A Diagnosis Strategy for Open-Circuit Submodule Faults in MMCs under Nearst Level Modulation Suitable for Different Powers
Wu Hong1, Wang Yue1, Xue Yinglin2, Liu Yi1, Li Pengkun1
1. State Key Laboratory of Electrical Insulation and Power Equipment Xi’an Jiaotong University Xi’an 710049 China; 2. State Power Economic Research Institute Beijing 102209 China
Abstract：With the increasing voltage and power level of modular multilevel converters (MMC), the number of its submodules (SMs) also increases, and the issue of its reliability is highlighted. The failure of IGBT in any SM can affect the normal operation of MMC and even further lead to the damage of other components, which eventually lead to the collapse of the whole system. Thus, it is necessary to detect the fault and locate the malfunctioning SMs accurately to improve its reliability. MMC’s SM open-circuit diagnosis strategy can be divided into two categories: hardware-based and software-based. Compared with the hardware-based strategy, the software-based strategies need no extra hardware, have low computational burden. However, it is difficult to set the empirical threshold of existing software-based strategies between different operating powers, which hinders its further development. To solve this issue, a diagnosis strategy for open-circuit SM faults in MMCs suitable for different operating powers is proposed. The SM switching function is predicted based on the number of SM inputs and the position of SM capacitor voltage sorting arrangement and then the corresponding SM capacitor voltage is predicted. On the basis, the fault is detected and located by judging whether the absolute error between the predicted value and the actual value of the SM capacitor voltage exceeds a threshold. Moreover, to further eliminate the effects of errors and prevent the existence of fault misdiagnosis situations, a time flag is used in both the detection process and location process. In the proposed strategy, to avoid the effects of misdiagnosis near the arm current-over-zero point, a current-over-zero filtering part is proposed. Based on the mathematical deduction, the principle of setting threshold is given. It is indicated that the proposed strategy eliminates the need to manually set the threshold when the MMC operating power changes, which greatly reduce the difficulty of setting the threshold compared with the existing strategies. At the same time, theoretical analysis verifies that the proposed strategy is not only suitable for NLM modulation strategy, but also can be extended to other MMC modulation strategies after adjusting the prediction method of SM switching function. A detailed real-time digital simulation model of the MMC-HVDC system is built in a hardware-in-the-loop platform. The power-stage model is emulated by the target machine and the control system is realized by the DSP TMS320F28335 control board. The experimental result verify that the proposed strategy can accurately diagnose two types of MMC SM open-circuit faults at different operating powers. It is observed that the absolute error of a Type I malfunctioning SM is high when the arm current is negative and the absolute error of a Type II malfunctioning SM is high when the arm current is positive, which verifies the correctness of the theoretical analysis. Before the fault occurs, the absolute error will not exceed the threshold so that misdiagnosis will not occur during normal operation. After the fault occurs, the absolute error exceeds the threshold, the system can quickly detect the fault and then locate the remaining malfunctioning SMs. Moreover, the proposed strategy integrates the advantages of existing strategies, including no extra hardware, low computational burden, fast diagnosis (<20 ms), and can cope with the cases of multiple SM failures in the arm.
武鸿, 王跃, 薛英林, 刘熠, 李鹏坤. 适用多功率的最近电平调制下MMC子模块开路故障诊断策略[J]. 电工技术学报, 2024, 39(1): 233-245.
Wu Hong, Wang Yue, Xue Yinglin, Liu Yi, Li Pengkun. A Diagnosis Strategy for Open-Circuit Submodule Faults in MMCs under Nearst Level Modulation Suitable for Different Powers. Transactions of China Electrotechnical Society, 2024, 39(1): 233-245.
