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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
16 May 2008
TL;DR: In this article, an optimization procedure has been developed, which calculates the optimal converter parameters (e.g. switching frequency or transformer design) with respect to the maximal power density and/or efficiency.
Abstract: Power density and efficiency are one of the major driving forces in the development of new power supplies for telecommunication and information industry. The phase-shift PWM and the series-parallel resonant DC-DC converter are promising topologies that can meet these demands at high power rates. Based on conventional criteria such as the number of semiconductors/passive components or voltage/current stress it is not possible to identify the topology that offers a higher power density or efficiency. Therefore, an optimization procedure has been developed, which calculates the optimal converter parameters (e.g. switching frequency or transformer design) with respect to the maximal power density and/or efficiency. This procedure is based on detailed analytical models for the converter, semiconductor losses, HF losses in the magnetic components as well thermal and geometrical models of the transformer. With the procedure a 5 kW series-parallel resonant converter and a phase shift converter with capacitive output and with current doubler have been optimized. With the calculated parameters a resonant converter prototype has been constructed and experimental results are presented.

39 citations

Proceedings ArticleDOI
Jonas E. Huber1, G. Ortiz1, Florian Krismer1, N. Widmer1, Johann W. Kolar1 
17 Mar 2013
TL;DR: In this paper, a comprehensive analytical model of the series-resonant-converter's static and dynamic behavior is provided, and a method to model the switching losses under ZCS conditions, which is based on the behavior of the stored charge in the semiconductors, is presented.
Abstract: In solid-state-transformer technology, the isolation and power transfer between low voltage and medium voltage side is performed by a high power DC/DC converter. This DC/DC converter provides a defined ratio between input and output voltages, whereby, in order to reduce switching losses, zero-current-switching modulation schemes are often mandatory. The series-resonant-converter operated in half-cycle discontinuous-conduction-mode possesses all the aforementioned features, thus making it highly attractive for solid-state-transformer applications. For this reason, a comprehensive analytical model of the converter's static and dynamic behavior is provided in this paper. In addition, a method to model the switching losses under ZCS conditions, which is based on the behavior of the stored charge in the semiconductors, is presented. This enables an efficiency/power density (η-ρ) Pareto optimization of the aforementioned converter system.

39 citations

Proceedings ArticleDOI
06 Feb 2000
TL;DR: In this article, a detailed discussion of the formation of the common-mode voltage for the VIENNA Rectifier I is given and a modified circuit topology which significantly reduces the switching frequency component of the voltage is given.
Abstract: Three-phase PWM rectifier systems in principle show a common-mode voltage with switching frequency between the mains neutral point and the center point of the output voltage. Without any counter-measures this leads to a high common-mode noise emission of the system and possibly to disturbances of the control unit of the converter being fed by the rectifier. In this paper a detailed discussion of the formation of the common-mode voltage for the VIENNA Rectifier I is given and a modified circuit topology which significantly reduces the switching frequency component of the common-mode voltage is given. The proposed circuit modification is applicable also to other three-phase PWM rectifier topologies. The filtering concept is analyzed by digital simulation and guidelines for the dimensioning of the filter components are given. The reduction of the common-mode noise is verified by EMI measurements taken from a 10 kW laboratory unit of a VIENNA Rectifier I. Finally, the advantages and drawbacks of the proposed filtering concept are compiled in the form of an overview.

39 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a control scheme that leads to low total harmonic distortion of the input currents in discontinuous conduction mode without relying on current measurements, and derive analytic expressions for the duty cycles and the threshold between discontinuous and continuous conduction modes.
Abstract: During light load conditions unidirectional power factor correction rectifiers, such as the VIENNA rectifier, enter discontinuous conduction mode, causing the relationship between average half-bridge voltage and duty cycle to become nonlinear and synchronously sampled current measurements not equaling the switching period average. Combined, these measurement and actuation errors result in distorted input currents at light load if no additional measures are taken. This work presents a control scheme that leads to low total harmonic distortion of the input currents in discontinuous conduction mode without relying on current measurements. The analytic expressions for the duty cycles and the threshold between discontinuous and continuous conduction mode are derived, the capability of supplying asymmetric loads is investigated and the effect on the noise spectrum relevant for the electromagnetic interference filter design is studied. Measurements of efficiency, total harmonic distortion, and conducted electromagnetic interference in discontinuous and continuous conduction mode are obtained on a 65 kW prototype operating at 290 to 530 V line-to-line RMS mains voltage range and supplying 800 V dc output voltage. The prototype, which is optimized for pulse load applications, achieves a power density of 9.56 kW/dm3 (157 W/in3) and 97.2 % efficiency at full load using 650 V Si insulated gate bipolar transistor (IGBTs) with 28 kHz switching frequency.

39 citations

Journal ArticleDOI
TL;DR: In this article, the authors present the analysis and operation of a three-phase pulsewidth modulation rectifier system formed by the star connection of three single-phase boost rectifier modules (Y-rectifier) without a mains neutral point connection.
Abstract: This paper presents the analysis and operation of a three-phase pulsewidth modulation rectifier system formed by the star-connection of three single-phase boost rectifier modules (Y-rectifier) without a mains neutral point connection. The current forming operation of the Y-rectifier is analyzed and it is shown that the phase current has the same high quality and low ripple as the Vienna rectifier. The isolated star point of Y-rectifier results in a mutual coupling of the individual phase module outputs and has to be considered for control of the module dc link voltages. An analytical expression for the coupling coefficients of the Y-rectifier phase modules is derived. Based on this expression, a control concept with reduced calculation effort is designed and it provides symmetric loading of the phase modules and solves the balancing problem of the dc link voltages. The analysis also provides insight that enables the derivation of a control concept for two phase operation, such as in the case of a mains phase failure. The theoretical and simulated results are proved by experimental analysis on a fully digitally controlled, 5.4-kW prototype.

39 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