A three-phase four-wire grid-connected photovoltaic system using a dual unified power quality conditioner

This paper proposes a photovoltaic (PV) power generation system, which is implemented by means of multilevel converters. The PV system is connected to utility grid and operates as a unified power quality conditioner (UPQC). Thus, the PV-UPQC system injects active power into the there-phase grid and, simultaneously, performs active power-line filtering, in order to improve the power quality. By using dual compensating strategy, the proposed PV-UPQC system is implemented by means of two back-to-back NPC converters sharing the same dc-bus, which is directly connected to the PV array. Both voltage and current controllers are implemented in the synchronous rotating reference frame (dq0-axis), such that they operate interconnected with the maximum power point tracking algorithm, as well as the dc-bus voltage controller. Simulation results are presented to verify the static and dynamic performances of the grid-tied PV-UPQC system.