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.

Sinusoidal Input Current and Average Speed Control of a Single-Phase Supplied Three-Phase Inverter Drive Without Electrolytic Capacitor

Abstract: Single-phase supplied variable speed drives are mostly realized as two-stage systems comprising a single-phase PFC rectifier and a three-phase inverter stage. The intrinsic power pulsation of single-phase converters with twice the grid frequency is typically buffered by a bulky electrolytic DC-link capacitor, which is a major drawback concerning converter volume, costs and especially lifetime. Therefore, this paper presents a novel and simple implementation of a Machine-integrated Power Pulsation Buffer (MPPB) concept, which utilizes the inertia of the rotating mass as an energy storage to cover a part or the full input power pulsation. This allows to either reduce or even eliminate the electrolytic capacitor resulting in a smaller and cheaper converter system with increased lifetime. The proposed MPPB control concept is fully implemented in software, which means that only simple couplings are added to the control structure. Since the hardware remains unaffected, this concept can also be easily applied to already existing drive systems. In addition to the derivation of the control scheme, the proper operation of the MPPB is verified for steady-state and transient operation by circuit simulations.

Improved stator design for an ultra-high speed spinning ball motor

Abstract: The ongoing miniaturization trend of electric machines increases the demand for higher rotational speeds to provide a required power level at decreased size. The goal of this project is to push the limits of rotor miniaturization by researching new concepts for bearingless machines with ultra-high rotational speeds exceeding 25 million rotations per minute (Mrpm). Using a simple machine stator consisting of air coils limits the achievable rotor torque, which results in acceleration times of several hours until the aforementioned rotational speeds are reached. This study outlines the torque generation mechanisms of the machine and investigates the stator losses, from which improved stator designs, based on a ferrite core, are derived. The latter significantly increase the motor torque at decreased losses and facilitate fast acceleration of the rotor.

Device for milling and drilling rock with high energy pulses, has electronic power switch through which high discharge current and high energy are introduced into the rock, during milling and drilling

Abstract: The device (1) has a pulse capacitor (2), an electronic power switch (9), an ignition device (14) and a primary winding (31) formed in ignition transformer (27). The voltage across a parallel capacitor (29) is made twice the value of secondary voltage, according to the ignition voltage stage throttle (20) connected to an electrode (18). High discharge current and high energy are introduced into the rock, through the power switch. After the discharge of pulse capacitor, the power switch is blocked again.

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.