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. © 2022 Electric Power Automation Equipment Press. All rights reserved.