Coupling Control Characteristics and Transient Synchronous Stability Enhancement Control Strategy of PLL-Based Grid-Connected VSC under Asymmetrical Grid Faults
Luo Yi, Yao Jun, Yang Dong, Xie Hai, Jin Rongyu, Zhao Linsheng
State Key Laboratory of Power Transmission Equipment Technology Chongqing University Chongqing 400044 China
Abstract：Under asymmetrical grid faults, there are not only violent dynamic interactions between the generation equipment and the power grid, but also between the positive sequence components and negative sequence components, which makes the transient synchronous instability of the renewable energy power generation (REPG) system very prominent. To solve this issue, with the dual-sequence phase-locked loop (PLL) control model, the coupling control characteristics between the positive and negative sequence components is revealed in this paper. Then, the influence of PLL control parameters, as well as the low voltage ride through (LVRT) reference on the transient behavior positive and negative sequence equivalent power angles is analyzed. In addition, to improve the transient synchronous stability of the REPG system under asymmetrical grid faults, a transient synchronous stability enhancement control strategy is proposed. Finally, the simulation and experimental verification are carried out. Firstly, considering the nonlinear control characteristics of PLL, a nonlinear transient model of PLL based on the separation of positive and negative sequence is established. Based on energy function, the transient synchronous stability instability criterion of REPG system under asymmetric faults is constructed, which can realize the quantitative evaluation of transient synchronous stability of the system. The influence of critical fault removal time, LVRT current references and proportional integral coefficient of PLL on the transient synchronous stability of the system is analyzed. Finally, a transient stability control strategy of REPG system under asymmetric faults is proposed. Simulation and experimental results show that, when the system adopts the traditional PLL control strategy in Ref.[6], the acceleration and deceleration energies of the system at stage 1 are ${{[S_{\text{acc1}}^{+}\text{ max}(S_{\text{dec1}}^{+})\text{ }S_{\text{acc1}}^{-}\text{ max}(S_{\text{dec1}}^{-})]}^{\text{T}}}=$[0.564, 0.518, 0.123, 0.421]T. In this case, $S_{\text{acc1}}^{+}$ is greater than max ($S_{\text{dec1}}^{+}$). Consequently, the transient synchronous instability occurs in the positive and negative sequence PLL. When the system adopts the proposed control strategy, the acceleration and deceleration energies of the system at stage 1 are$[S_{\text{acc1}}^{+}\text{ max}(S_{\text{dec1}}^{+}),$$S_{\text{acc1}}^{-}\text{ max}(S_{\text{dec1}}^{-}){{]}^{\text{T}}}=$[0.564 0.602 0.123 0.483]T. It can be seen from the calculation results that $S_{\text{acc1}}^{+}$ is smaller than max($S_{\text{dec1}}^{+}$) with the proposed control strategy is adopted. Therefore, there is no transient synchronous instability in the system. Consequently, the proposed control strategy can effectively improve the transient synchronization stability of REPG system under asymmetric faults. The following conclusions can be drawn from the simulation analysis: (1) The unbalance of q-axis potential in the positive and negative sequence terminal voltage is the key factor that causes the transient synchronous instability of the REPG system during the asymmetric faults. Moreover, there is the control coupling relationship between the positive and negative sequence PLL due to the interconnection of the positive and negative sequence impedance networks during the asymmetric faults. (2) The improper fault detection delay and LVRT current references may lead to transient synchronous instability due to the mismatch of acceleration and deceleration energies. (3) A transient stability control strategy of REPG system under asymmetric faults is proposed, which can improve the damping coefficient of the system during asymmetrical faults, as well as the transient synchronous stability of the system.
罗艺, 姚骏, 杨东, 谢海, 金容宇, 赵林生. 电网不对称故障下锁相同步型并网变流器控制耦合特性与暂态同步稳定增强控制策略[J]. 电工技术学报, 2026, 41(7): 2353-2367.
Luo Yi, Yao Jun, Yang Dong, Xie Hai, Jin Rongyu, Zhao Linsheng. Coupling Control Characteristics and Transient Synchronous Stability Enhancement Control Strategy of PLL-Based Grid-Connected VSC under Asymmetrical Grid Faults. Transactions of China Electrotechnical Society, 2026, 41(7): 2353-2367.
