Power-Synchronized Grid-Following Inverter Without a Phase-Locked Loop

This paper proposes a power-synchronized control strategy for grid-following inverters (GFLIs) to regulate their power exchange with the grid without any need for sensing/regulating the point of connection voltage. Contrary to conventional GFLIs, which rely on phase-locked loops for grid synchronization and have difficulties in weak grid conditions, the proposed strategy is power synchronized and utilizes the inverter terminal voltage for power control leading to its seamless performance in ultra-weak grids. Additionally, since the proposed approach does not require any voltage regulation at the point of connection to the grid, contrary to grid-forming inverters, it can reliably operate in stiff and/or series-compensated grids as well. The proposed approach benefits from a decoupling control structure that is tuned using a loop-shaping method. Compared to conventional GFLIs, this approach does not need any extra hardware; hence, it can easily be retrofitted into the existing large fleet of GFLIs. The performance of the proposed controller is evaluated in Matlab/PLECS for both weak and stiff grids, and the findings are experimentally validated in a scaled-down setup.