To reduce the probability of commutation failure(CF)of a line commutated converter based high-voltage direct current(LCC-HVDC)transmission,a DC chopper topology composed of power consumption sub-modules based on thyri...To reduce the probability of commutation failure(CF)of a line commutated converter based high-voltage direct current(LCC-HVDC)transmission,a DC chopper topology composed of power consumption sub-modules based on thyristor full-bridge module(TFB-PCSM)is proposed.Firstly,the mechanism of the proposed topology to mitigate CF is analyzed,and the working modes of TFB-PCSM in different operation states are introduced.Secondly,the coordinated control strategy between the proposed DC chopper and LCC-HVDC is designed,and the voltage-current stresses of the TFB-PCSMs are investigated.Finally,the ability to mitigate the CF issues and the fault recovery performance of LCC-HVDC system are studied in PSCAD/EMTDC.The results show that the probability of CF of LCC-HVDC is significantly reduced,and the performances of fault recovery are effectively improved by the proposed DC chopper.展开更多
该文基于系列文章1建立的电网换相换流器型高压直流(line commutated converter-based high voltage direct current,LCC-HVDC)阻抗模型,开展新能源基地经LCC-HVDC送出系统阻抗特性和振荡机理分析。首先,研究LCC-HVDC送端交流端口阻抗...该文基于系列文章1建立的电网换相换流器型高压直流(line commutated converter-based high voltage direct current,LCC-HVDC)阻抗模型,开展新能源基地经LCC-HVDC送出系统阻抗特性和振荡机理分析。首先,研究LCC-HVDC送端交流端口阻抗与阀本体交流阻抗、交流滤波器阻抗间的构成关系,分析直流线路、受端换流站、受端电网强度对送端换流站阀本体交流阻抗的主导影响;然后,研究送端换流站直流电流环对阀本体交流阻抗的重叠效应,分析送端换流站交流端口阻抗次/超同步频段负阻尼特性形成机理,并论述受端换流站和受端电网强度对送端交流端口阻抗特性的交互影响;接下来,建立新能源基地经LCC-HVDC送出系统等值模型,研究送端系统振荡边界条件,阐明LCC-HVDC对新能源并网点阻抗特性影响的变化规律,揭示直驱风机(permanent magnet synchronous generator,PMSG)、双馈风机(doubly-fed induction generator,DFIG)、光伏(photovoltaic,PV)不同类型新能源基地经LCC-HVDC送出系统次/超同步振荡机理;最后,不同类型新能源基地经LCC-HVDC送出系统仿真结果验证了该文提出的次/超同步振荡机理的正确性和通用性。展开更多
为研究分网接入方式下电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)系统的交互振荡模式及阻尼特征,基于系统的状态空间模型及系列文章(一)建立的运动方程模型,提取了表征逆变侧...为研究分网接入方式下电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)系统的交互振荡模式及阻尼特征,基于系统的状态空间模型及系列文章(一)建立的运动方程模型,提取了表征逆变侧电气与控制环节强耦合特性的多个弱阻尼交互振荡模式,研究了不同短路比工况下交互振荡模式的变化特征。在此基础上,通过复转矩系数法量化评估了整流侧/逆变侧内部自稳性路径及双极交互作用致稳性路径对主导交互振荡模式阻尼特性的贡献度。结果表明:1)不同短路比工况下交互振荡模式的阻尼比会进行重新分配;2)当逆变侧正负极短路比相差较大时,双极交互作用较弱,正负极系统的稳定性由2个交互振荡模式各自主导,且稳定性特征有所差异;3)当逆变侧正负极短路比相近时,双极间动态交互加强,交互振荡模式会同时主导参与系统两极的稳定性,正负极稳定性特征相似。展开更多
