Passivity-Oriented Analysis of Control Delay on Output Admittance Beyond the Nyquist Frequency of Grid-Following Inverters

Abstract

The interconnection stability of grid-connected inverters can be evaluated through the dissipative characteristics of the output admittance. While the influence of admittance components beyond the Nyquist frequency (NF) on stability has been recognized, the effects of control delays on high-frequency admittance behavior still merit further investigation. A detailed analysis of output admittance is presented, considering two primary delay sources: the system sampling period and the sampling instant. The absolute delay defined by the sampling frequency is quantitatively assessed, and the relative delay caused by the sampling instant affects both the depth and the span of the negative damping region. The results indicate that although increasing the sampling frequency mitigates nonpassive admittance effects above the NF, nonpassivity remains a key contributor to high-frequency instability. To address this issue, an admittance-based passive damping method is developed based on an admittance model that includes frequency aliasing effects to improve high-frequency stability. The experimental results validate the theoretical analysis and demonstrate the effectiveness of the proposed method.