Single-Stage Three-Phase Grid-Tied PV System With Universal Filtering Capability Applied to DG Systems and AC Microgrids

This paper proposes a single-stage three-phase four-wire grid-connected photovoltaic (PV) system operating with a dual compensating strategy and feedforward control loop (FFCL). Besides injection of active power into the grid, the PV system operates as a unified power quality conditioner (UPQC), suppressing load harmonic currents and compensating reactive power. Furthermore, regulated, balanced, and harmonic-free output voltages are provided to the load. Since the PV-UPQC is based on a dual compensation strategy, the series converter operates as a sinusoidal current source, whereas the parallel converter operates as a sinusoidal voltage source. Thus, seamless transition can be achieved from the interconnected to the islanding operation modes, and vice versa, without load voltage transients. Moreover, to overcome problems associated with sudden solar irradiation changes, fast power balance involving the PV array and the grid is obtained, since the FFCL acts on the generation of the series inverter current references. As a result, the dynamic responses of both inverter currents and dc-bus voltage are improved. Detailed analysis involving the active power flow through the inverters is performed allowing proper understanding of the PV-UPQC operation. Experimental results are presented to evaluate both dynamic and static performances of the PV-UPQC tied to the electrical distribution system.