Modeling and Analysis of a Digitally Controlled Grid-Connected Large-Scale Centralized PV System

Multi-inverter systems have been widely used for grid-connected large-scale centralized photovoltaic (LSCPV) plants. However, the problem of how time delays affect the stability of digitally controlled grid-connected LSCPV plants with multi-inverter systems has not been investigated sufficiently. This paper models a grid-connected LSCPV system as a cascade system and conducts a systematic study of the relationship between the time delay and the stability of a grid-connected LSCPV system. The analysis intuitively reveals the influence of the time delay on the stability of the grid-connected LSCPV system. The impact of the time delay on the stability range of the number of grid-connected inverters in LSCPV plants is discussed for the first time, and the stability range for a specific time delay is obtained from the root locus. In addition, considering the damping performance is negatively affected by the time delay, an improved capacitor-current-feedback active damping method is proposed to reduce the effects of the delay on the damping region and the robustness against variations in the grid impedance. Simulations and experimental results are presented to validate the theoretical analysis and the effectiveness of the proposed delay compensation method.