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.

Novel modulation schemes for conventional and sparse matrix converters facilitating reactive power transfer independent of active power flow

Abstract: Two novel modulation schemes are proposed which facilitate the transfer of reactive power from the load side to the mains side of a three-phase AC-AC sparse matrix converter (SMC) or a conventional matrix converter. The derivation of the modulation schemes, which rely on a decoupling of the output voltage and the input current formation, is described in detail. Furthermore, the operating limits concerning modulation index and reactive current magnitude are determined. Finally, digital simulations and measurements on a 7.5 kW prototype of a very sparse matrix converter verify all theoretical considerations.

A Novel Motor Topology for High-Speed Micro-Machining Applications

Abstract: In this paper, a novel motor topology (lateral stator machine) is proposed for various drilling applications where the space in the tool head is limited. The stator of the motor grows in one lateral direction, allowing for a compact direct drive design. Finite-element analysis (FEA) is carried out and the machine design is optimized for the specifications of a high-speed micro-machining spindle which is given as an example. The design procedure for those specifications is described in detail, where the torque is maximized while considering the space limitations and the loss constraints at the critical operating points. The construction of a lateral stator machine merged into a test bench is also described. The test bench is used for measuring the standstill torque of the machine in a configuration without bearings, such that only the electromagnetic torque is measured without any friction effects from the bearings. Moreover, the test bench can be modified to measure the no-load losses and separate the mechanical and electromagnetic components of it. Although described on a lateral stator machine, the measurement methodology of this paper can be applied to any electrical machine. Finally, measurement results are given and the design procedure is verified.

Design and experimental analysis of a DC to 1 MHz closed loop magnetoresistive current sensor

Abstract: This paper presents the improvement of a commercially available current sensor based on the anisotropic magneto-resistive effect for applications requiring high bandwidth current measurement such as high switching frequency single-phase and three-phase unity power factor PWM rectifier systems The sensor concept is of special interest as it could be packaged into compact power processing units and integrated power electronic modules In this paper the anisotropic magneto-resistive effect, as well as the analog interface electronic for signal conditioning for integrated current sensing are discussed The sensor functional principle, the advantages and limitations are shown in detail The measured sensor characteristics are also shown Finally, improvements are discussed which involves further reduction of the size and the offset calibration procedure

Power electronics interface for a 100 W, 500000 rpm gas turbine portable power unit

Abstract: A 100 W, 500000 rpm generator/starter for a gas turbine based portable power unit has been constructed. The permanent magnetic synchronous machine has an 8 kHz fundamental frequency and stator inductance of 3 /spl mu/H. The traditional voltage source inverter, VSI, is not an automatic choice for this type of machine due to the very high switching frequencies required. In this paper, voltage and current source topologies are compared for physical size, complexity and efficiency. Three topologies are selected for further investigation: the VSI with external inductances and high switching frequency, the VSI with block commutation and the current source inverter with block commutation. The paper presents the topology comparison, VSI design and experimental performance.

Active voltage balancing of DC-link electrolytic capacitors

Abstract: DC voltage links of three-phase power converters are frequently equipped with a series connection of two electrolytic capacitors because of high voltage level. For such a configuration, usually resistors have to be arranged in parallel to each capacitor in order to balance the partial voltages. These balancing resistors, however, have to be dimensioned regarding the worst-case scenario of capacitor's leakage currents; such leakage can lead to high permanent dissipative losses that also appear in case of low actual leakage currents. To avoid these losses to a very large extent, a novel low-cost and robust active unit for replacing the passive balancing resistors is introduced. The paper describes the operating principle of the circuit, analyses the fundamental relationships relevant for the balancing characteristic and gives guidelines concerning component selection. Furthermore, simulation results as well as measurements taken from a laboratory prototype are presented.

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.