IEEE Power Electronics Magazine - December 2016 - 29

P

ower electronics are facing continuous pressure to be cheaper and smaller,
have a higher power density, and, in some cases, also operate at higher temperatures. At the same time, power electronics products are expected to have
reduced failures because it is essential for reducing the cost of energy. New
approaches for reliability assessment are being taken in the design phase of
power electronics systems based on the physics-of-failure in components. In this
approach, many new methods, such as multidisciplinary simulation tools, strength testing
of components, translation of mission profiles, and statistical analysis, are involved to
enable better prediction and design of reliability for products. This article gives an overview of the new design flow in the reliability engineering of power electronics from the
system-level point of view and discusses some of the emerging needs for the technology in
this field.

Reliability Metrics in Power Electronics

IMAGE LICENSED BY INGRAM PUBLISHING

Modern society needs to become more energy efficient and use more renewable generation
to be sustainable. A key technology in this mission is power electronics, which convert electrical energy from one stage to another. In past decades, power electronics have been
widely installed in emerging energy conversion applications, such as renewables, motor
drives, aircraft, power quality/transmission, etc. The fast growth on the installed capacity
makes the failures of the power electronics system costly-due not only to the increased
maintenance and repair but also to the adverse impacts to other systems and loss of energy
commitments [1]-[6]. On the other hand, there has been continuous pressure for power
electronics manufacturers to reduce costs and keep their products competitive on the market. To satisfy the stringent reliability requirements while limiting the cost and development/
testing time, there is strong demand for more accurate evaluation and design of reliability
performance for power electronics converters.
Different from the conventional performance metrics for power electronics, such as efficiency, power density, total harmonics distortion, etc., reliability is a performance that is difficult to quantify and measure. In the past, most reliability information for power electronics
was collected at the component level from the statistics of failed products, and then experience-based handbooks were established as a foundation to predict the lifetime of the whole
converter system [1]. This approach has proven to be inaccurate as it is application independent, providing no clues for the root cause of failures or for design improvement. Research on
power electronics reliability has advanced in the last decades. However, an understanding of
the fundamental failure mechanisms of the power electronic components, the impact on the
reliability affected by multiphysical stressors (e.g., temperature, humidity, vibration, cosmic
radiation, etc.), and the interactions among them during operation is still lacking. Moreover,
the modeling of the impact and the need for a breakthrough in time-efficient reliability verification methods, coupled with demand from industry to reduce development costs, are great
scientific challenges.
A more advanced approach to predict the reliability of power electronics is shown in Figure 1.
In this method, a series of reliability tools are expected to be established and can be used to
transfer the mission profiles (i.e., the operating condition and environment of the system), as
well as the given converter designs, to a series of quantified reliability metrics defined in the
field of reliability engineering. In this approach, the applications of converter and reliability
performance are closely correlated, making it possible to accurately improve and verify the
design or operation of converters to achieve certain reliability specifications before they are
introduced into the market-this feature is significantly useful for power electronic system
manufacturers in reducing cost.

The Reliability Metrics for Power Electronics
The engineering definition of reliability is the probability that an item will perform a
required function without failure under stated conditions for a specified period of time [2].
Digital Object Identifier 10.1109/MPEL.2016.2615277
Date of publication: 20 December 2016

December 2016

z IEEE POWER ELECTRONICS MAGAZINE

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Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - December 2016

IEEE Power Electronics Magazine - December 2016 - Cover1
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