This paper presents stability analysis of a photovoltaic (PV) system with DC/DC flyback converter. Traditional methods of stability analysis have limitations due to the non-smooth nature of the converter, but it is possible to analyze a piecewise smooth system with the Filippov's method. Functions are presented for each of the surfaces defined by different switching states. Simulates the behavior of the converter using nominal operating parameters. Finally, we analyze the stability of the system, through a phase space diagram, varying the load resistance.