[1] 罗丹, 陈民铀, 赖伟, 等. 基于Harr小波变换重构开关序列的MMC子模块电容值在线监测方法[J]. 电工技术学报, 2022, 37(20): 5278-5289. Luo Dan, Chen Minyou, Lai Wei, et al.Online monitoring method for sub-module capacitance in modular multilevel converter based on Haar wavelet transform reconstruction switch sequence[J]. Transa-ctions of China Electrotechnical Society, 2022, 37(20): 5278-5289. [2] 束洪春, 代月, 安娜, 等. 基于交叉重叠差分变换的MMC-HVDC线路故障识别方法[J]. 电工技术学报, 2021, 36(1): 203-214, 226. Shu Hongchun, Dai Yue, An Na, et al.Fault identification method of MMC-HVDC line based on sequential overlapping derivative transform[J]. Trans-actions of China Electrotechnical Society, 2021, 36(1): 203-214, 226. [3] 束洪春, 代月, 安娜, 等. 基于线性回归的柔性直流电网纵联保护方法[J]. 电工技术学报, 2022, 37(13): 3213-3226, 3288. Shu Hongchun, Dai Yue, An Na, et al.Pilot protection method of flexible DC grid based on linear regression[J]. Transactions of China Electrotechnical Society, 2022, 37(13): 3213-3226, 3288. [4] 付华, 陈浩轩, 李秀菊, 等. 含边界元件的MMC-MTDC直流侧单端量故障辨识方法[J]. 电工技术学报, 2021, 36(1): 215-226. Fu Hua, Chen Haoxuan, Li Xiuju, et al.MMC-MTDC DC side single-ended quantity fault identification method with boundary elements[J]. Transactions of China Electrotechnical Society, 2021, 36(1): 215-226. [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] 徐海亮, 高铭琨, 吴瀚, 等. 海上风电场-MMC互联系统频率耦合建模及稳定性分析[J]. 电力系统自动化, 2021, 45(21): 92-102. Xu Hailiang, Gao Mingkun, Wu Han, et al.Frequency-coupling modeling and stability analysis of offshore wind farm-modular multilevel converter interconnection system[J]. Automation of Electric Power Systems, 2021, 45(21): 92-102. [7] 徐政. 海上风电送出主要方案及其关键技术问题[J]. 电力系统自动化, 2022, 46(21): 1-10. Xu Zheng.Main schemes and key technical problems for grid integration of offshore wind farm[J]. Automation of Electric Power Systems, 2022, 46(21): 1-10. [8] 徐政, 肖晃庆, 张哲任. 柔性直流输电系统[M]. 2版. 北京: 机械工业出版社, 2017. [9] Chen Xingxing, Liu Jinjun, Deng Zhifeng, et al.A diagnosis strategy for multiple IGBT open-circuit faults of modular multilevel converters[J]. IEEE Transactions on Power Electronics, 2021, 36(1): 191-203. [10] 武鸿, 王跃, 刘熠, 等. 基于广义电容电压不平衡度的MMC子模块开路故障诊断策略[J]. 电工技术学报, 2023, 38(14): 3909-3922. Wu Hong, Wang Yue, Liu Yi, et al.Open circuit fault diagnosis strategy of MMC sub-module based on generalized capacitor voltage unbalance[J]. Transactions of China Electrotechnical Society, 2023, 38(14): 3909-3922. [11] Choi U M, Blaabjerg F, Lee K B.Study and handling methods of power IGBT module failures in power electronic converter systems[J]. IEEE Transactions on Power Electronics, 2015, 30(5): 2517-2533. [12] Wang Jinyu, Liu Xiong, Xiao Qian, et al.Modulated model predictive control for modular multilevel converters with easy implementation and enhanced steady-state performance[J]. IEEE Transactions on Power Electronics, 2020, 35(9): 9107-9118. [13] Picas R, Zaragoza J, Pou J, et al.Reliable modular multilevel converter fault detection with redundant voltage sensor[J]. IEEE Transactions on Power Electronics, 2017, 32(1): 39-51. [14] An Quntao, Sun Lizhi, Zhao Ke, et al.Switching function model-based fast-diagnostic method of open-switch faults in inverters without sensors[J]. IEEE Transactions on Power Electronics, 2011, 26(1): 119-126. [15] Liu Chengkai, Deng Fujin, Cai Xu, et al.Submodule open-circuit fault detection for modular multilevel converters under light load condition with rearranged bleeding resistor circuit[J]. IEEE Transactions on Power Electronics, 2022, 37(4): 4600-4613. [16] Shao Shuai, Wheeler P W, Clare J C, et al.Fault detection for modular multilevel converters based