Grid-connected PV system consists of PV array,Grid-connected inverter,metering device and the power distribution system (as shown in figure 2-1).Solar panels make the PV energy to DC current,then the grid-connected inverter will make the DC current to AC current,which with same frequency and phase as grid voltage,after a setp-up transformer into the grid,and the grid-connected inverter is the key equipment of Grid-connected PV system.Grid-connected inverter EPV500KTP-TL,manufactured by Zhejiang Eifesun Energy Technology Co.,Ltd,is a type of power station PV Grid-connected Inverter with transformlesss,it can make the DC current generated by PV array to AC current that same frequency and phase as the grid,and feed into the Grid.