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.

Comprehensive analysis and comparative evaluation of the isolated true bridgeless Cuk single-phase PFC rectifier system

Abstract: In the public low voltage mains the stress caused by harmonic currents is strongly increased due to the higher demand of electronic equipment in everyday use. Therefore, standards were created in order to limit the harmonic currents injected into the network, thus maintaining a high voltage quality of these networks. Hence, converter systems with active PFC are indispensable, where in general the compliance of the created directives for lower harmonics can be easily fulfilled. Typically, in single-phase systems, boost PFC converter topologies are used, which offer a wide input voltage range and a controlled output voltage. Depending on the underlying applications, a subsequent reduction and/or isolation of the output voltage based on a DC/DC-converter is needed. The major disadvantages of this converter cascading are the reduction of the overall efficiency, the large component count and the increasing control complexity. In comparison to the conventional two-stage PFC converter system, the true bridgeless Cuk PFC rectifier system can perform the PFC functionality and the galvanic isolation in a single-stage, thus eliminating the mentioned disadvantages. In this paper a comprehensive analysis of the operation, design and limits of the recently proposed single-stage Cuk concept is investigated. In addition, a comparative evaluation concerning efficiency and power density against a conventional two-stage approach based on bridgeless PFC rectifier and a subsequent LLC-resonant DC/DC-converter is presented.

New circuit simulation applets for online education in power electronics

Abstract: This paper presents new online simulation applets based on Java technology. The applets are integrated into a series of student exercises which accompany the introductory and advanced lecture courses in power electronics at the Swiss Federal Institute of Technology Zurich. Furthermore, the new applets are available via the educational project iPES which is a free collection of Java applets for educational purposes. iPES has been translated into 12 languages and has currently more than 10,000 visits per month. The novel online simulation applets are easy to use and allow an unlimited simulation of converter topologies. The concept of embedding a circuit simulator in the form of a Java applet into a public accessible homepage allows the creation of power electronic and electrical engineering courses that are easy for students to access, highly flexible and require small administrative efforts for the lecturer. The paper will discuss the technical details of the online simulation project and will show how the integration of the online simulator significantly improves the educational value.

Novel online simulator for education of power electronics and electrical engineering

Abstract: In this paper a novel online simulator is introduced that is integrated into the educational project iPES which is a free collection of Java applets for educational purpose. iPES has been translated into 12 languages and has currently more than 10, 000 visits per month. The novel online simulator is optimized for power electronics, easy to use, and allows unlimited simulation of converter topologies. The concept of embedding a circuit simulator in the form of a Java applet into a webpage allows the creation of power electronic and electrical engineering courses that are easy for students to access, highly flexible and require a low administrative effort. The paper will discuss the status of the iPES project in detail including all shortcomings and will show how the integration of the online simulator significantly improves the educational value.

Mission profile optimized modularization of hybrid vehicle DC/DC converter systems

Abstract: Vehicles based on electrical drive trains become more and more attractive due to rising oil prizes and environmental reasons. In these vehicles usually different and/or varying voltage levels for the drive and the energy storage elements are employed in order to fully utilise the components and increase the system efficiency. The DC-links with different voltage levels are interconnected by bidirectional DC-DC converters. Due to the high power levels the converters are often realised by interleaved smaller units for increasing part load efficiency and power density.

Novel Principle for Flux Sensing in the Application of a DC + AC Current Sensor

Abstract: This paper presents a new concept for measuring DC and AC magnetic flux densities within a ferromagnetic material. It is based on a measurement of the material's magnetostriction, which is its relative change in length due to the magnetic flux density inside the material. This dimensional change is converted to an electrical signal using a piezoelectric strain sensor. An additional sinusoidal AC excitation of the core material provides higher sensitivity of the length measurement and overcomes the inherent high-pass characteristic of the piezoelectric sensor. Therefore, flux density signals from DC to the kilohertz range can be measured. The concept's feasibility is demonstrated with the design and implementation of an isolated DC + AC current sensor with a measurement range of $\pm 20\ \mbox{A}$ and a bandwidth from DC to 20 MHz.

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.