基于暂态电流波形相似度识别的柔性直流配电线路保护

Protection for Flexible DC Distribution System Based on Transient Current Waveform Similarity Identification

柔性直流配电系统可以更加灵活控制潮流、高效消纳直流负荷与分布式电源,是未来直流技术和配电系统结合的重要发展方向之一。但是由于电力电子设备耐受故障冲击电流能力差,保护需要利用数毫秒内的暂态信息识别故障区域,同时考虑高频下分布式电容和量测、通信误差影响,极具挑战。因此,提出一种基于暂态电流波形相似度识别的柔性直流配电系统直流线路主保护策略,与传统基于极性(直接量测幅值正负)的纵联保护相比,由于采用余弦相似度构成判据,更加有效提取多频段特征,受线路分布式电容影响较小,同时不需要严格的通信同步,相对于暂态量差动而言对于设备要求较低,可以快速准确识别直流故障区域。仿真结果表明所提保护策略能较好地满足直流配电系统对保护速动性与选择性的需求,数据窗长仅为0.3 ms,具有较好的抗分布式电容、过渡电阻和噪声能力,有一定的工程应用前景。

Flexible DC distribution system is an important development direction of future DC technology and distribution system.However,due to poor ability of power electronic equipment to withstand fault current,its protection needs to use transient information within a few milliseconds to identify fault area and,considering operation of protection based on transient unit,it is often confined by distributed line capacitance and communication error,thus resulting in a challenge.Hence,this paper proposes a new protection scheme for flexible distribution system based on cosine similarity of DC current waveform.Compared with the traditional current polarity comparison based pilot protection directly measuring current direction(positive or negative),this paper proposes cosine similarity criteria to efficiently extract the multi-band features of the transient current.The proposed method is robust to distributed capacitance,and not requires strict communication synchronization.Therefore,the proposed pilot protection has lower instrument requirements comparing with traditional transient current differential protection,and can quickly and accurately identify fault position.Simulation results show that the proposed protection scheme can identify internal faults in less than 0.3 ms with good reliability and high sensitivity.The proposed protection scheme is feasible for industry application and relatively robust to noise and high fault resistance,enabling the communication not to be strictly synchronized,and will not be affected by distributed line capacitance.