考虑电缆和架空线参数频变特性的直流电网阻抗建模

电缆和架空线固有特性不同，导致二者故障电流特性有所差异。分析直流电网阻尼特性可以对电网故障电流特性进行研究，但直流电网阻抗建模往往忽略输电线路参数的频变特性，使得建模结果无法精确反映直流电网的阻尼特性。针对此问题，本文基于矢量拟合提出了一种考虑输电线路参数频变特性的直流电网阻抗模型。此模型阻尼特性与依频模型直流电网扫频结果相比，均方根误差低于0.6，准确性高于简化模型；随后，基于该模型幅频特性对比分析了电缆与架空线电网故障电流时延、初始上升率和幅值的差异，同时明确了电网关键参数改变对电缆和架空线电网幅频特性的影响，得出了与架空线相比电缆电网故障电流对感性关键参数变化更敏感的结论。对称单极双端系统极间短路故障的仿真结果显示，桥臂电感上升时电缆电网故障电流上升率比架空线电网高24.96%，验证了阻抗建模及理论分析的正确性。

Impedance modeling of DC grid considering the frequency-dependent characteristics of cable and overhead line parameters

Due to the distinguished inherent characteristics, the fault current characteristics of cables are different with those of overhead lines. The fault current characteristics of DC grids can be analyzed by addressing the grid damping charac-teristics. However, the frequency-dependent characteristics of the transmission line parameters are usually ignored in the conventional DC grid modeling methods, which cannot accurately reflect the grid damping characteristics. Aiming at this issue, an impedance model of DC grids considering the frequency-dependent characteristics of the transmission line parameters based on vector fitting is proposed in this paper. Compared with the frequency sweeping results from simulation, the proposed model performs well in reflecting the damping characteristic of the DC grid, where the root square error is less than 0.6, informing that the proposed model is much accurate than the simplified model. Then, the proposed model is applied to analyze and compare the fault current features, i.e., time delays, initial rising rates, and amplitudes, of cables and overhead lines. Moreover, the impacts of the DC grid key parameters on the ampli-tude-frequency characteristics of the DC grids with cables and overhead lines are investigated. According to the anal-ysis, the fault currents of the DC grids with cables are more sensitive to the inductive key parameters than the grids with overhead lines. Finally, the simulation is conducted in a symmetrical monopolar two terminals DC grid with pole-to-pole fault. The simulation results show that the fault current rising rate of the DC grid with cables is 24.96% higher than that of the DC grid with overhead lines when the arm inductance is increased, which validates the pro-posed impedance model and the theoretical analysis results.