Model-Free Output-Admittance Reshaping for Stability Enhancement of Grid-Connected Inverters

arXiv:2610.32095v1 Announce Type: new Abstract: Grid-connected inverters can be unstable when their current-control loops interact with an uncertain external network. Returning the existing controller to improve damping also alters current tracking because tracking dynamics and output admittance are coupled. This paper adds a local model-free control (MFC) loop around the existing current controller to reduce output admittance while closely preserving nominal current-tracking dynamics. The added loop uses local inverter parameters without an external grid or neighbouring converter model. A Norton formulation separates reference tracking from the current response to terminal-voltage disturbances and establishes a tracking-preservation condition for admittance reshaping. Reducing the disturbance response makes the inverter behave more like an ideal controlled current source. Averaged-model simulations show reductions exceeding 65% in the magnitudes of all four dq output-admittance elements over 10-200 Hz, with closely preserved current-tracking dynamics. Generalised Nyquist analysis predicts small-signal stability for all sampled grid-impedance cases with MFC, compared with 90.0% without MFC.