on sliding mode observer[J]. IEEE Transactions on Power Electronics, 2013, 28(11): 4867-4872. [17] Shao Shuai, Watson A J, Clare J C, et al.Robustness analysis and experimental validation of a fault detection and isolation method for the modular multilevel converter[J]. IEEE Transactions on Power Electronics, 2016, 31(5): 3794-3805. [18] Deng Fujin, Chen Zhe, Khan M R, et al.Fault detection and localization method for modular multilevel converters[J]. IEEE Transactions on Power Electronics, 2015, 30(5): 2721-2732. [19] Zhou Dehong, Qiu Huan, Yang Shunfeng, et al.Submodule voltage similarity-based open-circuit fault diagnosis for modular multilevel converters[J]. IEEE Transactions on Power Electronics, 2019, 34(8): 8008-8016. [20] Kiranyaz S, Gastli A, Ben-Brahim L, et al.Real-time fault detection and identification for MMC using 1-D convolutional neural networks[J]. IEEE Transactions on Industrial Electronics, 2019, 66(11): 8760-8771. [21] Deng Fujin, Jin Ming, Liu Chengkai, et al.Switch open-circuit fault localization strategy for MMCs using sliding-time window based features extraction algorithm[J]. IEEE Transactions on Industrial Electronics, 2021, 68(10): 10193-10206. [22] Zhou Weihao, Sheng Jing, Luo Haoze, et al.Detection and localization of submodule open-circuit failures for modular multilevel converters with single ring theorem[J]. IEEE Transactions on Power Electronics, 2019, 34(4): 3729-3739. [23] Geng Zhi, Han Minxiao, Khan Z W, et al.Detection and localization strategy for switch open-circuit fault in modular multilevel converters[J]. IEEE Transa-ctions on Power Delivery, 2020, 35(6): 2630-2640. [24] Liu Chengkai, Deng Fujin, Heng Qian, et al.Fault localization strategy for modular multilevel converters under submodule lower switch open-circuit fault[J]. IEEE Transactions on Power Electronics, 2020, 35(5): 5190-5204. [25] Wang Zhen, Peng Li.Grouping capacitor voltage estimation and fault diagnosis with capacitance self-updating in modular multilevel converters[J]. IEEE Transactions on Power Electronics, 2021, 36(2): 1532-1543. [26] Wang Jun, Ma Hao, Bai Zhihong.A submodule fault ride-through strategy for modular multilevel converters with nearest level modulation[J]. IEEE Transactions on Power Electronics, 2018, 33(2): 1597-1608. [27] Hagiwara M, Akagi H.Control and experiment of pulsewidth-modulated modular multilevel converters[J]. IEEE Transactions on Power Electronics, 2009, 24(7): 1737-1746. [28] Lewis P T, Grainger B M, Al Hassan H A, et al. Fault section identification protection algorithm for modular multilevel converter-based high voltage DC with a hybrid transmission corridor[J]. IEEE Transactions on Industrial Electronics, 2016, 63(9): 5652-5662. [29] Soliman H, Wang Huai, Blaabjerg F.A review of the condition monitoring of capacitors in power electronic converters[J]. IEEE Transactions on Industry Applications, 2016, 52(6): 4976-4989. [30] Wang Zhongxu, Zhang Yi, Wang Huai, et al.A reference submodule based capacitor condition monitoring method for modular multilevel converters[J]. IEEE Transactions on Power Electronics, 2020, 35(7): 6691-6696. [31] Deng Fujin, Heng Qian, Liu Chengkai, et al.Capacitor ESR and C monitoring in modular multilevel converters[J]. IEEE Transactions on Power Electronics, 2020, 35(4): 4063-4075. [32] Wang Kun, Jin Lin, Li Guangdi, et al.Online capacitance estimation of submodule capacitors for modular multilevel converter with nearest level modulation[J]. IEEE Transactions on Power Electronics, 2020, 35(7): 6678-6681.
2024, Vol. 39 
