An Integrated PLL–LCL–VSG Framework for Improving Grid Synchronization and Power Quality in Multi-Inverter Photovoltaic Power Plants

Abstract

The penetration of PV power plants into modern power grids requires an integrated, coherent and reliable control architecture for inverters that is able to maintain the synchronization, frequency, and power quality with dynamic operations. In this work, we propose a PLL-LCL-VSG control architecture for grid-connected PV inverters that are used at peak-load times. Our system is a phase-locked loop (PLL) that synchronizes grids as per the standard, LCL filter to attenuate the harmonic, and a VSG controller to handle the frequency and virtual inertia. We developed a detailed MATLAB/Simulink model to measure the dynamic performance of our proposed control architecture for different load scenarios. The results of the simulation showed the correct synchronization with the RMS phase error of 0.19381° and phase-error settling time of 0.02355 s. The frequency was within the range 49.903 - 50.093 Hz with the maximum absolute frequency deviation of 0.097406 Hz. Harmonic analysis has shown that the THD reduces from 42.539% to 1.9054% (95.521% in the case of current THD) with the current THD decreasing by 22.691%. The inverter successfully provided 150 kW peak load with dynamic settling time of 0.085145 s and reactive power support up to 32.788 kVAr. The results indicate that the proposed PLL-LCL-VSG architecture increases the synchronization accuracy, frequency regulation capability, harmonic suppression and peak-load support performance. Thus, the proposed framework is a promising model to improve the stability and power quality of grid-connected photovoltaic generation plants during peak electricity demand.