A power system is a nonlinear one. When turbulence occurs in the power system, the stability of the system depends on the initial operating conditions and the nature of the turbulence. Nowadays renewable energy sources including photovoltaic have a key role to meet high demand of modern societies and to maintain voltage of the buses, while they also provide clean electrical energy. However, increasing the penetration level of photovoltaic systems will affect the power grid behavior. Hence, it is necessary to analyze the impact of their penetration level on the voltage stability, reliability and design of the grid, as well as the economic aspects. Investigating the voltage stability of the buses is significant in order to determine whether the amount of photovoltaic systems penetrations are enough to maintain the voltage of the bus and also to find the perfect and most beneficial location for these system in the power grid, which is discussed in this paper. In addition, a standard 30-bus test system stimulated by ETAP software, in order to evaluate the impact of Photovoltaic system penetration level on improving voltage stability. پرونده مقاله