考虑电缆和架空线参数频变特性的直流电网阻抗建模

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

直流电网的故障特性可通过分析电网阻尼的方式获取,但传统电网阻抗建模往往忽略线路参数的频变特性,建模结果无法准确反映电网阻尼特性。为对比分析电缆和架空线直流电网故障电流特性的差异,文中首先基于矢量拟合提出一种考虑线路参数频变特性的直流电网阻抗模型。接着,基于此模型的幅频特性,对比分析电缆与架空线直流电网故障电流时延、初始上升率和幅值的差异,并研究改变电网关键参数对2种电网故障特性的影响。所提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。最后,基于对称单极双端系统极间短路故障进行仿真。结果表明:桥臂电感值增加时电缆直流电网故障电流上升率比架空线高24.96%,验证了电缆直流电网故障电流对感性关键参数变化更敏感的结论。

The fault characteristics of direct current(DC)grids can be analyzed by addressing the grid damping characteristics.However,the frequency-dependent characteristics of the transmission line parameters are usually ignored in the conventional grid impedance modeling methods,which cannot accurately reflect the grid damping characteristics.To compare and analyze the fault currents characteristics of the DC grids with cables and overhead lines,an impedance model of DC grid considering the frequency-dependent characteristics of the transmission line parameters based on vector fitting is proposed in this paper.Then,the proposed model is applied to compare and analyze the fault current features including time delays,initial rising rates and amplitudes of the DC grids with cables and overhead lines.Meanwhile,the impacts of the DC grids key parameters on the fault current characteristics of the two DC grids are investigated.Compared with the sweeping results of the frequency-dependent line model,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 more accurate than the simplified model.Finally,the simulation is conducted in a symmetrical monopolar two-terminal 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 that the fault currents of the DC grids with cables are more sensitive to the inductive key parameters than the DC grids with overhead lines.