直流配电网在电能质量、稳定性、传输容量等方面具有交流配电网无可比拟的优势，逐渐占领配电网发展的高地。然而对于直流配电网线路保护方案的研究尚未完善，需要进一步探索。本文主要针对这一问题进行了分析研究，主要工作如下：

对VSC换流器和DC/DC直流变压器的工作原理和控制方式进行分析，利用PSCAD搭建±12kV辐射状中压直流配电网模型并进行正确性验证。

基于所搭建的仿真模型进行直流线路故障特征分析，研究电流故障分量极性以及线路零模功率在直流线路正常运行和出现单极故障时所表现出的差异特征，并进行故障识别判据的整定。最后通过仿真验证表明了该方法的快速有效性。

对直流线路的各种故障情况，分析直流线路在正常工况下与故障情况下直流线路所传输的一模功率幅值的差异特征并结合子馈线一模功率增量的正负得到区内、外故障识别判据；分析故障下直流线路正、负极电流暂态能量的差别进行故障选极判据的整定。仿真结果证明，本方法可以解决直流线路所出现的各种故障，并且在耐受过渡电阻和噪声干扰方面也具有良好的表现。

对直流配电网的直流线路引入限流电感作为边界元件，并利用小波包变换对其高频暂态能量进行提取，对比高频段暂态能量和的差别并结合主子馈线限流电感电压的正负进行故障区域的判别；通过引入Pearson相关系数进行直流线路故障前后高频暂态能量相关性的计算，并利用其值进行单、双极故障以及故障极的判别。仿真验证表明，该方法在耐受过渡电阻方面表现的更加优越，并且同样具有耐受噪声干扰的能力。

针对本文所提出的三种保护方法进行特点对比，得出了直流配电网整体保护方案的配置；然后针对基于MMC换流器的直流配电网进行本文所提保护方法的适应性验证，结果证实了本文所提保护方法的强适应性能力。

DC power distribution network has incomparable advantages over AC power distribution network in power quality, stability, transmission capacity and other aspects, and gradually occupies the highland of distribution network development. However, the research on the protection method of the DC distribution network is not perfect and needs further exploration. This paper mainly analyzes and studies this problem, and the main work is as follows:

The working principle and control method of the VSC converter and DC/DC transformer are analyzed, and the ±12kV radial medium-voltage DC distribution network model is built in PSCAD and the correctness is verified.

Based on the established simulation model, the fault characteristics of distribution lines are analyzed, and the polarity of fault current components and the difference characteristics of 0-mode power between normal operation of DC line and occurrence of single-pole fault are studied. Then, the fault identification criteria are set. And simulation results show that the method is fast and effective.

For various fault conditions of the DC line, the difference characteristics of amplitude of 1-mode power transmitted by DC lines under normal working conditions and fault conditions are analyzed, and the identification criteria of internal and external faults are obtained by combining the positive and negative of 1-mode power increment of sub-feeders. Meanwhile, the difference characteristics of the transient energy of the positive and negative current of the DC line under the fault occurring are analyzed to set the fault pole selection criterion. Subsequently, the simulation results show that this method can solve all kinds of faults of DC line, and has good performance in resisting transition resistance and noise interference.

The current-limiting inductor is introduced as boundary element of the DC distribution line in the established DC distribution network, and its high-frequency transient energy is extracted by wavelet packet transform. The difference of the sum of transient energy in high frequency band is compared and the fault area is identified by combining the positive and negative voltage of current-limiting inductor of the main feeder and sub-feeder lines. Then, the Pearson correlation coefficient is introduced to calculate the correlation of high frequency transient energy before and after distribution line fault to identify single-pole and pole-to-pole faults and fault poles. The simulation results show that this method is better in the tolerance of transition resistance and also has the ability to tolerate noise interference.

Finally, the performance of the three protection methods proposed in this paper is compared, and the configuration of the overall protection scheme of DC distribution network is obtained. And the adaptability of the proposed protection method is verified for DC distribution network based on MMC converter, and the results confirm the strong adaptability of the proposed protection method.

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