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This paper is mainly to develop a grid-connected photovoltaic simulation system with maximum power point tracking (MPPT) function using MATLAB software in order to simulate and predict the behaviors of the real photovoltaic system. An engineering model of the photovoltaic (PV) cell is first established and then combined with an MPPT algorithm, as well as models of an MPPT controller and a DC-DC converter, in order to verify the correctness of MPPT controller. A DC-AC inverter using double closed loop control system is used in this paper to track the characteristics of the grid. The outer DC voltage control loop is to keep the input DC voltage stable, and the inner grid current control loop is to ensure that the output current has the same frequency and phase angle as the grid voltage. PLL technique used in the control circuit of the inverter ensures the tracking accuracy of the output current. The simulation results show that the system not only achieves the maximum power point tracking function but also makes the outputs of the inverter are sine waveforms and have less ripple, and also the power factor is close to 1. Therefore the outputs of the inverter satisfy the demands of the grid-connected photovoltaic system.