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This paper presents a system stability analysis of a grid-connected inverter from a linear system viewpoint. A Photovoltaic (PV) inverter model is derived using a system identification method, specifically the Hammerstein-Wiener model. The PV inverter is supplied by a controllable DC power supply and the inverter output is connected to a 220 V utility grid. The input and output characteristics on the inverter terminals are collected and the nonlinear model of the inverter is obtained. The inverter model is decomposed into three parts follow as nonlinear input, linear middle part and nonlinear output. Both nonlinear parts are deemed static where the dynamical behavior is described by the middle part. The stability of the inverter is analyzed based on a linearized model of the nonlinear system. Frequency response analysis is performed for insight on the system dynamical behavior.