[1] 黄萌, 舒思睿, 李锡林, 等. 面向同步稳定性的电力电子并网变流器分析与控制研究综述[J]. 电工技术学报, 2024, 39(19): 5978-5994. Huang Meng, Shu Sirui, Li Xilin, et al.A review of synchronization-stability-oriented analysis and control of power electronic grid-connected converters[J]. Transactions of China Electrotechnical Society, 2024, 39(19): 5978-5994. [2] 张亚耀, 占萌. 锁相环型变换器并网系统暂态主导失稳特征分析[J]. 中国电机工程学报, 2023, 43(23): 9285-9297. Zhang Yayao, Zhan Meng.Dominant transient unstable characteristics of PLL-based grid-connected converters[J]. Proceedings of the CSEE, 2023, 43(23): 9285-9297. [3] 袁小明, 周蓉. 电力电子化并网设备激励下网络不对称故障分析的时变幅频对称分量法[J]. 中国电机工程学报, 2022, 42(16): 5811-5822, 6158. Yuan Xiaoming, Zhou Rong.Method of time-varying amplitude/frequency symmetrical components for network asymmetrical fault analysis excited by power electronic devices[J]. Proceedings of the CSEE, 2022, 42(16): 5811-5822, 6158. [4] 刘铖, 李守超, 张宇驰, 等. 基于I-ω响应关联特征的新能源电力系统暂态功角稳定判别方法[J]. 电工技术学报, 2024, 39(24): 7902-7916. Liu Cheng, Li Shouchao, Zhang Yuchi, et al.Transient angle stability discrimination method of new energy power system based on I-ω response correlation characteristics[J]. Transactions of China Electrotechnical Society, 2024, 39(24): 7902-7916. [5] 余墨多, 黄文焘, 邰能灵, 等. 逆变型分布式电源并网运行暂态稳定机理与评估方法[J]. 电工技术学报, 2022, 37(10): 2596-2610. Yu Moduo, Huang Wentao, Tai Nengling, et al.Transient stability mechanism and judgment for inverter interfaced distributed generators connected with public grids[J]. Transactions of China Electro-technical Society, 2022, 37(10): 2596-2610. [6] 裴金鑫, 姚骏, 黄森, 等. 电网短路故障下新能源并网变换器的暂态同步机制及其自适应稳定控制策略[J]. 中国电机工程学报, 2022, 42(16): 5922-5934, 6167. Pei Jinxin, Yao Jun, Huang Sen, et al.Transient synchronization mechanism and adaptive stability control strategy for renewable energy grid-connected converter under grid faults[J]. Proceedings of the CSEE, 2022, 42(16): 5922-5934, 6167. [7] Ma Shaokang, Geng Hua, Liu Lu, et al.Grid-synchronization stability improvement of large scale wind farm during severe grid fault[J]. IEEE Transactions on Power Systems, 2018, 33(1): 216-226. [8] Zhang Meiqing, Sun Li.PLL and additional frequency control constituting an adaptive synchronization mechanism for VSCs[J]. IEEE Transactions on Power Systems, 2020, 35(6): 4920-4923. [9] Göksu Ö, Teodorescu R, Bak C L, et al.Instability of wind turbine converters during current injection to low voltage grid faults and PLL frequency based stability solution[J]. IEEE Transactions on Power Systems, 2014, 29(4): 1683-1691. [10] 王诗雯, 刘飞, 刘沁怡, 等. 不对称故障下两级式光伏并网系统低电压穿越控制[J]. 电网技术, 2023, 47(1): 91-102. Wang Shiwen, Liu Fei, Liu Qinyi, et al.Low-voltage riding-through control strategy for two-staged grid-connected photovoltaic system under asymmetrical faults[J]. Power System Technology, 2023, 47(1): 91-102. [11] Liu Ruikuo, Yao Jun, Sun Peng, et al.Complex impedance-based frequency coupling characteristics analysis of DFIG-based WT during asymmetric grid faults[J]. IEEE Transactions on Industrial Electronics, 2021, 68(9): 8274-8288. [12] 彭星, 姜飞, 涂春鸣, 等. 不对称故障下光伏逆变器的最优电压支撑策略[J]. 电网技术, 2021, 45(11): 4259-4268. Peng Xing, Jiang Fei, Tu Chunming, et al.Optimal voltage support strategy for photovoltaic inverters under asymmetric faults[J]. Power System Technology, 2021, 45(11): 4259-4268. [13] 解宝, 李萍宇, 苏建徽, 等. 不平衡电网下并网逆变器阻抗建模及稳定性分析[J]. 