Protection of grid connected photovoltaic system during voltage sag

The grid-connected power electronic inverters are highly sensitive to grid disturbances and it is important to emphasize the necessity to reduce the effects of voltage disturbances on their operation. Among the wide range of power quality disturbances, voltage sags severely affect the performance of voltage source converters (VSC) operation of distributed generation (DG) units. In this paper, small signal model of photovoltaic, DC-DC boost converter and inverter are simulated in Matlab simulink software. The photovoltaic system is connected to a 20kV distribution feeder via a transformer. It can be seen if the voltage sag is happened in the system, the inverter switch current will be increased significantly. In order to protect the power electronic converters' switches during a voltage sag and increase the voltage sag ride through capability, use of fault current limiter (FCL), is proposed. It is shown that if the voltage sag happened with duration of half to thirty cycles, FCL limits the current of power electronic switches. So, the photovoltaic system although is kept connecting with grid during the voltage sag condition, the power electronic switches aren't harmed and have normal current during voltage sag duration.