基于平均模型的高压链式STATCOM功率模块直流电压失控机理
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摘要
高压链式STATCOM在重载时功率模块的直流电容电压容易控制,在空载时却可能发生失控。空载失控机理分析是解决该问题的关键。针对该机理问题,主要开展了如下研究:分别将串联阻抗、并联阻抗和控制电源能耗化简并绘制出等效电路图。基于平均模型将直流电容电压分解为直流分量和交流分量,交流电流分解为基波和谐波分量。并利用调制度等效开关函数,得到单个功率模块直流电容电压的数学方程。根据稳定性分析的小信号法,分别计算功率模块直流电容电压稳态分量和扰动分量。针对未采取均压控制和采取均压控制两种情况,推导并计算任意两个功率模块在重载和空载下的直流电压平衡方程,证明了换流链的直流电压平衡与调制度、开关频率等因素有关。提出一种改进均压控制策略,在空载时增加开关频率来改善均压性能。最后,经过35 kV装置的仿真和试验,结果表明:在空载时所提均压控制策略能够实现功率模块直流电容电压均衡,从而提高了装置的可靠性。
Cascaded STATCOM under high voltage is easily balanced during heavy loads but probably out of control at empty loads. Research on the mechanism of out-of-control at empty loads is the key to solution of this problem.Consequently, we emphatically research the main contents include as follows: ①Equivalent circuit diagram of serial impedance, parallel impedance and control power consumption are simplified and drawn, respectively. ②According to the average modeling theory, the DC capacitor voltage is decomposed into the direct current component and the alternating current component, the alternating current is decomposed into the fundamental wave and the harmonic component,and the modulation degree equivalent switch function is used to list the mathematical expression of the DC voltage of the single power module. ③According to the small signal method of stability analysis, the steady-state component and the disturbance component of the DC capacitor voltage of a power module are calculated. ④In the two cases whether the DC voltage balance control is adopted or not, the DC voltage balance equation of any two power modules of the convert chain at the heavy load and the light load is deduced and calculated, and the DC voltage balance is related to the modulation de-gree, switching frequency, and other factors.(5)An improved DC voltage balance control strategy is proposed. The switching frequency is increased to improve the voltage balancing performance at empty load. In the end, simulations and tests are used to compare the results under four typical operating conditions. The results show that the voltage-sharing control strategy proposed under empty-load conditions can achieve DC capacitor voltage equalization of the power module to increase reliability of the cascaded STATCOM.
Cascaded STATCOM under high voltage is easily balanced during heavy loads but probably out of control at empty loads. Research on the mechanism of out-of-control at empty loads is the key to solution of this problem.Consequently, we emphatically research the main contents include as follows: ①Equivalent circuit diagram of serial impedance, parallel impedance and control power consumption are simplified and drawn, respectively. ②According to the average modeling theory, the DC capacitor voltage is decomposed into the direct current component and the alternating current component, the alternating current is decomposed into the fundamental wave and the harmonic component,and the modulation degree equivalent switch function is used to list the mathematical expression of the DC voltage of the single power module. ③According to the small signal method of stability analysis, the steady-state component and the disturbance component of the DC capacitor voltage of a power module are calculated. ④In the two cases whether the DC voltage balance control is adopted or not, the DC voltage balance equation of any two power modules of the convert chain at the heavy load and the light load is deduced and calculated, and the DC voltage balance is related to the modulation de-gree, switching frequency, and other factors.(5)An improved DC voltage balance control strategy is proposed. The switching frequency is increased to improve the voltage balancing performance at empty load. In the end, simulations and tests are used to compare the results under four typical operating conditions. The results show that the voltage-sharing control strategy proposed under empty-load conditions can achieve DC capacitor voltage equalization of the power module to increase reliability of the cascaded STATCOM.
引文
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[13]陶兴华,李永东,宋义超,等.H桥级联型整流器直流电压平衡控制改进算法[J].高电压技术,2012,38(2):505-512.TAO Xinghua,LI Yongdong,SONG Yichao,et al.Improved DC-link voltage balancing method for cascaded H-bridge rectifier[J].High Voltage Engineering,2012,38(2):505-512.
