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This work presents a flexible thermal modeling methodology for power semiconductor modules. It allows time efficient simulation of temperature cycling for different module designs and operation profiles. To keep the model compact and flexible as well as accurate, the solid state heat conduction paths of the power modules are modeled by a 3D finite difference model. It is combined with an analytical heat sink model describing convective cooling. The temperature gradient of the cooling fluid is captured by a mass transportation model. The resulting linear state space model can be easily formulated in discrete time domain to allow a fast and detailed simulation of thermal load transients. With the balanced truncation based model reduction technique, the thermal state space model is efficiently reduced to allow fast analysis of thermal cycling and reliability issues. Finally, the thermal model is validated with measurements and data from the manufacture. [ABSTRACT FROM AUTHOR]

Electrochemical impedance spectroscopy can be used to obtain simulation models for the non-linear, non-stationary dynamic behavior of electrochemical power sources. Some extensions of porous-electrode theory are necessary for this purpose, which are not provided by standard EIS data evaluation software. This paper presents experimental data and consistent equivalent-circuit models for different dc conditions, regarding three electrochemical systems: supercapacitors as almost ideally blocking porous electrodes, lead/acid batteries under overcharge (water electrolysis) operation, and the same battery type under discharge/charge operation. The series inductance which masks the electrochemical behavior for frequencies as low as 100 Hz for a 100 Ah cell can be attributed mainly to the macroscopic cell geometry. The dependence of impedance parameters on direct current (non-linearity), temperature, state-of-charge, and previous discharge/charge regime is investigated. It is shown that model parameters extracted from the impedance spectra are closely linked with the charge-transfer kinetics, double-layer capacitance, transport limitation, and porous structure of the electrodes. Consequences for impedance-based determination of the battery''s state-of-charge or state-of-health are discussed. [Copyright &y& Elsevier]

With large scale battery systems being more and more used in demanding applications regarding lifetime, performance and safety, it is of great importance to utilize not only cells with a high cyclic and calendric lifetime but also to optimize the whole system architecture. The aim of this work is therefore, to highlight the benefits of a modular system architecture allowing the use of hybrid battery systems combining high power and high energy cells in a multi-technology system. To achieve an optimized performance, efficiency and lifetime for an electric vehicle the complete drive train topology has to be taken into account instead of optimizing one of the components individually. Consequently, the topic will be analyzed from the system’s point of view, addressing in particular the modularization of the battery as well as the power electronics needed to do so. It will be shown that a highly flexible battery system can be realized by dc-to-dc converters between a modular, hybrid battery system and the drive inverter. By the dc-to-dc converters the battery output voltages and the inverter input voltages are decoupled. Hence, the battery’s topology can be chosen unrestrictedly within a wide range and easily be interconnected to a common dc-link of a different voltage. The benefits of this flexibility will be analyzed in detail showing especially how the lifetime of the battery system can be improved and the impact on system weight. [ABSTRACT FROM AUTHOR]

[Display omitted] • Methodology for scalable LCA to compare ac and dc distribution systems. • Substantial reduction in material usage through shift from ac to dc microgrids. • Dc microgrid system with reduced emissions for almost all observed cases. • Energy mix identified as the main driver for climate change impact. Microgrids integrating local renewable energy sources at low-voltage level show promising potentials in realizing a reliable, efficient, and clean supply of electricity. Further improvements are expected when such a microgrid is operated based on direct current (dc) instead of alternating current (ac) infrastructure for power distribution commonly in use today. Our study aims to systemically quantify the gap between environmental impacts of microgrids at building level using the case study of power distribution within office buildings. For this purpose, a scalable comparative life cycle assessment (LCA) is conducted based on a technical bottom-up analysis of differences between ac and dc microgrids. Particularly, our approach combines the micro-level assessment of required power electronic components with the macro-level requirements for daily operation derived from a generic grid model. The results indicate that the environmental impacts of employed power electronics are substantially reduced by operating a microgrid based on dc power distribution infrastructure. Our sensitivity analyses show that efficient dc microgrids particularly lead to savings in climate change impact emissions. In addition, our study shows that the state-of-the-art scaling rules of power electronics currently used in LCAs leads to inaccurate results. In contrast, the proposed methodology applies a more technical approach, which enables a detailed analysis of the environmental impacts of power electronic components at system level. Thus, it provides the foundation for an evaluation criterion for a comprehensive assessment of technological changes within the framework of energy policy objectives. [ABSTRACT FROM AUTHOR]

Abstract: Reduction of oxygen was investigated on porous electrodes made of La1−x Ca x CoO3 (with 0≤ x ≤0.6) perovskite-structured oxides, prepared by a sol–gel process. It was found that both the reaction rate and the electrode active surface area (determined by cyclic voltammetry in a narrow capacitive potential range and by impedance spectroscopy) depend on the partial substitution ratio x, both displaying a maximum value for x nearly equal to 0.4. However, in spite of the parallel trend exhibited by the reduction current and the electroactive surface area parameter, the current varies much more with x, that is, while the change in the surface area amounts to approximately 40% over the explored x range, the current increases fivefold. Subsequent investigation of the electrode surface composition revealed that surface cobalt concentration (estimated by XPS analysis) deviates significantly from the nominal bulk composition (determined by EDX analysis). It follows a similar dependence on x, showing equally a maximum for x near to 0.4. Such a behaviour seems to have a greater effect on the reaction rate, since Co cations are the surface active sites for oxygen electro-reduction. [Copyright &y& Elsevier]