Multiple Open-Circuit Fault Diagnosis Method in NPC Rectifiers Using Fault Injection Strategy

This article proposes an open-circuit fault diagnosis method in power semiconductors of three-level neutral-point-clamped (3L-NPC) rectifiers by using a fault injection strategy. To enhance the anti-interference ability of the diagnosis method, an improvement is made in the traditional calculation method of phase-to-phase pole voltage residuals by selectively adopting the quantifying operation according to the current level. Then, the normalized and quantified residuals are obtained as the diagnosis variables. All signals for calculations are derived from the controller and pre-existing sensors, avoiding the requirement of extra hardware. To improve the diagnosis accuracy and speed, a fault injection strategy is designed. A preidentification method provides guidance for choosing the type of fault to inject. On this basis, the fault injection is implemented by revising the switching signals sent from the modulation module for a short time. In this way, inner-switch faults and outer-switch faults are easier to be differentiated, and the misdiagnosis of simultaneous multiple-switch faults is avoided. Therefore, the proposed diagnosis method is accessible to detect single-switch faults as well as multiple-switch faults in 3L-NPC rectifiers more accurately and fast. The experiments are carried out to confirm the effectiveness and the robustness of the proposed fault diagnosis method.

I. Introduction

Multilevel converters present great advantages compared with conventional and very well-known two-level converters, such as in low harmonic distortion and the high efficiency of power conversion [1]. One of the most common multilevel converter topologies is the three-level neutral-point-clamped (3L-NPC) converter, which has been largely employed in power supplies, solar photovoltaic systems, and power utility interfacing applications [2]–[4]. The reliability of NPC converters is of high priority in these applications. Since the multilevel converter is composed of many power switching devices, the possibility that a switching device suffers a fault increases, which is of great concern in recent years [5].