Impedance Measurement and Stability Analysis Based on Grid-Connected Inverter in D-Q Domain

In the context of weak AC grids, the significant growth in installed capacity of renewable energy sources has intensified the interactions among inverters and their interaction with the AC grid, severely affecting the safe and stable operation of the grid system. In response to this issue, this paper takes a small-disturbance perspective and, based on the "black box" testing, conducts impedance measurements on the characteristics of inverters and the grid. Subsequently, employing the Nyquist stability criterion, the paper presents a thorough analysis of the potential ramifications associated with grid-connection in scenarios where the internal parameters of the inverter are unknown and the system operates within a weak grid environment. Finally, the result is validated through simulation experiments.