Grid-Converter Stability Analysis Based on Bus Admittance Phase

Impedance-based stability analysis method is widely used for stability demonstration of interconnected converter systems. Prior work dominantly adopts the minor-loop gain, also known as the return-ratio matrix (RRM), as the stability indicator. However, this approach complicates the analysis by relying on both the magnitude and phase information. By alternatively selecting the total bus admittance as the stability indicator, this paper demonstrates that the number of phase shifting points (purely based on the phase information) in the eigenloci of total bus admittance, directly reflects the overall system stability for any interconnected converter system. Moreover, this paper establishes the relationship between the proposed method and two existing methods, i.e. the RRM-based method and passivity theory. The proposed method overcomes the conservative nature of the passivity theory and is effective for the stability analysis of non-minimum phase systems, where the RRM-based method cannot be directly applied. The comparative study is validated by the control hardware-in-the-loop model of an interconnected converter system.