A Circulating Current Suppressing Method for Modular Multilevel Converter Under Unbalanced Grid Voltage
Liang Yingyu1, Zhang Tao2, Liu Jianzheng3, Yang Qixun1, Liu Shu2
1.State Key Laboratory for Alternate Electrical Power System With Renewable Energy Sources North China Electric Power University Beijing 102206 China 2.Beijing Sifang Automation Co.Ltd Beijing 100085 China 3.State Key Laboratory of Control and Simulation of Power Systems and Generation Equipments Tsinghua University Beijing 100084 China
Abstract The circulating current within modular multilevel converters increases the peak/RMS value of the arm currents and the magnitude of the sub-module voltage fluctuation,and thus affects the safe operation of power electronic devices.Therefore,it is necessary to eliminate the circulating current.It is pointed that,under the unbalanced grid voltage,the second three-phase harmonic circulating current can be decomposed into positive,negative and,zero sequence components and the dc component of the three-phase circulating current is not necessary equal to each other by deriving and analyzing the phase unit instantaneous energy.The formulas of the dc component of the circulating current,i.e.the circulating current reference,are derived and a novel circulating current suppressing method,which is based on proportional-integral (PI) regulator and vector proportional-integral (VPI) regulator in parallel,is proposed.The tuning principle of the related control parameters is given.The novel circulating current suppressing method can be executed in the abc stationary reference frame so that coordinate transformation is not needed and thus it has a simple control structure.Besides that,the positive,negative,and zero sequence components of the second harmonic circulating current can be eliminated simultaneously and the method can achieve good control performance under balanced and unbalanced grid voltages.A 21-level MMC simulation model is set up in the PSCAD/EMTDC in order to validate the correctness and effectiveness of the proposed method.
Liang Yingyu,Zhang Tao,Liu Jianzheng等. A Circulating Current Suppressing Method for Modular Multilevel Converter Under Unbalanced Grid Voltage[J]. Transactions of China Electrotechnical Society, 2016, 31(9): 120-128.
[1] 孔明,汤广福,贺之渊,等.不对称交流电网下MMC-HVDC输电系统的控制策略[J].中国电机工程学报,2013,33(28):41-49. Kong Ming,Tang Guangfu,He Zhiyuan,et al.A control strategy for modular multilevel converter based HVDC of unbalanced AC systems[J].Proceedings of the CSEE,2013,33(28):41-49. [2] Deng F,Chen Z.A control method for voltage balancing in modular multilevel converters[J].IEEE Transactions on Power Electronics,2014,29(1):66-76. [3] Li Z,Wang P,Chu Z,et al.An inner current suppressing method for modular multilevel converters[J].IEEE Transactions on Power Electronics,2013,28(11):4873-4879. [4] 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].IEEE Transactions on Power Electronics,2015,30(1):387-397. [5] Tu Qingrui,Xu Zheng,Xu Lie.Reduced switching-frequency modulation and circulating current suppression for modular multilevel converters[J].IEEE Transactions on Power Delivery,2011,26(3):2009-2017. [6] Zhou Y,Jiang D,Guo J,et al.Analysis and control of modular multilevel converters under unbalanced conditions[J].IEEE Transactions on Power Delivery,2013,28(4):1986-1995. [7] 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. [8] Tu Qingrui,Xu Zheng,Huang H,et al.Parameter design principle of the arm inductor in modular multilevel converter based HVDC[C]//2010 International Conference on Power System Technology,Hangzhou,China,2010:1-6. [9] 屠卿瑞,徐政,郑翔,等.模块化多电平换流器型直流输电内部环流机理分析[J].高电压技术,2010,36(2):547-552. Tu Qingrui,Xu Zheng,Zheng Xiang,et al.Mechanism analysis on the circulating current in modular multilevel converter based HVDC[J].High Voltage Engineering,2010,36(2):547-552. [10]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):85-89,129. 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):85-89,129. [11]Antonopoulos A,Angquist L,Nee H P.On dynamics and voltage control of the modular multilevel converter[C]//13th European Conference on Power Electronics and Applications,Barcelona,Spain,2009. [12]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. [13]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].IEEE Transactions on Power Electronics,2015,30(1):408-421. [14]Lascu C,Asiminoaei L,Boldea I,et al.High performance current controller for selective harmonic compensation in active power filters[J].IEEE Transactions on Power Electronics,2007,22(5):1826-1835. [15]Mwasilu F,Justo J J,Ro K S,et al.Improvement of dynamic performance of doubly fed induction generator-based wind turbine power system under an unbalanced grid voltage condition[J].IET Renewable Power Generation,2012,6(6):424-434. [16]Trinh Q N,Lee H H.An advanced current control strategy for three-phase shunt active power filters[J].IEEE Transactions on Industrial Electronics,2013,60(12):5400-5410. [17]年珩,沈永波,宋亦鹏.不平衡及谐波电网电压下并网逆变器的直接功率控制策略[J].电网技术,2014,38(6):1452-1458. Nian Heng,Shen Yongbo,Song Yipeng.Direct power control strategy of grid connected inverter under unbalanced and harmonic grid voltage[J].Power System Technology,2014,38(6):1452-1458. [18]年珩,宋亦鹏.谐波电网下基于矢量比例积分电流调节器的双馈异步发电机运行控制技术[J].中国电机工程学报,2013,33(6):101-111. Nian Heng,Song Yipeng.DFIG operation control strategy under distorted grid conditions based on VPI current regulators[J].Proceedings of the CSEE,2013,33(6):101-111. [19]Yazdani A,Iravani R.Dynamic model and control of the NPC-based back-to-back HVDC system[J].IEEE Transactions on Power Delivery,2006,21(1):414-424. [20]章玮,王宏胜,任远,等.不对称电网电压下三相并网型逆变器的控制[J].电工技术学报,2010,25(12):103-110. Zhang Wei,Wang Hongsheng,Ren Yuan,et al.Investigation on control of three-phase grid-connected inverters under unbalanced grid voltage conditions[J].Transactions of China Electrotechnical Society,2010,25(12):103-110.
2016, Vol. 31 