与常规直流相比,永富直流逆变站存在功率全送和功率分送运行方式,而其处于分网接入方式时电网换相换流器高压直流输电(line commutated converter based high voltage directcurrent,LCC-HVDC)系统的交互振荡模式及特征尚不明确。针对...与常规直流相比,永富直流逆变站存在功率全送和功率分送运行方式,而其处于分网接入方式时电网换相换流器高压直流输电(line commutated converter based high voltage directcurrent,LCC-HVDC)系统的交互振荡模式及特征尚不明确。针对这一特殊运行方式,采用模块化建模的思路建立可以反映系统电气/控制回路间交互耦合路径的运动方程模型。在此基础上,依据系统整流侧-逆变侧、正极-负极间的交互耦合路径分解得到影响系统主导模式稳定性的3条扰动传递路径,即整流侧内部自稳性路径、逆变侧内部自稳性路径、双极交互作用致稳性路径。最后,设置不同工况下的案例,量化评估不同作用路径提供的阻尼大小,并通过仿真验证运动方程模型及扰动传递路径分析结果的正确性,为后续研究分网接入方式下LCC-HVDC系统交互振荡模式的阻尼特征提供模型基础。展开更多
Voltage source converter(VSC) based high voltage direct current(HVDC) transmission is most suited for the wind farm as it allows flexibility for reactive power control in multi-terminal transmission lines and transmit...Voltage source converter(VSC) based high voltage direct current(HVDC) transmission is most suited for the wind farm as it allows flexibility for reactive power control in multi-terminal transmission lines and transmits low power over smaller distance. In this work, a new method has been proposed to detect the fault, identify the section of faults and classify the pole of the fault in DC transmission lines fed from onshore wind farm. In the proposed scheme, voltage signal from rectifier end terminal is extracted with sampling frequency of 1 k Hz given as the input to the detection, classification and section discrimi-nation module. In this work, severe AC faults are also considered for section discrimination. Proposed method uses fuzzy inference system(FIS) to carry out all relaying task. The reach setting of the relay is 99.9% of the transmission line. Besides, the protection covers and discriminates the grounding fault with fault resistance up to 300 Ω.Considering the results of the proposed method, it can beused effectively in real power network.展开更多
研究应用于电网换相高压直流输电系统(line commutate converter based high voltage direct current,LCCHVDC)弱受端的链式静止同步补偿器(static synchronous compensator,STATCOM)控制策略,提高其暂态控制性能。首先,对基于比例...研究应用于电网换相高压直流输电系统(line commutate converter based high voltage direct current,LCCHVDC)弱受端的链式静止同步补偿器(static synchronous compensator,STATCOM)控制策略,提高其暂态控制性能。首先,对基于比例谐振控制器的分相瞬时电流控制策略进行了论述;其次,将专用降压变的短路阻抗等效至STATCOM主回路,则STATCOM等效直挂在虚拟35kV交流系统,提出虚拟35kV电压瞬时值前馈及其与幅值前馈的在线切换方法、以虚拟35kV电压为控制目标的暂态分相控制策略;最后,将所提出的控制策略运用在国内首套应用于LCCHVDC弱受端换流站的STATCOM中,仿真结果、RTDS试验和工程现场试验验证了其合理性与有效性。展开更多
