柔性中压直流配电网的一体化“序网络”故障分析方法与融合非确定性判据的直流保护新原理及其可靠性评估模型研究

The DC distribution grid is an important part of the future distribution system. However, researches on the fault analysis theory of DC networks that is widely applicable and can take into account the interaction between AC and DC sides, and DC protection systems that are both reliable and economical still face great challenges. Based on previous study, the project will address the following issues in terms of flexible medium voltage DC distribution grids. 1) Taking full consideration of the characteristic of flexible DC distribution networks, a fault analysis approach characterized by the "integrated AC/DC sequence network", and detailed models for analyzing comprehensive features of DC short-circuit and line-break faults will be proposed to provide a basis for implementing protection schemes. 2) By harmoniously combining deterministic and nondeterministic criteria, novel protection principles will be proposed. Considering the characteristic of flexible DC distribution networks, the configuration and coordination of main and backup protective relays, as well as the scope extension of the remote backup protection will be studied to deal with complicated fault scenarios, such as interaction of AC and DC zones, high resistance, pole-to-ground fault and current transformer overflow. The fault isolation strategy, based on the optimal deployment of DC circuit breakers and disconnectors and their coordination with converters, will be investigated as well. 3) The analytical and probabilistic models for reliability analysis of DC protections, with high timeliness and can be flexibly coupled and decoupled with the dynamic model of primary systems, will be proposed to differentiate diverse fault scenarios, and establish a "three-in-one" assessment and early-warning method of DC protections by combining with the experimental platform. The project will make a unique contribution to supply theoretical reference and technical support for improving the self-healing protection of DC systems and speeding up the modernization of distribution networks.

直流配电网是未来配电体系的重要组成部分，但能计及交直流交互影响且有较强普适性的直流网络故障分析理论、兼顾可靠性和经济性的直流保护研究仍面临极大挑战。本项目在前期研究基础上重点针对中压柔性直流配电网开展以下工作。1）充分考虑柔直配网实际，提出交直流“一体化序网络”故障分析方法，及直流纵、横向故障多态特征的精细化分析模型，为保护方案制定提供依据。2）研究确定性和非确定性判据有机融合的保护新原理，结合柔直配网特点拓展远后备保护范畴，实现主后备保护配置和配合方案，应对交互影响、高阻、单极、互感器溢出等复杂故障情景；研究基于直流断路器和隔离开关最优配置、与换流器等配合的故障隔离策略。3）提出直流保护可靠性分析的解析模型、概率模型，能与一次系统动态模型灵活解耦、具备时效性和区分度，并结合实验平台建立“三位一体”的直流保护评估和预警方法。旨在为完善直流自愈保护，加快配网现代化建设提供理论参考和技术支撑。

计及交直流交互影响且有较强普适性的直流配电网故障分析理论、兼顾可靠性和经济性的直流保护及故障隔离研究仍面临挑战，项目完成了以下工作。.（1）故障分析方面。研究了不同子模块MMC构成的直流配网横纵向故障特性，分析了接地方式的影响和优选方法。提出了交直流混合系统序分量网络分析方法。分析了直流故障对变压器偏磁和差动保护的影响及对策。为构建直流保护原理提供了理论依据。（2）保护新原理方面。1）研究了两种单端量保护原理：针对MMC、VSC共存的直流配网，提出了利用线路附加电感电压的故障识别方法；提出了基于限流电抗电压积分值的直流环网故障快速检测方法。快速判别故障区段和类型，具有较强的抗过渡电阻和抗干扰能力，作为直流线路双重主保护。2）研究了三种基于通信的保护原理。针对直流线路单极故障，分别提出了基于Hausdorff距离和Pearson相关系数的故障识别方法，以及基于电流故障分量相似度的直流线路纵联保护，克服重负荷下高阻故障、换流器闭锁、定值整定、电网运行方式等影响，用于后备保护。3）针对交直流交互影响，提出了换流站交直流故障辨识和保护配合方法。4）针对单端量、双端量保护的不足，提出基于聚类中心距离度量的直流线路保护原理。（3）故障隔离策略方面。研究了多类型换流器并存的复杂柔直电网故障隔离方案和限流式多端口DCCB，降低投资成本，具有较好的适用性。（4）保护可靠性方面。1）建立了母差保护误动和拒动概率模型，评估采样同步误差的影响。2）提出了保护二次回路故障诊断方法，提升保护运维工作效率。3）提出保护隐性故障识别方法，有效发现保护定值和配合等隐性故障。4）提出一种矩阵算法和BP神经网络相结合的二次系统故障定位方法。5）开展了直流保护测试平台建设。.项目研究为完善直流保护及故障隔离策略，加快配网现代化建设提供理论参考和技术支撑。