Active and reactive power operational region for grid-tied inverters

Regulations for grid-tied inverters, outlined in IEEE 1547, allow distributed energy resources to control the reactive power injected into or absorbed from the grid. The operational region of a grid-tied inverter has asymmetry around the PQ plane in terms of apparent power limitations and harmonics injected into the grid. This asymmetrical behavior, caused by the filter used to interface the inverter with the grid, must be considered in order to meet strict grid standards, e.g. IEEE 519 and 1547, for all desired operating points of a grid-tied inverter. The objective of this paper is to identify operational points available for grid-tied inverters and to explain how some operational points must be avoided due to undesirable characteristics, e.g. poor quality of the injected current waveform. This work (i) enables filter networks for distributed sources to be designed to meet grid requirements even under worst case operating conditions, (ii) provides distribution engineers with information regarding the feasible active and reactive power which can be generated by grid-tied inverters, and (iii) provides a basis for assessing operating point trajectories when altering the steady-state operation of grid-tied inverters. Simulation and experimental data are presented to verify the findings of this work.