PLL-less Active and Reactive Power Controller for Grid-Following Inverter

This paper presents a control scheme for single-phase grid-following inverters that does not rely on the phase-locked-loop (PLL) algorithm for synchronizing the injected current with the grid. The absence of the PLL avoids unstable low damping modes that are possibly originated from the PLL's nonlinear nature. Thereby, assuring the control scheme robustness, especially, in weak grid conditions. Furthermore, the proposed PLL-less control achieves tracking the commanded active and reactive power (PQ) set-point references in a single loop control scheme. Hence, reducing controller design complexity compared to conventional cascaded dual loop PQ control scheme. This work also illustrates the necessary conditions to assure that the control is asymptotically stable with weak resistive and inductive grids. Finally, several case studies are implemented to validate the theory developed.