基于暂态能量流的模块化多电平高压直流电网接地优化配置

Optimal Allocation of Grounding System in High Voltage Direct Current Grid with Modular Multi-Level Converters Based on Transient Energy Flow

对于采用架空线的基于模块化多电平换流器的高压直流(MMC-HVDC)电网,直流侧接地短路故障发生率高,严重危害电网安全。在各类影响因素中,接地方式对故障电流演化影响明显。该文从系统的宏观能量转移与耗散的角度提出了基于暂态能量流(TEF)分析的接地参数优化方法,对接地电阻、电抗参数及接地点位置等因素对MMC-HVDC电网直流短路故障电流的演化影响进行了分析。该方法以TEF抑制率和抑制效率为优化目标,以直流电网中接地阻抗参数取值、接地点为优化变量,同时考虑了中性线电抗和故障点的影响。该文选取四端双极MMCHVDC电网中的直流单极接地故障(PTGF)算例,基于PSCAD/EMTDC搭建了仿真模型进行分析和优化。仿真结果表明该参数优化方法能有效地指导接地参数的设计,抑制直流故障电流和健全极过电压。

For modular multi-level converter based high voltage direct current(MMC-HVDC)grid using overhead lines,the incidence of DC side grounding short circuit fault is high,which seriously endangers the safety of the power grid.Among all kinds of influencing factors,the grounding mode has an obvious influence on the evolution of fault current.In this paper,an optimization method of grounding parameters based on transient energy flow(TEF)analysis is proposed from the point of view of perspective of macroscopic energy transfer and dissipation of the system.The effects of grounding resistance,reactance parameters and grounding location on the evolution of DC short circuit fault current in MMC-HVDC grid are analyzed.In this method,the TEF suppression rate and suppression efficiency are taken as the optimization objectives,the grounding impedance parameters and the grounding location in the DC grid are taken as the optimization variables.Meanwhile,the influence of neutral line reactance and fault point are considered.In this paper,an example of four-terminal bipolar MMC-HVDC grid under DC pole-to-ground fault(PTGF)condition is selected and a simulation model is built based on PSCAD/EMTDC for analysis and optimization.The simulation results show that the parameter optimization method can effectively guide the design of grounding parameters,restrain DC fault current and overvoltage of healthy pole.