Optimal Decomposition Based Harmonic Stability Analysis of Grid-Connected Interlinking Converter Systems Considering the Coupling Interaction

As a typical hybrid AC/DC power configuration, the grid-connected interlinking converter system operates under influences from both its AC and DC sides. Stability analysis for such systems often employs a hybrid AC/DC admittance model. However, the emergence of right half-plane (RHP) poles within the AC-DC coupling term can compromise the reliability of the conventional method under specific conditions. To deal with aforementioned problems, this paper introduces a sufficient and necessary condition to guarantee that the coupling term does not contain any RHP pole. Building on this, an optimal decomposition based harmonic stability analysis method is proposed, which provides two different decomposed ways that preclude potential RHP poles in the minor-loop gain. This allows for a more general and reliable analysis of the harmonic stability of the entire system. Furthermore, oscillation mechanisms associated with the coupling interaction are investigated. The effectiveness of the proposed method is validated through three cases using Matlab/Simulink. Results reveals that the AC-DC coupling dynamic can elevate instability risk by reducing system resistance from -2.6 to -20.4 when the AC side is stable, while decrease risk by increasing system resistance from -5.5 to -1.5 when the DC side is stable.