Abstract：The offshore wind turbine is connected to the offshore modular multilevel converter (MMC) through cable lines, forming the offshore AC collection system. Due to both ends of the offshore AC transmission line being power electronic devices, there are certain risks to the reliability of differential protection based on dual terminal communication. Therefore, a protection strategy based on non-unit protection is more suitable. However, the fault current of offshore MMC has limited fault current amplitude, controlled phase angle, and a large number of harmonic components, resulting in the low reliability of traditional distance protection based on power frequency, making it difficult to meet the requirements of cable lines in offshore AC networks. Therefore, it is urgent to study non-unit protection schemes with high reliability. The time-domain distance protection based on faulty line's derivative equations has become a feasible technical route due to its advantages of fast action speed and not affected by the harmonic components. In view of this, this paper utilizes the fault active control ability of converters and proposes a non-unit time-domain distance protection of offshore AC transmission lines based on the π type model of cable lines. Firstly, in response to the problem of reduced performance of non-unit distance protection caused by the phase difference of fault currents between the two ends of the cable line, this paper designs a control strategy of specific frequency voltage based on the fault active control ability of converters. At the same time, the corresponding control of “voltage reduction control for current limiting” is proposed to achieve the non-blocking of converters during severe faults. Under the proposed control, the negative sequence fault component is modulated at a specific frequency through the phase-locked loop (PLL). The specific frequency components only exist between the converter and the fault point, avoiding the influence of the fault current from the offshore wind turbines, thus the accuracy of time-domain distance protection is guaranteed. Secondly, based on the specific frequency components, a π type model of the cable lines is further used to equivalent the fault circuit, and the influence of distributed capacitance of the cable on protection is studied. By deriving fault differential equations under different fault types, the physical connection between fault distance and fault resistance under single-ended information is clarified. Furthermore, the optimization algorithm based on the least squares method is used to fit the fault distance and fault resistance through multiple sets of information, achieving accurate calculation of the fault distance. The following conclusions can be drawn from the simulation analysis: (1) The proposed protection scheme can reliably operate under different fault locations, and the ranging error is within 5%, which can provide accurate information about the fault location. (2) When the fault occurs outside the protection zone of the cable, the proposed protection scheme will not malfunction. (3) The proposed protection scheme has good anti-interference performance. (4) The proposed protection scheme can operate accurately under different fault types under high fault resistance, which has significant advantages over the time-domain distance protection based on the R-L model and can better protect cable lines.
郑涛, 章若竹, 吕文轩, 刘森. 基于故障主动控制的海上风电交流汇集线路时域距离保护[J]. 电工技术学报, 2025, 40(1): 122-138.
Zheng Tao, Zhang Ruozhu, Lü Wenxuan, Liu Sen. Time-Domain Distance Protection of Offshore AC Transmission Lines Based on Fault Active Control Considering Distributed Capacitance's Impact. Transactions of China Electrotechnical Society, 2025, 40(1): 122-138.
