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.

On the Tradeoff Between Input Current Quality and Efficiency of High Switching Frequency PWM Rectifiers

Abstract: Due to their basic physical properties, power MOSFETs exhibit an output capacitance Coss that is dependent on the drain-source voltage. This (nonlinear) parasitic capacitance has to be charged at turn-off of the MOSFET by the drain-source current in rectifier applications that yield input current distortions. A detailed analysis shows that the nonlinear behavior of this capacitance is even more pronounced for modern super junction MOSFET devices. Whereas Coss increases with increasing chip area, the on-state resistance of the MOSFET decreases accordingly. Hence, a tradeoff between efficiency and input current distortions exists. A detailed analysis of this effect considering different semiconductor technologies is given in this study and a Pareto curve in the η-THDI space is drawn that clearly highlights this relationship. It is further shown that the distortions can be reduced considerably by the application of a proper feedforward control signal counter- acting the nonlinear switching delay due to Coss. The theoretical considerations are verified by experimental results taken from 10-kW laboratory prototypes with the switching frequencies of 250 kHz and 1 MHz.

Balancing circuit for a 5kV/50ns pulsed power switch based on SiC-JFET Super Cascode

Abstract: In many pulse power applications there is a trend to modulators based on semiconductor technology. For these modulators high voltage and high current semiconductor switches are required in order to achieve a high pulsed power. Therefore, often high power IGBT modules or IGCT devices are used.

Analysis of the design space of single-stage and two-stage LC output filters of switched-mode AC power sources

Abstract: This paper proposes a systematic approach to design the output filter of a 10 kW, low-voltage 400 V ll,rms , fouroutput phase, hard-switched AC source based on the Three-Level Neutral Point Clamped Voltage Source Converter topology. Given specifications of the AC source, such as the voltage quality, the control performance or the conducted EMI at the output of the source, are translated into corresponding families of curves in the parameter space of the output filter. The area/volume enclosed by these curves represents the design space of the output filter in which all tuples (L f , C f ), e.g. for a single-stage LC-filter, fulfill every single AC source specification. From all possible filter parameters in the design space, the set of parameters resulting in the smallest filter volume, the lowest filter weight, the highest filter efficiency and/or the lowest filter costs can be selected.

Ultra-High-Energy-Density Converter for Portable Power

Abstract: Mesoscale gas turbine generator systems are a promising solution for high energy and power density portable devices. This paper presents an overview of a two-stage system with a power output of 100 W. There is a need for catalytic combustion and new ceramic materials. An existing turbine expander and a compression system are downscaled and a high-speed test-bench setup for the electrical system has been built. A simulation toolbox for small thermal machines and model-based control and diagnostics are developed.

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.