通过在电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)逆变侧交流母线装设静止同步补偿器(static synchronous compensator,STATCOM),来达到抑制换相失败的目的。然而研究发现...通过在电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)逆变侧交流母线装设静止同步补偿器(static synchronous compensator,STATCOM),来达到抑制换相失败的目的。然而研究发现,在弱交流系统工况下,STATCOM的控制系统(特别是交流电压控制外环)与LCC锁相环之间存在相互作用,会对后者的稳定可行域造成不利影响,进而可能引发整个混合系统的小干扰失稳现象。针对此现象,该文提出一种适用于弱交流系统下含STATCOM的LCC-HVDC系统的新型附加阻尼协调控制(supplementarydampingcoordination control,SDCC),该方法基于LCC锁相环输出频率信息,引入阻尼系数以附加分量形式反馈到STATCOM定交流电压控制器外环输入中。基于Matlab的特征根理论分析及基于PSCAD/EMTDC的详细电磁暂态仿真结果表明,提出的SDCC控制可以有效抑制含STATCOM的LCC-HVDC系统中LCC锁相环增益过大引起的系统小干扰失稳现象,从而提高系统的稳定裕度。展开更多
当电网换相换流器高压直流输电(linecommutated converter based high voltage direct current,LCC-HVDC)逆变侧交流母线处含有静止同步补偿器(static synchronous compensator,STATCOM)时,LCC-HVDC与STATCOM均需要各自的锁相环(ph...当电网换相换流器高压直流输电(linecommutated converter based high voltage direct current,LCC-HVDC)逆变侧交流母线处含有静止同步补偿器(static synchronous compensator,STATCOM)时,LCC-HVDC与STATCOM均需要各自的锁相环(phase-locked-loop,PLL)为其控制系统提供基准。该文考虑LCC与STATCOM锁相环各自动态建立含STATCOM的LCC-HVDC系统的小干扰模型,采用经典特征根分析方法,通过对比LCC-HVDC系统与含STATCOM的LCC-HVDC系统二者之间的锁相环与控制系统参数可行域的差异,研究STATCOM对LCC-HVDC小干扰稳定裕度的影响。最后,通过理论计算,对比有无STATCOM投入时LCC-HVDC系统在不同SCR与不同PLL参数下的最大传输有功功率(maximum available power,MAP)及临界短路比(critical short circuit ratio,CSCR)的变化规律。研究结果表明,当LCC-HVDC连接较弱系统时,控制系统之间的耦合作用对LCC锁相环的稳定可行域产生负面影响,可能引发由于LCC锁相环增益过大而导致的整个混合系统的小干扰失稳现象。展开更多
随着高压直流输电工程的不断投产,以及风电项目的增多,越来越多的风电场出现在电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)受端换流站近区,两者构成的系统存在振荡风险。为此,...随着高压直流输电工程的不断投产,以及风电项目的增多,越来越多的风电场出现在电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)受端换流站近区,两者构成的系统存在振荡风险。为此,该文针对直流受端馈入站与近区风电场系统的振荡特性展开研究。首先,建立并验证系统的状态空间模型,基于该模型计算出系统特征值,确定LCC-HVDC与风电场共同参与的振荡主导模式并进行参与因子分析。进一步地,通过对比是否接入LCC-HVDC的主导模式,得到LCC-HVDC的接入会削弱系统阻尼的结论。最后,从系统额定容量、交流系统短路比、风电场并网线路长度等方面探究系统稳定性的影响因素,并分析系统的不同短路比、潮流比对风机网侧换流器(grid-side converter,GSC)外环控制和换流站定电流控制器性能的影响。展开更多
当直驱风电场距离电网换相型高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)的整流站较近时,两者间的次同步交互作用机理及特性尚不明确,现有分析方法难以揭示扰动传递过程及子系统间的耦合关系...当直驱风电场距离电网换相型高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)的整流站较近时,两者间的次同步交互作用机理及特性尚不明确,现有分析方法难以揭示扰动传递过程及子系统间的耦合关系。针对上述问题,该文首先建立直驱风电场经LCC-HVDC送出系统的线性化模型,并基于系统闭环互联传递函数框图揭示次同步频率扰动在直驱风电场与LCC-HVDC之间的传递路径。然后,通过阻尼重构分离出次同步交互作用对次同步振荡(sub-synchronous oscillation,SSO)模式阻尼的影响,并分析控制器参数对SSO模式阻尼的影响。结果表明,直驱风电机组直流电容主导的SSO模式存在不稳定风险;直驱风电场与LCC-HVDC之间的扰动传递路径呈现"8"字型耦合关系,导致两者间存在次同步交互作用;直驱风电机组外环、LCC-HVDC定电流控制器的比例系数增大或积分系数减小时,SSO模式阻尼增大。展开更多
