不平衡状态下MMC双回路环流抑制策略
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摘要
模块化多电平换流器(MMC)的内部环流将会增加换流器的功率损耗,降低桥臂容量利用率;同时加剧桥臂电流畸变,影响开关器件的安全运行。因此,需要采取有效的控制手段抑制环流。该文通过详细的相单元瞬时能量理论推导,得到MMC内部环流和环流抑制控制器输出电压间的交互作用会造成环流四倍频分量增加的结论。在基于准比例谐振调节器的环流抑制策略基础上,添加环流辅助控制回路,提出了一种环流抑制能力增强型的双回路环流抑制策略。通过合理整定调节器参数可以改善环流抑制控制器的闭环零极点分布,增强控制系统的稳定性,同时提高环流抑制控制器在谐振频率附近处的环流抑制能力。在PSCAD/EMTDC中搭建三相MMC详细仿真模型,验证了双回路环流抑制策略的正确性和有效性。
The inner circulating current of modular multilevel converter(MMC) will increase the power loss and reduce the capacities utilization of the bridge inevitably. Even worse, the bridge current distortion will be intensified, which will endanger the safe operation. Therefore, it is necessary to suppress the inner circulating current. Via the more detailed phase-unit instantaneous energy analysis,this paper reveals that the quadruple-line frequency components of the inner circulating current will be increased due to the interaction between the circulating current at double line-frequency and the output voltage of the circulating current suppressing controller. Then, a suppression-enhanced double-loop circulating current suppressing strategy is proposed. Moreover, by reasonably tuning the controller parameters, the distribution of closed-loop poles can be improved, the system stability as well as the suppression ability can be enhanced significantly. A detailed three-phase MMC model is established in PSCAD/EMTDC environment, the correctness and effectiveness of the proposed strategy get verified.
The inner circulating current of modular multilevel converter(MMC) will increase the power loss and reduce the capacities utilization of the bridge inevitably. Even worse, the bridge current distortion will be intensified, which will endanger the safe operation. Therefore, it is necessary to suppress the inner circulating current. Via the more detailed phase-unit instantaneous energy analysis,this paper reveals that the quadruple-line frequency components of the inner circulating current will be increased due to the interaction between the circulating current at double line-frequency and the output voltage of the circulating current suppressing controller. Then, a suppression-enhanced double-loop circulating current suppressing strategy is proposed. Moreover, by reasonably tuning the controller parameters, the distribution of closed-loop poles can be improved, the system stability as well as the suppression ability can be enhanced significantly. A detailed three-phase MMC model is established in PSCAD/EMTDC environment, the correctness and effectiveness of the proposed strategy get verified.
引文
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[17]Shi Xiaojie,Wang Zhiqiang,Liu Bo,et al.Characteristic investigation and control of a modular multilevel converter-based HVDC system under single-line-to-ground fault conditions[J].IEEETransactions on Power Electronics,2014,30(1):408-421.
[18]张建坡,赵成勇,敬华兵.比例谐振控制器在MMC-HVDC控制中的仿真研究[J].中国电机工程学报,2013,33(21):53-62.Zhang Jianpo,Zhao Chengyong,Jing Huabing.Simulating research of proportional resonant controllers in MMC-HVDC[J].Proceedings of the CSEE,2013,33(21):53-62.
[19]班明飞,申科,王建赜,等.基于准比例谐振控制的MMC新型环流抑制器[J].电力系统自动化,2014,38(11):85-89.Ban Mingfei,Shen Ke,Wang Jianze,et al.A novel circulating current suppressor for modular multilevel converters based on quasi-proportional-resonant control[J].Automation of Electric Power Systems,2014,38(11):85-89.
[20]伍小杰,杨超,公铮,等.基于多谐振控制器的MMC简化环流抑制策略[J].电工技术学报,2016,31(13):74-81.Wu Xiaojie,Yang Chao,Gong Zheng,et al.Simplified circulating current suppressing strategy for MMCbased on multi-resonant controller[J].Transactions of China Electrotechnical Society,2016,31(13):74-81.
[21]Tan P C,Loh P C,Holmes D G.High-performance harmonic extraction algorithm for a 25 kV traction power quality conditioner[J].IEE ProceedingsElectric Power Applications,2004,151(5):505-512.
[22]韩民晓,熊凌飞,丁辉.利用电压倾斜控制的VSC-MTDC稳定性分析[J].电网技术,2015,39(7):1808-1813.Han Minxiao,Xiong Lingfei,Ding Hui.Stability analysis of VSC-MTDC with voltage droop control[J].Power System Technology,2015,39(7):1808-1813.
[2]Debnath S,Qin J,Bahrani B,et al.Operation,control,and applications of the modular multilevel converter:a review[J].IEEE Transactions on Power Electronics,2014,30(1):37-53.
[3]Nami A,Liang J,Dijkhuizen F,et al.Modular multilevel converters for HVDC applications:review on converter cells and functionalities[J].IEEETransactions on Power Electronics,2015,30(1):18-36.
[4]Zhou Yuebin,Jiang Daozhuo,Guo Jie,et al.Analysis and control of modular multilevel converters under unbalanced conditions[J].IEEE Transactions on Power Delivery,2013,28(4):1986-1995.
[5]Moon J W,Kim C S,Park J W,et al.Circulating current control in MMC under the unbalanced voltage[J].IEEE Transactions on Power Delivery,2013,28(3):1952-1959.
