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.

99% Efficient Isolated Three-Phase Matrix-Type DAB Buck–Boost PFC Rectifier

Abstract: Three-phase power factor correction rectifiers are an essential area of power electronics, supplying a direct current load with tens of kilowatts, or more, from the public three-phase mains and achieving sinusoidal input currents. In many applications, isolation is required between the mains and the load, for example, due to safety reasons or different grounding schemes. This paper describes the modulation, design, and realization of a buck–boost-type, unity-power-factor, isolated matrix-type, dual-active-bridge, three-phase rectifier. It uses a circuit similar to a conventional dual-active-bridge converter, but employs a direct matrix converter to connect the high-frequency transformer's primary winding to the mains. A soft-switching modulation scheme is proposed and comprehensively analyzed, deriving closed-form solutions and numerical optimization problems to calculate switching times that achieve minimal conduction losses. Based on this analysis, the design of an 8-kW 400-V rms three-phase ac to 400-V dc prototype is discussed, striving for the highest possible efficiency. Using 900-V SiC mosfet s and a transformer with an integrated inductor, a power density of ${\text{4}}\; {\text{kW}\cdot \text{dm}^{-3}}$ ( ${\text{66}}\; {\text{W}\cdot \text{in}^{-3}}$ ) is achieved. Measurement results confirm an ultrahigh full-power efficiency of 99.0% at nominal operating conditions and 98.7% at 10% lower input voltage.

A gate drive circuit for silicon carbide JFET

Abstract: In this paper, a gate drive circuit for a 1300 V/4 A SiC-JFET is proposed and evaluated experimentally for a switching frequency of 200 kHz. Furthermore, a comparison of the switching behavior of a SiC-JFET/Si-MOSFET cascode and of the SiC-JFET driven by the proposed gate drive circuit is shown.

Interactive Power Electronics Seminar (iPES)-a web-based introductory power electronics course employing Java-applets

Abstract: This paper introduces the Interactive Power Electronics Seminar-iPES-a new software for teaching a basic course on power electronic circuits and systems. iPES is constituted by HTML text with Java-applets for interactive animation, circuit design and simulation and visualization of electromagnetic fields and is comprised of an easy-to-use self-explaining graphical user interface. The software does need just a standard web-browser, i.e. no installations are required. iPES can be accessed via the World Wide Web or from a CD-ROM in a stand-alone PC by students and professionals. Since the Java applets are simple to handle, a student can immediately start working and can fully concentrate on the theory of a problem. Due to the underlying software technology iPES is very flexible and can be used for on-line learning and be easily integrated into an e-learning platform. The aim of this paper is to give an introduction to the iPES-project and to show different areas covered. The e-learning software is available at no cost in English, German, Japanese and Korean. More translations, e.g. into Spanish and French will be available in the future. The web page is continuously updated in four-week intervals.

A Semiconductor Area Based Assessment of AC Motor Drive Converter Topologies

Abstract: In order to find the optimal converter topology for a given ac motor drive, as defined by its mission profile, suitable assessment criteria have to be applied. A new semiconductor chip area based approach is proposed to compare and assess different motor drive converter topologies. It determines the total semi-conductor chip area based on the drive's operating point and the optimal partitioning of the transistor and diode chip areas. This approach not only provides a distinct figure-of-merit for comparison but also enables the semiconductor costs of different converter topologies to be determined. The chip area based comparison has been successfully used to assess three 3-phase ac-dc-ac converter topologies for a 15 kW (20 HP) motor drive. It is shown that the Voltage DC-Link Back-to-Back Converter based drive provides the best overall performance in terms of chip area, cost, efficiency, and available nominal torque.

VIENNA rectifier II-a novel single-stage high-frequency isolated three-phase PWM rectifier system

Abstract: Based on an analysis of basic realization possibilities, the structure of the power circuit of a new single-stage three-phase boost-type PWM rectifier system (VIENNA Rectifier II) is developed. This system has continuous sinusoidal time behavior of the input currents and high-frequency isolation of the output voltage which is controlled in a highly dynamic manner. As compared to a conventional two-stage realization, this system has substantially lower complexity and allows to realize several isolated output circuits with minimum effort. The basic function of the new PWM rectifier system is described based on the conducting states occurring within a pulse period. Furthermore, a straightforward space vector oriented method for the system control is proposed which guarantees a symmetric magnetization of the transformer. Also, it makes possible a sinusoidal control of the mains phase currents in phase with the associated phase voltages. By digital simulation the theoretical considerations, the stresses on the power semiconductors of the new converter system are determined. Finally, problems of a practical realization of the system are discussed, as well as the direct start-up and the short circuit protection of the converter. Also, the advantages and disadvantages of the new converter system are compiled in the form of an overview.

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.