Low-Frequency Passivity Characterization of Grid-Forming Inverter

This paper focuses on the system stability of grid-forming (GFM) control through passivity criterion. An accuracy small-signal impedance model under dq-frame is established, which is used to analyze the influence of controller coefficients on system stability by passivity theory. And the inherent characterization for the risk of low-frequency resonance is revealed, indicating that its non-passivity region always exists, regardless of controller coefficients and specific control schemes. Finally, the theoretical analysis is verified by simulation results and the experiment test.