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Tolstoy G.,KTH Royal Institute of Technology | Peftitsis D.,KTH Royal Institute of Technology | Rabkowski J.,KTHRoyal Institute of Technology | Rabkowski J.,Warsaw University of Technology | And 2 more authors.
IEEE Transactions on Power Electronics | Year: 2014

Silicon carbide (SiC) bipolar junction transistors (BJTs) require a continuous base current in the on-state. This base current is usually made constant and is corresponding to the maximum collector current and maximum junction temperature that is foreseen in a certain application. In this paper, a discretized proportional base driver is proposed which will reduce, for the right application, the steady-state power consumption of the base driver. The operation of the proposed base driver has been verified experimentally, driving a 1200-V/40-A SiC BJT in a dc-dc boost converter. In order to determine the potential reduction of the power consumption of the base driver, a case with a dc-dc converter in an ideal electric vehicle driving the new European drive cycle has been investigated. It is found that the steady-state power consumption of the base driver can be reduced by approximately 60%. The total reduction of the driver consumption is 3459 J during the drive cycle, which is slightly more than the total on-state losses for the SiC BJTs used in the converter. © 2013 IEEE. Source


Yildirim H.C.,Aalto University | Marquis G.,Aalto University | Marquis G.,KTHRoyal Institute of Technology
Analysis and Design of Marine Structures - Proceedings of the 5th International Conference on Marine Structures, MARSTRUCT 2015 | Year: 2015

In the past decade, High Frequency Mechanical Impact (HFMI) has significantly developed as a reliable, effective and user-friendly method for post-weld fatigue strength improvement technique for welded steel structures. The evaluation and features of developing guideline within the International Institute of Welding (IIW) for the design of structures improved using HFMI is briefly discussed. So far, the extra fatigue strength benefit for HFMI-treated high strength steels has been mostly shown for constant amplitude loading. This paper reports 68 available HFMI-improved welds subjected to overloads or pre-fatigue loads at various loading conditions prior to fatigue testing. These loading conditions are often seen for marine structures. © 2015 Taylor & Francis Group, London. Source


Eichhorn M.,French German Research Institute of Saint Louis | Pollnau M.,KTHRoyal Institute of Technology
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2014

We review the physics underlying the process of spontaneous emission, with a special focus on spontaneous emission into a resonator mode. We define the mode volume, verify the fundamental modal dimensions, present the spectral mode profile, the coherence time, the Q-factor, the Füchtbauer-Ladenburg equation, and the Purcell factor, and discuss their influence on different types of lasers. We obtain the relation between peak emission cross section, radiative lifetime, and emission linewidth. By interpreting spontaneous emission as stimulated emission driven by vacuum fluctuations, we derive the spontaneous-emission rate into a resonator mode and establish physical expressions for the fractions of spontaneous emission and total decay from the upper laser level into this mode. Furthermore, we discuss coupling of the atomic system with the coherent field inside a lasing resonator mode, resulting in the formation of a Mollow triplet, and demonstrate that it leads to a reduction of the spontaneous-emission rate by a factor of 2. © 1995-2012 IEEE. Source


Grishin A.M.,KTHRoyal Institute of Technology | Grishin A.M.,INMATECH | Grishin A.M.,Petrozavodsk State University
Materials Research Express | Year: 2016

Hard aluminum magnesium boride films were fabricated by RF magnetron sputtering from a single stoichiometric AlMgB14 ceramic target. X-ray amorphous AlMgB14 films are very smooth. Their roughness does not exceed the roughness of Si wafer and Corning glass used as the substrates. Dispersion of refractive index and extinction coefficient were determined within 300 to 2500 nm range for the film deposited onto Corning glass. Stoichiometric in-depth compositionally homogeneous 2 μmthick films on the Si(100) wafer possess the peak values of nanohardness 88 GPa and Young's modulus 517 GPa at the penetration depth of 26 nmand, respectively, 35 GPa and 275 GPa at 200 nmdepth. Friction coefficient was found to be 0.06. The coating scratch adhesion strength of 14Nwas obtained as the first chipping of the coating whereas its spallation failure happened at 21 N. These critical loads and the work of adhesion, estimated as high as 18.4 Jm-2, surpass characteristics of diamond like carbon films deposited onto tungsten carbide-cobalt (WC- Co) substrates. © 2016 IOP Publishing Ltd. Source


Esparza A.,Polytechnic University of Valencia | Aguero J.C.,University of Newcastle | Rojas C.R.,KTHRoyal Institute of Technology | Godoy B.I.,University of Newcastle
Automatica | Year: 2011

In this paper, we generalize existing fundamental limitations on the accuracy of the estimation of dynamic models. In addition, we study the large sample statistical behavior of different estimation-based controller design strategies. In particular, fundamental limitations on the closed-loop performance using a controller obtained by Virtual Reference Feedback Tuning (VRFT) are studied. We also extend our results to more general estimation-based control design strategies. We present numerical examples to show the application of our results. © 2011 Elsevier Ltd. All rights reserved. Source

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