Extended Linear Modulation Based Full Bridge Modular Multilevel Converter for Adjustable Speed Drives

The modular multilevel converters (MMC) are gaining popularity for medium voltage adjustable speed drives (ASD) due to modularity and efficiency. However, the MMC drives experiences high ripple voltage in submodule (SM) capacitor during low speed operation. In this paper, an extended linear modulation range operation of full-bridge (FB) submodule based MMC drives is proposed to reduce the ripple voltage. In addition, comparative study of the minimum energy storage requirement for the proposed drive and conventional MMC drive is also presented. This analysis includes the motor operating parameters (power factor, current, etc.,) variation due to the load torque profile is also considered for its effective evaluation. The detailed analysis reveals that the capacitor voltage ripple is significantly lesser with extended linear modulation when compared to the conventional modulation, making FB-MMC as a potential candidate for drives. The effectiveness of the proposed operation scheme is validated using PSCAD simulation study.