In this thesis, a detailed interaction analysis between the internal grid of a Photovoltaic ( PV ) power plant and the AC grid is performed. This study is approached obtaining the small - signal model of the PV power plant, including a specif ic model of the inverter control, the medium voltage cable layout, a Power Plant C ontroller (PPC) and the AC grid. This model includes the dynamics associated to the PPC as well as the detailed control of the PV inverters. Based on this model, the oscillat ion modes of the system are highlighted and a participation factor analysis is performed to identify which variables can be problematic. This analysis is carried out for different grid strength conditions and different cable impedance values. The derived l inear model and the subsequent mathematical analysis results are validated through time domain simulations.