基于单端高频电流量的MMC-MTDC输电线路保护方案

为克服传统高压直流输电线路保护利用单端电气量无法可靠区分区内、外故障的缺陷，提出一种通过广义S变换提取直流线路故障电流高频频带幅值特征的单端量保护新方法。该方法在配备有混合直流断路器的直流线路发生故障时，利用1000~2500 Hz各采样频率电流横差值在区外明显小于区内的特征，构造了区内、外故障判据。利用300~1000 Hz的特征频率在单极接地故障时故障极特征频率电流幅值比非故障极大，以及两极短路故障时两极的特征频率电流幅值近似相等的特征，构造了故障启动判据和选极判据。在RTDS仿真平台搭建了风光储联合发电站经高压直流外送的三端柔性直流输电系统模型。仿真结果表明，所提方法能快速、可靠地识别故障类型和故障范围。同时，仿真验证了基于混合直流断路器的直流故障穿越方案的有效性。

Transmission line protection scheme of MMC-MTDC based on single terminal high frequency current

A new single terminal protection that extracts the amplitude characteristics of the high frequency band of the DC line fault current through a generalized S-transform is presented to overcome the defect of traditional HVDC transmission line protection. That problem is where the single terminal relaying cannot differentiate between internal and external faults. The research shows that when the DC line equipped with a hybrid DC circuit breaker fails, the transverse current difference of sampling frequency from 1000 Hz to 2500 Hz is obviously smaller when the external fault occurs than when the internal fault occurs. Fault criteria are established. The current amplitude of the characteristic frequency of the fault pole is greater than that of the non-fault in the case of single pole-to-ground fault. The current amplitude of the characteristic frequency of the two poles is approximately equal when a two poles short circuit occurs. The fault starting and pole selection criteria are built using a characteristic frequency from 300 Hz to 1000 Hz. On the RTDS simulation platform, a three terminal flexible HVDC system model of wind-solar-storage hybrid power generation station transmitted through HVDC is built. The simulation results show that the fault type and area can be identified rapidly and reliably. The effectiveness of the proposed DC fault ride-through scheme based on a hybrid DC circuit breaker is verified using an RTDS simulation experiment. This work supported by the National Natural Science Foundation of China (No. 51967016 and No. 51567020).