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.

Spannungsumsetzungsvorrichtung fuer einen gleichspannungsverbraucher

Abstract: In a converter 1 for a d.c. voltage consumer 2 supplied via a single or multi-phase a.c. voltage source 3, between the a.c. voltage source 3 and the d.c. voltage consumer 2 is arranged a rectifier 5 and an intermediate circuit 6 for controlling the voltage in the d.c. voltage consumer 2. The intermediate circuit 6 is associated with a control device 29. The control device 29 is connected at the input of the d.c. voltage consumer 2 with external voltage and/or current adjusting or monitoring devices. The output of the control device 29 is applied to a control input of a switching device 24. The switching device 24 is arranged between an electric energy store 26 and a magnetic energy store 19 and the intermediate circuit 6 is provided between the energy storage element 26 and the magnetic energy store 19. The switching device 24 may be a bipolar transistor (46, Fig 5), two devices (24, 56 Fig 6), GTO thyristors (97-99, Figs 12 and 16), IGBT (Figs 13, 14, 17 and 20). The d.c. voltage consumer 2 may be used for welding 33, 34.

Analysis and practical relevance of CM/DM EMI noise separator characteristics

Abstract: This Paper details two different contributions related to practical CM/DM EMI measurements. A first part investigates sources and implications of measurement errors that result for CM/DM separators in a practical measurement environment with a particular focus on the recently presented input impedance criterion for CM/DM separators. Furthermore, the realization of an active CM/DM separator, which features competitive separation capabilities (DMTR/CMRR > 51 dB and CMTR/DMRR > 47 dB for frequencies up to 10MHz), is presented.

Design and experimental verification of a novel 1.2 kW 480V/sub AC//24V/sub DC/ two-switch three-phase DCM flyback-type unity power factor rectifier

Abstract: The basic principle of operation of a novel three-phase two-switch unity power factor flyback rectifier is analyzed and a system control concept is proposed. The stresses on the power components are calculated in an analytical form and used for designing a converter with an input voltage range of 480V/spl plusmn/10% and 24V/50A DC output The theoretical considerations are verified by an experimental analysis of a laboratory prototype of the system.

iGSE-C $_{\mathrm{x}}$ – a New Normalized Steinmetz Model for Class II Multilayer Ceramic Capacitors

Abstract: Ferroelectric Class II ceramic capacitors allow for highly compact converter realizations, but are showing relatively high losses for large-signal excitations which must be taken into account in the system dimensioning. Recent literature introduced the iGSE-C $_{\mathrm{Q}}$ , a Steinmetz model based on the macroscopic capacitor Q-U hysteresis, allowing to accurately predict the losses of X7R capacitors. However, the model is specific for each single device, i.e., is insufficient to characterize losses in devices of the same series and manufacturer, which are employing the same dielectric material but with different voltage rating or nominal capacitance value. In this publication, based on basic physical properties we propose a new Steinmetz model, the iGSE-C $_{\mathrm{X}}$ based on the relative dielectric material D-E hysteresis, which is applicable to all devices of a capacitor series. The iGSE-C $_{\mathrm{X}}$ loss modeling technique is demonstrated for the TDK X7R, the TDK X7T, as well as the Knowles Syfer X7R series. Finally, the iGSE-C $_{\mathrm{X}}$ is employed to estimate the large-signal losses of the capacitors of a three-phase inverter and shown to offer sufficient accuracy for a first power circuit design.

Next Generation Measurement Systems with High Common-Mode Rejection

Abstract: There is an increasing importance for floating measurements with high bandwidth in the field of power electronics, driven by the need to characterize power converters utilizing latest wide bandgap devices which offer very fast voltage transitions. In this paper, the required Common-Mode Rejection Ratio (CMRR) as the most important performance metric of a floating or isolated measurement system is analyzed and quantified for different converter realizations with the aim to limit the resulting time-domain error voltage. Afterwards, state of the art isolated single-ended probes are investigated and analyzed in terms of practical applicability and sensitivity regarding variations of the measurement setup, specifically looking at non-ideal connections between probe and converter, often inevitable in power electronic applications. It is found that the performance of isolated single-ended probes quickly degrades when additional connecting wires are used between the circuit under test and probe input. To overcome this inherent limitation of any single-ended approach, an isolated differential structure is presented that combines the advantages of conventional high-voltage differential probes and isolated single-ended probes. Finally, challenges involved when designing a matched differential system are discussed, in particular the influence of amplitude and phase imbalance on the maximum achievable CMRR. Especially the required phase accuracy which needs to be around six times higher than the amplitude accuracy is very hard to realize over the whole frequency range of interest. It turns out, however, that thanks to the passive common-mode filtering already present in state of the art single-ended approaches, CMRR values of around 30–40 dB in the difference-stage enable significant performance improvement for the differential structure.

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.