Grid impedance identification method for grid-connected inverter considering grid background harmonics

Abstract

The invention provides a grid impedance identification method for a grid-connected inverter considering grid background harmonics. The method comprises steps that firstly, a voltage of the grid-connected inverter and the arm-side current are measured by a voltage sensor and a current sensor respectively, and the voltage and the arm-side current are converted by a proportional integral controller to obtain modulated voltage signals; secondly, a high-frequency voltage signal is injected into the modulated voltage signals and then inputted into the grid-connected inverter through a control system, the voltage of the grid-connected inverter is updated, the grid side current of the grid-connected inverter is measured by the current sensor, and the updated voltage and the grid side current are respectively substituted into a voltage extraction module and a current extraction module; and lastly, an improved complex filter is utilized to extract a high frequency voltage signal and a high frequency current signal of the grid of the grid connected inverter, and an impedance value of the grid is obtained through calculation. The method is advantaged in that the improved complex filter takes into account the effects of 5th and 7th high frequency background harmonics of the grid, and identification accuracy of grid impedance is improved.

Description

technical field [0001] The invention relates to the technical field of power electronics, in particular to a grid-connected inverter grid impedance identification method considering grid background harmonics. Background technique [0002] In recent years, with the rapid expansion of the installation scale of new energy grid-connected inverters, more and more power grids have shown the characteristics of "weak grids", and their impedance is also increasing, which affects the stability of grid-connected inverters. Running has had a huge impact. For the control of grid-connected inverters in weak grids, the use of impedance-based stability criteria is an important method to study the interaction between grid-connected inverters and the grid, and this criterion needs to obtain accurate grid impedance information , therefore, it is of great significance to study the grid impedance identification method. Commonly used grid impedance identification methods mainly include passive ...

AI Technical Summary

Problems solved by technology

[0005] Aiming at the technical problem that the existing grid impedance identification methods do not consider the background harmonics of the grid, resulting in low identification accuracy of the grid impedance, the present invention proposes a grid-connected inverter grid impedance identification method that considers the grid background harmonics. The improved complex filter is used to extract the high-frequency voltage signal and high-frequency current signal from the voltage extraction module and the current extraction module respectively to obtain the impedance value of the power grid. The complex filter adopted in the present invention adds 5 times and 7 times background of the power grid Harmonic suppression module can improve the accuracy of grid impedance identification, thereby reducing the impact of grid background harmonics on grid impedance identification

Images