针对过往电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCCHVDC)交直流系统的强度指标缺乏严密理论基础的问题,该文研究计及LCC-HVDC交直流系统静态电压稳定的强度指标定义方法。首先,定...针对过往电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCCHVDC)交直流系统的强度指标缺乏严密理论基础的问题,该文研究计及LCC-HVDC交直流系统静态电压稳定的强度指标定义方法。首先,定量分析单馈入LCC-HVDC系统不同控制方式对交直流系统静态电压稳定的影响。其次,提出一种能够衡量交直流系统电压稳定裕度的综合短路比(integrated short circuit ratio,ISCR)强度指标。该指标考虑了交直流系统的实际潮流信息,能够同时应用于交直流系统的规划、设计和运行阶段;兼顾了LCC-HVDC系统的直流功率–电压动态特性,能够研究控制方式差异性对其影响;同时,基于静态电压稳定极限定义的临界综合短路比(critical integrated short circuit ratio,CISCR)指标取值恒为1,因而能够刻画互联交流电网对直流系统的临界电压支撑强度。最后,考虑额定运行工况和负荷动态变化过程的算例分析结果,及不同强度指标的对比分析,均表明了采用ISCR和CISCR指标的有效性。展开更多
当直驱风机(direct-drive permanent magnet synchronous generator,D-PMSG)位于电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)整流站近区时,系统的次同步振荡(subsynchronous os...当直驱风机(direct-drive permanent magnet synchronous generator,D-PMSG)位于电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)整流站近区时,系统的次同步振荡(subsynchronous oscillation,SSO)特性尚不清晰,相关研究有待开展。针对上述问题,基于D-PMSG经LCC-HVDC送出系统,利用模块化分块建模法建立小信号模型,用特征值与参与因子研究了系统SSO模式中D-PMSG与LCC-HVDC的参与情况,并用特征值分析了系统参数对SSO阻尼的影响。研究结果表明:存在D-PMSG与LCC-HVDC共同参与的SSO模式,且LCC-HVDC接入为系统SSO提供负阻尼;当D-PMSG输电线路阻抗、GSC控制器外环积分系数增大时,SSO模式阻尼减小;当GSC控制器外环比例系数、D-PMSG直流侧电容、D-PMSG的风速、LCC-HVDC定电流控制器的比例系数增大时,SSO模式阻尼增大。基于PSCAD/EMTDC时域仿真结果,验证理论分析的正确性。展开更多
近年来,电网换相换流器型高压直流输电(line commutated converter based on high voltage direct current,LCC-HVDC)系统的稳定性问题得到广泛关注,多位专家学者建议采用谐波状态空间(harmonic state space,HSS)等线性周期时变建模方...近年来,电网换相换流器型高压直流输电(line commutated converter based on high voltage direct current,LCC-HVDC)系统的稳定性问题得到广泛关注,多位专家学者建议采用谐波状态空间(harmonic state space,HSS)等线性周期时变建模方法对其分析。然而,HSS不可避免地提高了建模的复杂度与维数,在面对大规模交直流系统时具有局限性。同时,LCC-HVDC包含多类型谐波耦合,各部分耦合对稳定性的影响大小尚未得到充分论证。为此,文中以HSS为底层理论建立LCC-HVDC的耦合阻抗矩阵,揭示高压直流输电系统内部的谐波耦合机理。进一步,通过多频电路等效思想,提出三相系统多维阻抗的降维方法,将耦合阻抗矩阵无损降维成单入单出阻抗,以此分析不同次数的谐波耦合对阻抗特性与稳定性的影响。结果表明,考虑到13次谐波截断可以有效提升高压直流输电系统阻抗模型精度,但对稳定性分析结果的影响小于忽略工况变化、简化逆变侧带来的误差。展开更多
随着双馈风电和高压直流输电(high-voltage direct-current,HVDC)在电力系统中的比例越来越大,电网换相换流器型HVDC(line-commutated converter based HVDC,LCC-HVDC)与双馈风电场、弱电网互联时会存在交互稳定问题,且振荡频率会呈现...随着双馈风电和高压直流输电(high-voltage direct-current,HVDC)在电力系统中的比例越来越大,电网换相换流器型HVDC(line-commutated converter based HVDC,LCC-HVDC)与双馈风电场、弱电网互联时会存在交互稳定问题,且振荡频率会呈现频率耦合特征。针对LCC-HVDC整流站存在的频率耦合现象,采用3-D傅里叶变换建立阻抗模型,分析LCC产生频率耦合现象的机理,进行各个影响因素对LCC频率耦合程度的敏感性分析。最后,研究频率耦合特性对LCC整流站、双馈风场、弱电网互联系统稳定性分析的影响,并通过时域仿真验证所得结论。展开更多
