环网型混合五端直流输电系统的建模与仿真

Modeling and Simulation of Hybrid Five-terminal HVDC Transmission System

随着直流输电技术发展日益成熟,大规模可再生能源的并网和多落点受电的研究正在成为直流输电行业的研究热点。利用PSCAD建立混合五端直流输电仿真模型,该模型可将我国西北部地区丰富的可再生能源通过架空线远距离输送给中东部负荷密集区,并根据沿海岛屿的具体情况,实现海上风电场的并网或者孤岛供电。模型中用四端互联形成环网结构,且在两电平VSC站和HB-MMC站直流母线出口处加装大功率二极管阀组,用以限制直流系统故障下故障电流的穿越;然后,对系统直流侧接地故障后的运行特性进行仿真分析。仿真结果表明,所搭建的混合五端环网直流输电系统在稳态下能够安全稳定运行,在直流线路接地故障时能够隔离故障电流。

With the DC transmission technology becoming more mature, the problems of how to connect renewable energy resources to power grid and how to supply enough power to the users in different regions are becoming the hotspots in the research of HVDC. A simulation model of a hybrid five-terminal HVDC transmission system is designed by using PSCAD, which can be used for transmitting the rich renewable energy in northwest to cent ral and eastern China that are in urgent need of electricity power using overhead lines over long distance. The design also takes the demand of the offshore islands into account, and can achieve offshore wind power integration or power supply to the islands. In the model, there are four terminals interconnected into ring network architecture, and high power diode valves are installed at the exit of the DC bus in the two-level VSC station and HB-MMC station, which is used to cut off the fault current when DC system fault occurs. What’s more, the article analyzes the operating characteristics of the system when ground fault on the DC side occurs through simulation. Simulation results show that the established hybrid five-terminal HVDC transmission system can achieve stable and safe operation in steady state, and can effectively isolate the fault current when ground fault of DC lines occurs.