[1] Wu Jie, Wang Zhixin, Wang Guoqiang.The key technologies and development of offshore wind farm in China[J]. Renewable and Sustainable Energy Reviews, 2014, 34: 453-462. [2] 迟永宁, 梁伟, 张占奎, 等. 大规模海上风电输电与并网关键技术研究综述[J]. 中国电机工程学报, 2016, 36(14): 3758-3771. Chi Yongning, Liang Wei, Zhang Zhankui, et al.An overview on key technologies regarding power transmission and grid integration of large scale offshore wind power[J]. Proceedings of the CSEE, 2016, 36(14): 3758-3771. [3] Bian Chunyuan, Liu Shangyue, Xing Haiyang, et al.Research on fault-tolerant operation strategy of rectifier of square wave motor in wind power system[J]. CES Transactions on Electrical Machines and Systems, 2021, 5(1): 62-69. [4] Bresesti P, Kling W L, Hendriks R L, et al.HVDC connection of offshore wind farms to the transmission system[J]. IEEE Transactions on Energy Conversion, 2007, 22(1): 37-43. [5] 蔡旭, 杨仁炘, 周剑桥, 等. 海上风电直流送出与并网技术综述[J]. 电力系统自动化, 2021, 45(21): 2-22. Cai Xu, Yang Renxin, Zhou Jianqiao, et al.Review on offshore wind power integration via DC transmission[J]. Automation of Electric Power Systems, 2021, 45(21): 2-22. [6] 郑黎明, 贾科, 毕天姝, 等. 海上风电接入柔直系统交流侧故障特征及对保护的影响分析[J]. 电力系统保护与控制, 2021, 49(20): 20-32. Zheng Liming, Jia Ke, Bi Tianshu, et al.AC-side fault analysis of a VSC-HVDC transmission system connected to offshore wind farms and the impact on protection[J]. Power System Protection and Control, 2021, 49(20): 20-32. [7] 刘其辉, 逄思敏, 吴林林, 等. 大规模风电汇集系统电压不平衡机理、因素及影响规律[J]. 电工技术学报, 2022, 37(21): 5435-5450. Liu Qihui, Pang Simin, Wu Linlin, et al.The mechanism, factors and influence rules of voltage imbalance in wind power integration areas[J]. Transactions of China Electrotechnical Society, 2022, 37(21): 5435-5450. [8] 顾雪平, 白岩松, 李少岩, 等. 考虑风电不确定性的电力系统恢复全过程两阶段鲁棒优化方法[J]. 电工技术学报, 2022, 37(21): 5462-5477. Gu Xueping, Bai Yansong, Li Shaoyan, et al.Two stage robust optimization method for the whole-process power system restoration considering wind power uncertainty[J]. Transactions of China Electrotechnical Society, 2022, 37(21): 5462-5477. [9] 杨权, 梁永昌, 魏建荣, 等. 多谐波源下分布式电源并网逆变器的谐波抑制策略[J]. 电工技术学报, 2023, 38(11): 2908-2920. Yang Quan, Liang Yongchang, Wei Jianrong, et al.Research on harmonic suppression strategy of grid connected inverter under multi-harmonic sources[J]. Transactions of China Electrotechnical Society, 2023, 38(11): 2908-2920. [10] Shi Lei, Adam G P, Li Rui, et al.Control of offshore MMC during asymmetric offshore AC faults for wind power transmission[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020, 8(2): 1074-1083. [11] 王渝红, 陈诗昱, 曾琦, 等. 连接无源网络的MMC-HVDC系统交流故障穿越附加控制策略[J]. 高电压技术, 2021, 47(5): 1658-1665. Wang Yuhong, Chen Shiyu, Zeng Qi, et al.Additional AC fault ride-through control strategy of MMC-HVDC connected to a passive network[J]. High Voltage Engineering, 2021, 47(5): 1658-1665. [12] Xu Kehan, Zhang Zhe, Lai Qinghua, et al.Study on fault characteristics and distance protection applicability of VSC-HVDC connected offshore wind power plants[J]. International Journal of Electrical Power & Energy Systems, 2021, 133: 107252. [13] Zhong Ying, Kang Xiaoning, Jiao Zaibin, et al.A novel distance protection algorithm for the phase-ground fault[J]. IEEE Transactions on Power Delivery, 2014, 29(4): 1718-1725. [14] Li Bin, Liu Junyu, Wang Xin, et al.Fault studies and distance protection of transmission lines connected to DFIG-based wind farms[J]. Applied Sciences, 2018, 8(4): 562. [15] 侯俊杰, 樊艳芳, 钟显, 等. 适应于风电接入系统的抗高阻接地时域方程距离保护研究[J]. 电力系统保护与控制, 2018, 46(1): 122-128. Hou Junjie, Fan Yanfang, Zhong Xian, et al.Research on high resistance grounding time domain equation based distance protection for wind power accessed power system[J]. Power System Protection and Control, 2018, 46(1): 122-128. [16] 杨增力, 孔祥平, 王力军, 等. 适用于双馈风电场联络线的距离保护方案[J]. 电工技术学报, 2016, 31(24): 252-260. Yang Zengli, Kong Xiangping, Wang Lijun, et al.Distance protection scheme for interconnection line of doubly-fed induction generator based wind farm[J]. Transactions of China Electrotechnical Society, 2016, 31(24): 252-260. [17] Chen Xu, Yin Xianggen, Zhang Zhe.Impacts of DFIG-based wind farm integration on its tie line distance protection and countermeasures[J]. IEEJ Transactions on Electrical and Electronic Engineering, 2017, 12(4): 553-564. [18] Biswas S, Nayak P K.A new approach for protecting TCSC compensated transmission lines connected to DFIG-based wind farm[J]. IEEE Transactions on Industrial Informatics, 2021, 17(8): 5282-5291. [19] 陈学伟, 高厚磊, 向珉江, 等. 基于电子式互感器微分输出的改进R-L模型距离保护算法[J]. 