Johann W. Kolar

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.

A novel three-phase three-switch three-level unity power factor boost-type pwm rectifier

Abstract: Based on the combination of a three-phase diode bridge and a DC/DC boost converter a new three-phase three-switch three-level PWM rectifier system is developed. It can be characterized by sinusoidal mains current consumption, controlled output voltage and low blocking voltage stress on the power transistors. The application could be, e.g., for feeding the DC link of a telecommunications power supply module. The stationary operational behavior, the control of the mains currents and of the output voltage are analyzed. Finally, the stresses on the system components are determined by digital simulation and compared to the stresses in a conventional PWM rectifier system.

Design and Development of a 26-Pole and 24-Slot Bearingless Motor

Abstract: Several processes in chemical, pharmaceutical, biotechnology and semiconductor industry require contactless levitation and rotation through a hermetically closed process chamber. A highly interesting topology for these applications is the ldquobearingless slice motorrdquo concept, where already some research has been done in the past. This paper presents the design, optimization and development of a 26-pole and 24-slot bearingless motor, which promises high acceleration and bearing performance and an ultra-compact setup. A prototype with a large rotor diameter and a large air-gap has been built to verify the simulation results by experiments.

Novel hybrid 12-pulse line interphase transformer boost-type rectifier with controlled output voltage

Abstract: This paper describes two novel hybrid 12-pulse line interphase transformer rectifier systems with integrated single-switch or two-switch boost-type output stage. The boost stage allows controlling the output voltage to a constant value independent of line voltage or output power variations. In combination with low complexity and/or high reliability the hybrid rectifier concept therefore is of potential interest for supplying electrically powered actuators of future more-electric-aircrafts. The principle of operation and the dimensioning of the systems are discussed. Furthermore, a control concept guaranteeing a symmetric distribution of the load current to the individual systems of the two-switch topology is proposed. The theoretical considerations are experimentally confirmed for a 10 kW laboratory prototype. Finally, the single- and the two-switch system are comparatively evaluated concerning input current ripple, power factor, and overall efficiency.

Increase of tape wound core losses due to interlamination short circuits and orthogonal flux components

Abstract: High performance laminated core materials are nowadays used in several different applications, from some Watts to some Megawatts and from some tens of Hertz to some hundreds of Kilohertz. Cutting laminated or tape wound cores in order to obtain a desired geometry results in higher core losses mainly due to the introduction of short circuits between layers of magnetic material and also due to the flux which is perpendicular to the layer plane as given for the fringing field of inductors or the stray field of transformers. This paper verifies the influence of some machining methods on the increase of core losses and shows an approach to keep the effect minimized. Furthermore, the importance of considering core losses due to perpendicular flux is verified for a cut core inductor and a transformer arrangement.

Teaching thermal design of power electronic systems with web-based interactive educational software

Abstract: For designing reliable power electronic systems it is essential to understand basic thermal issues like the stationary and transient relation of the power semiconductor losses the junction temperature and the application of thermal equivalent circuits. Also, thermal properties are of special importance in connection with further increasing the compactness of power converter systems. The aim of this paper is to give an introduction into the basic theory of heat energy conduction and thermal design which should serve as an addition to the Java applets compiled in a the iPES-Thermal, a module of the interactive educational software iPES which is freely available at www.ipes.ethz.ch and employed at the ETH Zurich for supporting an introductory course on power electronics.

I and i

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 …

Multilevel inverters: a survey of topologies, controls, and applications

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.

Recent Advances and Industrial Applications of Multilevel Converters

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.