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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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Proceedings ArticleDOI
27 Jun 2016
TL;DR: In this paper, a comparative evaluation of inverter concepts considered by a team of ETH Zurich, FH-IZM and Fraza company for the GOOGLE Little Box Challenge is given.
Abstract: In recent years, driven by worldwide growing environmental awareness the research in power electronics was focusing on the development of highly efficient but mostly bulky converter systems e.g. for interfacing renewable energy to the grid. The GOOGLE Little Box Challenge was impulse to give the power density again more attention by motivating engineers worldwide to design a single-phase solar inverter system at the cutting edge of what is technically possible. In this paper a comparative evaluation of inverter concepts considered by a team of ETH Zurich, FH-IZM and Fraza company for the GOOGLE Little Box Challenge is given. Based on the lessons learned from the participation in the competition, for the considered inverter concepts the achievable efficiency, power density and the optimal modulation scheme are identified with a multi-objective ηρ-Pareto optimization. This provides a sound basis for the redesign of the existing system pushing the forefront of power density even further.

108 citations

Proceedings ArticleDOI
Andrija Stupar1, Thomas Friedli1, J. Minibock1, Mario Schweizer1, Johann W. Kolar1 
06 Mar 2011
TL;DR: In this paper, an efficiency-optimized, nearly 99% efficient, 5 kW three-phase buck-type PFC rectifier with 400 V output is presented, which is used to optimize the converter design for efficiency at full load.
Abstract: In telecom applications, the vision for a total power conversion efficiency from the mains to the output of PoL converters of 95% demands for an optimization of every conversion step, i.e. the PFC rectifier front-end should show an outstanding efficiency in the range of 99%. For recently discussed 400 V DC distribution bus voltages a buck-type PFC rectifier is a logical solution. In this paper, an efficiency-optimized, nearly 99% efficient, 5 kW three-phase buck-type PFC rectifier with 400 V output is presented. Methods for calculating losses of all components are described, and are used to optimize the converter design for efficiency at full load. Special attention is paid to semiconductor losses, which are shown to be dominant, with the parasitic device capacitance losses being a significant component. A prototype of the proposed rectifier is constructed which verifies the accuracy of the models used for loss calculation and optimization.

107 citations

Proceedings ArticleDOI
S. Waffler1, Johann W. Kolar1
01 Oct 2007
TL;DR: In this paper, a low-loss, constant-frequency, zero-voltage switching (ZVS) modulation strategy for bi-directional, cascaded, buck-boost DC/DC converters, used in a hybrid electrical vehicle (HEV), is presented and its benefits over state-of-the-art converters and soft-switching solutions are discussed in a comparative evaluation.
Abstract: A novel low-loss, constant-frequency, zero-voltage-switching (ZVS) modulation strategy for bi-directional, cascaded, buck-boost DC/DC converters, used in a hybrid electrical vehicle (HEV), is presented and its benefits over state-of-the-art converters and soft-switching solutions are discussed in a comparative evaluation. To obtain ZVS with the purposed modulation strategy, the buck+boost inductance is selected and the switches are gated in a way that the inductor current has a negative offset current at the beginning and the end of each pulse period. This allows the MOSFET switches to turn on when the anti-parallel body diode is conducting. As the novel modulation strategy is a software-only solution, there are no additional expenses for active or passive components compared to conventional modulation implementations. Furthermore, an analytical and simulation investigation predicts an excellent efficiency over the complete operating range and a higher power density for a multi-phase converter equipped with the low-loss modulation. Experimental measurements performed with a converter prototype verify the mode of operation and the ZVS principle.

106 citations

Proceedings ArticleDOI
16 May 2008
TL;DR: In this article, a dual active bridge, which can transfer 25 kW bidirectionally between a 5 kV and a 700 V dc bus at a switching frequency of 50 kHz, is presented.
Abstract: In the area of power electronics there is a general trend to higher power densities and efficiency. In order to continue this trend new devices, which enable high switching frequencies at higher power levels or show reduced losses at moderate switching frequencies are required. High voltage switches based on a series connection of SiC JFETs and one MOSFET in cascode connection meet these demands. For investigating the performance of the SiC based switch and its influence on the power density/efficiency a dual active bridge, which could transfer 25 kW bidirectionally between a 5 kV and a 700 V dc bus at a switching frequency of 50 kHz, is presented in this paper. There, especially the design of the high voltage/high frequency transformer and the switching as well as the static behaviour of the SiC switch is investigated in detail by simulations and experimental results in this paper.

106 citations

Journal ArticleDOI
TL;DR: This work presents an automated design procedure for series parallel resonant converters employed in electrostatic precipitator (ESP) power supplies, which reduces the designer effort significantly.
Abstract: This work presents an automated design procedure for series parallel resonant converters (LCC) employed in electrostatic precipitator (ESP) power supplies, which reduces the designer effort significantly. The requirements for the power supplies in ESP applications and means to derive an accurate mathematical model of the LCC converter, such as the power loss from commercial insulated-gate bipolar transistors, are described in detail in this paper. The converter parameters, such as resonant tank elements, are selected in order to improve the overall efficiency of the system, when a typical ESP energization operation range is considered. The analysis comprises two different control strategies: the conventional variable frequency control and the dual control. Both control strategies are analyzed by comparing semiconductor losses of five commercial modules. Finally, the circuit operation and design are verified with a 60 kW LCC resonant converter test setup.

106 citations


Cited by
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Journal ArticleDOI

[...]

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