Power Flow and Stability Analyses of a Multifunctional Distributed Generation System Integrating a Photovoltaic System With Unified Power Quality Conditioner

This paper presents detailed studies involving sizing, stability analysis, and power flow through the series and parallel power converters in a multifunctional three-phase distributed generation (DG) system composed of a single-stage photovoltaic (PV) system integrated into a unified power quality conditioner (UPQC). The UPQC operates as a bidirectional interface when the DG system is placed between the grid and either generic loads or ac microgrid. In the grid-connected mode, the DG system performs active power-line conditioning, while injecting the energy produced by the PV array into the grid. In islanded operation, the system can act as ac grid forming via a parallel inverter, whether there is the presence of an energy storage system. A complete study involving the power flow through the PV-UPQC is mandatory to achieve the overall understanding of the system operation and designing the power converters properly. For this purpose, sizing curves are presented and discussed. Furthermore, two strategies aimed at limiting and/or decreasing the power processed by the series and parallel inverters are presented and discussed in detail. Both simulation and experimental results are presented to evaluate the static and dynamic performances of the PV-UPQC system operating grid connected and grid islanded.