Abstract：Active power backflow is an inherent problem of cascaded H-bridge (CHB) PV grid- tied inverters under the asymmetric grid voltage fault conditions, which may result in the system not having a balanced operation point, the continuous increase of H-bridge DC-bus voltage, and shutdown and disconnection due to overvoltage protection. Aiming at this issue, this paper took the single-phase short-circuit fault with the highest incidence of power grid fault as the research goal, reviewed the existing control methods, and quantitatively analyzed their limitations, that is, it is impossible to avoid active power backflow in the scenario of deep power grid voltage drop and low output power of PV array. On this basis, an active power backflow suppression strategy suitable for cascaded modular medium-voltage PV power generation system under single-phase short-circuit fault was proposed. According to the actual output active power of PV array, the operation of the system is divided into two areas. By reasonably designing the system regulation and adopting different control methods in different operation areas, the adaptability of the CHBPV grid-tied inverter to different output powers and different grid drop depths is improved, and the fault ride through ability of the system is also improved. Finally, the effectiveness and feasibility of the proposed control strategy were verified by the experimental results.
杜磊, 赵涛, 冯之健, 王明达, 吴孟泽. 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, Wang Mingda, Wu Mengze. Active Power Backflow Suppression of Cascaded Module Medium-Voltage PV Power Generation System During Single-Phase Short-Circuit Fault. Transactions of China Electrotechnical Society, 2022, 37(20): 5201-5213.
 涂春鸣, 葛钦, 肖凡, 等. 基于光伏电源支撑的多端口固态变压器故障穿越策略[J]. 电工技术学报, 2020, 35(16): 3498-3508. Tu Chunming, Ge Qin, Xiao Fan, et al.Fault ride-through control strategy of solid state transformer with PV power generation[J]. Transactions of China Electrotechnical Society, 2020, 35(16): 3498-3508.  陈仲, 孙健博, 许亚明, 等. 采用输出周期脉冲循环的级联H桥型逆变器功率均衡方法[J]. 电工技术学报, 2020, 35(4): 827-838. Chen Zhong, Sun Jianbo, Xu Yaming, et al.Power balance method of cascaded H-bridge inverter based on pulse circulation in output period[J]. Transactions of China Electrotechnical Society, 2020, 35(4): 827-838.  Zhang Xing, Wang Mingda, Zhao Tao, et al.Topolo-gical comparison and analysis of medium-voltage and high-power direct-linked PV inverter[J]. CES Transa-ctions on Electrical Machines and Systems, 2019, 3(4): 327-334.  王书征, 赵剑锋, 姚晓君, 等. 级联型光伏并网逆变器在光照不均匀条件下的功率平衡控制[J]. 电工技术学报, 2013, 28(12): 251-261. Wang Shuzheng, Zhao Jianfeng, Yao Xiaojun, et al.Power balanced controlling of cascaded inverter for grid-connected photovoltaic systems under unequal irradiance conditions[J]. Transactions of China Elec-trotechnical Society, 2013, 28(12): 251-261.  郭小强, 贾晓瑜. 非隔离型级联H5光伏逆变器共模漏电流特性分析[J]. 电工技术学报, 2018, 33(2): 361-369. Guo Xiaoqiang, Jia Xiaoyu.Analysis of common mode leakage current for transformerless cascaded H5 PV inverter[J]. Transactions of China Electrotech-nical Society, 2018, 33(2): 361-369.  王付胜, 张德辉, 戴之强, 等. 级联H桥光伏并网逆变器混合调制策略[J]. 电工技术学报, 2016, 31(增刊1): 137-145. Wang Fusheng, Zhang Dehui, Dai Zhiqiang, et al.A hybrid control scheme of cascaded H-bridge inverters for grid-connection photovoltaic systems[J]. Transa-ctions of China Electrotechnical Society, 2016, 31(S1): 137-145.  Yu Yifan, Konstantinou G, Townsend C D, et al.Delta-connected cascaded H-bridge multilevel con-verters for large-scale photovoltaic grid integration[J]. IEEE Transactions on Industrial Electronics, 2017, 64(11): 8877-8886.  李宇泽, 周念成, 侯健生, 等. 计及光伏发电低电压穿越不确定性的主动配电网短路电流概率评估[J]. 