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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
TL;DR: A hybrid inverter concept for switch-mode power amplifiers as used, e.g. in power-hardware-in-the-loop testing, features a significant increase of the full-range system bandwidth and improves by more than an order of magnitude for the considered 100 kVA example system compared with a conventional approach.
Abstract: A hybrid inverter concept for switch-mode power amplifiers as used, e.g. in power-hardware-in-the-loop testing is proposed. A main converter operating from the supplying DC voltage generates a multilevel output voltage by means of parallel-interleaved operation of several bridge legs and combination of the bridge leg output voltages with coupled inductors into a multilevel waveform. A second, series-connected inverter features a floating DC bus with only a fraction of the main converter's DC voltage, which enables a significantly higher switching frequency. The series inverter compensates the deviation of the main inverter's multilevel output voltage from the reference voltage, whereby pulse-width modulation with sawtooth carriers is employed, and hence defines the effective switching frequency of the hybrid inverter's overall output voltage. This allows for a higher output filter cutoff frequency and ultimately features a significant increase of the full-range system bandwidth, which improves by more than an order of magnitude for the considered 100 kVA example system compared with a conventional approach. Finally, closed-loop circuit simulations verify the high performance of the proposed system.

14 citations

Journal ArticleDOI
TL;DR: It is shown that the use of 3-D instead of 2-D simulation tools is obligatory for motors with large air gaps for achieving sufficient simulation accuracy.
Abstract: This paper presents an optimization-procedure yielding for minimal acceleration times for different speed ranges using the example of a magnetically levitated slice motor with a large air gap. The optimization is based on a set of analytical equations together with selected 3-D finite element method simulations with the aim to optimize both the stator geometry and the number of drive turns. It is shown that the use of 3-D instead of 2-D simulation tools is obligatory for motors with large air gaps for achieving sufficient simulation accuracy. The relevant equations for the optimization are derived, and the accuracy of the proposed method is verified by measurements on a prototype system.

14 citations

Proceedings ArticleDOI
13 Nov 2014
TL;DR: In this paper, a multi-cell converter approach for a telecom rectifier module breaking through the efficiency and power density barriers of traditional single-cell converters is shown, based on scaling laws of the system performances, such as the losses generated by the semiconductors and the harmonic spectrum, in dependence of the number of converter cells.
Abstract: In this paper, a multi-cell converter approach for a telecom rectifier module breaking through the efficiency and power density barriers of traditional single-cell converter systems is shown. The potential of the multi-cell approach for high efficiency is derived from fundamental scaling laws of the system performances, such as the losses generated by the semiconductors and the harmonic spectrum, in dependence of the number of converter cells. Furthermore, a comprehensive optimization of the entire system with respect to efficiency and volume has been performed and the applied component loss models are described in detail. The achievable performance of the system is compared to a leading edge state-of-the-art single-cell converter system which currently sets the benchmark in terms of efficiency and power-density. In addition, the degrees of freedom of multi-cell converter systems in terms of converter operation are outlined and optimum control schemes are derived.

14 citations

Proceedings ArticleDOI
03 Mar 1996
TL;DR: In this paper, the authors presented a combined power amplifier system consisting of a linear amplifier unit with a switchedmode (class D) current dumping stage arranged in parallel, which can be considered as a master-slave system with a guiding linear amplifier and a supporting class D slave unit.
Abstract: The paper presents a combined power amplifier system consisting of a linear amplifier unit with a switched-mode (class D) current dumping stage arranged in parallel. With this topology, the fundamental drawback of conventional linear power amplifiers-the high loss-is avoided. Compared to a pure class D (switching) amplifier, the presented system needs no output filter to reduce the switching frequency harmonics. This filter (usually of multi-stage type) generally deteriorates the transient response of the system and impairs the feedback loop design. Furthermore, the low-frequency distortions of switching amplifiers caused by the interlock delay of their power transistors are avoided with the presented switched-mode assisted linear amplifier system. This can be considered as a master-slave system with a guiding linear amplifier and a supporting class D slave unit. The paper describes the operating principle of the system, analyzes the fundamental relationships for the circuit design and presents simulation results. Finally, various further topologies of switched-mode assisted linear amplifiers are given.

14 citations

Proceedings ArticleDOI
01 Nov 2007
TL;DR: In this article, a comparison of two-, three-and four-phase bearingless slice motors (BSM) concepts based on performance indices such as power losses, power electronics requirements and cost-related realisation issues is performed.
Abstract: The fact that bearingless slice motors (BSM) are widely used in pump systems in the semiconductor industry and for medical applications has caused the attention of other industries for this emerging technology Here, costs, power consumption and pump volume play an important role Since the mechanical setup of the motor has a strong impact on these issues five different motor and converter setups are comparatively evaluated and discussed in this paper The comparison will be carried out for two-, three- and four-phase BSM concepts based on performance indices such as power losses, power electronics requirements and cost-related realisation issues

14 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