Universal control method for single phase grid-connected and islanded converters

A universal control method to operate the single phase inverters was proposed recently. The proposed method can operate the inverter regardless of whether it is connected to a stiff grid, to a weak grid, or to a load. Moreover, the transition between these modes of operation can be performed seamlessly. This feature makes the proposed method promising for smart microgrid applications where flexible and autonomous operation of the inverter is required. The proposed method is self-synchronizing and does not need a dedicated phase-locked loop (PLL). There are no switching actions required in the proposed control structure when the system´s operational modes change. This paper expands on the concept by incorporating the case where the output filter of the inverter is an LCL filter. Moreover, a current limiting mechanism is proposed to avoid over-current caused by grid voltage magnitude drops.