Optimal Suppression Strategy for Capacitor Voltage Ripples of Hybrid MMCs Under Unbalanced Grid Voltages

Submodule (SM) capacitor voltage ripples in modular multilevel converters (MMCs) can be suppressed by harmonic injection strategy, which reduce the volume and cost of MMCs. The existing methods using dual strategy for hybrid MMCs only consider steady-state conditions. Harmonic strategies unbalanced grid conditions use single applied single-phase faults. To address above issues, this paper proposes an optimal second-order current third-order Firstly, mathematical model MMC under voltages is established. Then ripple characteristics SM are analyzed to reveal relationship between arm power ripples. Based on developed instantaneous model, parameters calculated. A simulation built PSCAD/EMTDC verify effectiveness proposed strategy. results show excellent performance suppressing