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.

Closed-Loop di/dt&dv/dt control and dead time minimization of IGBTs in bridge leg configuration

Abstract: In order to optimize the clamped inductive load (hard) switching behavior of IGBTs in voltage source power electronic converters, i.e. to ensure a defined switching behavior independent of the load current level, the DC-link voltage or the junction temperature, in recent publications an IGBT gate drive for controlling diC/dt and dvCE/dt has been proposed and experimentally verified for chopper circuits. In this paper, the necessary modifications of the gate drive concept for applications with IGBTs in bridge leg configuration are investigated. For the purpose of a safe operation and a minimum distortion of the generated output voltage waveform, a reciprocal interlocking of the bridge leg's IGBTs is introduced in addition. Finally, the proposed concept is experimentally verified for regular operation and for different types of short circuits of the load.

Novel Concepts for Integrating the Electric Drive and Auxiliary Dc-Dc Converter for Hybrid Vehicles

Abstract: Cost, volume and weight are three major driving forces in the automotive area. This is also true for hybrid vehicles which attract more and more attention due to increasing fuel costs and air pollution. In hybrid vehicles the energy distribution system causes a significant share of the volume and the costs. In order to reduce the costs and the volume of this system two new concepts for integrating the dc-dc converter, which transfers the power between the low and the high voltage bus, functionally in the inverter/drive system are presented in this paper. These concepts are verified by simulations and experimental results.

Modulation Concepts for the Control of a Two-Phase Bearingless Slice Motor Utilizing Three-Phase Power Modules

Abstract: Future application areas for bearingless pump systems will demand for highly compact and cost effective designs. This trend mainly has a major impact on the power electronics part of these systems. Up to now, full-bridge converters have been used in order to independently control the phases of the active magnetic bearing and the drive system. With the use of an interleaved half-bridge topology, the number of required power semiconductors is reduced by 25%. In this paper, novel modulation techniques are presented and comparatively evaluated in order to achieve a similar dynamic performance of the pump system as with the conventional full-bridge topology. The effects of a phase shift and of higher harmonics in the duty cycles are analyzed in detail. The proposed concepts are then implemented on a DSP board, and their feasibility is shown on a highly compact 1.5-kW prototype of the converter which is realized with two integrated three-phase power modules. Furthermore, it is shown that the higher harmonics injection does not have an impact on the average speed of the impeller and thus on the constant output flow of the pump.

Three-Phase Two-Phase-Clamped Boost-Buck Unity Power Factor Rectifier Employing Novel Variable DC Link Voltage Input Current Control

Abstract: Battery chargers supplied from the three-phase mains are typically realized as two-stage systems consisting of a three-phase PFC boost-type rectifier with an output DC link capacitor followed by a DC/DC buck converter if boost and buck functionality is required. In this paper, a new modulation scheme for this topology is presented, where always only one out of three rectifier half-bridges is pulse width modulated, while the remaining two phases are clamped and therefore a higher efficiency is achieved. This modulation concept with a minimum number of active half-bridges, denoted as 1/3 rectifier, becomes possible if in contrast to other modulation schemes the intermediate DC link voltage is varied in a six-pulse voltage fashion, while still sinusoidal grid currents in phase with their corresponding phase voltages and a constant battery output voltage are obtained. In this paper, a detailed description of the novel 1/3 rectifier's operating principle and the corresponding control structure are presented and the proper closed loop operation is verified by means of a circuit simulation. Finally, the performance gain of the 1/3 rectifier control scheme compared to conventional modulation schemes is evaluated by means of a virtual prototype system.

Investigation of Exterior Rotor Bearingless Motor Topologies for High-Quality Mixing Applications

Abstract: The selection of a suitable topology is a crucial part of the design process of a machine. In particular, the slot/pole combination of a bearingless motor has a strong influence on the levitation and drive characteristics. In this paper, several feasible slot/pole combinations for a bearingless motor in exterior rotor construction are investigated, and the important characteristics of each possible topology are discussed in detail. In the end, a comparison between the presented topologies is undertaken, and the optimal motor topology is designed and implemented in a prototype setup.

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.