基于改进动态时间弯曲距离算法的直流配电网线路纵联保护方案

故障阻断型换流器构建的直流配电网采用主动限流控制后，将导致故障电流特性复杂化，严重影响保护的动作性能。在对直流配电网主动限流控制下故障电流特性进行分析的基础上，根据区内、外故障下线路两侧电流波形的差异，提出了一种基于改进动态时间弯曲距离(DTW)算法的线路纵联保护方案。该方案利用线路两侧电流采样值时间序列计算DTW，根据区内故障下DTW值远大于区外故障下DTW值的特征识别故障线路。通过电压梯度构成启动判据，对DTW算法起始时刻进行自校正，同时引入加权函数对DTW算法进行改进，以抑制边缘效应，从而有效降低同步误差对保护的影响，提高保护可靠性。算例分析表明所提保护方案在不同电网运行方式下均可正确区分区内、外故障，适应性强，同时具有良好的耐受过渡电阻和分布电容电流的能力。

Pilot protection scheme for DC distribution network based on improved dynamic time warping distance algorithm

After active current-limiting control is adopted in DC distribution network constructed by the fault-blocking converter, the characteristics of short circuit current will be complicated, which severely affect the performance of the protection. Based on the analysis of short circuit current characteristics under active current-limiting control of DC distribution network, a pilot protection scheme based on improved DTW(Dynamic Time Warping distance) algorithm is proposed according to the difference in current waveforms on both sides of the line during internal and external faults. The DTW is calculated by the time series of current sampling values on both sides of the line. Then, the fault line can be identified according to the feature that the DTW value under internal fault is much larger than that under external fault. The starting criterion is constituted by voltage gradient to self-calibrate the starting time of DTW algorithm. Furthermore, a weighting function is introduced to improve the DTW algorithm to suppress edge effects. As a result, the influence of synchronization errors on protection is effectively reduced, and protection reliability is improved. Case analysis shows that the proposed protection scheme can correctly distinguish internal and external faults in different power grid operation modes with strong adaptability. In the meantime, the transition resistance and distributed capacitance current can be well tolerated.