Influence of Zero Sequence Voltage Injection on Circulating Current Control of Full-Bridge Modular Multilevel Converter for Capacitor Voltage Ripple Minimization

摘要

With dc short circuit fault ride through capabilities, full-bridge submodule (FBSM) based modular multilevel converter (FB-MMC) has gained much interests as the FBSM capacitance can be reduced significantly when the modulation index equals to 1.414. In this paper, the analytic expression of the injected circulating current, which minimizes the FBSM voltage ripple of the FB-MMC is derived. Based on these derivations, the impact of zero sequence voltage injection (ZSVI) on the injected circulating current is analyzed in detail. It is shown that, with ZSVI, the amplitude of the injected circulating current can be reduced about 14% for achieving FBSM voltage ripple minimization, which has benefits to decrease the current stress of the semiconductor devices. Finally, the correctness of the presented analysis is verified by comparative simulation results on a ± 200kV/600 MW FB-MMC system.