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Keywords

grid-connected inverter; weak grid; impedance reshaping; grid impedance identification; dual harmonic injection

Abstract

Under weak grid conditions, the interaction between the control function of the grid-connected inverter and the grid impedance will reduce the phase margin of the inverter, aggravate the harmonic oscillations, and even lead to instability of the grid-connected systems. Traditional impedance reshaping strategies for grid-connected inverters can improve the stable operation of the grid-connected system. However, with the growing integration of large shares of new energy sources and new types of loads, the grid impedance presents random variations, which undermines the effectiveness of traditional impedance reshaping strategies designed for fixed scenarios. To solve this problem, an impedance reshaping strategy based on dual harmonic injection for grid-connected inverters is proposed. First, the equivalent impedance model of an LCL-type inverter is derived using mathematical methods, and the limitation of the traditional voltage feedforward strategy is analyzed under wide variations in grid impedance. Then, by injecting dual-harmonic disturbance signals into the grid-connected inverter, real-time and accurate grid impedance information is obtained. This information is used to dynamically adjust the traditional impedance reshaping strategy, ensuring sufficient phase margin under wide variations in grid impedance and improving the adaptability of the inverter to different grid working conditions. Finally, a simulation model is built in MATLAB/Simulink to verify the correctness and effectiveness of the proposed impedance reshaping strategy under weak grid conditions.

DOI

10.19781/j.issn.1673-9140.2025.03.024

First Page

222

Last Page

232

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