Grid Sensitivity Considerations On Multiple Parallel Inverters Systems

This paper discusses the possible interaction of grid-connected photovoltaic (PV) generators when a large number of equally rated inverter modules is connected in parallel. Such interaction is analyzed looking at the influence of the grid voltage on the inverter controlled current, which is called grid sensitivity in this paper, and at the impedance multiplication effect, where the grid impedance, seen by each inverter module, is multiplied by the number of inverters. This paper extends an existing mathematical description of the parallel inverter systems and discusses the effects of some current control actions. The proposed analysis is applied on the equivalent single inverter case, where the grid sensitivity is discussed using different current controllers. Finally, this analysis has been verified by simulation and by using an experimental setup comprising three 5.0 k V A grid-connected inverters working in parallel.