Abstract：In the case of grid-side faults, the grid-connected converter (GCC) of the photovoltaic DC grid-connected system (PV-DCGS) should reduce the output power in real time based on the variations of AC grid voltage. At the same time, the PVs are required to reduce active power according to the power command issued by the central controller. During the low voltage ride through (LVRT) period, due to the difference in control response speed between GCC and PVs, and the delay in system command processing, the unbalanced power within PV-DCGS will occur, resulting in DC bus voltage deviation. Traditionally, energy-dissipating devices are used to absorb the excess power to suppress the rising magnitude of the DC bus voltage. However, the investment cost and maintenance complexity will increase accordingly. To address these issues, this paper proposes a fast method for reducing the unbalanced power of PV-DCGS under grid-side faults, which can limit the deviation of DC bus voltage to an acceptable range. First, the structure of PV-DCGS is introduced and the influence of the variation of the system power command on the DC bus voltage is analyzed. Second, the variation characteristic of the internal calculation voltage of GCC during LVRT is revealed. Then, the voltage variation trajectory formula is constructed and the variation characteristics of the key coefficients of the constructed formula are analyzed. Third, the weighted proximity is introduced to calculate the key coefficients of the constructed formula. The exact voltage variation trajectory formula can be obtained by the calculated key coefficients. Finally, the expected power command can be obtained by putting appropriate length of voltage data into the constructed formula, and effective DC bus voltage suppression can be achieved. The simulation model of the PV-DCGS is built on the PSCAD/EMTDC electromagnetic simulation platform, which verifies the feasibility and effectiveness of the proposed method. Simulations on different types of short-circuit faults are performed. The comparison of the voltage variation trend between the simulation system and the actual power system shows that the variation trend of the internal calculation voltage of GCC in the simulation system is similar to that of the actual power system. In order to quickly calculate the key coefficients of the constructed voltage formula, the data window length should be selected appropriately. The simulation results show that when the data window length is selected between 5~20 ms, the calculation error of key coefficients is less than 5%. Considering the reliability of calculation results, the data window length of this paper is selected at 20ms. Under the selected data window length, different transition resistances of AC grid faults are tested. The results show that the key coefficients of the constructed voltage formula can be calculated reliably, and the calculation error of the dominant term is smaller than 10%. To further illustrate the effectiveness of the proposed calculation method for key coefficients, the simulation waveforms of three-phase symmetrical fault are carried out. The results show that the numerical results of the constructed voltage formula are similar to those of the simulation waveform, the calculation error is within 5%. Compared with the traditional centralized control method, the proposed method can effectively suppress the peak value of the DC bus voltage to the acceptable range (≤1.05(pu)) during LVRT period. In conclusion, the proposed method can quickly and reliably calculate the system power command required for LVRT by using the voltage data of the external AC system at the initial fault stage, which shortens the excess power and its duration, resulting in the reduction of DC voltage deviation. With the proposed method, the GCC and PVs are free from operating at unexpected DC overvoltage range (>1.05(pu)). In addition, the proposed method weakens the dependence on additional energy-dissipating equipment and reduces the investment cost.
李俊涛, 贾科, 董学正, 毕天姝. 网侧故障下光伏直流并网系统不平衡功率快速平抑方法[J]. 电工技术学报, 2024, 39(5): 1340-1351.
Li Juntao, Jia Ke, Dong Xuezheng, Bi Tianshu. A Fast Method for Suppressing Unbalanced Power in Photovoltaic DC Grid-Connected System under Grid-Side Faults. Transactions of China Electrotechnical Society, 2024, 39(5): 1340-1351.
