Analysis of Wideband Oscillation of Hybrid MMC Interfacing Weak AC Power System

The wideband oscillation of the hybrid modular multilevel converter (MMC)induced by excessive power infeed under weak ac system integration is analyzed in this article. A closed-loop state-space-based time-domain small-signal model firstly established to investigate instability problem. Different from findings two-level voltage-source-converters (VSCs) or half-bridge MMCs, root locus analysis and participation factor article reveal that frequency involved control loops are highly related operation status. When MMC operates as a rectifier, low-frequency observed with d-channel loop mainly participated. In contrast, high-frequency occurs q-channel when an inverter. This phenomenon explored aid two simplified loop-gain-based s-domain models, which derived referring selective modal approach. To suppress oscillation, sensitivity regarding impact parameters on phase margin conducted recognize effective parameter adjustment methods. results validated detailed electromagnetic simulations.