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Condition Monitoring and Reliability Oriented Design of Power Electronic Systems

Fernando González


  • DIRECTORS: Jon San Sebastián and Manuel Arias
  • UNIVERSITY: Universidad de Oviedo


Power electronic systems, in charge of the conversion of electrical power format, are currently arising due to the increasing interest in technologies such as electric mobility or renewable energy generation. However, their use in critical infrastructures brings with rigorous specifications in terms of reliability, both in terms of useful lifetime and failures in operation. The ever-increasing strict design requirements, in terms of efficiency and power density, along with the harsh environmental operating conditions, lead to more demanding requirements in terms of reliability. All in all, there has been an increasing interest in the reliability improvement of power electronic converters both from the research community and the industry. This improvement comes along with a reduction of costs, due to the enlarged useful lifetime of the system and the lower associated maintenance costs.

The reliability of power electronic systems is based on the reliability of its components, which is determined by the utilization profile in operation. Among them, power semiconductor devices are the most critical components in terms of reliability, being mainly stressed by temperature. Therefore, the reliability improvement of these components results in the reliability improvement of the power electronic system.

In this context, the main objective of this thesis is the reliability improvement of the power semiconductors in power electronic converters. To this aim, different condition monitoring methods have been proposed for these devices in order to detect the degradation before the failure takes place. Moreover, the useful lifetime of the power semiconductors in a traction converter has been analyzed, considering a typical utilization profile, in order to study the influence of different design variables and propose strategies for lifetime improvement.

Since failures in power semiconductors take place in their package, the internal design of the device defines how the monitoring can be accomplished. Therefore, its analysis is required, resulting in two proposals of condition monitoring systems for devices realized with one chip (singlechip) or with several chips in parallel (multichip). These systems are based on the real time monitoring of the operating conditions of each device, which are then employed to estimate their junction temperature and to detect their degradation. The proposed systems have been integrated in different converter prototypes and have been tested in operation in different scenarios, analyzing their possible implementation and validating their performance.

Afterwards, a study of the reliability of power semiconductor devices in a urban electric bus traction converter application is carried out, considering different application mission profiles. Based on this study, the most relevant reliability metrics of the system are extracted, and the influence of different design variables on these metrics is analyzed. Finally, a regulation strategy of the cooling capability of the cooling system of the power devices is proposed, aiming to reduce the thermal cycling of these devices caused by the typical mission profile of the application.

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