[14]常非,王一,梅红明,等.35 k V直挂式角接链式STATCOM控制策略[J].高电压技术,2016,42(1):121-126.CHANG Fei,WANG Yi,MEI Hongming,et al.Control strategies of35 kV transformerless delta connection chain STATCOM[J].High Voltage Engineering,2016,42(1):121-126.
[15]于雁南,杨荣峰,徐殿国,等.级联H桥SVG的无差拍控制[J].高电压技术,2017,43(1):50-58.YU Yannan,YANG Rongfeng,XU Dianguo,et al.Deadbeat control of cascaded H-bridge static var generator[J].High Voltage Engineering,2017,43(1):50-58.
[16]DAVOUDI A,JATSKEVICH J.Realization of parasitics in state-space average-value modeling of PWM DC-DC converters[J].IEEE Transactions on Power Electronics,2017,21(4):1142-1147.
[17]BALIKCI A,AKPINAR E.A multilevel converter with reduced number of switches in STATCOM for load balancing[J].Electric Power Systems Research,2015,164(123):164-173.
[18]吴国营,张波.电流模式变换器的完整小信号模型及环路补偿[J].电工技术学报,2008,23(10):83-87.WU Guoying,ZHANG Bo.Whole small signal model and compensation for regulators with current programmed mode[J].Transactions of China Electrotechnical Society,2008,23(10):83-87.
[19]贺明智,许建平,游小杰,等.环路延时对数字峰值电压控制开关变换器瞬态性能的影响[J].中国电机工程学报,2009,29(6):1-7.HE Mingzhi,XU Jianping,YOU Xiaojie,et al.Time delay effect on transient performance of digital peak voltage controlled switching converter[J].Proceedings of the CSEE,2009,29(6):1-7.
[2]张扬,常亮,杨小品.±100 Mvar高压STATCOM直接电流分相谐振控制参数整定方法及RTDS仿真实验[J].电力系统保护与控制,2016,44(15):27-32.ZHANG Yang,CHANG Liang,YANG Xiaopin.Parameter setting on independent phase resonant control of STATCOM under higher voltage and RTDS simulation experiment[J].Power System Protection and Control,2016,44(15):27-32.
[3]FARIVAR G,TOWNSEND C D,HREDZAK B,et al.Low-capacitance cascaded H-bridge multilevel STATCOM[J].IEEE Transactions on Power Electronics,2017,32(3):1744-1754.
[4]耿俊成,刘文华,袁志昌.链式STATCOM电容电压不平衡现象研究(一)仿真和试验[J].电力系统自动化,2003,27(16):53-57.GENG Juncheng,LIU Wenhua,YUAN Zhichang.Research on the voltage unbalance of DC capacitors of cascade STATCOM.part one:simulations and experiments[J].Automation of Electric Power Systems,2003,27(16):53-57.
[5]耿俊成,刘文华,袁志昌.链式STATCOM电容电压不平衡现象研究(二)数学模型[J].电力系统自动化,2003,27(17):35-39.GENG Juncheng,LIU Wenhua,YUAN Zhichang.Research on the voltage unbalance of DC capacitors of cascade STATCOM.Part Two Mathematical Model[J].Automation of Electric Power Systems,2003,27(17):35-39.
[6]LIU Z,LIU B,DUAN S,et al.A novel DC capacitor voltage balance control method for cascade multilevel STATCOM[J].IEEE Transactions on Power Electronics,2012,27(1):14-27.
[7]赵波,郭剑波,周飞.链式STATCOM相间直流电压平衡控制策略[J].中国电机工程学报,2012,32(34):36-41.ZHAO Bo,GUO Jianbo,ZHOU Fei.DC voltage balance control strategy among phases for cascaded STATCOM[J].Proceedings of the CSEE,2012,32(34):36-41
[8]冯宇鹏,王先为,吴金龙,等.基于负序电流前馈的星型链式STATCOM链间均压策略[J].电网技术,2016,40(5):1502-1508.FENG Yupeng,WANG Xianwei,WU Jinlong,et al.Clustered DCvoltage balancing control of star-connected cascaded STATCOMbased on negative current feed-forward control[J].Power System Technology,2016,40(5):1502-1508.
