摘要
电网不对称故障会产生电压负序和零序分量,并激发换流变压器注入更大的低次谐波,增大功率器件承受的电气应力,且基于电压源换流器高压直流输电(voltage source converter based high voltage direct current,VSC-HVDC)系统的交流阻抗在变压器特征谐波频段大部分呈容性,使系统在该频段易发生谐振,导致换流站热过载和波形质量问题凸显。因此,讨论换流站交、直流侧谐波相互作用的机理,建立从交流侧看入换流站的正负序交流低频阻抗模型,提出等效增大换流站输出阻抗支路谐波电阻的方法,全面扼制换流站输出阻抗支路谐波电流,且不影响系统基波电阻。利用电力系统仿真软件EMTDC建立了VSC-HVDC模型,对柔性直流输电系统中的谐振问题以及主动抑制方法进行仿真研究。仿真结果表明,所提出控制策略能有效抑制谐振过电压,因此,提高了柔性直流输电系统不对称故障下运行的安全性。
Converter transformer will produce more lower-order harmonics under core saturation due to grid unbalance fault, which increases the electrical stress of power devices, simultaneously may be amplified by network resonance between finite ac network and capacitive AC impedance of voltage source converter based high voltage direct current（VSC-HVDC） transmission system at low frequency band. In the paper, based on the positive-sequence and negative-sequence impedance models of converter established at low frequency band, resonance problem was analyzed and the factor in determining resonance frequency was obtained. A novel method to suppress the resonant overvoltage and over current was proposed using a virtual harmonic resistor. The virtual harmonic resistor is an additional algorithm that simulates the role of a resistor in the output impedance branch of converter but without influence on its fundamental frequency resistor. Simulation results from software of electro-magnetic transient in DC system（EMTDC） show that the proposed control strategy can suppress the resonant overvoltage and improve the safety of VSC-HVDC under the condition of unbalanced fault.
出处
《中国电机工程学报》
EI
CSCD
北大核心
2014年第30期5352-5359,共8页
Proceedings of the CSEE
基金
国家自然科学基金项目(51277013
51277014)
湖南省研究生创新项目(CX2013B373)~~
关键词
阻抗频率特性
谐振
不对称故障
虚拟谐波电阻
柔性直流输电系统
impedance frequency characteristics resonance
unbalanced fault
virtual harmonic resistor
voltage source converter based high voltage direct current（VSC-HVDC）
