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.

Design considerations and experimental results of a 100 W, 500 000 rpm electrical generator

Abstract: Mesoscale gas turbine generator systems are a promising solution for high energy and power density portable devices This paper focuses on the design of a 100 W, 500 000 rpm generator suitable for use with a gas turbine The design procedure selects the suitable machine type and bearing technology, and determines the electromagnetic characteristics The losses caused by the high frequency operation are minimized by optimizing the winding and the stator core material The final design is a permanent-magnet machine with a volume of 3 cm3 and experimental measurements from a test bench are presented

Theoretical and experimental results of a mesoscale electric power generation system from pressurized gas flow

Abstract: In many process applications where throttling is used to reduce pressure, the potential to obtain net work output is sacrificed to the throttling process. Examples are throttling valves of gas pipelines and conventional throttles in automotive applications or turbo expanders as used in cryogenic plants. With a new pressure reduction system that produces electricity while expanding the gas, the lost potential to obtain work output can be recovered. To achieve a high power density, this energy generation system requires an increased operating speed of the electrical machine and the turbomachinery. This paper presents a miniature compressed-air-to-electric-power system, based on a radial turbine with a rated rotational speed of 490 000 rpm and a rated electric power output of 150 W. A comprehensive description including turbine, diffuser and permanent magnet (PM) generator is given. Finally, measurements of the compressed-air-to-electric-power system with a maximum rotational speed of over 600 000 rpm, a maximum electric output power of 170 W, a maximum torque of 5.2 mN m and a turbine efficiency of 52% are presented.

ZVS Modulation Scheme for Reduced Complexity Clamp-Switch TCM DC–DC Boost Converter

Abstract: DC–DC boost converter zero-voltage-switching (ZVS) modulation schemes such as triangular current mode (TCM) offer a highly efficient operation but suffer from large switching frequency variations, which are complicating the EMI filter design and the digital control. As a solution, a tri-state boost converter operated in ZVS mode, referred to as clamp-switch TCM (CL-TCM) operation can be introduced, which allows to limit the switching frequency variation significantly. This paper presents two variations of the CL-TCM boost converter with reduced number of active switches in the circuit, which are suitable for high input-to-output voltage conversion ratios. In addition, the ZVS modulation schemes, its limitations, the converter design and the controller implementation are presented and analyzed in detail for both converter topologies. The timing calculations for the switching signals are provided for two operating modes, either offering a minimized switching frequency variation and minimized RMS inductor current or a constant switching frequency operation, which in turn comes at the expense of an increased RMS inductor current. The ZVS operation and the operating modes are experimentally verified using a hardware prototype.

Analysis and design of a 1200 V All-SiC planar interconnection power module for next generation more electrical aircraft power electronic building blocks

Abstract: Compact, light weight and efficient Power Electronic Building Blocks are seen as fundamental components of future More Electric Power Systems, e.g. More Electrical Aircraft. Core elements supporting the trend are power modules employing solely SiC MOSFETs. In order to take advantage of the high switching speed enabled by SiC, novel modules concepts must be investigated. For example, low inductance planar interconnection technologies, integrated buffer capacitors and damping networks are possible solutions to mitigate switching overvoltages and oscillations at the switching node occurring for conventional modules. In this paper, the analysis and the design of a novel ultra-low inductance 1200 V SiC power module featuring an integrated buffer-damping network are discussed. The power module is first described and characterized with impedance measurements. Afterwards, a general optimization procedure for the sizing and the selection of the integrated components is presented and measurements are performed to verify the analysis and to highlight the improvements of the proposed solution.

Voltage-dependent capacitors in power electronic multi-domain simulations

Abstract: We discuss multi-domain simulation of power electronic systems where non-linear capacitors have a significant impact on the system behaviour, e.g. employing the MOSFET output capacitor Coss for soft switching or employing nonlinear thermal models in coupled electrical-thermal simulations. It is shown which errors can result from approximating non-linear capacitors with simple linear ones as proposed e.g. for Coss in datasheets. Furthermore a highly efficient implementation of non-linear capacitors in numerical circuit simulators is proposed.

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.