A review of active/reactive power control strategies for PV power plants under unbalanced grid faults

Fault ride through (FRT) capability is one of the challenges faced in the medium to high voltage large-scale grid-tied photovoltaic power plants (PVPPs). Besides that, due to the high penetration of installed distributed generation (DG) units, the grid voltage enhancement under unbalanced faults is a requirement of several standards and grid codes. The controller of the grid-connected inverter consists mainly of two parts: the selection of the reference active/reactive power and the calculation of the reference currents under faults. This paper reviews various strategies which are proposed in the reported literature for calculating the reference current as well as selecting the reference active/reactive power based on the grid voltage. The performances of these control strategies are investigated on the 150 kW NPC grid-connected multi-string PVPP, which is considered as the state of the art for medium power PVPPs. The PVPP is connected to the 12.47 kV medium voltage distribution system where different fault situations is simulated.