Impedance Reshaping of GFM Converters with Selective Resistive Behaviour for Small-signal Stability Enhancement

Grid Forming converters (GFM), based on virtual synchronous machine, Synchronverter, and droop-based control, provide an inductive impedance behaviour at the Point of Common Coupling (PCC). A controller has very limited capability to shape this inductive behaviour for small-signal instability prevention. In this paper, a virtual resistor (R
v
) is utilized to shape the GFM controller impedance, Z
inv
, in wide-frequency range. It aids to get high GFM converter impedance at the PCC, Z
pcc
, in low-frequency range. Moreover, cross-coupling terms of virtual inductor (L
v
) is utilized to decouple the converter impedance in the dq-frame at the PCC. The combined effect of R
v
and L
v
reshapes the converter impedance with selective resistive behaviour in low-frequency range. The proposed structure is analysed with bode plots and generalised Nyquist plots for a small-signal stability enhancement. A validation case is presented to verify the stability analysis.