Output Impedance Derivation and Small-Signal Stability Analysis of a Power-Synchronized Grid Following Inverter

In recent years, grid-following inverters (GFLIs) and grid-forming inverters (GFMIs) have established their position as the mainstream synchronization techniques for the grid integration of inverter-based resources into power systems. However, both of these integration techniques have their shortcomings in weak, strong, and/or series-compensated grids. Recently, in the literature, a power synchronized GFLI has been proposed that does not suffer from the issues exhibited in GFLIs and GFMIs. This article provides an analytical output impedance of this power-synchronized GFLI that uses a linear parameter-varying controller (LPV-PSGFLI). This impedance is then used for impedance-based stability analysis via the Nyquist stability criterion. In addition, the derived impedance is validated via system identification, and a comparison between a conventional GFLI and an LPV-PSGFLI is made under various system strengths. It is seen that the LPV-PSGFLI can inject power into the grid, whereas the conventional GFLI fails when both are integrated into a very weak grid. Finally, the accuracy of the impedance-based stability analysis using the derived output impedance is validated in Matlab/PLECS and in experiments in various scenarios.