Open-circuit fault diagnosis for single-phase cascaded H-bridge rectifiers in electrical traction systems

The single-phase power electronic traction transformer (PETT) is a power device to realize the higher efficiency and reduction of weight in railway traction system. The single-phase cascaded H-bridge rectifiers (CHBR) are an important part of the single-phase PETT. In order to ensure its reliability, an open-circuit fault diagnosis method based on the mixed logical dynamic (MLD) model and the state estimator is built for the open-circuit fault of a single IGBT. The MLD model and the state estimator of the CHBR are constructed under both normal and faulty conditions, and the residual characteristics are analyzed in the two states. Fault diagnosis is achieved according to the residuals including fault information. The proposed method requires no additional sensor. Experimental results verify the availability and accuracy of the proposed method, and the location of the fault can be accomplished in a fundamental cycle.

I. Introduction

Compared with the industrial frequency transformer, the power electronic traction transformer (PETT) has the advantages of light weight, small volume, high efficiency, and environ-mental friendship. It is very suitable for high speed electric multiple units (EMUs). The first electric locomotive prototype which's the core electric traction device is the PETT has been put into trial. The single-phase PETT will be an important choice for future development of railway traction system. Most of research mainly focus on PETT topology and corresponding control technology in recent years [1]–[3]. However, for single-phase PETT applied to the railway traction system, how to ensure its safety and stable operation is also a key research point. The front-end for the PETT, single-phase cascaded H-bridge rectifiers (CHBR) are a core part of the system. The reliability of a large number of IGBTs is the key to the stable operation of the system. In the actual module, both IGBTs and anti-parallel diodes would experience open-circuit fault or short-circuit fault. The failure of the diode will cause transient over-voltage or over-current, and short-circuit fault of the IGBT will also cause over-current. These faults will eventually appear as an open-circuit fault. Therefore, research on the open-circuit fault can reflect the main fault phenomenon of IGBTs.