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Johann W. Kolar

Other affiliations: Alstom, Infineon Technologies, Bosch  ...read more
Bio: Johann W. Kolar is an academic researcher from ETH Zurich. The author has contributed to research in topics: Rectifier & Three-phase. The author has an hindex of 97, co-authored 965 publications receiving 36902 citations. Previous affiliations of Johann W. Kolar include Alstom & Infineon Technologies.


Papers
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Journal ArticleDOI
TL;DR: In this article, the authors derived the efficiency limit for an inductive power transfer between two flat half-filled disc coils based on a model for the eddy current losses in the coils and the losses due to electromagnetic radiation.
Abstract: The efficiency limit for an inductive power transfer between two flat half-filled disc coils is derived based on a model for the eddy current losses in the coils and the losses due to electromagnetic radiation. Analytic approximations for the coupling factor of the coils and eddy current losses are proposed and experimentally verified. It is shown that the approximative terms allow us to express the maximum efficiency of the coil pair analytically. If the strand diameter of the coil is sufficiently small, the efficiency depends only on the strand diameter, diameter of the coils, and the gap between the coils—but not on the operating frequency. Therefore, increasing the frequency does not result in higher efficiency but allows to reduce the coil thickness.

12 citations

Journal ArticleDOI
TL;DR: In this article, a novel injection scheme to improve the input current harmonics of a hybrid 12-pulse line-interphase-transformer rectifier with controlled output voltage by a two-switch boost-type output stage is presented.
Abstract: ∗∗ Member ∗ A novel injection scheme to improve the input current harmonics of a hybrid 12-pulse line-interphase-transformer rectifier with controlled output voltage by a two-switch boost-type output stage is presented in this paper. A theoretical derivation of the modulation for achieving purely sinusoidal input currents is introduced. Finally, the proposed scheme is analyzed and verified by numerical simulations and experimental results.

12 citations

Proceedings ArticleDOI
07 Nov 2002
TL;DR: In this article, the parasitic effects being responsible for the low-frequency distortions of DC output voltage and/or current are analyzed analytically and quantified for different operating conditions, and the minimization of the influence of the parasitic effect by proper pre-control is discussed.
Abstract: According to the experimental analysis of a 5 kW wide input voltage range three-phase three-switch buck-derived unity power factor PWM rectifier, the ideally constant DC output current does show a low-frequency distortion for open-loop control operation which is translated into low-frequency harmonics of the mains current. This distortion cannot be eliminated completely by closed-loop control since the controller bandwidth has to be limited for stability reasons and/or in order to avoid an excitation of the LC input filter. In this paper the parasitic effects being responsible for the low-frequency distortions of DC output voltage and/or current are analyzed analytically and quantified for different operating conditions. Furthermore, the minimization of the influence of the parasitic effects by proper pre-control is discussed. All theoretical considerations are confirmed by digital simulations.

12 citations

Proceedings ArticleDOI
01 Nov 2015
TL;DR: In this paper, the authors present the modeling and multi-objective optimization of a 25D inductor-based Fully Integrated Voltage Regulator (FIVR) with respect to efficiency and area power density.
Abstract: This work presents the modeling and the multi-objective optimization of a 25D inductor-based Fully Integrated Voltage Regulator (FIVR) with respect to efficiency η and/or chip area power density α, ie based on the η-α-Pareto-front, for microprocessor applications The Voltage Regulator consists of a four-phase interleaved buck converter operated in Continuous Conduction Mode (CCM) The rated power of the considered converter is 1W, and input and output voltages are constant and equal to Vin = 17V and Vout = 085V The optimization employs analytical models for the switches, which reside on chip and are manufactured in a 32nm CMOS SOI process, and for the passive components, ie racetrack inductors with magnetic core material and deep-trench capacitors that are fabricated in a silicon interposer The optimization procedure considers thermal aspects and disregards solutions that lead to excessive component temperatures According to the optimization results, either high efficiencies, greater than 90%, or high area power densities, with chip power densities greater than 20W/mm2 and interposer power densities higher than 15W/mm2 are achievable The optimized design point, selected from the η-α-Pareto-front, features an efficiency of 901%, interposer power density of 0309W/mm2, and a chip power density of 274W/mm2

12 citations

Proceedings ArticleDOI
01 Oct 2007
TL;DR: In this paper, a magnetically coupled damping layer is introduced for attenuating unwanted oscillations in active rectifiers, which can be implemented using standard materials and printed circuit board manufacturing processes.
Abstract: To increase the power density of active rectifiers, the switching frequency and switching-speed have to be raised considerably. However, the very fast switching transients induce a strong voltage and current ringing. In this paper, a novel magnetically coupled damping layer is introduced for attenuating these unwanted oscillations. The proposed damping layer can be implemented using standard materials and printed circuit board manufacturing processes. The system behavior is analyzed in detail and design guidelines are given. The effectiveness of the introduced layer is determined by layout parasitics, which are calculated with the partial element equivalent circuit method and compared to impedance measurements. The performance of the damping layer is demonstrated by simulations and verified via measurements on a laboratory prototype.

11 citations


Cited by
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Journal ArticleDOI

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08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: The most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-Clamped (flying capacitor), and cascaded multicell with separate DC sources are presented and the circuit topology options are presented.
Abstract: Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.

6,472 citations

Journal ArticleDOI
TL;DR: This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial applications to then center the discussion on the new converters that have made their way into the industry.
Abstract: Multilevel converters have been under research and development for more than three decades and have found successful industrial application. However, this is still a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. The aim of this paper is to group and review these recent contributions, in order to establish the current state of the art and trends of the technology, to provide readers with a comprehensive and insightful review of where multilevel converter technology stands and is heading. This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial applications to then center the discussion on the new converters that have made their way into the industry. In addition, new promising topologies are discussed. Recent advances made in modulation and control of multilevel converters are also addressed. A great part of this paper is devoted to show nontraditional applications powered by multilevel converters and how multilevel converters are becoming an enabling technology in many industrial sectors. Finally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

3,415 citations

01 Sep 2010

2,148 citations