I- Introduction

II- Principle of Operation

III- Open-Circuit Fault Analysis

IV- Fault-Diagnosis and Post-Fault Operation

V- Simulation Results

VI- Conclusion

References

Abstract

Due to several advantages, three-phase Dual Active Bridge (DAB) converter is widely used in numerous applications nowadays. On the other hand, this converter is very vulnerable to Transistor Open-Circuit Fault (TOCF). Therefore, a faulttolerant (FT) scheme has been proposed in this paper to solve the problem. First, normal and faulty conditions are investigated, and according to the results, a fault-diagnosis (FD) approach is introduced. Using the outcomes of FD unit, a new post-fault strategy is proposed for the converter. The FD method is based on the DC component of transformer phase currents, and the basis of FT technique is shedding the faulty phase. Some benefits of the proposed scheme are preventing the shut-down of the system, no overvoltage or overcurrent, no additional power components, and insensitivity to operational conditions. Simulation results are also provided to confirm the analyses, and evaluate the performance of the proposed scheme.

INTRODUCTION

Power electronic converters are used in many industries such as renewable energy systems, transportation, and aerospace. All these industries are striving to improve the reliability of the systems with cost-effective solutions. Additionally, apart from the human safety risks, failures in converters may lead to economic loss as a result of stoppage of the system as well as maintenance costs. As a solution for the problem, Fault-Tolerant (FT) converters have been proposed and become a wide research area in recent literature [1]. FT converters are proposed for a variety of applications, including an AC-AC converter [2], a multi-level converter in [3] and a quasi-Z-source inverter in [4]. Fault-Diagnosis (FD) techniques are the main part of the FT converters, which usually can identify the location of the fault [5]. Many FD methods are proposed for semiconductor faults [1]. Generally, after the detection of the fault, several post-fault strategies can be employed to guarantee the continuity of system operation in spite of the failure. Some of these strategies are as follows: redundancy, reconfiguration, and soft shutdown. Furthermore, according to a survey about failed power converters, the most vulnerable components of a converter are power semiconductors. It is important to note that semiconductor faults account for 31% of failures in converter systems [1]. These faults are categorized into two main groups, including, short-circuit (SC) and open-circuit (OC) faults [1]. If not dealt with properly, both types can lead to serious damages. Typically, sufficient mechanisms are embedded in gate-drivers and power converters for SC protection. Unlike the SC fault, an OC fault usually remains undetected for a long time, deteriorating the performance of the system and can damage all the components. In addition, an OC fault in a power converter can occur as a result of the switch failure or a driver breakdown and it accounts for a large percent of semiconductor failures [6]. In addition, Dual Active Bridge (DAB), thanks to its numerous advantages, is extensively used in numerous applications. This converter has the benefits of high-power density, bidirectional power transfer, galvanic isolation, and so forth. All these benefits have paved the way for the usage of DAB in several applications, namely, electric vehicle, highfrequency-link power conversion systems, and battery storage systems[7]. Additionally, three-phase topology of the converter is usually preferred, in terms of efficiency and power-density, in industrial applications [8]. Having a large number of power semiconductors besides the corresponding gate-drivers, has made three-phase DAB seriously vulnerable to the power semiconductor failure. Even if a TOCF occurs in only one transistor of the converter, damage to other components, including 11 healthy switches, and the shutdown of the system will be unavoidable. Therefore, devising FD and FT techniques for this converter is necessary, in order to mitigate the consequence of TOCF and ensure the service continuity. In [9], faults on DC buses are investigated and techniques for tackling this problem is proposed.