基于暂态特征信息融合的多端柔性直流输电线路故障辨识与系统保护研究

Modular Multilevel Converters-Based Multi-Terminal Direct Current（MMC-MTDC）transmission lines can achieve multi power sources supply and multi load points receiving, is the important bridge to flexible access and secure interconnection of renewable energy, shouldering the significant mission of electricity transmission from energy base to load center in China and energy transnational interconnection. Reliable and effective protective relaying of DC transmission line is the key to ensure the safe operation of MMC-MTDC system. At present, the research on MMC-MTDC transmission line protection is in its infancy, and many basic scientific issues need to be researched and explored. This research project intends to combine theory analysis and electromagnetic transient simulation, research on the mathematical model of transient characteristic harmonic component’s transfer between both sides of converter in MMC-MTDC system, and establish a fault transient characteristic harmonic analysis method; Based on topology structure and fault control features in MMC-MTDC transmission system, the research is expected to clarify the fault identification mechanism in MMC-MTDC system and reveal the variation law of transient characteristic harmonic on both sides of converter in each terminal after faults, realize fault identification and system protection of MMC-MTDC transmission lines based on AC/DC transient characteristics information fusion. This research project will make important progress and breakthrough, which can provide important technical support for safe operation of MMC-MTDC transmission system protective relaying, and is of great significance to large-scale renewable energy integration, the improvement of reliability of power supply and security and stability of power grid in our country.

多端柔性直流输电线路能够实现多电源供电、多落点受电，是新能源灵活接入与安全并网的重要桥梁，肩负着我国能源基地向负荷中心输送电能、能源跨国互联的重要使命。可靠、有效的直流线路继电保护是保障多端柔性直流输电系统安全运行的关键。目前多端柔性直流输电线路保护很多基础科学问题仍有待研究、探索。本项目拟采用理论分析与电磁暂态仿真相结合的方法，研究多端柔性直流输电系统换流器两侧暂态特征谐波传递模型,建立故障暂态特征谐波分析方法；结合多端柔性直流输电系统拓扑结构特性、故障控制特性，明晰多端柔性直流输电线路故障辨识机理，揭示故障后系统中各端换流器暂态特征信息变化规律，提出基于交直流暂态特征信息融合的多端柔性直流输电线路故障辨识与系统保护方案。本项目取得重要进展和突破，可为多端柔性直流输电系统的继电保护安全运行提供重要技术支撑，对我国大规模新能源接入、提高电力系统供电可靠性及电网安全稳定性具有重要意义。

多端柔性直流电网能够实现多电源供电、多落点受电，运行方式更为灵活，对于消纳集中式光伏场站、海上风电场等新能源具有重要作用，随着双碳目标、构建新型电力系统国家战略的推进，电力系统中含换流站关键节点数量日益增多，但传统含换流站关键节点故障分析方法存在系统整体阶次高而无法精确解析，导致故障分析精度差，造成故障定位不准确、保护速动性差的问题，含换流站关键节点交直流侧故障分析对保护装置的研制将起到关键作用。本项目优化了多端柔性直流输电系统数学模型与电磁暂态模型，研究了换流器两侧暂态特征谐波的映射关系，揭示了不同故障条件下系统各端换流器两侧暂态特征谐波的变化规律，建立了交直流两侧高精度故障电流计算模型，在电容器放电阶段考虑了从电网侧馈送的电流，将暂稳态故障电流计算误差从传统方法的10%左右降低到1%以下；提出基于电磁时间反转和相量状态估计的故障定位方法，结合更加精确的交直流两侧故障电流计算模型，使得线路故障定位误差降低一个数量级；结合故障后表征系统故障的暂态特征量变化规律与谐波传递特性，提出了基于暂态边界能量、暂态谐波电流的多端柔性直流线路保护方案等故障辨识与系统保护方案，所提保护方案能够在4.7ms内完成故障识别，满足了多端柔性直流输电线路保护快速性与选择性要求；结合多端柔性直流输电系统控制响应特性，提出了基于虚拟能量、控制特征量响应的多端柔性直流输电系统控保协同方案，所提控保协同方案便于控制和保护的集成设计，提高了换流站控保系统的可靠性，是未来换流站控保系统的发展方向。项目研究成果解决了换流器两侧特征谐波传递机理不明晰的关键科学问题，建立了换流站交直流两侧故障特征识别与暂态保护的理论框架，为含有换流器场景下的故障特征分析、暂态保护技术发展和继电保护装置研发奠定了重要基础。项目研究成果可为多端柔性直流输电、逆变型电源接入和直流配电网等场景下的故障分析、故障辨识与暂态保护提供理论基础。