[9]史丽萍,曹雪祥,陈丽兵,等.改进的STATCOM相内直流电容电压平衡控制策略[J].电力系统自动化,2015,39(2):119-126.SHI Liping,CAO Xuexiang,CHEN Libing,et al.An improved DCcapacitor voltage balance control strategy among phases for STAT-COM[J].Automation of Electric Power Systems,2015,39(2):119-126.
[10]姚钢,方瑞丰,李东东,等.链式静止同步补偿器的直流电容电压平衡控制策略[J].电力系统保护与控制,2015,43(18):23-30.YAO Gang,FANG Ruifeng,LI Dongdong,et al.DC capacitor voltage balancing control of cascaded static synchronous compensator[J].Power System Protection and Control,2015,43(18):23-30.
[11]郭小强,李建,张学,等.电网电压畸变不平衡情况下三相PWM整流器无锁相环直流母线恒压控制策略[J].中国电机工程学报,2015,35(8):2002-2008.GUO Xiaoqiang,LI Jian,ZHANG Xue,et al.Constant DC voltage control strategy for three-phase PWM rectifier without phase-locked loop under distorted and unbalanced conditions[J].Proceedings of the CSEE,2015,35(8):2002-2008.
[12]吴丽然,吴命利.基于调制波重构的级联H桥型变流器直流电压均衡控制原理分析[J].电工技术学报,2017,32(22):1-12.WU Liran,WU Mingli.Principle of DC voltage balancing control strategy based on modulation signal reconstruction for cascaded H-bridge converter[J].Transactions of China Electrotechnical Society,2017,32(22):1-12.
[13]陶兴华,李永东,宋义超,等.H桥级联型整流器直流电压平衡控制改进算法[J].高电压技术,2012,38(2):505-512.TAO Xinghua,LI Yongdong,SONG Yichao,et al.Improved DC-link voltage balancing method for cascaded H-bridge rectifier[J].High Voltage Engineering,2012,38(2):505-512.
[14]常非,王一,梅红明,等.35 k V直挂式角接链式STATCOM控制策略[J].高电压技术,2016,42(1):121-126.CHANG Fei,WANG Yi,MEI Hongming,et al.Control strategies of35 kV transformerless delta connection chain STATCOM[J].High Voltage Engineering,2016,42(1):121-126.
[15]于雁南,杨荣峰,徐殿国,等.级联H桥SVG的无差拍控制[J].高电压技术,2017,43(1):50-58.YU Yannan,YANG Rongfeng,XU Dianguo,et al.Deadbeat control of cascaded H-bridge static var generator[J].High Voltage Engineering,2017,43(1):50-58.
[16]DAVOUDI A,JATSKEVICH J.Realization of parasitics in state-space average-value modeling of PWM DC-DC converters[J].IEEE Transactions on Power Electronics,2017,21(4):1142-1147.
[17]BALIKCI A,AKPINAR E.A multilevel converter with reduced number of switches in STATCOM for load balancing[J].Electric Power Systems Research,2015,164(123):164-173.
[18]吴国营,张波.电流模式变换器的完整小信号模型及环路补偿[J].电工技术学报,2008,23(10):83-87.WU Guoying,ZHANG Bo.Whole small signal model and compensation for regulators with current programmed mode[J].Transactions of China Electrotechnical Society,2008,23(10):83-87.
[19]贺明智,许建平,游小杰,等.环路延时对数字峰值电压控制开关变换器瞬态性能的影响[J].中国电机工程学报,2009,29(6):1-7.HE Mingzhi,XU Jianping,YOU Xiaojie,et al.Time delay effect on transient performance of digital peak voltage controlled switching converter[J].Proceedings of the CSEE,2009,29(6):1-7.