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.

Comparative Evaluation of Overload Capability and Rated Power Efficiency of 200V Si/GaN 7-Level FC 3-Φ Variable Speed Drive Inverter Systems

Abstract: Variable speed drive systems in e.g. robotics applications are challenged with discontinuous operation cycles and short-time overload current requirements of 2-3 times nominal load. As the motor itself constitutes a large thermal time constant compared to the semiconductor devices in the inverter, latter create a bottleneck for the increased losses during overload operation. Hence, special focus has to be laid on the inverter overload capability, preferably without overdimensioning the system. In this paper a transient thermal model of optimized cooling approaches for 200V GaN and Si packages is empirically deduced. The model is then used to design a 7-Level Flying Capacitor inverter (7L FCi) aiming for 99% efficiency at nominal load for facilitated motor integration and 3 times overload capability. Consequently, the number of parallel switches, switching frequencies and the volume of passive components such as the flying capacitors and the output filter inductor is considered. In order to omit oversizing the inverter and the output inductor for overload operation, an unorthodox way of increasing the switching frequency during overload is proposed. It is concluded, that the small chip size of the 200V GaN devices compared the 200V Si devices poses additional challenges when dealing with overload operation.

Control method and device for the active compensation of power supply- or load dependent fluctuations of the power flow of a power electronic converter system

Abstract: The invention relates to a control method for the active compensation of fluctuations of a power flow of a power electronic converter system, wherein the converter system has a main converter (2) for the transfer of power between a DC port and an output port, as well as a buffer capacity C connected in parallel to the DC port and with a buffer capacity voltage uC, wherein a compensator (4) is connected in parallel to the buffer capacity C, which has a coupling converter (41) and an energy storage means (42), wherein the coupling converter (41) is designed to supply energy to the energy storage means (42) or to remove same. The method involves the following steps: determining an output pout,AC delivered by the main converter at the output port; determining, based on the output pout,AC* delivered by the main converter at the output port, a desired value of an output pK,out* to be discharged or received by the compensator (4) and/or a desired value for an energy storage means current iE* of the compensator (4); actuating the coupling converter (41) such that the output discharged or received by the compensator and/or the energy storage means current follows the corresponding desired value.

Full-SiC integrated power module based on planar packaging technology for high efficiency power converters in aircraft applications

Abstract: Compact, light-weight, efficient and reliable power converters are fundamental for the future of More Electrical Aircraft (MEA). Core elements supporting the electrification of the aerospace industry are power modules (PMs) employing exclusively SiC MOSFETs. In order to fully exploit the high switching speeds enabled by SiC, and to address the challenges arising from the parallelization of power devices, novel PM concepts must be investigated. In this paper, highly symmetrical layouts, low inductance planar interconnection technologies, and integrated buffer capacitors are explored to realize a high efficiency, fast-switching, and reliable full-SiC PM for MEA applications. A comprehensive assessment of a number of performance metrics against state-of-the-art full-SiC PMs demonstrates the benefits of the proposed design approach and manufacturing technologies. Moreover, by integrating temperature and current sensors, intelligent functions, which are crucial for the safe application of power electronics in MEA, are added to the developed PM. In this context, the use of MOSFETs’ Temperature Sensitive Electrical Parameters for online junction temperature estimation is demonstrated, allowing for non-invasive, i.e. without the need for dedicated sensors, thermal monitoring. Additionally, a highly compact gate driver, reducing the overall system volume and complexity, is designed and integrated in the housing of the PM. Finally, switching waveforms are measured during operation of the PM at 500V and 200A, proving the performance improvement enabled by the low inductance layout, the integrated snubber, and the gate driver.

Apparatus for simulating the phase currents of a three phase, three-point pulsed rectifier system

Abstract: The invention relates to an apparatus for simulating the mains phase currents of a three-phase, three-point pulsed rectifier system, and to a method for controlling this apparatus, in which case the voltage which occurs across the associated ballast inductance 6 or 7 or 8 is determined in each respective phase and is supplied to an integrator stage 26 so that the integration results ideally in a signal 27 which is proportional to the actual phase current To allow this current simulation to be adjusted 28 during operation, the current flowing via 19 into the output voltage neutral point 14 is detected via a current measurement apparatus 29, and the measurement signal 30 is applied to the input of an amplifier stage which is formed from the elements 31, 32 and 33 and inverts or does not invert the output depending on the level of a control signal 34, and whose output 37 for each phase is passed to one input of a summing amplifier 38, to whose second input 39 the phase current simulation signal 27 is applied The simulation error 40 determined by 38 is supplied to an amplification and control element 41, whose output 42 is passed on by means of an electronic switching element 44, which is controlled via a control signal 43, and possibly with the interposition of a further control element 46, to the summing amplifier 24 which is connected upstream of the integrating element 26 and provides the nominal-actual comparison for the adjustment control loop

Elektronischer Leistungswandler und Verfahren zu dessen Ansteuerung.

Abstract: Die Erfindung betrifft einen elektronischen Leistungswandler sowie ein Verfahren zur Steuerung eines solchen Wandlers. Ein elektronischer Leistungswandler weist Teiltransformatoren (2) auf, die zur Bildung einer Summe von Ausgangsspannungen kombiniert sind. Fur jede der Phasen ist eine Schalteinrichtung (1a, 1b, 1c) dazu eingerichtet, eine positive oder negative Phasenspannung oder die Spannung Null an die primarseitige Wicklung eines zugeordneten Teiltransformators (2) anzulegen. Im Betrieb des Wandlers wird mit einer Modulationsfrequenz eine Folge von Spannungspulsen mit der alternierend positiven und negativen jeweiligen Phasenspannung an die primarseitige Wicklung des zugeordneten Teiltransformators (2) gelegt, wobei eine Zeitdauer jedes der Spannungspulse proportional zum momentanen Betrag der jeweiligen Phasenspannung ist, und wobei die Spannungspulse der Schalteinrichtungen (1a, 1b, 1c) synchron zueinander erzeugt werden und jeweils steigende und fallende Flanken der Spannungspulse in jeder Pulshalbperiode zeitlich symmetrisch bezuglich eines gemeinsamen Mittelpunktes liegen. Dadurch resultiert eine Leistungsabgabe an eine Last (16), welche jeweils uber eine Periode der Modulationsfrequenz gemittelt, konstant ist.

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.