[1] 周孝信, 陈树勇, 鲁宗相, 等. 能源转型中我国新一代电力系统的技术特征[J]. 中国电机工程学报, 2018, 38(7): 1893-1904, 2205. Zhou Xiaoxin, Chen Shuyong, Lu Zongxiang, et al.Technology features of the new generation power system in China[J]. Proceedings of the CSEE, 2018, 38(7): 1893-1904, 2205. [2] 辛保安, 郭铭群, 王绍武, 等. 适应大规模新能源友好送出的直流输电技术与工程实践[J]. 电力系统自动化, 2021, 45(22): 1-8. Xin Baoan, Guo Mingqun, Wang Shaowu, et al.Friendly HVDC transmission technologies for large-scale renewable energy and their engineering practice[J]. Automation of Electric Power Systems, 2021, 45(22): 1-8. [3] 张智刚, 康重庆. 碳中和目标下构建新型电力系统的挑战与展望[J]. 中国电机工程学报, 2022, 42(8): 2806-2819. Zhang Zhigang, Kang Chongqing.Challenges and prospects for constructing the new-type power system towards a carbon neutrality future[J]. Proceedings of the CSEE, 2022, 42(8): 2806-2819. [4] 何晓坤, 胡仁杰, 陈武. 一种适用于新能源中压直流汇集的无环流零电流软开关三电平谐振式复合全桥变换器[J]. 电工技术学报, 2023, 38(19): 5274-5287. He Xiaokun, Hu Renjie, Chen Wu.A novel circulating current free zero current switching three-level resonant composite full bridge converter for new energy medium voltage DC collection system[J]. Transactions of China Electrotechnical Society, 2023, 38(19): 5274-5287. [5] 黄欣科, 王环, 周宇, 等. 兆瓦级光伏中压直流并网变换器研制及实证应用[J]. 电力系统自动化, 2022, 46(14): 150-157. Huang Xinke, Wang Huan, Zhou Yu, et al.Development and empirical application of megawatt-level medium-voltage DC photovoltaic grid-connected converter[J]. Automation of Electric Power Systems, 2022, 46(14): 150-157. [6] Nasiri M, Arzani A, Guerrero J M.LVRT operation enhancement of single-stage photovoltaic power plants: an analytical approach[J]. IEEE Transactions on Smart Grid, 2021, 12(6): 5020-5029. [7] Saxena V, Kumar N, Singh B, et al.A voltage support control strategy for grid integrated solar PV system during abnormal grid conditions utilizing interweaved GI[J]. IEEE Transactions on Industrial Electronics, 2021, 68(9): 8149-8157. [8] Naqvi S B Q, Singh B. A PV-battery system resilient to weak grid conditions with regulated power injection and grid supportive features[J]. IEEE Transactions on Sustainable Energy, 2022, 13(3): 1408-1419. [9] 孙佳航, 冯忠楠, 黄景光, 等.基于改进VSG的风光储联合发电系统低电压穿越控制策略[J/OL]. 电网技术, 2023: 1-14. https://doi.org/10.13335/j. 1000-3673.pst.2022.0717. Sun Jiahang, Feng Zhongnan, Huang Jingguang, et al.Low-voltage ride-through control strategy of wind-storage co-generation system based on improved VSG[J/OL]. Power System Technology, 2023: 1-14. https://doi.org/10.13335/j.1000-3673.pst.2022.0717. [10] 王诗雯, 刘飞, 庄一展, 等. 基于有功指令共享的两级式光伏并网系统低电压穿越控制策略[J]. 电力自动化设备, 2023, 43(4): 99-105. Wang Shiwen, Liu Fei, Zhuang Yizhan, et al.Active-power-command-sharing low-voltage ride-through control strategy for two-stage PV grid-connected system[J]. Electric Power Automation Equipment, 2023, 43(4): 99-105. [11] Zhao Tao, Feng Zhijian, Wang Mingda, et al.An optimized LVRT control strategy of cascaded modular medium-voltage inverter for large-scale PV power plant[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2022, 10(6): 7744-7759. [12] 谭爱国, 吴颖颖, 王传启, 等. 基于保障低压穿越能力的风电机组撬棒自适应投切策略研究[J]. 