基于等效行波的柔性直流电网差动保护研究

Study on Differential Protection Based on Equivalent Travelling-wave for VSC-based DC Grid

直流线路保护是高压大容量柔性直流电网亟需解决的关键问题之一。针对目前的通信技术难以满足传统行波差动保护对高速采样数据的实时传输要求这一突出问题,文章提出了基于等效行波的柔性直流电网差动保护方法。作为单端量主保护的后备保护,该方法仅利用少量能表征原故障电流行波关键信息的模极大值进行数据交互,在线路两端重构出能完美复现原故障电流行波的等效故障电流行波,不但大大减少了构造行波差动保护判据所需的通信数据量,而且可实现柔性直流电网故障区域和区内直流线路不同类型故障的可靠、快速识别。最后,在PSCAD/EMTDC中搭建了四端环形柔性直流电网,对所提的基于等效行波的柔性直流电网差动保护方案进行了仿真验证。

Protection for DC transmission lines is one of the key problems that urgent to be solved in constructing highvoltage and large-capacity VSC-based DC grid in the future. Aiming at the prominent problem that the current communication technology is difficult to meet the requirements of real time transmission of high-speed sampling data proposed by traditional differential protection based on travelling-wave, a new differential protection scheme based on equivalent travelling-wave for VSC-based DC grid is presented by this paper. As a backup protection for primary protection based on single-erminal electrical quantities, a small amount of exchanged modulus maxima which can represent the critical information of the original fault-current travelling-wave are used to reconstruct the equivalent fault current travelling-wave which can perfectly reproduce the original fault-current travelling-wave in this scheme. As a resultnot only the communication data needed to construct the differential protection criterion is greatly reduced but also the reliable and fast identification of fault location and different types of faults in the internal area could be realized. Finally, a four-terminal loop VSC-based DC grid model is built in PSCA/EMTDC, and the differential protection scheme based on equivalent travellingwave is simulated and verified.