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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, a new inductor concept is proposed, where the winding is directly integrated into the printed circuit board (PCB), while at the same time the usually large high-frequency conduction losses are mitigated.
Abstract: The design of power electronic converters is subject to extreme cost pressure, especially in the automotive sector. Consequently, each component needs to be optimized regarding material and manufacturing cost. The latter is especially important for magnetic components, as the expensive wire-wrapping process has a significant impact on the overall production costs. In this article, a new inductor concept is proposed, where the winding is directly integrated into the printed circuit board (PCB), while at the same time the usually large high-frequency conduction losses are mitigated. This is achieved by using the fringing field around a single air gap or several (distributed) air gaps for compensating the adverse magnetic skin and proximity fields within the winding. Consequently, low ac to dc resistance ratios are achieved and the required copper cross-section of the winding can effectively be reduced. Furthermore, a thermal model for the printed circuit board winding is derived, which allows for designing PCB windings close to the thermal limit, and therefore inductors with very high power densities are obtained. Finally, the findings of this article are verified by experimental measurements and a simplified design sequence is described.

21 citations

Patent
03 Feb 2010
TL;DR: In this paper, a switching device for switching a current between a first connection (1) and a second connection (2), comprising a series connection of at least two JFETs (J 1 -J 6 ), was proposed.
Abstract: The invention relates to a switching device for switching a current between a first connection ( 1 ) and a second connection ( 2 ), comprising a series connection of at least two JFETs (J 1 -J 6 ), of which a lowest JFET (J 1 ) is connected to the first connection ( 1 ), or the lowest JFET (J 1 ) is connected in a cascade circuit to the first connection ( 1 ) via a control switch (M), and at least one further JFET (J 2 -J 5 ), which is connected in series to the lowest JFET (J 1 ), wherein the JFET (J 6 ) farthest away from the lowest JFET (J 1 ) is referred to as the uppermost JFET (J 6 ) and is connected with the drain connection to the second connection ( 2 ), and wherein a stabilization circuit (D 11 -D 53 ) is connected between the gate connections of the JFETs (J 1 -J 6 ) and the first connection ( 1 ) in order to stabilize the gate voltages of the JFETs (J 1 -J 6 ). An additional circuit ( 4 ), which draws the potential at the gate connection (G 6 ) of the uppermost JFET (J 6 ) to the potential at the drain connection (D 6 ) of the uppermost JFET (J 6 ), is switched between the gate connection (G 6 ) of the uppermost JFET (J 6 ) and the second connection ( 2 ).

21 citations

11 Mar 2008
TL;DR: In this paper, the numerical optimization of a radial eddy current position sensor to achieve a large output signal is dealt with, where a valid simulation model must be able to model the magnetic coupling between the sensor components as well as skin and proximity effect.
Abstract: Eddy current sensors are widely used in active magnetic bearing systems to determine the position of the levitated rotor. This work is dealing with the numerical optimization of a radial eddy current position sensor to achieve a large output signal. A valid simulation model must be able to model the magnetic coupling between the sensor components as well as skin- and proximity effect. The Partial Element Equivalent Circuit (PEEC) method is best suited for these demands. In this paper, parameters of an existing sensor layout are investigated numerically, regarding the sensor output signal in dependency on parameters as excitation frequency and winding ratios. Furthermore, alternative layout geometries are discussed and compared to the classical sensor layout.

21 citations

Proceedings ArticleDOI
01 Jun 2015
TL;DR: In this paper, five different forced cooling options for a slotless-type ultra-high-speed permanent magnet machine are compared and a simplified case study shows that the power density can be more than doubled by the selection of a proper cooling system.
Abstract: High-speed electrical machines are gaining an increasing attention as they enable higher power densities in several applications such as micro-machining spindles and turbo compressors. This brings along an important challenge in thermal management due to the higher loss densities in the machine. Therefore, a careful thermal analysis is required along with the electromagnetic and mechanical analysis during the design phase of the machines. In this paper, five different forced cooling options for a slotless-type ultra-high-speed permanent-magnet machine are compared. Fast and sufficiently accurate thermal models are derived for analyzing these cooling concepts such that the cooling system design could be integrated in the machine optimization procedure, which would not be feasible when using computationally very intensive methods such as 3-D Finite-Element-Method (FEM) or Computational-Fluid-Dynamics (CFD). Measurements are carried out on the stator of an off-the-shelf 1 kW, 280 000 r/min machine to experimentally compare different cooling methods and to show the validity of the thermal models. A simplified case study shows that the power density can be more than doubled by the selection of a proper cooling system.

21 citations

Proceedings ArticleDOI
01 Nov 2010
TL;DR: In this article, the authors present a novel Lorentz-type, slotless self-bearing motor concept which overcomes most limitations of previously presented high-speed AMBs.
Abstract: Active magnetic bearings are a preferred choice for supporting rotors spinning at high-speed due to low friction losses and no wear. However, the rotational speed in previous bearing topologies has been limited by complex rotor constructions, high rotor losses, or position control instabilities at high speed. This paper presents a novel Lorentz-type, slotless self-bearing motor concept which overcomes most limitations of previously presented high-speed AMBs. An analytical model for motor torque and bearing forces is presented and a design for 500 000 rpm is verified with FE simulations, showing exceptionally low negative stiffness cross coupling. Finally, a prototype system is described.

21 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