[6]Liang Yingyu,Liu Jianzheng,Zhang Tao,et al.Arm current control strategy for MMC-HVDC under unbalanced conditions[J].IEEE Transactions on Power Delivery,2017,32(1):125-134.
[7]Ben-Brahim L,Gastli A,Trabelsi M,et al.Modular multilevel converter circulating current reduction using model predictive control[J].IEEE Transactions on Industrial Electronics,2016,63(6):3857-3866.
[8]郝亮亮,张静,顾亚旗,等.基于桥臂能量预测的模块化多电平换流器子模块故障优化容错控制策略[J].电工技术学报,2018,33(16):3697-3706.Hao Liangliang,Zhang Jing,Gu Yaqi,et al.Submodule fault tolerant optimal control strategy of modular multilevel converter based on estimation of bridge energy[J].Transactions of China Electrotechnical Society,2018,33(16):3697-3706.
[9]岳雨霏,徐千鸣,马伏军,等.基于子模块电压波动估计的MMC双环二倍频环流抑制策略[J].电工技术学报,2017,32(10):20-32.Yue Yufei,Xu Qianming,Ma Fujun,et al.Dual-loop2nd circulating current strategy based on estimated capacitor voltage fluctuation of sub-module for modular multilevel converter[J].Transactions of China Electrotechnical Society,2017,32(10):20-32.
[10]李凯,赵争鸣,袁立强,等.基于能量平衡的降低模块化多电平变换器子模块电容电压波动控制策略[J].电工技术学报,2017,32(14):17-26.Li Kai,Zhao Zhengming,Yuan Liqiang,et al.Control strategy based on the energy balance for reducing submodule capacitor voltage fluctuation of modular multilevel converter[J].Transactions of China Electrotechnical Society,2017,32(14):17-26.
[11]施恩泽,吴学智,荆龙,等.网压不平衡下环流注入对模块化多电平换流器的影响分析[J].电工技术学报,2018,33(16):3719-3731.Shi Enze,Wu Xuezhi,Jing Long,et al.Analysis of the impact on modular multilevel converter with circulating current injection under unbalanced grid voltage[J].Transactions of China Electrotechnical Society,2018,33(16):3719-3731.
[12]Tu Qingrui,Zheng Xu,Xu Lie.Reduced switchingfrequency modulation and circulating current suppression for modular multilevel converters[J].IEEE Transactions on Power Delivery,2011,26(3):2009-2017.
[13]Tu Qingrui,Xu Zheng,Chang Yong,et al.Suppressing DC voltage ripples of MMC-HVDC under unbalanced grid conditions[J].IEEE Transactions on Power Delivery,2012,27(3):1332-1338.
[14]Li Shaohua,Wang Xiuli,Yao Zhiqing,et al.Circulating current suppressing strategy for MMC-HVDC based on nonideal proportional resonant controllers under unbalanced grid conditions[J].IEEETransactions on Power Electronics,2015,30(1):387-397.
[15]梁营玉,张涛,刘建政,等.不平衡电网电压下模块化多电平换流器的环流抑制策略[J].电工技术学报,2016,31(9):120-128.Liang Yingyu,Zhang Tao,Liu Jianzheng,et al.Acirculating current suppressing method for modular multilevel converter under unbalanced grid voltage[J].Transactions of China Electrotechnical Society,2016,31(9):120-128.
[16]徐政,管敏渊.柔性直流输电系统[M].北京:机械工业出版社,2013.
[17]Shi Xiaojie,Wang Zhiqiang,Liu Bo,et al.Characteristic investigation and control of a modular multilevel converter-based HVDC system under single-line-to-ground fault conditions[J].IEEETransactions on Power Electronics,2014,30(1):408-421.
[18]张建坡,赵成勇,敬华兵.比例谐振控制器在MMC-HVDC控制中的仿真研究[J].中国电机工程学报,2013,33(21):53-62.Zhang Jianpo,Zhao Chengyong,Jing Huabing.Simulating research of proportional resonant controllers in MMC-HVDC[J].Proceedings of the CSEE,2013,33(21):53-62.
[19]班明飞,申科,王建赜,等.基于准比例谐振控制的MMC新型环流抑制器[J].电力系统自动化,2014,38(11):85-89.Ban Mingfei,Shen Ke,Wang Jianze,et al.A novel circulating current suppressor for modular multilevel converters based on quasi-proportional-resonant control[J].Automation of Electric Power Systems,2014,38(11):85-89.
[20]伍小杰,杨超,公铮,等.基于多谐振控制器的MMC简化环流抑制策略[J].电工技术学报,2016,31(13):74-81.Wu Xiaojie,Yang Chao,Gong Zheng,et al.Simplified circulating current suppressing strategy for MMCbased on multi-resonant controller[J].Transactions of China Electrotechnical Society,2016,31(13):74-81.
[21]Tan P C,Loh P C,Holmes D G.High-performance harmonic extraction algorithm for a 25 kV traction power quality conditioner[J].IEE ProceedingsElectric Power Applications,2004,151(5):505-512.
[22]韩民晓,熊凌飞,丁辉.利用电压倾斜控制的VSC-MTDC稳定性分析[J].电网技术,2015,39(7):1808-1813.Han Minxiao,Xiong Lingfei,Ding Hui.Stability analysis of VSC-MTDC with voltage droop control[J].Power System Technology,2015,39(7):1808-1813.