Photovoltaic solar electricity and solar thermal has the highest potential of all the renewable energies, since solar energy is a practically unlimited resource and available everywhere. These days photovoltaic energy has the potential to play an important role in the transition towards a sustainable energy supply system, to cover a significant share of the electricity needs, and is expected to be one of the key energy technologies of this century. This paper presents a grid-connected photovoltaic (PV) system with the functionality of on-line Maximum Power Point Tracking (MPPT) at different irradiation and temperatures. The used Simulation data characteristics for climatic changes is similarly to the real Egyptian climatic data. The integration topology based on two-stage power conditioning modules, boost converter and three phase voltage source inverter. Therefore, the proposed MPPT algorithm implemented to the boost converter to enable PV arrays to operate at maximum power point during variable climate and irradiation conditions. Fuzzy logic algorithm (MPPT) technique control applied for on-line adapting the boost converter's duty cycle. The Boost output is feeding the two level PWM inverter DC link. Accordingly, the Inverter modulation depth is tuning to have constant AC voltage and frequency for grid integration requirements. In addition, the three-phase output current is in phase with the voltage to optimize the PV power utilization .The results show that proposed on-line fuzzy algorithm performance has a fast response, stable and reliable to have MPP for the PV system during the different irradiation.