柔性直流电网保护与故障穿越基础理论及关键技术

The flexible DC grid is an important technological revolution in the development and reformation of power system. The existence of non-linear power electronic equipment, complex operating conditions of power grid and the high pressures of fault disposal makes fast protection, fault ride-through, reclosure and self-recovery become the key issues in science and technology at present. Aiming at the topology, operation strategies and application requirement of the flexible DC grid, based on studying the core difficulties of fault identification and isolation, research on the fundamental theories and key technologies on the fast protection of DC grid and fault ride-through will be done, including the fault coupling characteristics between the AC and DC sides on the basis of flexible DC fault characteristics. Proposing the fast protection principle and technology which has a good adaptability, speed, sensitivity, reliability and is fit for various DC grid topologies. The coupling mechanism between the electrostatic field and the ionic flow field in flexible DC grid is discussed. The intelligent reclosure principle and technology based on line partial pressure characteristics, fault character prediction method and low current injection are proposed. The mechanism of fault ride-through on the base of fault current limiting is studied. The key technology for flexible DC grid fault ride-through which combines the fault protection, current limitation and breaking devices is proposed. The achievements will be the important foundation and technical guarantee for the safe and reliable operation of the flexible DC power grid.

柔性直流电网是电力系统发展变革中的一次重要技术革命。非线性电力电子设备接入、复杂的电网运行状态以及高强度的故障处理压力使得如何快速保护、故障穿越以及重合自愈成为其面临的关键科学技术问题。本项目以柔性直流电网的拓扑结构、运行策略和应用要求为目标，从其故障识别与隔离的核心难点出发，研究柔性直流电网快速保护与故障穿越的基础理论和关键技术。具体包括：以柔性直流故障特性为基础研究柔性直流电网直流侧和交直流侧的故障耦合机理，提出满足不同柔性直流电网拓扑适应性和保护速动性、选择性与可靠性等要求的快速保护新原理与技术。探讨柔性直流电网静电场和离子流场耦合机理，提出基于线路分压特性的故障性质预判方法和低电流注入的智能重合新原理与技术。研究以故障限流为基础的故障穿越机理，提出故障保护与限流和开断设备一二次相融合的柔性直流电网故障穿越关键技术。成果将是柔性直流电网安全可靠运行的重要基础和技术保障。

柔性直流电网在大规模新能源并网外送、区域电网互联等方面优势突出，是新型电力系统发展的重要方向。然而，复杂的电网形态和非线性电力电子设备的深入参与使得柔性直流电网在故障辨识、故障穿越以及故障自愈等方面面临巨大挑战。本项目以柔性直流电网故障可靠穿越与快速自愈为目标，研究了柔性直流电网故障耦合特性和快速保护原理、柔性直流电网静电场与离子流场的耦合机理分析与智能重合原理、柔性直流电网故障限流及与故障穿越关键技术三方面研究工作。在柔性直流电网故障耦合机理与快速保护原理方面，分析了柔性直流电网故障演化规律和耦合特性，提出了满足柔性直流电网动作速度和可靠性要求的直流线路快速单端量保护新原理和快速电流差动保护新原理与主后备保护方案，并研制了保护装置样机。在柔性直流电网电场耦合机理与智能重合原理方面，分析了柔性直流线路电场耦合机理和分压特性，提出了基于主动式小电流注入的智能重合闸策略和基于直流线路残压特性的DCCB自适应重合闸策略，有效消除柔性直流电网重启/重合于永久性故障时的二次过流冲击危害。在柔性直流电网故障穿越匹配协调机理方面，提出了具有自适应限流能力的新型故障限流器与直流断路器，并从拓扑结构、参数设计、控制策略等多个层面研究限流、保护、断流与重合的协调配合，确保直流电网在故障情况下的安全可靠穿越。研究成果能够为柔性直流电网安全可靠运行奠定坚实的理论和技术基础。