Characteristics Analysis of Capacitor Voltage Ripples and Dimensioning of Full-Bridge MMC With Zero Sequence Voltage Injection

Compared to the conventional half-bridge submodule-based modular multilevel converter (MMC), the full-bridge submodule (FBSM) capacitance of FB-MMC can be reduced significantly with consideration of negative voltage state of the FBSM, which has benefits to cost and size reduction. This paper analyzes the characteristics of the FBSM voltage fundamental frequency and second-order harmonic fluctuations of the FB-MMC without and with zero sequence voltage injection (ZSVI) comparatively. The analyses show that ZSVI has almost no impacts on the FBSM voltage fundamental frequency fluctuations, while the second-order harmonic components become 5/6 times of the one without. Based on these analyses, with the same fluctuation constraint as the case without ZSVI, the FBSM capacitance dimensioning method is also presented. The correctness of the presented analyses is verified by comparative simulation results on a ±200 kV FB-MMC system and experimental results on a laboratory platform. The simulation and experimental results indicate that the FBSM capacitance of the FB-MMC can achieve a reduction about 10% with ZSVI.