一种混合双端直流输电线路暂态保护方案

为保证混合双端型高压直流输电系统安全运行，论文分析了混合双端直流输电线路两端边界元件的幅频特性。根据区内外故障下线路暂态电压瞬时能量差值的不同特征，利用改进局部均值分解方法（local mean decomposition，LMD）来提取故障分量，论文提出了一种基于改进型LMD分解的直流线路暂态保护方法。该方法有效降低了经典LMD分解在处理直流故障信号时的端点效应和滑动误差对仿真数据的影响。最后利用PSCAD仿真软件搭建了LCC-MMC混合双端型高压直流输电线路仿真模型，利用该仿真模型输出直流输电线路区内和区外故障仿真结果。并利用Matlab对故障数据进行处理，进行了算法仿真。仿真结果表明暂态电压信号的瞬时能量值在区内故障状态下明显高于区外故障和无故障状态。仿真结果验证了所提保护方法的正确性。该方法能够快速可靠的实现故障判别，具有较强的实用性。

A Transient Protection for Hybrid Double-ended DC Transmission Line

In order to ensure the safe operation of the hybrid HVDC transmission system, the amplitude-frequency characteristics of the boundary elements at the two ends of the hybrid double-ended DC transmission line is analyzed in this paper. According to different features in the condition of fault occurring on internal or external faults on the line, a DC line transient protection scheme based on improved local mean decomposition is proposed. The fault component of transient voltage instantaneous energy are extracted by using the improved LMD method. This method effectively reduces the influence of the endpoint effect and sliding error of the classical LMD on the simulation data when dealing with DC fault signals. Finally, the simulation model of LCC-MMC hybrid bipolar HVDC transmission line is built in PSCAD. The simulation model was used to output the simulation results of DC transmission line in different conditions of the fault occurring. The MATLAB is used to process the fault data and the algorithm is simulated. The simulation result shows that the instantaneous energy curve of the transient voltage signal on no fault or the external fault occurring is significantly lower than that of the internal fault occurring. The simultion result shows the protection principle presented is correct.This method can realize fault identification quickly and reliably, and has strong practicability.