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There exists a strongly nonlinear relationship between photovoltaic array and the ambient temperature and irradiance. It will result in an unstable output power. When the array is partially shaded, power-voltage characteristic curve has multiple peaks and the traditional MPPT(maximum power point tracking) methods lose their effectiveness. This paper presents an incremental conductance method based on voltage scanning. Firstly the peak where the maximum power point locates is acquired through voltage scanning Then incremental conductance method is used to search the more accurate maximum power point using the voltage acquired before. Lastly the maximum-power-point voltage and reference current can be located. Reference current is directly used in grid connecting control. With PI controller, we can decouple the LC grid-connected current under synchronous rotating coordinate system. The inverter output current gets in accord with the reference current and its phase gets identical with the phase of grid voltage. Unity power factor is achieved. Simulation results verify the described MPPT method's effectiveness and the stability of the grid control system.