A Self-Adapted Compositive Modulation Method for Full-Bridge Modular Multilevel Converter

This paper proposes a self-adapted compositive modulation (SACM) method for full-bridge modular multilevel converter (FB MMC) under boosted modulation index, aiming at reducing the total harmonic distortion (THD) of AC voltage with low switching frequency. The SACM synthesizes the nearest-level modulation (NLM) and self-adapted pulse width modulation (SAPWM). The integer numbers of full-bridge submodules (FBSM) are switched in with NLM while the decimal numbers of FBSMs are switched in using SAPWM. The SAPWM is designed sufficiently considering the output characters of FBSMs under boosted modulation index. It can adjust the carrier phase difference of FBSMs in upper and lower arms according to their output states. As a result., the levels of the inner electromotive force is increased in the entire fundamental period. Moreover, the modified capacitors voltage balance scheme is utilized in the SACM to maintain low switching frequency. The feasibility of the SACM is verified through simulation.