Modular Multilevel Converter Impedance Computation Based on Periodic Small-Signal Analysis and Vector Fitting

Instability and oscillation issues originating in high-voltage direct current (HVDC) systems comprising modular multilevel converters (MMCs) are gaining increasing interest the research community. To detect such phenomena advance, considerable effort has been devoted recently to developing MMC models for small-signal analysis. The derivation of is a challenging task due topology complex control structure MMCs, which results them having multi-frequency response. address this issue, scholars developed methods based on dynamic phasors harmonic state-space modelling, which, however, require extensive pen-and-paper computations. In paper, periodic analysis (PAC) adopted determine numerically several MMCs transfer functions. Such functions can be computed between any electrical circuit node or input/output port, without need recast three-phase average model derive linear equivalent one, possibly DQ-frame. We show how vector fitting allows converting these algebraic representations, profitably used design study their stability following some parameter changes. showcase feature, we exploit one DC-side instability point-to-point HVDC system.