基于故障暂态波形时频特征的柔性直流配电网保护与故障定位

VSC (voltage source converter)-DC distribution system can effectively integrate the RES (renewable energy sources) and DC loads due to its flexible control, less power conversion losses, higher short-circuit capacity and better power quality and will be the focus of the future researches within the distribution system. DC system protection and fault location is one the keys factors for its healthy operations. Due to the face that DC distribution system will be designed based on partially equipped DC circuit breakers and half-bridge MMC (modular multilevel converter) topologies, the protection and fault location will face the challenges as: influenced by the non-linear characteristics of the power electronic devises and its variable control algorithms, the DC system fault performances cannot be precisely analyzed and modeled. The DC breaker operation time is within several ms and the protections have to detect and distinguish faults within a very short period of time. Meanwhile, using a short fault transient, a fast and accurate fault location is required to isolate the faulted area accompanied by the isolators and DC breakers. Considering all the challenges and factors, this project will analyze the DC fault transient characteristics for different topologies and controls of converter and faults. Then based on the relationship between the time/frequency domain fault transients and the fault distance, new protection algorithms using both single and double-ended measurement are provided. The research work will continuously investigate fast and accurate fault location schemes that use both the wide-area measurement and the capacitor band injection to effectively distinguish and isolate the faults and ensure the equipment security and the system operation efficiency. The research works of this project will lay a strong foundation for the development of the future VSC-DC distribution system.

柔性直流配网可实现分布电源与直流负荷高效、灵活并网，减小能量多级变换损失、提升短路容量与电能质量，是未来配网研究重点，其中保护与故障定位技术是其安全运行关键。由于直流配网将基于部分直流断路器和半桥MMC拓扑结构设计，保护与定位面临挑战：受换流器控制策略影响，直流故障特性无法线性等值，暂态波形难以准确提取，保护缺乏理论依据；直流断路器数毫秒动作，保护难以同时实现快速性与选择性；故障定位需要利用有限故障数据准确获知故障位置，利用直流断路器与快速开关配合清除故障。因此，项目将考虑不同换流器控制策略，研究直流故障发展过程及其暂态波形特征提取方法；进而基于故障暂态波形时域、频率特征与故障距离对应关系，提出基于单端量测与双端量测的保护新原理，快速、有选择性识别故障；在此基础上，分别利用多点暂态电流方向量测与系统内电容元件投切定位故障，实现故障清除，保证直流配电网安全、高效运行，为直流配网发展奠定基础。

柔性直流配电网保护需要配合直流断路器在几个毫秒内高速动作，以防止快速上升的故障冲击电流损害系统中的电力电子换流设备。然而受到换流设备拓扑结构和故障控制方式影响，直流故障暂态特征变化多样，保护难以准确提取故障信息并在复杂多分支的配电系统中定位故障。为此，本项目分析了直流短路过程时、频域故障特征，提出了故障暂态时域电流分阶段线性解析方法，解决了控制切换非线性状态下难以准确分析故障特征的问题，建立了基于换流设备开关回路分析的高频阻抗模型，高频下换流设备在不同控制参数和控制策略时阻抗特征恒定，为保护与故障定位奠定基础；提出了基于单端波形曲率的高速保护方法，大幅度提升保护的动作速度和耐受故障电阻能力，提出了基于双端高频阻抗比较的纵连保护新原理，利用短路后稳定的高频阻抗特征准确判断区内外故障；提出了基于换流设备主动注入扰动特征的故障定位方法，确保了在故障特征消失后可以精确区分故障区段。.在理论研究的基础上，与国内二次设备生产厂商合作，研制了直流配电系统保护装置，第三方测试显示其最小保护动作时间小于1ms，与现有直流保护相比，动作时间缩短3倍，保护装置已经在在云南干塘子±30kV光伏直流升压汇集电站（2019年投运）、张北基地±10kV多端直流配电实证工程（2020年投运）挂网，运行效果良好。.项目研究过程中发表SCI期刊论文16篇，EI期刊论文18篇，授权美国发明专利4项，授权国家发明专利12项，培养博士生3人、硕士生7人。本人入选中国科协“青年人才托举工程”，担任CIGRE B5-48“短路电流受限电源的电网保护”工作组秘书、中国能源行业配网系统标准化技术委员会委员、IEEE PES（中国）保护与控制系列技术分委会副主任理事，中国电工技术学会青工委副秘书长；担任IET Renewable Power Generation 期刊编委、IEEE Open Access Journal of Power and Energy 等多个SCI期刊编委，担任多个国内外学术会议分会场主席，多次做关于直流配电网保护控制专题报告。