INTEGRATION OF SMALL-SCALE PHOTOVOLTAIC SYSTEMS INTO SECONDARY DISTRIBUTION GRIDS USING PHASE-LOCKED LOOP METHOD TO IMPROVE STABILITY

Abstract

With the increasing share of renewable energies in the global energy mix, solar photovoltaic systems, especially small-scale and rooftop systems, have grown significantly. However, the increasing penetration of these systems into secondary distribution grids has created new challenges in the areas of dynamic stability, power quality, and grid synchronization. This paper examines all the mentioned aspects of a specific 10 kW integrated PV system connected to the secondary of the secondary distribution network, including various standards such as grid, operation under severe faults, and control methods related to small-scale photovoltaic power plants. The main innovation of this research is the use of the SOGI-PLL (based on the second-order generalized integrator) structure as a synchronization method in the secondary distribution network, simultaneously considering the weak network conditions, the presence of harmonics, and the requirements of the low-voltage transient (LVRT). Unlike traditional methods such as Delay-PLL, which have poor performance in polluted and weak network conditions, the proposed method, using the SOGI filter and frequency feedback loop, is able to accurately extract the fundamental frequency component from the polluted voltage and maintains its stability in networks with low short-circuit ratio (SCR=5). In this paper, we conclude that the phase-locked loop method is suitable for integrating small-scale grid-connected photovoltaic systems to achieve better stability in the distribution network.