红, 于思奇, 等. 基于短路比指标的风电汇集系统稳定性分析[J]. 电力自动化设备, 2022, 42(8): 72-78. Wu Linlin, Li Yunhong, Yu Siqi, et al.Stability analysis of dense wind power area based on short circuit ratio index[J]. Electric Power Automation Equipment, 2022, 42(8): 72-78. [13] CIGRE. Connection of wind farms to weak AC networks: CIGRE Working Group B4.62.[S]. CIGRE, 2016. [14] Taylor C W.电力系统电压稳定[M]. 王伟胜, 译. 北京: 中国电力出版社, 2002. [15] 周瑀涵, 辛焕海, 鞠平. 基于广义短路比的多馈入系统强度量化原理与方法:回顾、探讨与展望[J]. 中国电机工程学报, 2023, 43(10): 3794-3811. Zhou Yuhan, Xin Huanhai, Ju Ping.System strength quantification principle and method of multi-infeed systems based on generalized short-circuit ratio: reviews, discussions and outlooks[J]. Proceedings of the CSEE, 2023, 43(10): 3794-3811. [16] 管敏渊, 徐政. 向无源网络供电的MMC型直流输电系统建模与控制[J]. 电工技术学报, 2013, 28(2): 255-263. Guan Minyuan, Xu Zheng.Modeling and control of modular multilevel converter based VSC-HVDC system connected to passive networks[J]. Transactions of China Electrotechnical Society, 2013, 28(2): 255-263. [17] 杨超然, 宫泽旭, 洪敏, 等. 外环动态影响下变流器广义阻抗判据的适用性分析[J]. 中国电机工程学报, 2021, 41(9): 3012-3024. Yang Chaoran, Gong Zexu, Hong Min, et al.Applicability analysis of the generalized-impedance stability criterion for converters considering the outer-loop dynamics[J]. Proceedings of the CSEE, 2021, 41(9): 3012-3024. [18] Skogestad S, Postelethwaite I.Multivariable Feedback Control[M]. New York: Wiley Publishing, 1996. [19] Rygg A, Molinas M, Zhang Chen, et al.A modified sequence-domain impedance definition and its equivalence to the dq-domain impedance definition for the stability analysis of AC power electronic systems[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2016, 4(4): 1383-1396. [20] 孙焜, 姚伟, 文劲宇. 双馈风电场经柔直并网系统次同步振荡机理及特性分析[J]. 中国电机工程学报, 2018, 38(22): 6520-6533. Sun Kun, Yao Wei, Wen Jinyu.Mechanism and characteristics analysis of subsynchronous oscillation caused by DFIG-based wind farm integrated into grid through VSC-HVDC system[J]. Proceedings of the CSEE, 2018, 38(22): 6520-6533. [21] Rosso R, Engelken S, Liserre M.Robust stability investigation of the interactions among grid-forming and grid-following converters[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020, 8(2): 991-1003. [22] 闵勇, 陈磊, 姜齐荣. 电力系统稳定分析[M]. 北京: 清华大学出版社, 2016. [23] 李龙源, 付瑞清, 吕晓琴, 等. 接入弱电网的同型机直驱风电场单机等值建模[J]. 电工技术学报, 2023, 38(3): 712-725. Li Longyuan, Fu Ruiqing, Lü Xiaoqin, et al.Single machine equivalent modeling of weak grid connected wind farm with same type PMSGs[J]. Transactions of China Electrotechnical Society, 2023, 38(3): 712-725. [24] 吴琛, 刘晨曦, 黄伟, 等. 提升新能源电力系统稳定性的构网型变流器选址定容方法[J]. 电力系统自动化, 2023, 47(12): 130-136. Wu Chen, Liu Chenxi, Huang Wei, et al.Siting and sizing method of grid-forming converters for improving stability of power system with renewable energy[J]. Automation of Electric Power Systems, 2023, 47(12): 130-136.
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