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.

Elektrischer Leistungswandler zur DC/DC-Wandlung mit dualen aktiven Brücken

Abstract: #CMT# #/CMT# A first bridge circuit converts a first direct voltage into a first alternating voltage, and a second bridge circuit converts a second direct voltage into a second alternating voltage. The first and second alternating voltages are applied to first terminals (A, B) and second terminals (P,Q) of alternating-voltage intermediate circuit. The bridge circuits include controlled switching elements to generate constant alternating voltage successively so that the direct voltages of five different levels are applied to corresponding sides of alternating voltage intermediate circuit. #CMT# : #/CMT# An independent claim is included for a method for operating electronic data processing device for determination of control method of bridge converter. #CMT#USE : #/CMT# Dual active bridge converter for central or high voltage application. #CMT#ADVANTAGE : #/CMT# The efficient operation, high flexibility, high degree of freedom, high power density and low switching loss of dual active bridge converter are ensured. #CMT#DESCRIPTION OF DRAWINGS : #/CMT# The drawing shows the circuit diagrams of the HDAB converter. A,B : First terminals P,Q : Second terminals.

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 a 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.

Impact of iron dust on electromechanical systems: A case study

Abstract: Several actuators (e.g. permanent magnet (PM) machines, magnet valves), sensors (e.g. reed sensors, Hall sensors, inductive proximity switches) and emerging inductive energy harvesting systems rely on a clean environment and/or well-defined magnetic conditions. However, in industrial environments iron dust or iron powder may be present, as e.g. resulting from machining, i.e. drilling or milling of mechanical parts or from mechanical wear, and could accumulate in the vicinity of magnetic components. Accordingly, a model for describing the magnetostatic properties of iron dust is required for analyzing a potentially negative impact on the operating behavior. The model derived in this paper is based on the B-H curve of an underlying base material (C45E steel in the presented case) and two further coefficients, representing the influence of powder density and the imperfect magnetic junction at the interfaces between iron particles. The model is then utilized for investigating the influence of iron dust on the operation of a recently introduced kinetic energy harvesting (KEH) system, as a case study. Three-dimensional finite element method (3-D FEM) simulations show that in this case the flux is actually enhanced by iron dust accumulated in front of the harvester. The paper concludes with an experimental verification of the iron dust B-H model and an experimental analysis of the KEH performance degradation due to iron dust.

Constant duty cycle sinusoidal output inverter with sine amplitude modulated high frequency link

Abstract: Despite the increasing performance of power semi-conductors and passives components, limited timing resolution in off-the-shelf available digital control hardware often prevents the switching frequency in kW-scale dc/ac power conversion to be increased above several MHz for the sake of extreme power densities. In this paper an alternative approach to generate a sinusoidal output voltage, based on constant duty cycle frequency shift control of a high frequency resonant inverter stage and a subsequent synchronous cycloconverter, is analyzed. The design of the presented converter is facilitated by means of a derived mathematical model. A novel closed-loop control system is proposed which achieves tight regulation of the output voltage by means of controlling the switching frequencies of the involved bridge legs operated in resonant mode. Characteristic waveforms of the dc/ac converter during steady-state and load transients are presented. Two distinct implementations of the resonant inverter stage, constituting an intermediate voltage or intermediate current link, are analysed and compared.

Geometrical Optimization of Medium-Frequency Air-Core Transformers for DCX Applications

Abstract: This article analyzes the potential of air-core transformers (ACTs) for realizing medium-voltage high-power isolated dc–dc converters. ACTs, i.e., transformers without magnetic cores, are particularly interesting for their simple construction and reduced weight. However, the reduced magnetizing inductance, the reduced magnetic coupling, and the stray fields are challenging aspects for the design of ACTs. A comprehensive model of the ACT (e.g., magnetic field patterns, skin and proximity losses, shield’s eddy currents, harmonics, insulation constraints, and thermal limit) is proposed and verified with measurements obtained with a prototype. Afterward, a complete multiobjective optimization of a series resonant converter (SRC) operating as a dc transformer (DCX) between two 7 kV buses with a rated power of 166 kW is conducted. Two different geometries are considered for the ACT: concentric cylindrical coils and planar spiral coils. As a result, the optimal ACT (operated at 162 kHz) features extreme power densities of 7.5 kW/dm3 and 31 kW/kg, which confirms the superiority of ACTs regarding the gravimetric power density. The calculated efficiencies are 99.5% and 98.7% for the ACT and the complete dc–dc converter, respectively. Finally, the different tradeoffs are highlighted and analyzed, e.g., mass, volume, efficiency, switching frequency, part-load behavior, and insulation distance.

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.