电力系统保护与控制, 2021, 49(18): 98-109. Tan Aiguo, Wu Yingying, Wang Chuanqi, et al.Adaptive switching strategy for a wind turbine crowbar based on the guarantee of low voltage ride-through capability[J]. Power System Protection and Control, 2021, 49(18): 98-109. [13] Musarrat M N, Fekih A.A fault-tolerant control framework for DFIG-based wind energy conversion systems in a hybrid wind/PV microgrid[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2021, 9(6): 7237-7252. [14] 杨兴雄, 束洪春, 单节杉, 等. 计及阻容式撬棒动作时间的双馈风机短路电流分析[J]. 电工技术学报, 2021, 36(22): 4716-4725. Yang Xingxiong, Shu Hongchun, Shan Jieshan, et al.Short circuit current analysis of DFIG considering resistance-capacitance type crowbar protection action time[J]. Transactions of China Electrotechnical Society, 2021, 36(22): 4716-4725. [15] He Yufei, Wang Minghao, Xu Zhao.Coordinative low-voltage-ride-through control for the wind-photovoltaic hybrid generation system[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020, 8(2): 1503-1514. [16] Xia Yanghong, Long Teng.Chopperless fault ride-through control for DC microgrids[J]. IEEE Transactions on Smart Grid, 2021, 12(2): 965-976. [17] Zhao Tao, Chen Daolian.Active power backflow control strategy for cascaded photovoltaic solid-state transformer during low-voltage ride through[J]. IEEE Transactions on Industrial Electronics, 2022, 69(1): 440-451. [18] Wan Wenfeng, Bragin M A, Yan Bing, et al.Distributed and asynchronous active fault management for networked microgrids[J]. IEEE Transactions on Power Systems, 2020, 35(5): 3857-3868. [19] Stanisavljevic A M, Katic V A.Magnitude of voltage sags prediction based on the harmonic footprint for application in DG control system[J]. IEEE Transactions on Industrial Electronics, 2019, 66(11): 8902-8912. [20] 严伟, 王淑超, 刘翔, 等. 光伏系统快速功率控制和应用(英文)[J]. 中国电机工程学报, 2019, 39(增刊1): 213-224. Yan Wei, Wang Shuchao, Liu Xiang, et al.System level PV fast power control technology and application[J]. Proceedings of the CSEE, 2019, 39(S1): 213-224. [21] 国家质量监督检验检疫总局, 中国国家标准化管理委员会. 光伏发电站接入电力系统技术规定: GB/T 19964—2012[S]. 北京: 中国标准出版社, 2013. [22] 杜磊, 赵涛, 冯之健, 等. 单相短路故障条件下级联模块中压光伏发电系统的有功功率回流抑制[J]. 电工技术学报, 2022, 37(20): 5201-5213. Du Lei, Zhao Tao, Feng Zhijian, et al.Active power backflow suppression of cascaded module medium-voltage PV power generation system during single-phase short-circuit fault[J]. Transactions of China Electrotechnical Society, 2022, 37(20): 5201-5213. [23] 刘宿城, 李响, 秦强栋, 等. 直流微电网集群的大信号稳定性分析[J]. 电工技术学报, 2022, 37(12): 3132-3147. Liu Sucheng, Li Xiang, Qin Qiangdong, et al.Large signal stability analysis for DC microgrid clusters[J]. Transactions of China Electrotechnical Society, 2022, 37(12): 3132-3147. [24] 姚卫波, 徐晔, 黄克峰, 等. 基于前馈解耦的交直流混合微电网双向AC-DC变换器控制策略研究[J]. 电气技术, 2022, 23(5): 25-33. Yao Weibo, Xu Ye, Huang Kefeng, et al.Research on bidirectional AC-DC converter feedforward decoupling control strategy of hybrid AC/DC microgrid[J]. Electrical Engineering, 2022, 23(5): 25-33. [25] 贾科, 刘浅, 杨彬, 等. 计及锁相环动态特性的逆变电源故障暂态电流解析[J]. 电网技术, 2021, 45(11): 4242-4251. Jia Ke, Liu Qian, Yang Bin, et al.Transient fault current analysis of the inverter-interfaced renewable energy sources considering the dynamic characteristics of the phase-locked loop[J]. Power System Technology, 2021, 45(11): 4242-4251.
2024, Vol. 39 
