Back Flash Overvoltage Damages All DC/AC Converters in Photovoltaic Systems

This research addresses real faults in photovoltaic (PV) systems in Cuba, as these faults result in damage to all converters, whether in operation or not, when atmospheric discharge strikes nearby. This phenomenon occurs in PV systems connected to the grid through a power transformer with an ungrounded connection on the converter side. The research examines the phenomenon of impulsive overvoltages originating from the grounding system of PV installations after lightning. A simplified model was created using MATLAB/Simulink, encompassing PV system devices with converters, surge protection devices (SPDs), metal oxide varistors (MOVs), a grounding system, and an impulsive overvoltage source simulating a lightning strike. The simulation results suggest that these overvoltages have a detrimental effect on the coordination of the SPDs and MOVs inside the inverter, which in turn damages the inverter and other devices in the PV system. This research is pioneering in its approach to addressing this phenomenon in PV systems, characterized by this study as back flash overvoltage (BFO). BFO impacts the devices connected to direct current (DC) and alternating current (AC) branches. The model demonstrates that modifying the output transformer connection on the low-voltage side (the converter side) to a grounded star connection significantly reduces the occurrence of damage to the inverter and other components of the PV system. The BFO has not been adequately addressed in international standards pertaining to safety in PV installations. The paper concludes with a series of recommendations pertaining to the implementation of the proposed solution.