Modified p-q theory applied to flexible photovoltaic systems at the 3-phase 4-wire distribution grids

This paper proposed corrected p-q control strategy for achieving maximum benefits from the photovoltaic (PV) systems when installed in 3-phase 4-wire distribution grids which have unbalanced and distorted nature. The PV is controlled to act as a flexible photovoltaic (FPV) system by combining active power filter functionality. The control system utilize corrected p-q control strategy and simple maximum power point tracking (MPPT) method to generate reference current for FPV system to inject maximum available power of PV array to grid and compensate current unbalance, load current harmonics, load reactive power demand and load neutral current. All of these functions may be accomplished either individually or simultaneously. With such a control, the combination of grid-interfacing inverter and the 3-phase 4-wire linear/non-linear unbalanced load at point of common coupling appears as balanced linear load to the grid. This new control concept is demonstrated with PSCAD/EMTDC software.