混合型MMC降低子模块电容电压波动的优化策略
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摘要
模块化多电平换流器(multilevel modular converter,MMC)在高压直流输电(high voltage direct current,HVDC)领域得到了广泛的应用。由半桥以及全桥子模块构成的MMC因具备主动使换流器直流侧输出极间零电压以适应短路故障条件的能力,引起了国内外学者的广泛关注。首先,从混合型MMC的开关函数角度出发,对理想情况下混合型MMC进行建模,建立了子模块电容电压基频、二倍频波动数学模型,并提出单位降容比的概念,研究了调制比对子模块电容电压波动的影响。其次,提出提高调制比的抑制子模块电容电压波动配合策略,有效降低子模块电容电压波动。在此基础上,提出基于三次谐波注入的新增半桥子模块数目优化方法,减少半桥子模块的新增数目,解决了单纯提高变比带来的全桥电容电压降落的副作用。最后,在PSCAD/EMTDC中搭建双端±160 kV混合型MMC的仿真模型,验证了所提降容策略的正确性和有效性。
Modular multilevel converter (MMC) has been widely used in high voltage direct current (HVDC). The MMC,which consists of half bridge and full bridge submodules,has attracted the attention of domestic and foreign scholars because of the self-cleaning ability of DC short-circuit fault. According to the switching function of the hybrid MMC,the hybrid MMC is modeled under the ideal condition,and the fundamental frequency voltage fluctuation on the capacitor of the submodule is analyzed. A coordination strategy is proposed,which suppresses capacitor voltage fluctuation of sub-module by over modulation. On this basis,a newmethod for optimizing the number of half-bridge sub-modules based on third harmonic injection is proposed,which reduces the number of newadded half-bridge sub-modules and alleviates the side effects of fullbridge capacitance voltage drop caused by simply increasing the modulation ratio. Finally,the correctness and validity of the proposed strategy are verified by simulation of a two-end ± 160 kV hybrid MMC in PSCAD/EMTDC.
Modular multilevel converter (MMC) has been widely used in high voltage direct current (HVDC). The MMC,which consists of half bridge and full bridge submodules,has attracted the attention of domestic and foreign scholars because of the self-cleaning ability of DC short-circuit fault. According to the switching function of the hybrid MMC,the hybrid MMC is modeled under the ideal condition,and the fundamental frequency voltage fluctuation on the capacitor of the submodule is analyzed. A coordination strategy is proposed,which suppresses capacitor voltage fluctuation of sub-module by over modulation. On this basis,a newmethod for optimizing the number of half-bridge sub-modules based on third harmonic injection is proposed,which reduces the number of newadded half-bridge sub-modules and alleviates the side effects of fullbridge capacitance voltage drop caused by simply increasing the modulation ratio. Finally,the correctness and validity of the proposed strategy are verified by simulation of a two-end ± 160 kV hybrid MMC in PSCAD/EMTDC.
引文
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[15]LI Xiaoqian,LIU Wenhua,SONG Qiang,et al.An enhanced MMCtopology w ith DC fault ride-through capability[C]//Proceedings of the 39th Annual Conference of the IEEE Industrial Electronics Society.IEEE,2013:6182-6188.
[16]李少华,王秀丽,李泰,等.混合式MMC及其直流故障穿越策略优化[J].中国电机工程学报,2016,36(7):1849-1858.LI Shaohua,WANG Xiuli,LI Tai,et al.Optimal design for hybrid M M C and its DC fault ride-through strategy[J].Proceedings of the CSEE,2016,36(7):1849-1858.
[17]LIN Weixing,JOVCIC D,NGUEFEU S,et al.Full bridge MMCconverter optimal design to HVDC operational requirements[J].IEEE Transactions on Pow er Delivery,2016,31(3):1342-1350.
[18]ZENG R,XU L,YAO L,et al.Design and operation of a hybrid modular multilevel converter[J].IEEE Transactions on Pow er Electronics,2015,30(3):1137-1146.
[19]刘钟淇,宋强,刘文华.基于模块化多电平变流器的轻型直流输电系统[J].电力系统自动化,2010,34(2):53-58.LIU Zhongqi,SONG Qiang,LIU Wenhua.VSC-HVDC system based on modular multilevel converters[J].Automation of Electric Pow er System,2010,34(2):53-58.
[20]LU M Z,HU J B,ZENG R,et al.Imbalance mechanism and balanced control of capacitor voltage for a hybrid modular multilevel converter[J].IEEE Transactions on Pow er Electronics,2018,33(7):5686-5696.
[2]MARQUARDT R.Modular multilevel converter:An universal concept for HVDC-netw orks and extended DC-bus-applications[C]//Power Electronics Conference(IPEC),2010 International.IEEE,2010:502-507.
