Grid-connected Inverter Impedance Estimation Considering Grid Impedance and Frequency Coupling in the Stationary Frame

When the impedance criterion is used to analyze the stability of the three-phase inverter-grid system, the impedance acquisition of the grid-connected inverter is particularly important. In the stationary reference frame, the equivalent admittance accurately characterizes the impedance characteristics of the inverter. But it varies with the grid impedance and contains the frequency coupling component. This makes it difficult to measure the admittance accurately by the off-the-shelf frequency response analyzer (FRA). In this paper, a method is proposed to estimate the inverter impedance, which takes into account the influence of grid impedance and the frequency coupling effect. Consequently, correct stability analysis of the grid-inverter system is guaranteed. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed method.