电工技术学报, 2020, 35(3): 564-576. Li Yuze, Zhou Niancheng, Hou Jiansheng, et al.Probabilistic evaluation of short-circuit currents in active distribution grids considering low voltage ride-through uncertainty of photovoltaic[J]. Transactions of China Electrotechnical Society, 2020, 35(3): 564-576.  袁辉, 辛焕海, 王康, 等. 弱电网下远端严重电压跌落时逆变器并网失稳机理分析[J]. 电力系统自动化, 2018, 42(22): 38-43. Yuan Hui, Xin Huanhai, Wang Kang, et al.Instability mechanism analysis of inverters connected to weak grid during severe voltage sag on remote grid side[J]. Automation of Electric Power Systems, 2018, 42(22): 38-43.  Taul M G, Wang Xiongfei, Davari P, et al.An overview of assessment methods for synchronization stability of grid-connected converters under severe symmetrical grid faults[J]. IEEE Transactions on Power Electronics, 2019, 34(10): 9655-9670.  Zhao Tao, Zhang Xing, Wang Mingda, et al.Analysis and suppression of resonant current envelope ripple of LLC converter in cascaded modular PV solid state transformer[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2021, 9(3): 3744-3757.  Zhao Tao, Chen Daolian.Analysis and suppression of active power backflow of three-phase common DC-bus cascaded H-bridge PV grid-connected inverter during LVRT[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2022, 10(1): 745-759.  Tafti H D, Maswood A I, Konstantinou G, et al.Flexible control of photovoltaic grid-connected cascaded H-bridge converters during unbalanced voltage sags[J]. IEEE Transactions on Industrial Electronics, 2018, 65(8): 6229-6238.  Wu Pingheng, Chen Y T, Cheng Potai.The delta-connected cascaded H-bridge converter application in distributed energy resources and fault ride through capability analysis[J]. IEEE Transactions on Industry Applications, 2017, 53(5): 4665-4672.  Sharma R, Das A.Analysis of solar PV fed cascaded H-bridge converter during low voltage ride oper-ation[C]//IEEE International Conference on Power Electronics, Drives and Energy Systems, Jaipur, India, 2020: 1-6.  王书征, 李先允, 许峰. 不对称电网故障下级联型光伏并网逆变器的低电压穿越控制[J]. 电力系统保护与控制, 2019, 47(13): 84-91. Wang Shuzheng, Li Xianyun, Xu Feng.Low voltage ride-through controlling of cascaded inverter for grid-connected photovoltaic systems under asymmetric grid fault[J]. Power System Protection and Control, 2019, 47(13): 84-91.  Li Haiguo, Gao Zihan, Ji Shiqi, et al.An inrush current limit method for SiC-based multi-level grid-connected converter during low-voltage ride-through[C]//IEEE Applied Power Electronics Conference and Exposition (APEC), Phoenix, 2021: 2044-2049.  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.  赵涛. 基于级联H桥拓扑的光伏并网逆变器及其应用中的关键技术研究[D]. 合肥: 合肥工业大学, 2020.  Liu Tao, Yang Xu, Chen Wenjie, et al.High-efficiency control strategy for 10kV/1MW solid-state transformer in PV application[J]. IEEE Transactions on Power Electronics, 2020, 35(11): 11770-11782.  Wang Mingda, Zhang Xing, Zhao Tao, et al.Module power balance control strategy for three-phase cascaded H-bridge PV inverter under unbalanced grid voltage condition[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2021, 9(5): 5657-5671.  Rodriguez P, Pou J, Bergas J, et al.Decoupled double synchronous reference frame PLL for power con-verters control[J]. IEEE Transactions on Power Elec-tronics, 2007, 22(2): 584-592.  Tsunoda A, Hinago Y, Koizumi H.Level-and phase-shifted PWM for seven-level switched-capacitor inverter using series/parallel conversion[J]. IEEE Transactions on Industrial Electronics, 2014, 61(8): 4011-4021.  Chen Wei, Gu Yilei, Lu Zhengyu.A novel three level full bridge resonant DC-DC converter suitable for high power wide range input applications[C]//IEEE Applied Power Electronics Conference and Expo-sition, Anaheim, 2007: 373-379.