Open-Circuit Fault Diagnosis in NPC Rectifiers Using Reference Voltage Deviation and Incorporating Fault-Tolerant Control

This article proposes an open-circuit (OC) fault diagnosis method in three-level neutral-point-clamped (NPC) rectifiers. In this method, OC faults are detected based on the deviation between actual and expected reference voltages, which are obtained without complex calculation, precise modeling, and extra hardware. More importantly, this method innovatively incorporates fault-tolerant control into the diagnosis process to locate the faulty switch more accurately and quickly. Fault-tolerant control is triggered before confirming the faulty switch. It can completely or partly eliminate reference voltage distortion caused by any outer-switch faults. Making use of this feature, outer- and inner-switch faults can be differentiated by checking whether reference voltages return to normal. Unlike other invasive methods that amplify fault characteristics, this method does not aggravate fault consequences. Using fault-tolerant control to replace the invasive location step of other methods can make a timely intervention of OC faults and save computing resources used for fault diagnosis and tolerance. Also, this method considers different operating states of NPC rectifiers, including modulation index and power factor variation. Moreover, this method can be easily extended to multiple-switch and clamping diode fault diagnosis. Experiments are carried out to confirm the effectiveness of the proposed fault diagnosis method.