昆柳龙多端直流线路故障恢复及换流站在线退站的系统稳定特性分析

Analysis on System Stability Characteristic of DC Line Fault Recovery and Converter Station Online Disconnection of KLL MTDC

近年来,多端直流系统已经成为颇具竞争力的跨区域大功率输送方案。昆柳龙(昆北-柳州-龙门)多端直流工程将多端直流的工程实践提升到特高压水平。昆柳龙直流系统包含1个常规直流换流站(昆北)和2个柔性直流换流站(柳州、龙门),系统运行方式灵活,在故障清除及恢复过程中需在3个换流站之间进行控制协同,因此控制保护及配套稳定控制系统无法直接沿用常规双端直流工程设计。首先介绍了用于系统稳定性分析的多端直流线路故障恢复及在线退站动作时序,接着分析了送端交流系统在大功率扰动下的频率响应特性,并研究了多端直流故障恢复功能对电网安全稳定影响,提出了各故障下的稳定控制措施,并以昆柳龙直流投产后的年方式数据为基础,通过数值仿真进行了验证。研究成果可为昆柳龙及其他多端直流工程的控制保护功能设计提供参考。

Recently multi-terminal HVDC system(MTDC)has become a competitive alternative for inter-area large power transmission.The Kunbei-Liuzhou-Longmen(KLL)MTDC project promotes MTDC practice to ultra-high voltage level.It is composed of one LCC(Kunbei)and two VSC(Liuzhou,Longmen)converter stations in parallel,the operation mode of the system is flexible.And in the process of fault clearing and recovery,control coordination among three converter stations is needed.Thus,the conventional control and protection system for bi-terminal HVDC and the associated special protection scheme(SPS)cannot be directly adopted in KLL multi-terminal HVDC.This paper first introduces the MTDC line fault recovery(DCFR)and converter station online disconnection(CSOD)of KLL MTDC that used in system analysis,and the frequency response characteristic of the sending end AC system when it suffers a significant power imbalance.Then,the impacts of DCFR and CSOD and the corresponding SPS are studied and verified by transient stability simulation using real operational planning data.The study provides a reference for the SPS design of KLL MTDC and other MTDCs.