环网式MTDC系统直流故障电流初始阶段的高频等效分析模型
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摘要
对于电压源型变流器(voltage source converter,VSC)的多端直流(multi-terminal DC,MTDC)系统来说,一个主要的技术挑战是如何在直流故障的初始阶段快速地切除故障线路。然而,现有的保护技术以及故障分析方法研究大多基于数值仿真,缺乏可靠的理论分析。基于这一问题,提出了适用于环网式MTDC系统的高频等效分析模型,可用于计算系统发生直流故障初始阶段的故障电流。该模型将VSC的并联电容器等效为短路状态,因此可以用降阶的RL以及RLC电路模型来计算直流线路中起始阶段的故障电流。此外,本文也评估了常用的RL模型与高频等效模型这两种模型之间的误差,以及考虑不同故障位置时的计算误差。最后,基于PSCAD/EMTDC平台进行了大量的数值仿真验证,结果表明高频等效模型完全可以用来计算MTDC系统初始阶段的直流故障电流,且结果的准确性能够满足工程要求。
Isolation of the fault DC lines during the initial fault period after is a major challenge in the multi-terminal DC(MTDC)system based on voltage source converter(VSC).Existing protection schemes and fault analysis methods are mainly based on the numerical simulations,which are lack of the reliable theoretical analysis.In this paper,a high frequency equivalent model of VSC based MTDC system is proposed for the fault current calculation of the system in the initial stage of DC fault.In the proposed model,the parallel connected capacitors of VSCs are regarded as short-circuited,and the initial fault current calculation can be reduced as a reducedorder RL and RLC circuit.In addition,the errors between the transient fault current calculation based on the high frequency equivalent model and the fundamental RL model are also evaluated.Numerous simulation are studied based on PSCAD/EMTDC.The results demonstrate that the proposed high-frequency equivalent model can be utilized for initial DC fault analysis of VSC based MTDC system under different fault locations and the accuracy of results can meet the engineering requirements.
Isolation of the fault DC lines during the initial fault period after is a major challenge in the multi-terminal DC(MTDC)system based on voltage source converter(VSC).Existing protection schemes and fault analysis methods are mainly based on the numerical simulations,which are lack of the reliable theoretical analysis.In this paper,a high frequency equivalent model of VSC based MTDC system is proposed for the fault current calculation of the system in the initial stage of DC fault.In the proposed model,the parallel connected capacitors of VSCs are regarded as short-circuited,and the initial fault current calculation can be reduced as a reducedorder RL and RLC circuit.In addition,the errors between the transient fault current calculation based on the high frequency equivalent model and the fundamental RL model are also evaluated.Numerous simulation are studied based on PSCAD/EMTDC.The results demonstrate that the proposed high-frequency equivalent model can be utilized for initial DC fault analysis of VSC based MTDC system under different fault locations and the accuracy of results can meet the engineering requirements.
引文
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[16]LI C,ZHAO C,XU J,JI Y,et al.A pole-to-pole short-circuit fault current calculation method for DC grids[J].IEEE Transactions on Power Systems,2017,32(6):4943-4953.
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[18]XU L,YAO L Z,SASSE C.Grid integration of large DFIGbased wind farms using VSC transmission[J].IEEE Transactions on Power Systems,2007,22(3):976-984.
[2]李宇骏,徐政,刘高任.提高电力系统惯性水平的风电场和VSC-HVDC协同控制策略[J].中国电机工程学报,2014,34(34):6021-6031.LI Yujun,XU Zheng,LIU Gaoren.Coordinated control of wind farms and VSC-HVDC using capacitor energy and kinetic energy of DFIGs to improve inertia level of power systems[J].Proceedings of the CSEE,2014,34(34):6021-6031.
[3]LI Y J,ZHAO X,STERGAARD J,et al.Coordinated control strategies for offshore wind farm integration via VSC-HVDCfor system frequency support[J].IEEE Transactions on Energy Conversion,2017,32(3):843-856.
[4]BUCHER M K,FRANCK C M.Contribution of fault current sources in multi-terminal HVDC cable networks[J].IEEETransactions on Power Delivery,2013,28(3):1796-1803.
[5]YANG J,FLETCHER J E,O'REILLY J.Short-circuit and ground fault analyses and location in VSC-based dc network cables[J].IEEE Transactions on Industrial Electronics,2012,59(10):3827-3837.
[6]TANG L,OOI B T.Locating and isolating DC faults in multiterminal DC systems[J].IEEE Transactions on Power Delivery,2007,22(3):1877-1884.
[7]XU J,GOLE A M,ZHAO C.The use of averaged-value model of modular multilevel converter in DC grid[J].IEEE Transactions on Power Delivery,2015,30(2):519-528.
[8]LI R,XU L,HOLLIDAY D,et al.Continuous operation of radial multi-terminal HVDC systems under DC fault[J].IEEETransactions on Power Delivery,2016,31(1):351-361.
[9]MORCHED A S,TENCH G A,KUNDUR P.Accurate calculation of asymmetrical fault currents in comples power systems[J].IEEE Transactions on Power Systems,1981,PAS-100(8):3785-3790.
[10]SWEETING D.Applying IEC 60909,fault current calculations[J].IEEE Transactions on Industrial Application[J].2012,48(2):575-580.
[11]SALEH K A,ZEINELDIN H H,AL-HINAI A.A three-phase fault currents calculation method used for protection coordination analysis[C]//2014 IEEE PES T&D Conference.Exposition,July14-17,2014,Chicago,USA.New York:IEEE,2014:1-5.
[12]HAN P,WANG S.Parameter coordination of modular multilevel converter for robust design during DC pole to pole fault[C]//2012 China International Conference on Electricity Distribution,September 10-14,2012,Shanghai,China.New York:IEEE,2012:1-5.
[13]BUCHER M K,FRANCK C M.Analytic Approximation of fault current contribution from AC networks to MTDC networks during pole-to-ground faults[J].IEEE Transactions on Power Delivery,vol.2016,31(1):20-27.
[14]RAFFERTY J,XU L,MORROW D J.DC fault analysis of VSC based multi-terminal HVDC systems[C]//10th IET International Conference on AC and DC Power Transmission,December4-5,2012,Birmingham,UK.New York:IEEE,2012:1-6.
[15]ZHANG Z,XU Z.Short-circuit current calculation and performance requirement of HVDC breakers for MMC-MTDC systems[J].IEEE Transactions on Electrical&Electronic Engineering,2016,11(2):168-177.
[16]LI C,ZHAO C,XU J,JI Y,et al.A pole-to-pole short-circuit fault current calculation method for DC grids[J].IEEE Transactions on Power Systems,2017,32(6):4943-4953.
[17]BEERTEN J,BELMANS R.Analysis of power sharing and voltage deviations in droop-controlled DC grids[J].IEEETransactions on Power Systems,2013,28(4):4588-4597.
[18]XU L,YAO L Z,SASSE C.Grid integration of large DFIGbased wind farms using VSC transmission[J].IEEE Transactions on Power Systems,2007,22(3):976-984.