Open-Circuit Fault Characteristics and Location Methods of Switch Elements for Cascaded Power Electronic Transformers

Abstract

Power electronic transformers (PETs) play an important role in AC/DC hybrid distribution networks. However, the fault probability of a PET is higher because of the use of many power electronic devices. The short-circuit protection of a PET is relatively mature, but studies on its open-circuit faults are limited to insulated gate bipolar transistors (IGBTs) in the cascaded H-bridge (CHB). Therefore, other types of open-circuit faults result in dead zones in the fault location process. In this paper, the open-circuit fault characteristics of switch elements at different positions of a PET are analyzed, and a protection circuit is designed for the possible overvoltage caused by the open-circuit fault in the CHB. Moreover, the fault location methods of switch element open-circuit faults are proposed. The proposed methods could adapt to the diversity of control modes, power directions and load levels. The correctness and effectiveness of the methods are verified via simulation tests. This work provides a basis for the implementation of fault-tolerant control and protection of PETs.