A Novel Stability Analysis Method for Large-Scale Photovoltaic System

Abstract

According to the interaction between the inverter and the grid in the large-scale photovoltaic grid-connected system, an auxiliary system based on grid connection of a single inverter is introduced. Research shows that the stability of the inverter output current in large-scale photovoltaic grid-connected systems depends on the stability of the auxiliary system and the stability of the inverter itself. But the stability of the total grid-connected current depends only on the stability of the auxiliary system. Therefore, a method for stability analysis of large-scale photovoltaic grid-connected systems is proposed. For a large-scale photovoltaic grid-connected system that is connected to the ideal grid through the grid impedance Zg after the inverters of the same specification and model are connected in parallel, the stable determination conditions are: (1) The inverter itself is stable, that is, a single inverter is stable when it is directly connected to the ideal power grid; (2) A single inverter in a large-scale PV grid-connected system is stable through the grid impedance nZg to the ideal grid. The stability analysis method can transform the research on the stability of large-scale photovoltaic grid-connected systems into the stability of the grid-connected system of a single inverter. For the multi-inverter parallel grid-connected system with uniform specifications and models, the stability analysis method is applicable regardless of whether all inverter current loop input reference currents are identical. The simulation results verify the correctness of the theoretical analysis.