The expansion of the electricity grid connected photovoltaic sources requires the development of solutions for solving problems caused by disturbances in the electrical network due to their strong variable character of energy sources. The power generation of grid-connected photovoltaic plants is increasing all over the world and these plants a crucial part of the future electric energy system. To restrict the level of electromagnetic disturbance, currently effective technical solutions are based on power electronics. This paper deals with the issue of power quality alteration, by assessing the power electronics equipment operation mode on the grid-connected PV plants both on normal and restricted conditions operation. A general analysis was performed in the first section, to identifying the current state-of-the art of photovoltaic plants and their influence on power quality and an example was designed, starting from a real electric distribution system in order to create a general image of issues and solutions.