计及多端直流断路器的直流电网故障分析与继电保护研究

继电保护是直流电网安全稳定运行的重要保障，故障分析则是继电保护的理论基础。现有故障分析主要关注直流电网在故障初期的响应特性，未充分考虑换流站闭锁与直流断路器动作等开关事件的影响；现有继电保护主要关注直流线路主保护，而直流线路后备保护和直流断路器失灵保护仍有待深入研究。针对上述问题，本项目以采用多端直流断路器的直流电网为研究对象，围绕其故障分析与继电保护展开以下研究：1）分析开关事件的动态响应特性以及不同设备之间的故障耦合特性，从而提出计及开关事件的直流电网故障分析方法；2）结合开关事件与故障特征之间的关联特性，提取区内和区外故障的特征差异，进而提出计及开关事件的直流线路单端量后备保护原理；3）充分挖掘多端直流断路器失灵和非失灵工况的特征差异，进而构建基于就地信息的多端直流断路器失灵保护原理。本项目旨在为直流电网故障分析与继电保护提供新的理论和方法，为直流电网的工程应用提供关键技术支撑。

Relay protection is an important guarantee for the safe and stable operation of DC grids, and fault analysis is the theoretical basis of the relay protection. At present, the fault analysis mainly focuses on the response characteristic of DC grids during the initial fault stage, however, the impacts of the switch events such as converter blocking and DC circuit breaker operating are not fully considered. The existing relay protections mainly focus on the main protection of DC transmission lines, however, the backup protection of DC transmission lines and failure protection of DC circuit breakers remain to be further researched. Considering these above problems, this project focuses on the fault analysis and relay protection of the DC grid with multiport DC circuit breakers (MDCCBs), and the research can be divided into the following parts. 1) The dynamic response of switching events and the fault coupling characteristic of multiple devices are analyzed, and then a fault analysis method, which considers the impacts of switch events, is proposed for DC grids. 2) Combining the relation between the switch events and fault characteristics, the characteristic differences of the internal and external faults are extracted, and then a backup protection principle, which considers the impacts of switching events and only uses the single-terminal electric quantities, is proposed for DC transmission lines. 3) The characteristic differences during the failure and non-failure conditions of the MDCCB are revealed, and then a local information based MDCCB failure protection is proposed. This project aims to provide new theories and methods for fault analysis and relay protection of the DC grid, thereby providing key technical support for the engineering application of the DC grid.