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.

Detailed Modeling and In-Situ Calorimetric Verification of Three-Phase Sparse NPC Converter Power Semiconductor Losses

Abstract: The three-phase (3- $\Phi $ ) three-level (3-L) sparse neutral point clamped converter (SNPCC) combines a 3-L matrix stage and a 3- $\Phi $ two-level (2-L) inverter stage to generate 3-L switched output voltages with a reduced transistor count (10 instead of 12 or 18) compared with the classical 3-L NPCC or 3-L active NPCC structure, targeting variable-speed drive (VSD) systems with low ripple of the motor phase currents or bidirectional 3- $\Phi $ power factor correcting (PFC) rectifier systems with reduced boost inductor volume. This article analyzes and experimentally characterizes the performance of an IGBT-based 3- $\Phi 3$ -L SNPCC and describes, for the first time, a hybrid current commutation effect between inverter-stage diodes and matrix-stage IGBTs that occurs when operating with lower modulation indices and leads to increased switching losses (up to ${20}{\%}$ ). The proposed new semiconductor loss modeling approach accounts for this effect successfully, which is verified ( $< {10}{\%}$ error) on an 800- ${\text {V}}_{\text {dc}}$ , 7.5-kW SNPCC hardware demonstrator using a new in-situ calorimetric method that facilitates accurate stage-level semiconductor loss measurements. Heat spreading effects caused by the asymmetrical losses injection and thermal decoupling between two in-situ loss measurement blocks are carefully checked with finite-element method (FEM) simulations. Furthermore, an experimental evaluation of common-mode (CM) and differential-mode (DM) high-frequency (HF) voltage-time area ripples (as a generic measure for the required filtering effort) for three typical symmetrical and asymmetrical modulation switching state sequences is provided together with the semiconductor loss characterization. Utilizing a low-switching-loss asymmetric modulation scheme that operates the 3-L matrix stage and the 2-L inverter stage with the effective switching frequencies of 16 kHz and 5.3 kHz, respectively, the 3-L SNPCC demonstrator finally achieves a high rated power (7.5 kW, load current phase shift $\phi = 0$ ) semiconductor efficiency of 98.8%.

Transformer, voltage converter and method for transmitting electric power

Abstract: The present invention relates to the transmission of electric power by means of a transformer for a three-port voltage converter. For this purpose, there is in particular provision for an additional winding that can be included in the power transmission or not, depending on the mode of operation of the voltage converter.

Ac/dc converter having step-up/step-down converter phase modules

Abstract: The invention relates to a converter for transmitting electrical energy between a direct current voltage (DC) system and an alternating current voltage system, comprising a positive DC input voltage rail (1) and a negative DC input voltage rail (2) on the DC voltage side and at least two output phase connections (a, b, c) on the AC voltage side. For each of the output phase connections (a, b, c) there is a phase converter (10a, 10b, 10c), which is connected to the positive DC input voltage rail (1) and the negative DC input voltage rail (2) on a first side, and to said out put phase connection (a; b; c) on a second side, and is designed as a step-up/step-down converter. The converter has a controller which is designed such that, during the operation of the converter, said controller operates each of the phase converters (10a, 10b, 10c) periodically either purely as a step-down converter or purely as a step-up converter, according to a relationship of a DC input voltage relative to instantaneous values of output phase voltages to be generated at the output phase connections (a, b, c).

Vergleich, Dimensionierung und Realisierung einphasiger Power Factor Correctors minimalen Realisierungsaufwands

Abstract: Zukunftig wird es zu strengeren Vorschriften bezuglich Netzruckwirkungen von Gleichrichtern kommen. Wahrend Diodenbrucken einfach, kompakt und billig sind, weist ihr Netzstrom niederfrequente Oberschwingungen auf. In den letzten Jahren wurden verschiedene Gleichrichter entwickelt, die durch eine aktive Stromregelung niederfrequente Stromoberschwingungen vermeiden. Der deutlich reduzierte Filteraufwand ermoglicht kleinere und kompaktere Gesamtsysteme. In dieser Arbeit werden vier solche Schaltungen vorgestellt und verglichen. Das Hauptaugenmerk liegt auf einer einfachen, kostengunstigen Realisierung, wie es seitens der Industrie gefordert wird. Bei der Dimensionierung wird besonders auf die systematische Auswahl der Leistungshalbleiter eingegangen.

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.