In the voltage source converter based high-voltage direct current(VSC-HVDC)grids,fast and reliable protections are the key technologies.The traditional protection schemes are easily affected by fault resistance,line d...In the voltage source converter based high-voltage direct current(VSC-HVDC)grids,fast and reliable protections are the key technologies.The traditional protection schemes are easily affected by fault resistance,line distributed capacitance,etc.Meanwhile,the influence of fault current limiting strategy(FCLS)has not been fully considered.In this paper,the fault characteristics under FCLS and the feasibility of traditional travelling wave protections are analyzed.To improve the reliability and sensibility,a similarity comparison based pilot protection scheme is proposed,which focuses on the relationship between the fault characteristics and the state of the protected transmission line,with the establishment of a precise frequencydependent transmission line model.The criteria based on the similarity comparison calculated by cross-wavelet can identify the fault effectively.Meanwhile,the protection scheme can also endure the influence of error synchronization.Finally,the protection performance is verified in the PSCAD/EMTDC under different fault conditions.展开更多
基金supported by National Natural Science Foundation of China(No.51877077)。
文摘To reduce the probability of commutation failure(CF)of a line commutated converter based high-voltage direct current(LCC-HVDC)transmission,a DC chopper topology composed of power consumption sub-modules based on thyristor full-bridge module(TFB-PCSM)is proposed.Firstly,the mechanism of the proposed topology to mitigate CF is analyzed,and the working modes of TFB-PCSM in different operation states are introduced.Secondly,the coordinated control strategy between the proposed DC chopper and LCC-HVDC is designed,and the voltage-current stresses of the TFB-PCSMs are investigated.Finally,the ability to mitigate the CF issues and the fault recovery performance of LCC-HVDC system are studied in PSCAD/EMTDC.The results show that the probability of CF of LCC-HVDC is significantly reduced,and the performances of fault recovery are effectively improved by the proposed DC chopper.
文摘该文基于系列文章1建立的电网换相换流器型高压直流(line commutated converter-based high voltage direct current,LCC-HVDC)阻抗模型,开展新能源基地经LCC-HVDC送出系统阻抗特性和振荡机理分析。首先,研究LCC-HVDC送端交流端口阻抗与阀本体交流阻抗、交流滤波器阻抗间的构成关系,分析直流线路、受端换流站、受端电网强度对送端换流站阀本体交流阻抗的主导影响;然后,研究送端换流站直流电流环对阀本体交流阻抗的重叠效应,分析送端换流站交流端口阻抗次/超同步频段负阻尼特性形成机理,并论述受端换流站和受端电网强度对送端交流端口阻抗特性的交互影响;接下来,建立新能源基地经LCC-HVDC送出系统等值模型,研究送端系统振荡边界条件,阐明LCC-HVDC对新能源并网点阻抗特性影响的变化规律,揭示直驱风机(permanent magnet synchronous generator,PMSG)、双馈风机(doubly-fed induction generator,DFIG)、光伏(photovoltaic,PV)不同类型新能源基地经LCC-HVDC送出系统次/超同步振荡机理;最后,不同类型新能源基地经LCC-HVDC送出系统仿真结果验证了该文提出的次/超同步振荡机理的正确性和通用性。
