MMC-MTDC线路双极永久性故障快速识别方法研究

摘要

对于采用“半桥子模块+直流断路器”模式的多电平多端柔性直流输电系统,直流线路发生双极故障断开直流断路器后,若能快速检测出线路故障为永久性故障或瞬时性故障,则有助于提升MMC-MTDC系统和与之连接的可再生能源系统的运行稳定性.文章分析了永久性故障、瞬时性故障和保护误动等不同场景下断路器动作后电气量特征,发现可以用正负极电压之差是否为零来识别永久性故障;进一步采用强局部加权回归方法滤除电压信号中的高频分量,实现暂态过程中线路永久性故障的快速识别.%MMC based multi-terminal HVDC (MMC-MTDC) has application prospects in grid connection and power transmission of wind power,photovoltaic and other renewable energy.When a bipolar fault occurs in MMC based multi-terminal HVDC (MMC-MTDC) systems that use halfbridge sub-modules and DC breakers,the faulted line must be tripped by DC breakers.If an instantaneous fault is identified immediately after the breakers are tripped,the MMC-MTDC system can be restored to stable operation by reclosing the breakers quickly.Therefore,fast permanent fault identification is beneficial to the operational stability of MMC-MTDC system and renewable energy system.By analyzing the characteristics of DC line voltage under different fault conditions (permanent fault,instantaneous fault and protection mal-operation),it is found that the difference between positive pole voltage and negative pole voltage of the line with permanent faults is zero,while that of the line with instantaneous faults is not zero.According to this feature the permanent fault can be identified.Furthermore the robust locally weighted regression approach is used in this paper to realize the fast permanent fault identification in transient process.