Solar PV-Supported Multi-functional UPQC for Three-Phase System Using VCO-less-FLL

This paper demonstrates a three-phase multi-functional unified power quality conditioner (MF-UPQC) powered by solar photovoltaic (PV) using a voltage-controlled oscillator-less frequency-locked loop (VCO-less-FLL). The proposed system consists of an active shunt and series compensator linked with a shared DC link. The proposed MF-UPQC system offers clean energy and power quality (PQ) enhancement features such as harmonic elimination and balancing of source current, reactive power compensation, and mitigation of source voltage sag/swell/distortion. Furthermore, the VCO-less-FLL is proposed in this paper for proper grid synchronization under constant and changing frequency conditions. Results obtained from MATLAB/Simulink and a real-time simulator are presented to assess the performance of the MF-UPQC for various disturbances in source voltage (sag/swell/distortion) with dynamic nonlinear loading and variation in solar irradiance.The results show that the source current is balanced and sinusoidal, while the load voltage is held constant against the supply voltage variation. In addition to the mentioned conditions, the system was also tested under a supply frequency variation of 2Hz and found that the VCO-less-FLL continued the grid synchronization without altering the system operation. The system follows total harmonic distortion (THD) standards set by IEEE-519 and IEEE-1159 for source current and load voltage.