Optimal Second-Harmonic Current Injection for Capacitor Voltage Fluctuation Reduction in Hybrid MMCs Under Grid-Side SLG Faults

The second-harmonic injection strategy for modular multilevel converters (MMCs) can effectively suppress the capacitor voltage fluctuation in steady states. However, under grid-side single-line-to-ground (SLG) faults will be more severe. Moreover, there is no research on mitigation of SLG hybrid MMC with mixed half-bridge and full-bridge sub-modules. To address this issue MMCs, an optimal current scheme mitigating proposed paper. mathematical models arm power fluctuations are firstly developed both states faults. Then, principle presented. reduced by suppressing three-phase fluctuations. A model has been established PSCAD/EMTDC to verify its effectiveness feasibility. Simulation results show that average reduction rate reach 55.77% strategy.