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 concept of the SWISS rectifier preventing input current distortions at sector boundaries

Abstract: This paper describes a new modulation concept for the uni- and bidirectional SWISS rectifier which mitigates input current distortions at the gird voltage sector boundaries. An analytical model is derived and compared to simulations, showing that these distortions are increasing the input current THD significantly. Furthermore, an algorithm is presented which allows the calculation of a temporary pulse width modulation for the SWISS Rectifier's active 3rd harmonic current injection network which mitigates the distortions. Simulations show that the AC input currents' THD can be reduced from 4.2 % to 0.8 % on a prototype system. The concept is verified by measurement results taken on a bidirectional 7.5 kW SWISS Rectifier prototype.

A novel concept for balancing of the phase modules of a three-phase unity power factor Y-rectifier

Abstract: The isolated star point of a three-phase star-connection of single-phase unity power factor PWM rectifier systems (Y-rectifier) results in a mutual coupling of the individual phase module outputs, i.e. the individual DC link voltage control loops. Starting from the theoretical analysis of a series connection of two DC-DC boost converters a control-oriented equivalent circuit of the three-phase Y-rectifier system is derived in analytically closed form. Based on this a robust multivariable control is designed which ensures constant DC link voltage levels for unsymmetric disturbances, i.e. step load changes of the phase modules, All theoretical findings are verified via numerical simulations.

Acoustic noise in inductive power components

Abstract: This paper deals with the acoustic emissions of PWM-operated inductive components in the medium frequency range. It is shown with measurements that the noise emissions are primarily caused by magnetostriction, an induction-dependent dimensional change of the magnetic core. The influences of various modulation parameters on the sound pressure level spectra of two prototypes are measured and analyzed. It is confirmed that the emitted sound is proportional to the square of the magnetic flux density.

Prediction techniques compensating delay times caused by digital control of a three-phase buck-type PWM rectifier system

Abstract: The digital control of a three-phase, three switch buck-type rectifier system is analyzed hi this paper. Three main sources of delay times in the control loop can be identified for the implementation on a digital signal processor, namely: the delay time due to the sampling of the control quantities; the one due to the calculation time of the DSP; and the one due to the sample-and-hold function of the PWM modulator. Their influence on the stability of the inner current control loop is discussed and two prediction methods for compensation, namely a linear prediction and the Smith prediction, are comparatively evaluated. The control performance and the effect of the delay times and the prediction methods are finally shown by simulation results and through and measurements on a 5 kW prototype.

Direct three-phase single-stage flyback-type power factor corrector

Abstract: Based on the work of Hui and Chung (see ibid., vol. 33, no. 15, p.1274-76, 1997) a three-phase converter system consisting of three single-phase flyback-type AC/DC converter modules in star-connection is proposed and investigated.

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.