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.

Computationally Efficient Integration of Complex Thernal Multi-Chip Power Module Models into Circuit Simulators

Abstract: For analyzing reliability or short-term overload conditions of power electronic systems, it is necessary to know transient temperatures of the power semiconductors. Directly coupling thermal and circuit simulators increases the simulation time by orders of magnitude, therefore making such an approach impractical. A well-known solution to this problem is to extract thermal equivalent circuits from 3D-field simulations and to insert them directly into the circuit simulator. In this paper we discuss the poor scaling performance of this state-of-the-art approach. There is an enormous increase in simulation time if there are more than just a few chips thermally modeled. We propose a general procedure at the circuit simulator solver level to increase the calculation speed of such a coupled simulation significantly.

Combined Radial-Axial Magnetic Bearing for a 1 kW, 500,000 rpm Permanent Magnet Machine

Abstract: Ultra-high-speed and high-power-density drives are attracting much interest in today's industry. For instance, there are several investigations into mesoscale gas turbine generator systems and turbocompressors for fuel cells. In all ultra-high-speed machinery the bearing is a key technology. Therefore, this paper focuses on the design of a 500,000 rpm active magnetic bearing suitable for use in a 1 kW PM machine to complete an ultra-high-speed electrical drive system. The design procedure selects the suitable magnetic bearing type to keep the system compact and small. The electromagnetic characteristics are determined, the results for the rotor dynamic analysis are presented and the air friction losses caused by the high frequency operation are evaluated. The final design is a combined radial-axial magnetic bearing with a volume of 50 cm3.

An Ultra Sparse Matrix Converter with a Novel Active Clamp Circuit

Abstract: The ultra sparse matrix converter (USMC) is a AC-DC-AC converter that requires only 9 power switches compared to the 18 switches required for a conventional matrix converter. The simplified input switch configuration restricts this converter to unidirectional power flow applications in which the maximum displacement angle between input and output voltages and currents is plusmnpi/6. A novel clamp circuit is therefore used to protect the converter from overvoltages incurred under regeneration conditions. This paper presents the design of a 5.5 kVA USMC which uses space vector modulation in combination with a zero current commutation scheme at the input rectifier stage. The design of the system is detailed and the hardware implementation of the converter is described. Experimental results demonstrate the operation of the clamp circuit and show that the converter draws sinusoidal currents from the input and supplies sinusoidal currents to the output with a conversion efficiency of up to 94%.

Space vector based analysis of the variation and control of the neutral point potential of hysteresis current controlled three-phase/switch/level PWM rectifier systems

Abstract: This paper treats the control of the the capacitive output voltage center point of a unidirectional three-phase three-level PWM rectifier system. It is shown that, for hysteresis control of the input phase currents and resistive fundamental mains behavior, the center point potential can be controlled by an offset of the phase current reference values. Based on the results of a digital simulation, the transfer function is determined which describes the dynamic behavior of the system part to be controlled. Furthermore, the dimensioning of the center point voltage control is discussed. There, the considerations are related to an application of the PWM rectifier system for supplying the DC link of an uninterruptible power supply (8 kW rated power). Finally, the control behavior for stationary operation and for a step change of the load of the output voltage center point is examined for verifying the controller dimensioning. >

Magnetically levitated slice motors - an overview

Abstract: This publication gives a comprehensive overview over different concepts of magnetically levitated motors with slice-shaped rotors that differ in their construction and the way the bearing and drive forces are created After a description of the technical principle of the topologies the motor concepts are then compared by different criteria such as the acceleration behavior, the compactness and the complexity of the control The qualitative comparison is supported by performance measurements on the laboratory prototypes

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.