DC-link capacitors are an important part in the majority of power electronic converters which contribute to cost, size and failure rate on a considerable scale. From capacitor users' viewpoint, this paper presents a review on the improvement of reliability of dc link in power electronic converters from two aspects: 1) reliability-oriented dc-link design solutions; 2) conditioning monitoring of dc-link capacitors during operation. Failure mechanisms, failure modes and lifetime models of capacitors suitable for the applications are also discussed as a basis to understand the physics-of-failure. This review serves to provide a clear picture of the state-of-the-art research in this area and to identify the corresponding challenges and future research directions for capacitors and their dc-link applications.

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Power electronics has progressively gained an important status in power generation, distribution, and consumption. With more than 70% of electricity processed through power electronics, recent research endeavors to improve the reliability of power electronic systems to comply with more stringent constraints on cost, safety, and availability in various applications. This paper serves to give an overview of the major aspects of reliability in power electronics and to address the future trends in this multidisciplinary research direction. The ongoing paradigm shift in reliability research is presented first. Then, the three major aspects of power electronics reliability are discussed, respectively, which cover physics-of-failure analysis of critical power electronic components, state-of-the-art design for reliability process and robustness validation, and intelligent control and condition monitoring to achieve improved reliability under operation. Finally, the challenges and opportunities for achieving more reliable power electronic systems in the future are discussed. Index Terms-Capacitors, design for reliability (DFR), insulated-gate bipolar transistor (IGBT) modules, physics-offailure (PoF), power electronics, robustness validation. I. INTRODUCTIONP OWER electronics enables efficient conversion and flexible control of electric energy by taking advantage of the innovative solutions in active and passive components, circuit topologies, control strategies, sensors, digital signal processors, and system integrations. While targets concerning efficiency of power electronic systems are within reach, the increasing reliability requirements create new challenges due to the following factors:1) mission profiles critical applications (e.g., aerospace, military, more electrical aircrafts, railway tractions, automotive, data center, and medical electronics); 2) emerging applications under harsh environment and long operation hours [e.g., onshore and offshore wind tur-Manuscript

voltage ride-through of single-phase transformerless photovoltaic inverters," IEEE Trans. Industry Applications, in press.

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Abstract-Reliability analysis is an important tool for assisting the design phase of a power electronic converter to fulfill its life-cycle specifications. Existing converter-level reliability analysis methods have two major limitations: 1) based on constant failure rate models and 2) lack of considerations of long-term operation conditions (i.e., mission profile). Although various studies have been presented on power electronic component-level lifetime prediction based on wear-out failure mechanisms and mission profile, it is still a challenge to apply the same method to the reliability analysis of converters with multiple components. Component lifetime prediction based on associated models provides only a Bx lifetime information (i.e., the time when X% items fail), but the time-dependent reliability curve is still not available. In this paper, a converter-level reliability analysis approach is proposed based on time-dependent failure rate models and longterm mission profiles. Two different methods to obtain the component-level time-to-failure are illustrated by a case study of dc/dc converters for a 5 kW fuel cell based backup power system. The reliability analysis of the converters with and without redundancy is also performed to assist the decision making in the design phase of the fuel cell power conditioning stage.Index Terms-Fuel cell system, system-level reliability, Weibull distribution, power semiconductor, capacitor, reliability block diagram.

Bond wire fatigue is one of the dominant failure mechanisms in IGBT modules. However, the bond wire lifetime is not easily predictable and measurable to date due to several challenges. To overcome this challenge, this paper proposes a Monte Carlo based analysis method to predict the lifetime consumption of bond wires in a Photovoltaic (PV) inverter under long-term operation. The parameter distributions of IGBTs due to manufacturing variation and the annual stress profiles due to intermittent nature of solar irradiance and ambient temperature are taken into consideration. The proposed method enables a more realistic lifetime prediction with a specified confidence level compared to the state-of-the-art approaches. A study case on IGBT modules in a 10 kW three-phase PV inverter demonstrates the procedure and the results of the analysis. Finally, the lifetime distribution of bond wires permits to estimate the risk of unreliability of a single IGBT in a Photovoltaic (PV) inverter.978-1-4799-6735-3/15/$31.00 ©2015 IEEE