Analysis and control of PV inverters operating in VAR mode at night

PV inverters are an important element of the future smart grids. Not only they contribute to the active power generation as distributed generators (DGs), but also they can help grid voltage/frequency stability by generating VAR. Although the number of PV installations is rapidly growing, the effective utilization of PV inverters remains low. As even if inverters are to operate in VAR mode during night hours, they still need some active power to compensate for their internal losses, regulate the DC bus and provide the desired level of reactive power. This paper will provide a detailed analysis of PV inverters' operation in VAR compensation mode when active power is not available. A new control scheme is proposed that enables inverter to absorb little active power from grid, regulate its DC bus voltage within limits, and inject the desired level of reactive power. Simulation and experimental results are provided to validate the analysis.