Research on Harmonic Characteristics of Photovoltaic Power Grid Based on Multi-Scale Analysis

This study aims to address the challenge of multi-scale coupling of harmonics in high penetration photovoltaic power grids on power quality. A multi-scale collaborative analysis framework for harmonic characteristics in time, frequency, and space is constructed, and a theoretical model and composite suppression strategy that integrates transient wavelet decomposition, wideband admittance modeling, and hierarchical responsibility evaluation are proposed. Through the verification of the integrated experimental platform of light storage and charging, a millisecond level transient harmonic feature extraction algorithm is established under sudden changes in light illumination. Based on db4 wavelet decomposition, high-frequency switch harmonics and low-frequency resonant components are time-frequency separated. Combined with sliding window Fourier transform, a mapping relationship between steady-state power fluctuations and harmonic content is constructed; Derive the expression for the output impedance of the inverter, quantify the influence of grid inductance on resonance frequency, and construct a broadband impedance matrix for the distribution network; Using multi dependent variable complex domain partial least squares method to decouple background harmonics, a three-layer spatial responsibility evaluation model is established to control the quantification error of harmonic contribution within 5%. Experiments have shown that the multi-scale composite control strategy reduces the transient THD peak from 18.3% to 4.1%, achieves a suppression rate of 88.5% for the 5th harmonic THD in weak current networks, increases the system damping ratio by 60%, and improves the convergence speed of the prediction algorithm by 40% compared to traditional methods. The research results provide theoretical support and technical paths for harmonic control in photovoltaic power grids. The relevant methods can be extended to optimize the power quality of other distributed energy grid connected systems, achieving precise analysis and efficient control of the entire chain of harmonic generation propagation suppression.