Impedance Analysis and Parameter Optimization of GFM Converter Based on Sensitivity Analysis

With the increasing proportion of renewable energy in the power system, the stability of renewable energy grid connection system has increasingly become an important factor causing the instability of the power system. The oscillation problem of the renewable energy grid connection system is a typical small signal problem, and the impedance analysis method is still an effective method to analyze the stability of the grid connection system. According to the investigation of several renewable energy grid-connected oscillation accidents recently, it is found that the frequency range of small signals leading to the unstable oscillation of the grid-connected system is very wide, which called broadband oscillation. The broadband oscillation of the grid-following (GFL) grid-connected system has been widely studied, but the broadband stability analysis of the grid-forming (GFM) renewable energy system with various control structure topologies is still not comprehensive. Therefore, this paper will analyze its small signal model based on the topology of the grid-connected converter with cascaded inner loop control. Then the control parameters of several important control structures are introduced, and the influence of each parameter on impedance characteristics is analyzed. The accuracy of the parameter influence law is proved by the curve of impedance characteristic, and the parameter optimization suggestions are given at last.