A New Method for Broadband Oscillation Analysis of the Grid-Following Converter

The impedance-based method is widely used to analyze the stability issues of the grid-following (GFL) converter. However, this method lacks clear physical meaning, and also has limitations in stability determination and explaining the broadband oscillation phenomenon. Therefore, this article aims to propose a more general stability analysis method for the GFL converter to address these shortcomings. First, this article theoretically derives that the magnitude of the GFL converter impedance increases with the increase in voltage, while the phase remains unchanged. Then, a new stability analysis method is proposed. This method analyzes the dynamic interaction between the point of common coupling (PCC) fundamental frequency voltage and nonfundamental frequency voltage, further revealing the instability mechanism of the GFL converter. This method has a clear physical meaning. Based on this, a new stability discrimination interval based on admittance is obtained. Compared with the traditional impedance-based method, this method can more accurately determine the stability of the GFL converter grid-connected system, especially for cases where the resistive component in the line impedance is larger. In addition, this method can clearly explain the broadband oscillation phenomenon of the GFL converter. Finally, the effectiveness of the method proposed is verified through experiments.