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Author

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
02 Oct 1993
TL;DR: In this paper, the peak, mean, and RMS values of the component currents of a three-phase single-switch discontinuous inductor current mode boost rectifier are calculated analytically.
Abstract: In this paper the peak, mean, and RMS values of the component currents of a three-phase single-switch discontinuous inductor current mode boost rectifier are calculated analytically. The values are given in rated form in dependency on the output power and on the ratio of output voltage to the amplitude of the mains voltage. Furthermore, the influence of the voltage transfer ratio on the shape of the mains currents and on the power factor of the system is analyzed. The theoretical analysis is verified by digital simulation and a good consistency is achieved. Finally, the approach of the converter dimensioning based on the graphical representation of the calculation results is described and illustrated using a specific example. The correctness of the dimensioning is verified by measurements on a laboratory model. >

87 citations

Proceedings ArticleDOI
10 Sep 2000
TL;DR: In this paper, a three-phase unity power factor rectifier with a buck-derived input stage and a DC/DC boost converter output stage is presented, which has a wide input voltage range and a continuous sinusoidal time behavior of the input currents lying in phase with the input voltages.
Abstract: A new three-phase unity power factor rectifier with a three-switch buck-derived input stage and a DC/DC boost converter output stage is presented. This system has a wide input voltage range and a continuous sinusoidal time behavior of the input currents lying in phase with the input voltages which is also guaranteed in case of a failure in one phase of the mains. The input currents are controlled using a switching state sequence showing minimum switching losses. A multi-loop system control is realized by an outer output voltage controller and an inner-loop buck+boost inductor current controller. Furthermore active damping of the input filter resonance is provided. For increasing the output power of the system a parallel connection of two interleaved units is proposed. There, a low input current ripple is achieved, and the cut-off frequency of the input filter can be shifted to higher frequencies (resulting in improved control dynamics and a more compact design downsizing of the inductors and of the input filter).

87 citations

Journal ArticleDOI
TL;DR: This publication gives a comprehensive overview over different concepts of magnetically levitated motors with slice-shaped rotors that differ in their construction and the way the bearing and drive forces are created.
Abstract: This paper provides a comprehensive overview of different concepts of magnetically levitated slice motors with ring-shaped rotors that differ in their construction and the way the bearing forces and drive torque are created. After a general classification of magnetic bearings and the description of the technical principle of the topologies, the design constraints for a fair topology comparison are specified. Mechanical, magnetic, electrical, and thermal design considerations are discussed and supported by 3-D finite-element method simulations. Four promising motor topologies are compared qualitatively and quantitatively by different criteria, such as acceleration behavior, compactness, bearing stability, and complexity of the control. The comparative evaluation is supported by performance measurements on laboratory prototypes.

86 citations

Proceedings ArticleDOI
22 May 2016
TL;DR: In this paper, an ultra compact Power Pulsation Buffer (PPB) is designed for a 2kW PV-inverter application by means of a comprehensive Pareto optimization.
Abstract: In single-phase power conversion systems, typically bulky electrolytic capacitors are installed in order to cope with the intrinsic double-line frequency power pulsation. However, since the voltage ripple at the dc bus is typ. limited to just a few percent of the nominal voltage, only a small fraction of the actually stored energy in the capacitors is used for the power decoupling. In this paper an auxiliary buffer converter is employed, shifting the double-line frequency power pulsation away from dc bus to a buffer capacitor. Being relieved from strict voltage ripple requirements, a larger voltage ripple is allowed across the buffer capacitor, significantly reducing the capacitance requirement. In this paper an ultra compact Power Pulsation Buffer (PPB) is designed for a 2kW PV-inverter application by means of a comprehensive Pareto optimization. Besides compensating the power pulsation, the PPB must be able to quickly stabilize the dc bus in case of abrupt load variations and maintain an average buffer capacitor voltage. In this paper, a novel cascaded control structure is presented, meeting all aforementioned control objectives. A constructed prototype of the optimized PPB is presented in the paper and experimental measurements verify the outstanding performance of the proposed control system.

86 citations

Proceedings ArticleDOI
07 Jul 2011
TL;DR: In this paper, an approach to accurately calculate the reluctance of an air gap is introduced, which is based on a modular concept where a simple basic geometry is used as a building block to describe different three dimensional air gap shapes.
Abstract: An approach to accurately calculate the reluctance of an air gap is introduced. The approach is easy to handle as it is based on a modular concept where a simple basic geometry is used as a building block to describe different three dimensional air gap shapes. A high degree of accuracy is achieved as the approach is based on an analytical field solution.

86 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