多端柔性直流电网快速方向纵联保护方案

A Fast Directional Pilot Protection Scheme for the MMC-based MTDC Grid

直流线路保护是柔性直流电网发展的关键问题,其主要技术难点在于快速可靠地识别故障区段。传统交流系统保护和常规直流输电系统保护原理很难适用于柔性直流电网。根据柔性直流电网故障暂态特征以及一次设备固有构成,该文提出一种基于线路边界元件的新型快速方向纵联故障识别判据,以及一种实用可靠的故障选极判据,并设计相应的线路保护方案。最后,在PSCAD/EMTDC仿真平台上搭建四端模块化多电平换流器(modular multilevel converter,MMC)型直流电网模型,通过大量的仿真算例验证该保护原理的可行性,以及在硬件成本、动作速度、耐受过渡电阻能力等方面的突出优势。

DC line protection is the key problem of the multi-terminal flexible dc grid, because it is hard to identify the fault location fast and reliably. The protection principles of traditional ac system and line commutated converter （LCC） based dc system are not suitable for the flexible dc grid. Therefore, according to the fault characteristics of the flexible dc grid and inherent constitution of the primary equipments, this paper proposed a novel directional pilot protection principle based on the boundary element, and a simple fault pole selection method. Meanwhile, the corresponding dc line protection strategy was also designed. Finally, a four-terminal modular multilevel converter （MMC） based dc grid model was built on the PSCAD/EMTDC platform. Lots of simulation cases were carried out to verify the feasibility of the proposed protection strategy, as well as the advantages in terms of hardware requirement, action speed, insusceptibility to the transition resistor and so on.