文摘为研究分网接入方式下电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)系统的交互振荡模式及阻尼特征,基于系统的状态空间模型及系列文章(一)建立的运动方程模型,提取了表征逆变侧电气与控制环节强耦合特性的多个弱阻尼交互振荡模式,研究了不同短路比工况下交互振荡模式的变化特征。在此基础上,通过复转矩系数法量化评估了整流侧/逆变侧内部自稳性路径及双极交互作用致稳性路径对主导交互振荡模式阻尼特性的贡献度。结果表明:1)不同短路比工况下交互振荡模式的阻尼比会进行重新分配;2)当逆变侧正负极短路比相差较大时,双极交互作用较弱,正负极系统的稳定性由2个交互振荡模式各自主导,且稳定性特征有所差异;3)当逆变侧正负极短路比相近时,双极间动态交互加强,交互振荡模式会同时主导参与系统两极的稳定性,正负极稳定性特征相似。
文摘与常规直流相比,永富直流逆变站存在功率全送和功率分送运行方式,而其处于分网接入方式时电网换相换流器高压直流输电(line commutated converter based high voltage directcurrent,LCC-HVDC)系统的交互振荡模式及特征尚不明确。针对这一特殊运行方式,采用模块化建模的思路建立可以反映系统电气/控制回路间交互耦合路径的运动方程模型。在此基础上,依据系统整流侧-逆变侧、正极-负极间的交互耦合路径分解得到影响系统主导模式稳定性的3条扰动传递路径,即整流侧内部自稳性路径、逆变侧内部自稳性路径、双极交互作用致稳性路径。最后,设置不同工况下的案例,量化评估不同作用路径提供的阻尼大小,并通过仿真验证运动方程模型及扰动传递路径分析结果的正确性,为后续研究分网接入方式下LCC-HVDC系统交互振荡模式的阻尼特征提供模型基础。
文摘Voltage source converter(VSC) based high voltage direct current(HVDC) transmission is most suited for the wind farm as it allows flexibility for reactive power control in multi-terminal transmission lines and transmits low power over smaller distance. In this work, a new method has been proposed to detect the fault, identify the section of faults and classify the pole of the fault in DC transmission lines fed from onshore wind farm. In the proposed scheme, voltage signal from rectifier end terminal is extracted with sampling frequency of 1 k Hz given as the input to the detection, classification and section discrimi-nation module. In this work, severe AC faults are also considered for section discrimination. Proposed method uses fuzzy inference system(FIS) to carry out all relaying task. The reach setting of the relay is 99.9% of the transmission line. Besides, the protection covers and discriminates the grounding fault with fault resistance up to 300 Ω.Considering the results of the proposed method, it can beused effectively in real power network.
文摘研究应用于电网换相高压直流输电系统(line commutate converter based high voltage direct current,LCCHVDC)弱受端的链式静止同步补偿器(static synchronous compensator,STATCOM)控制策略,提高其暂态控制性能。首先,对基于比例谐振控制器的分相瞬时电流控制策略进行了论述;其次,将专用降压变的短路阻抗等效至STATCOM主回路,则STATCOM等效直挂在虚拟35kV交流系统,提出虚拟35kV电压瞬时值前馈及其与幅值前馈的在线切换方法、以虚拟35kV电压为控制目标的暂态分相控制策略;最后,将所提出的控制策略运用在国内首套应用于LCCHVDC弱受端换流站的STATCOM中,仿真结果、RTDS试验和工程现场试验验证了其合理性与有效性。