电工技术学报, 2014, 29(6): 283-289. Chen Xuewei, Gao Houlei, Xiang Minjiang, et al.Improved R-L model distance protection algorithm based on differential output of electronic transducers[J]. Transactions of China Electrotechnical Society, 2014, 29(6): 283-289. [20] Zheng Tao, Lü Wenxuan, Zhuang Xinyi, et al.Improved time-domain distance protection for asymmetrical faults based on adaptive control of MMC in offshore AC network[J]. International Journal of Electrical Power & Energy Systems, 2023, 152: 109229. [21] 罗强. 过渡电阻对柔直近端交流线路距离保护的影响研究[D]. 武汉: 华中科技大学, 2019. Luo Qiang.Impact of transition resistance on distance protection of the AC transmission line near the MMC-HVDC system[D]. Wuhan: Huazhong University of Science and Technology, 2019. [22] 曹帅, 向往, 姚良忠, 等. 风电经混合型MMC-HVDC并网的交直流故障穿越策略[J]. 电力系统自动化, 2018, 42(7): 37-43, 49. Cao Shuai, Xiang Wang, Yao Liangzhong, et al.AC and DC fault ride-through strategies for wind power integration via hybrid MMC-HVDC[J]. Automation of Electric Power Systems, 2018, 42(7): 37-43, 49. [23] Li Rui, Yu Lujie, Xu Lie.Offshore AC fault protection of diode rectifier unit-based HVDC system for wind energy transmission[J]. IEEE Transactions on Industrial Electronics, 2019, 66(7): 5289-5299. [24] Zheng Tao, Wang Yunpeng, Lü Wenxuan, et al.Fault identification scheme for UPFC compensated transmission line based on characteristic voltage active injection[J]. International Journal of Electrical Power & Energy Systems, 2022, 137: 107851. [25] 齐金玲, 李卫星, 晁璞璞, 等. 直驱风机故障穿越全过程的通用电磁暂态建模方法[J]. 中国电机工程学报, 2022, 42(4): 1428-1442. Qi Jinling, Li Weixing, Chao Pupu, et al.Generic electromagnetic transient modeling method for complete fault ride-through processes of direct-driven wind turbine generators[J]. Proceedings of the CSEE, 2022, 42(4): 1428-1442. [26] 郑涛, 庄心怡, 吕文轩. 海上风电柔直换流站负序电流参考值选取及保护适应性分析[J]. 电力系统自动化, 2023, 47(3): 133-141. Zheng Tao, Zhuang Xinyi, Lü Wenxuan.Negative sequence current reference selection and protection adaptability analysis of flexible DC converter station for offshore wind power[J]. Automation of Electric Power Systems, 2023, 47(3): 133-141. [27] 胡正阳, 高丙团, 张磊, 等. 风电机组双向支撑能力分析与自适应惯量控制策略[J]. 电工技术学报, 2023, 38(19): 5224-5240. Hu Zhengyang, Gao Bingtuan, Zhang Lei, et al.Bidirectional support capability analysis and adaptive inertial control strategy of wind turbine[J]. Transactions of China Electrotechnical Society, 2023, 38(19): 5224-5240. [28] AlFuhaid A S, El-Sayed M A. A recursive least-squares digital distance relaying algorithm[J]. IEEE Transactions on Power Delivery, 1999, 14(4): 1257-1262. [29] 范兴明, 封浩, 张鑫. 最小二乘算法优化及其在锂离子电池参数辨识中的应用[J]. 电工技术学报, 2024, 39(5): 1577-1588. Fan Xingming, Feng Hao, Zhang Xin.Optimization of least squares method and its application in parameter identification of lithium-ion battery model[J]. Tran-sactions of China Electrotechnical Society, 2024, 39(5): 1577-1588. [30] 张尔佳, 余墨多, 黄文焘, 等. 谐波电流注入式微电网主动保护方法[J]. 电力系统自动化, 2023, 47(23): 172-179. Zhang Erjia, Yu Moduo, Huang Wentao, et al.Active protection method for microgrids based on harmonic current injection[J]. Automation of Electric Power Systems, 2023, 47(23): 172-179. [31] 郑园, 杨勇, 贾东亮, 等. 压控电压源二阶巴特沃斯高通滤波器的优化设计[J]. 电子技术, 2012, 39(2): 34-36, 33. Zheng Yuan, Yang Yong, Jia Dongliang, et al.Optimal design of voltage-controlled voltage source second-order unit gain butterworth high-pass filter[J]. Electronic Technology, 2012, 39(2): 34-36, 33. [32] 陈鹤林, 徐政, 唐庚, 等. 海上风电场MMC-HVDC并网系统暂态行为分析[J]. 电力系统自动化, 2014, 38(12): 112-118. Chen Helin, Xu Zheng, Tang Geng, et al.Transient behavior analysis of offshore wind farm integration system with MMC-HVDC[J]. Automation of Electric Power Systems, 2014, 38(12): 112-118. [33] 温志文, 刘昊霖, 贾科, 等. 风电接入海上换流站的交流汇集出线高速保护[J]. 中国电机工程学报, 2024, 44(12): 4775-4788. Wen Zhiwen, Liu Haolin, Jia Ke, et al.High-speed protection of AC collection lines connecting wind power to offshore converter stations[J]. Proceedings of the CSEE, 2024, 44(12): 4775-4788. [34] 马家璇. 海上风电经柔直送出系统交流汇集线路的保护方案研究[D]. 北京: 华北电力大学, 2023. Ma Jiaxuan.Research on protection for AC transmission line of the offshore wind power transmission system based on MMC-HVDC[D]. Beijing: North China Electric Power University, 2023.
2025, Vol. 40 
