低频输电系统中运行频率对变流器稳定性影响分析

Analysis on impact of operating frequency on stability of converter connected to low frequency transmission system

为分析低频工况下运行频率对并网变流器小干扰稳定性的影响,分析了包含频率变量的锁相环、电流内环、LC滤波器和线路的动态方程,推导了对应的小信号模型,建立了变流器和电网的阻抗模型,展示了变流器阻抗模型不受运行频率影响的机理。组建了变流器并网系统的闭环特征方程,使用根轨迹法揭示了运行频率的变化对并网变流器小干扰稳定性的影响规律。基于MATLAB/Simulink平台,分别搭建了运行频率为20Hz和50Hz的变流器并网系统仿真模型,仿真结果与理论分析一致。

In order to analyze the impact of operating frequency on small-signal stability of grid-connected converter under the low frequency condition,the dynamic equations of phase locked loop,current inner loop,LC filter and line which containing frequency variables are analyzed,the corresponding small-signal models are derived,the impedance models of converter and power grid are established,and the mechanism that the converter impedance model is not affected by operating frequency is discovered.The closed-loop characteris⁃tic equation of grid-connected converter system is established.The root locus method is employed to reveal the influence laws of the variation of operating frequency on the small-signal stability of grid-connected converter.Based on MATLAB/Simulink platform,the grid-connected converter system with operating fre⁃quencies of 20 Hz and 50 Hz are established respectively,and the simulative results consistent with the the⁃oretic analysis.