Minimizing Required DC Sources of Cascaded H-Bridge Multilevel Converter for Fault Suppression in Active Distribution Networks

Abstract

Single-line ground (SLG) faults are the most common faults in distribution networks. Cascaded H-bridge multilevel converters (CHMCs) can be employed to suppress fault current and potential and prevent hazards promptly. However, their application is limited by their high cost and large size. This article proposes a cost- and size-efficient implementation method of single-phase CHMC for fault suppression, performed by minimizing the required dc sources. In this method, the output voltage vector of CHMC is reconstructed during fault elimination by two mutually perpendicular subvoltage vectors, one perpendicular and the other parallel to the target output current vector of CHMC. The subvoltage parallel to the target output current, which provides all required active power output, is generated using an H-bridge cell supplied by a dc source with minimized capacity. The remaining H-bridge cells generate the subvoltage perpendicular to the target output current without any dc source employment since they are solely responsible for reactive power output, thus maintaining their dc capacitor voltages. The simulation study and experimental validation have been conducted, and the results demonstrate that not only is the proposed method cost- and size-effective but also effectively ensures SLG fault elimination.