Fault Detection and Tolerant Control of IGBT Open-Circuit Failures in Modular Multilevel Matrix Converters

The modular multilevel matrix converter (M3C) is a topology that can realize direct ac-to-ac power conversion. To increase the reliability of the M3C, submodule (SM) fault ride-through capability is required to avoid unscheduled shutdown caused by the failures of power components in its SMs, such as the open-circuit fault of insulated gate bipolar transistors. Although this kind of fault has been widely studied for the regular dc–ac modular multilevel converter (MMC), the existing fault diagnosis criteria and fault-tolerant control processes are not directly applicable to the M3C. To solve this problem, this article analyzes the behavior of the M3C under open-circuit faults and proposes a suitable fault detection criterion for the M3C by transferring the observation errors of circulating currents into specific values. Meanwhile, since the observers can only identify two types of faults but not accurately locate the faulty device in a full-bridge SM, a modified fault tolerance process is proposed. Moreover, this article proposes a method to obtain the actual maximum intrinsic errors (AMIEs) of the observers to determine fault diagnosis thresholds under different load conditions. A downscaled M3C prototype with 27 SMs is built, and experimental results are presented to validate the effectiveness of the proposed fault detection criterion, the fault-tolerant control process, and the AMIE-obtaining method.