文摘通过在电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)逆变侧交流母线装设静止同步补偿器(static synchronous compensator,STATCOM),来达到抑制换相失败的目的。然而研究发现,在弱交流系统工况下,STATCOM的控制系统(特别是交流电压控制外环)与LCC锁相环之间存在相互作用,会对后者的稳定可行域造成不利影响,进而可能引发整个混合系统的小干扰失稳现象。针对此现象,该文提出一种适用于弱交流系统下含STATCOM的LCC-HVDC系统的新型附加阻尼协调控制(supplementarydampingcoordination control,SDCC),该方法基于LCC锁相环输出频率信息,引入阻尼系数以附加分量形式反馈到STATCOM定交流电压控制器外环输入中。基于Matlab的特征根理论分析及基于PSCAD/EMTDC的详细电磁暂态仿真结果表明,提出的SDCC控制可以有效抑制含STATCOM的LCC-HVDC系统中LCC锁相环增益过大引起的系统小干扰失稳现象,从而提高系统的稳定裕度。
文摘当电网换相换流器高压直流输电(linecommutated converter based high voltage direct current,LCC-HVDC)逆变侧交流母线处含有静止同步补偿器(static synchronous compensator,STATCOM)时,LCC-HVDC与STATCOM均需要各自的锁相环(phase-locked-loop,PLL)为其控制系统提供基准。该文考虑LCC与STATCOM锁相环各自动态建立含STATCOM的LCC-HVDC系统的小干扰模型,采用经典特征根分析方法,通过对比LCC-HVDC系统与含STATCOM的LCC-HVDC系统二者之间的锁相环与控制系统参数可行域的差异,研究STATCOM对LCC-HVDC小干扰稳定裕度的影响。最后,通过理论计算,对比有无STATCOM投入时LCC-HVDC系统在不同SCR与不同PLL参数下的最大传输有功功率(maximum available power,MAP)及临界短路比(critical short circuit ratio,CSCR)的变化规律。研究结果表明,当LCC-HVDC连接较弱系统时,控制系统之间的耦合作用对LCC锁相环的稳定可行域产生负面影响,可能引发由于LCC锁相环增益过大而导致的整个混合系统的小干扰失稳现象。
文摘随着高压直流输电工程的不断投产,以及风电项目的增多,越来越多的风电场出现在电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)受端换流站近区,两者构成的系统存在振荡风险。为此,该文针对直流受端馈入站与近区风电场系统的振荡特性展开研究。首先,建立并验证系统的状态空间模型,基于该模型计算出系统特征值,确定LCC-HVDC与风电场共同参与的振荡主导模式并进行参与因子分析。进一步地,通过对比是否接入LCC-HVDC的主导模式,得到LCC-HVDC的接入会削弱系统阻尼的结论。最后,从系统额定容量、交流系统短路比、风电场并网线路长度等方面探究系统稳定性的影响因素,并分析系统的不同短路比、潮流比对风机网侧换流器(grid-side converter,GSC)外环控制和换流站定电流控制器性能的影响。
文摘当直驱风电场距离电网换相型高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)的整流站较近时,两者间的次同步交互作用机理及特性尚不明确,现有分析方法难以揭示扰动传递过程及子系统间的耦合关系。针对上述问题,该文首先建立直驱风电场经LCC-HVDC送出系统的线性化模型,并基于系统闭环互联传递函数框图揭示次同步频率扰动在直驱风电场与LCC-HVDC之间的传递路径。然后,通过阻尼重构分离出次同步交互作用对次同步振荡(sub-synchronous oscillation,SSO)模式阻尼的影响,并分析控制器参数对SSO模式阻尼的影响。结果表明,直驱风电机组直流电容主导的SSO模式存在不稳定风险;直驱风电场与LCC-HVDC之间的扰动传递路径呈现"8"字型耦合关系,导致两者间存在次同步交互作用;直驱风电机组外环、LCC-HVDC定电流控制器的比例系数增大或积分系数减小时,SSO模式阻尼增大。
文摘针对过往电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCCHVDC)交直流系统的强度指标缺乏严密理论基础的问题,该文研究计及LCC-HVDC交直流系统静态电压稳定的强度指标定义方法。首先,定量分析单馈入LCC-HVDC系统不同控制方式对交直流系统静态电压稳定的影响。其次,提出一种能够衡量交直流系统电压稳定裕度的综合短路比(integrated short circuit ratio,ISCR)强度指标。该指标考虑了交直流系统的实际潮流信息,能够同时应用于交直流系统的规划、设计和运行阶段;兼顾了LCC-HVDC系统的直流功率–电压动态特性,能够研究控制方式差异性对其影响;同时,基于静态电压稳定极限定义的临界综合短路比(critical integrated short circuit ratio,CISCR)指标取值恒为1,因而能够刻画互联交流电网对直流系统的临界电压支撑强度。最后,考虑额定运行工况和负荷动态变化过程的算例分析结果,及不同强度指标的对比分析,均表明了采用ISCR和CISCR指标的有效性。
