A Novel Fault-Tolerant Control Method for Modular Multilevel Converter with an Improved Phase Disposition Level-Shifted PWM

This paper proposes a novel fault-tolerant control method for modular multilevel converter (MMC) with an improved level-shifted carrier PWM, based on the concept of virtual voltage. First, an improved phase disposition level-shifted (PD-LS) PWM with only one carrier in each arm is adopted. Then, based on the virtual voltage idea, a simplified control method is proposed to realize fault-tolerant operation without carriers reconfiguration. Compared with traditional fault-tolerant control methods, due to the reduced carriers generation and decreased comparisons between carriers and modulation waves, the modulation process of the proposed scheme can be dramatically simplified during both the pre-fault and the post-fault process. The effectiveness of the proposed method is verified by simulation and experiment results.