[3]LYU Y,LI C,HSIEH Y H,et al.Capacitor voltage ripple reduction w ith state trajectory analysis for modular multilevel converter[C]//Applied Pow er Electronics Conference and Exposition.IEEE,2017:1829-1836.
[4]徐政.柔性直流输电系统[M].北京:机械工业出版社,2013:65-66.
[5]KONSTANTINOU G,POU J,CAPELLA G J,et al.Interleaved operation of three-level neutral point clamped converter legs and reduction of circulating currents under SHE-PWM[J].IEEETransactions on Industrial Electronics,2016,63(6):3323-3332.
[6]PICAS R,CEBALLOS S,POU J,et al.Closed-loop discontinuous modulation technique for capacitor voltage ripples and sw itching losses reduction in modular multilevel converters[J].IEEETransactions on Pow er Electronics,2015,30(9):4714-4725.
[7]MERLIN M M C,GREEN T C.Cell capacitor sizing in multilevel converters:Cases of the modular multilevel converter and alternate arm converter[J].IET Pow er Electronics,2015,8(3):350-360.
[8]LI B,ZHANG Y,WANG G,et al.A modified modular multilevel converter w ith reduced capacitor voltage fluctuation[J].IEEETransactions on Industrial Electronics,2015,62(10):6108-6119.
[9]PICAS R,POU J,CEBALLOS S,et al.Optimal injection of harmonics in circulating currents of modular multilevel converters for capacitor voltage ripple minimization[C]//Ecce Asia Dow nunder.IEEE,2013:318-324.
[10]LI R,WILLIAMS B W,FLETCHER J E.Influence of third harmonic injection on modular multilevel converter-based highvoltage direct current transmission systems[J].IET Generation,Transmission&Distribution,2016,10(11):2764-2770.
[11]HUANG M,ZOU J L,MA X K.Hybrid modular multilevel converter w ith redistributed pow er to reduce submodule capacitor voltage fluctuation[J].IEEE Transactions on Pow er Electronics,2018,33(8):6595-6607.
[12]赵聪,李耀华,李子欣,等.混合模块化多电平变流器电容优化设计[J].中国电机工程学报,2017,37(19):5717-29.ZHAO Cong,LI Yaohua,LI Zixin,et al.Capacitance optimization design of hybrid modular multilevel converter[J].Proceedings of the CSEE,2017,37(19):5717-5729.
[13]张建坡,赵成勇,孙海峰,等.模块化多电平换流器改进拓扑结构及其应用[J].电工技术学报,2014,29(8):173-179.ZHANG Jianpo,ZHAO Chengyong,SUN Haifeng,et al.Improved topology of modular multilevel converter and application[J].Transactions of China Electrotechnical Society,2014,29(8):173-179.
[14]向往,林卫星,文劲宇,等.一种能够阻断直流故障电流的新型子模块拓扑及混合型模块化多电平换流器[J].中国电机工程学报,2014,34(29):5171-5179.XIANG Wang,LIN Weixing,WEN Jinyu,et al.A new topology of sub-modules w ith DC fault current blocking capability and a new type of hybrid M M C converter[J].Proceedings of the CSEE,2014,34(29):5171-5179.
[15]LI Xiaoqian,LIU Wenhua,SONG Qiang,et al.An enhanced MMCtopology w ith DC fault ride-through capability[C]//Proceedings of the 39th Annual Conference of the IEEE Industrial Electronics Society.IEEE,2013:6182-6188.
[16]李少华,王秀丽,李泰,等.混合式MMC及其直流故障穿越策略优化[J].中国电机工程学报,2016,36(7):1849-1858.LI Shaohua,WANG Xiuli,LI Tai,et al.Optimal design for hybrid M M C and its DC fault ride-through strategy[J].Proceedings of the CSEE,2016,36(7):1849-1858.
[17]LIN Weixing,JOVCIC D,NGUEFEU S,et al.Full bridge MMCconverter optimal design to HVDC operational requirements[J].IEEE Transactions on Pow er Delivery,2016,31(3):1342-1350.
[18]ZENG R,XU L,YAO L,et al.Design and operation of a hybrid modular multilevel converter[J].IEEE Transactions on Pow er Electronics,2015,30(3):1137-1146.
[19]刘钟淇,宋强,刘文华.基于模块化多电平变流器的轻型直流输电系统[J].电力系统自动化,2010,34(2):53-58.LIU Zhongqi,SONG Qiang,LIU Wenhua.VSC-HVDC system based on modular multilevel converters[J].Automation of Electric Pow er System,2010,34(2):53-58.
[20]LU M Z,HU J B,ZENG R,et al.Imbalance mechanism and balanced control of capacitor voltage for a hybrid modular multilevel converter[J].IEEE Transactions on Pow er Electronics,2018,33(7):5686-5696.