Harmonic State Space Analysis of the Influence of AC System Strength on Harmonic Coupling Characteristics of Photovoltaic Grid-Connected System

Most existing renewable energy power generation sites are connected to the AC grid with the help of power electronic converters. However, the wide application of multiple types of power electronic converters has led to complex harmonic interaction phenomena in power grids. In this paper, the harmonic state space method is used to establish a mathematical model of the two-stage LCL Photovoltaic (PV) grid-connected system, and the mathematical mechanism of the harmonic coupling characteristics of the grid-connected system is clarified. Subsequently, this paper utilizes the mathematical model to verify the phenomenon that the PV array output voltage/AC side background voltage has a harmonic excitation effect on the grid-connected current of the grid-connected system, proposing that when the strength of the external AC system is increased, the aforementioned excitation effect is enhanced, and vice versa. Finally, this paper uses time domain simulation to verify the accuracy of the model and conclusions.