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 bidirectional buck-type PFC converter systems for interfacing residential DC distribution systems to the smart grid

Abstract: This paper discusses three-phase bidirectional high-power factor mains interfaces for application in smart-houses featuring a local DC distribution grid. The DC grid demanded power can be supplied by local DC generators, such as renewable power sources, and/or by the public three-phase AC mains, which gives the option of feeding back power into the mains in case of a low local power consumption. In order to generate a local 400V DC bus, bidirectionally connected to the European three-phase low voltage AC mains rated at 400V line-to-line, buck-type converter topologies are required. Several possible converter concepts are initially presented and further comparatively evaluated based on the following performance indices: total required semiconductor chip area, overall efficiency, overall passive components volume, and required EMI filter damping. As result of the comprehensive evaluation, the Bidirectional 3rd Harmonic Injection Active Filter Type Rectifier with DC/DC Output Stage is identified as most advantageous topology for the realization of a bidirectional buck-type PFC rectifier in the considered power range of 5 to 10 kW.

New calorimetrie power transistor soft-switching loss measurement based on accurate temperature rise monitoring

Abstract: Modern GaN and SiC power semiconductors require new experimental methods for determining switching losses as the widely accepted double-pulse-test (DPT) fails to accurately capture the dissipated energy during a switching transition because of electrical measurement limitations imposed by the very fast switching of WBG devices. In this paper, a new calorimetric measurement principle which relies on temperature rise monitoring of an aluminum heat sink during continuous operation of the attached power semiconductor is presented. Unlike traditional calorimetric methods, a single measurement can be performed in minutes. Using the proposed measurement principle, a soft-switching performance evaluation of selected 600 V GaN, SiC and Si power transistors is provided.

A new concept for reconstruction of the input phase currents of a three-phase/switch/level PWM (VIENNA) rectifier based on neutral point current measurement

Abstract: A novel concept utilizing the neutral point current information which is gained by an AC current sense transformer or a shunt for observer-based continuous reconstruction of the input phase currents of a three-phase/switch/level boost-type PWM (VIENNA) rectifier system is proposed. The basic principle of operation and the dimensioning of the observer circuit which in modified form also could feature an output voltage earth fault detection are discussed in detail. Furthermore, results of a practical application of the system in connection with a highly dynamic ramp comparison mains current control of a 10 kW laboratory model of the VIENNA rectifier are given.

Multi-port multi-cell DC/DC converter topology for electric vehicle's power distribution networks

Abstract: In today's electric vehicles (EV), power density is a key criterion for electrical systems, due to the strongly limited available space. Thereby, a high integration level of the electric distribution network is inevitable. In this paper, a novel multi-port multi-cell (MPMC) topology is proposed, which combines the features of two independent two-port converter systems, which are commonly used in state-of-the-art EVs. Consequently, this results in a higher overall power-density of the overall electric distribution system. The proposed converter comprises multiple identical subconverters (cells), where each cell processes the same share of the total converter power. Furthermore, as will be shown in this paper, the multi-cell approach mitigates several technological design challenges arising in single-cell solutions, where, in contrast to the multi-port multi-cell approach, extremely high output currents and high step-down ratios are required. Finally, a MPMC control strategy is introduced, which guarantees stable operation and balanced cell powers in the converter for all operating points.

Comparative evaluation of IPT resonant circuit topologies for wireless power supplies of implantable mechanical circulatory support systems

Abstract: Today's implantable blood pumps, such as Left Ventricular Assist Devices (LVAD) are powered by means of a percutaneous driveline, which constitutes a severe risk of infection to the patient Inductive Power Transfer (IPT) technology offers a solution to replace the driveline by a wireless energy link In this paper, three commonly used IPT resonant circuit topologies are compared regarding power transfer efficiency and heating of the tissue In the course of the analysis, the main advantages and disadvantages of each topology are identified and as a result it was found that regarding the heating of the tissue, the series-series compensated topology is the most promising solution for Transcutaneous Energy Transfer (TET) systems capable to provide a peak power transmission of up to 30 W Operated at the resonant frequency using an efficiency optimal control, the series-series compensation topology achieves the highest DC-to-DC power conversion efficiency in the coil coupling and output power range, but requires a higher complexity of the control system, and more important, it shows an increasing secondary side coil power loss with decreasing coil coupling factor In contrast, the operation near the frequency for load independent voltage gain using a load impedance control technique achieves similar power conversion efficiencies at high coil coupling factors, but offers a lower complexity of the overall TET system The peak DC-to-DC efficiency measured with a hardware prototype is 97 % at a coil separation distance of 10 mm, a primary and secondary coil diameter of 70 mm and ideal coil alignment Even at a coil separation distance of 20 mm and an output power of 5W, the efficiency is 905 %

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.