FAULT-TOLERANT CONTROL SCHEME OF MODULAR MULTILEVEL CONVERTER IN MEDIUM-VOLTAGE MOTOR DRIVE APPLICATIONS

Abstract

This paper proposes a fault-tolerant control scheme for a modular multilevel converter (MMC) in medium-voltage motor drives. The redundant submodules (SMs) are implemented in each converter arm to bring advantages during healthy and fault-tolerant operations. During the healthy operation, redundant SMs are controlled to function as a normal half-bridge SM, which helps reduce the SM capacitor voltages, improving the system's reliability and loss reduction. During the fault-tolerant operation, the failure SMs are only bypassed in one converter arm, and the other arm’s SMs keep functioning; thus, it utilizes redundant SMs for future failure SMs. The injected scheme is also performed to ensure low voltage ripples on the SM capacitors during the low-speed operation. The feasibility of the proposed control scheme has been verified by simulation results for the 4160-V/1-MW MMC-fed induction motor drive system.