并联型多端直流输电系统运行方式研究

LCC通过反转电压极性实现整流和逆变的转换，可能导致并联型多端直流输电系统功率短时中断。为此，提出一种基于LCC的并联型三端直流输电系统接线方案，分析可能存在的运行方式及转换方法，提出极性转换、电压控制站投退的控制顺序和故障极紧急停运策略。基于PSCAD/EMTDC平台建立三端直流输电系统仿真模型，仿真极性转换、电压控制站投退和故障极紧急退出实验。仿真结果表明该多端系统换流站功率反转不影响其余换流站功率稳定运行，并且能够安全隔离故障设备，快速恢复健全系统稳定运行。

Operation mode research on parallel multi-terminal HVDC transmission system

LCC conversion between rectification and inversion by voltage reversal may force multi-terminal HVDC transmission system to be power interrupted for a short time. So a connection scheme based LCC for parallel three terminal HVDC transmission system is presented, the possible operation modes and conversion methods are analyzed, the control sequences of pole conversion and DC voltage controlling station input and output and emergency exit strategy for fault pole are presented. Based on the platform of PSCAD/EMTDC, the three terminal HVDC simulation model is built to carry out the simulation on pole conversion, DC voltage controlling station input and output, and emergency exit of fault pole. The simulation results show that power reversal of one converter station based the multi-terminal HVDC would not affect others station, and could isolate fault devices safely to recover the stable operation of sound system quickly. This work is supported by National Key Research and Development Program of China (No. 2016YFB0900603) and Science and Technology Project of State Grid Corporation of China (No. 52094017000W).