中文摘要：

为了准确评估混合双馈入直流系统中电网换相换流器高压直流输电（line commutated converter based high voltage direct current,LCC-HVDC）子系统的受端系统强度,对LCC-HVDC子系统的有效短路比进行研究。第一,基于牛顿最优潮流算法,分析混合双馈入直流系统中电压源换流器高压直流输电（voltage source converter based HVDC,VSC-HVDC）子系统采用不同的功率输送方向和控制方式时,对LCC-HVDC子系统的交流系统电压支撑强度的影响关系。第二,计算VSC-HVDC子系统的等效阻抗,提出能够有效评估混合双馈入系统中LCC-HVDC子系统有效短路比的等值有效短路比指标。利用该指标可将混合双馈入直流系统中LCC-HVDC子系统等效为受端交流系统电压支撑强度与之相同的单馈入直流输电系统。最后,基于PSCAD/EMTDC进行仿真分析,仿真结果证明了VSC-HVDC对LCC-HVDC子系统影响关系的正确性以及等值有效短路比指标的有效性。

英文摘要：

The effective short circuit ratio of line commutated converter based high voltage direct current（LCC-HVDC） sub-system in dual-infeed hybrid HVDC system was investigated to evaluate the system strength of LCC-HVDC. Firstly, the voltage support strength of AC system was analyzed when different power flow directions and different controled strategies were adopted in voltage source converter（VSC） based on optimal power flow by Newton approach. Secondly, the equivalent impedance of VSC-HVDC was calculated, and the effective short circuit ratio of the LCC-HVDC was quantified by a proposed ＂equivalent effective short circuit ratio＂ index. The LCC-HVDC in dual-infeed hybrid HVDC system could be equivalent to a single-infeed HVDC system which had the same voltage support strength by the index. Simulation results in PSCAD/EMTDC show that the analysis on the effects of VSC-HVDC to LCC-HVDC proved to be accurate and the ＂equivalent effective short circuit ratio＂ index is effective.