文摘当直驱风机(direct-drive permanent magnet synchronous generator,D-PMSG)位于电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)整流站近区时,系统的次同步振荡(subsynchronous oscillation,SSO)特性尚不清晰,相关研究有待开展。针对上述问题,基于D-PMSG经LCC-HVDC送出系统,利用模块化分块建模法建立小信号模型,用特征值与参与因子研究了系统SSO模式中D-PMSG与LCC-HVDC的参与情况,并用特征值分析了系统参数对SSO阻尼的影响。研究结果表明:存在D-PMSG与LCC-HVDC共同参与的SSO模式,且LCC-HVDC接入为系统SSO提供负阻尼;当D-PMSG输电线路阻抗、GSC控制器外环积分系数增大时,SSO模式阻尼减小;当GSC控制器外环比例系数、D-PMSG直流侧电容、D-PMSG的风速、LCC-HVDC定电流控制器的比例系数增大时,SSO模式阻尼增大。基于PSCAD/EMTDC时域仿真结果,验证理论分析的正确性。
文摘近年来,电网换相换流器型高压直流输电(line commutated converter based on high voltage direct current,LCC-HVDC)系统的稳定性问题得到广泛关注,多位专家学者建议采用谐波状态空间(harmonic state space,HSS)等线性周期时变建模方法对其分析。然而,HSS不可避免地提高了建模的复杂度与维数,在面对大规模交直流系统时具有局限性。同时,LCC-HVDC包含多类型谐波耦合,各部分耦合对稳定性的影响大小尚未得到充分论证。为此,文中以HSS为底层理论建立LCC-HVDC的耦合阻抗矩阵,揭示高压直流输电系统内部的谐波耦合机理。进一步,通过多频电路等效思想,提出三相系统多维阻抗的降维方法,将耦合阻抗矩阵无损降维成单入单出阻抗,以此分析不同次数的谐波耦合对阻抗特性与稳定性的影响。结果表明,考虑到13次谐波截断可以有效提升高压直流输电系统阻抗模型精度,但对稳定性分析结果的影响小于忽略工况变化、简化逆变侧带来的误差。
文摘随着双馈风电和高压直流输电(high-voltage direct-current,HVDC)在电力系统中的比例越来越大,电网换相换流器型HVDC(line-commutated converter based HVDC,LCC-HVDC)与双馈风电场、弱电网互联时会存在交互稳定问题,且振荡频率会呈现频率耦合特征。针对LCC-HVDC整流站存在的频率耦合现象,采用3-D傅里叶变换建立阻抗模型,分析LCC产生频率耦合现象的机理,进行各个影响因素对LCC频率耦合程度的敏感性分析。最后,研究频率耦合特性对LCC整流站、双馈风场、弱电网互联系统稳定性分析的影响,并通过时域仿真验证所得结论。
基金supported by National Natural Science Foundation of ChinaState Grid Joint Fund for Smart Grid(No.U2066210)National Natural Science Foundation of China(No.52007003)。
文摘In the voltage source converter based high-voltage direct current(VSC-HVDC)grids,fast and reliable protections are the key technologies.The traditional protection schemes are easily affected by fault resistance,line distributed capacitance,etc.Meanwhile,the influence of fault current limiting strategy(FCLS)has not been fully considered.In this paper,the fault characteristics under FCLS and the feasibility of traditional travelling wave protections are analyzed.To improve the reliability and sensibility,a similarity comparison based pilot protection scheme is proposed,which focuses on the relationship between the fault characteristics and the state of the protected transmission line,with the establishment of a precise frequencydependent transmission line model.The criteria based on the similarity comparison calculated by cross-wavelet can identify the fault effectively.Meanwhile,the protection scheme can also endure the influence of error synchronization.Finally,the protection performance is verified in the PSCAD/EMTDC under different fault conditions.