多端柔性直流电网故障限流与快速保护技术研究

Flexible DC power transmission technique has some advantages, such as active and reactive power controlling independantly, no requiring to chang voltage polarity in the case of power flow turnover, etc. Multiterminal flexible DC grid (MTDC), which is derived from the development of flexible DC transmission technique, is very suitble for multi-source supplying power and multi-location consuming power, and it will become an important grid configuration in the future energy interconnection network. Although MTDC grid has many technical advantages, its topology and the problem of serious overcurrent in the event of direct current side faults are some severe challenges for fault current limiting and protection techniques. Consequently, these key techniques have already restricted the application of giant capacity multiterminal flexible DC power transmission and grids. Therefore, on the basis of analyzing the fault characteristics of MTDC grid, this project focuses on the following items: research and design the fault current limiting scheme through additional circuit, whose performance of current limiting and operation economics will be considered together; research on extra high speed DC busbar protection principle based on polarity comparison; explore non unit extra high speed protection method for DC line using the border characteristic of additional circuit; explore the fast pilot protection principle based on polarity/direction comparison for MTDC grid; explore the identification method of non fault disturbance signals; design a set of protection and control scheme for MTDC grid, and explore the MTDC gird protection device sample. The aim of the project is to propose whole protection and control theores and realization techniques including the fault current limiting for MTDC grid, and provide the technical support to multiterminal flexible DC power transmission and grid.

柔性直流输电技术具有有功和无功独立控制、潮流翻转无需改变电压极性等优点，由其发展而成的多端柔性直流电网非常适合多电源供电和多落点受电，将是未来能源互联网的一种重要电网形态。尽管存在诸多技术优势，但是柔性直流电网的拓扑结构及直流侧故障时严重的过流问题对故障限流和保护控制技术提出了严峻的挑战，制约了大容量多端柔性直流输电/电网的应用。对此，本课题在多端柔性直流电网故障分析的基础上重点开展以下研究：研究设计兼顾限流性能和经济性的外加电路限流方案；研究极性比较式超高速直流母线保护原理技术；研究以外加电路为边界的单端量直流线路超高速保护原理，研究极性/方向比较式直流电网快速纵联保护原理；研究非故障干扰信号的识别方法；研究设计多端柔直电网整体保护方案；研制柔性直流电网保护样机。通过本课题研究，旨在推出包括限流技术在内的柔性直流电网整套保护控制理论与实现技术，为多端柔性直流输电/电网的发展提供技术支撑。

柔性直流输配电技术具有控制灵活、能向无源网络供电、无换相失败问题和不需无功补偿等优点，在清洁能源并网及输配电领域极具优势。但是，由于柔性直流电网的低阻抗特性以及换流器件的脆弱性，直流侧故障产生的大电流易导致换流站的闭锁。为避免闭锁问题，对故障线路的识别和隔离速度要求极高。目前，应用于柔直工程中的保护参考传统直流输电线路的保护原理，其性能有待进一步验证。为此，本课题在故障限流与快速保护方面开展了深入研究，设计了故障限流电路，提出了单/双端量的保护方法，研制了直流保护样机。主要成果为：（1）设计了一种多端柔性直流电网故障限流方案，通过对晶闸管的控制将限流电阻投入故障回路，进而实现对故障电流的限制，避免了正常运行时的损耗以及过流引起的换流站的闭锁问题；（2）提出了一种基于两电平的多端柔直电网保护方案，基于电流行波极性比较可快速识别故障的直流线路，基于采样值差动电流，实现了直流母线的快速保护；（3）提出了基于MMC的柔直电网直流线路单端量快速保护方法，由于线路两端限流电抗器对高频信号的阻滞作用，区内外故障时线路端点的暂态电压首波时间存在显著差异，由此可快速识别区内外故障；（4）提出了基于限流电感电压极性的柔直电网纵联保护方法，根据柔直线路发生区内外故障时两端限流电感上的电压极性差异，可快速识别故障的线路；（5）提出了一种柔直电网故障性质识别与自适应重合闸方案，根据直流断路器辅助电路产生的行波信号在暂时性与永久性故障时的极性差异，可快速识别故障性质，进而实现自适应重合闸；（6）研制了直流线路保护样机，基于以上单/双端量保护原理，开发出了快速保护样机，RTDS闭环测试结果表明，该原理样机动作快速（单端：2ms内；双端：4ms内），性能可靠。.上述理论成果为多端柔直电网故障限流和快速保护提供技术支持，而保护样机的研制为理论成果的工程应用奠定了基础，具有重要的理论价值和良好的工程应用前景。