高电压技术, 2023, 49(12): 5196-5206. Xie Bao, Li Pingyu, Su Jianhui, et al.Impedance modeling and stability analysis of grid-connected inverter under unbalanced grid[J]. High Voltage Engineering, 2023, 49(12): 5196-5206. [14] He Xiuqiang, He Changjun, Pan Sisi, et al.Synchronization instability of inverter-based generation during asymmetrical grid faults[J]. IEEE Transactions on Power Systems, 2022, 37(2): 1018-1031. [15] Wang Zhi, Guo Li, Li Xialin, et al.PLL synchronization transient stability analysis of a weak-grid connected VSC during asymmetric faults[J]. IEEE Transactions on Power Electronics, 2024, 39(2): 2140-2154. [16] 李红, 粟时平, 唐铭泽, 等. 不对称故障下考虑电压跌落程度的新能源逆变器控制策略[J]. 电力系统保护与控制, 2023, 51(1): 21-32. Li Hong, Su Shiping, Tang Mingze, et al.Control strategy of renewable energy inverter considering voltage sag degree under asymmetric faults[J]. Power System Protection and Control, 2023, 51(1): 21-32. [17] Guo Xiaoqiang, Zhang Xue, Wang Baocheng, et al.Asymmetrical grid fault ride-through strategy of three-phase grid-connected inverter considering network impedance impact in low-voltage grid[J]. IEEE Transactions on Power Electronics, 2014, 29(3): 1064-1068. [18] Chang Yuanzhu, Hu Jiabing, Tang W, et al.Fault current analysis of type-3 WTs considering sequential switching of internal control and protection circuits in multi time scales during LVRT[J]. IEEE Transactions on Power Systems, 2018, 33(6): 6894-6903. [19] 姚骏, 孙鹏, 刘瑞阔, 等. 弱电网不对称故障期间双馈风电系统动态稳定性分析[J]. 中国电机工程学报, 2021, 41(21): 7225-7237. Yao Jun, Sun Peng, Liu Ruikuo, et al.Dynamic stability analysis of DFIG-based wind power system during asymmetric faults of weak grid[J]. Proceedings of the CSEE, 2021, 41(21): 7225-7237. [20] Chang Yuanzhu, Kocar I, Hu Jiabing, et al.Coordinated control of DFIG converters to comply with reactive current requirements in emerging grid codes[J]. Journal of Modern Power Systems and Clean Energy, 2022, 10(2): 502-514. [21] 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. [22] Gu Jiateng, Zhao Rende, He Jinkui, et al.Enhanced excitation converter with parallel/series DC-link based on TAB for DFIG to improve the LVRT capability under severe grid faults[J]. IEEE Transactions on Power Electronics, 2023, 38(10): 12304-12308. [23] 万子镜, 田震, 王伟, 等. 基于平滑切换的不平衡工况下直驱风机故障穿越控制策略[J]. 电力系统自动化, 2023, 47(19): 138-146. Wan Zijing, Tian Zhen, Wang Wei, et al.Smooth switching based fault ride-through control strategy for direct-driven wind turbine under unbalance condition[J]. Automation of Electric Power Systems, 2023, 47(19): 138-146. [24] Mortazavian S, Mohamed Y A I. Analysis and augmented model-based control design of distributed generation converters with a flexible grid-support controller[J]. IEEE Transactions on Power Electronics, 2019, 34(7): 6369-6387. [25] 熊连松, 修连成, 康志亮, 等. 不平衡工况下电网电压序分量快速提取方法[J]. 电力系统自动化, 2019, 43(11): 144-151. Xiong Liansong, Xiu Liancheng, Kang Zhiliang, et al.Fast extraction method of grid voltage sequence components in unbalanced conditions[J]. Automation of Electric Power Systems, 2019, 43(11): 144-151. [26] 风电场接入电力系统技术规定第1部分:陆上风电: GB/T 19963.1—2021 GB/T 19963.1—2021[S]. 2021. [27] 郝艺, 周瑀涵, 刘晨曦, 等. 含跟网型储能的新能源多馈入系统小扰动电压支撑强度分析[J]. 电工技术学报, 2024, 39(11): 3569-3580. Hao Yi, Zhou Yuhan, Liu Chenxi, et al.Small-disturbance voltage support strength analysis for renewable multi-infeed system with grid-following energy storage[J]. Transactions of China Electro-technical Society, 2024, 39(11): 3569-3580. [28] 李锐博, 颜湘武, 蔡光, 等. 离散域下基于轮换计算的跟/构网逆变器混联系统暂态稳定性求解算法[J]. 电工技术学报, 2025, 40(9): 2780-2794. Li Ruibo, Yan Xiangwu, Cai Guang, et al.Transient stability solver for grid-following/forming-converter hybrid system based on alternating calculation in discrete domain[J]. Transactions of China Electro-technical Society, 2025, 40(9): 2780-2794.
2026, Vol. 41 
