scispace - formally typeset
Search or ask a question
Author

Johann W. Kolar

Other affiliations: Alstom, Infineon Technologies, Bosch  ...read more
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.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, the virtual flux method is used to extract the mains voltage from the switching state, dc voltage, and line currents, and the three phase currents are generated using a decoupling hysteresis current controller.
Abstract: This paper proposes a new simple method of three- phase, sensorless mains voltage, power control with near constant switching frequency based on a decoupling hysteresis current controller (DHC), and the virtual-flux concept. The virtual flux method is used to extract the mains voltage from the switching state, dc voltage, and line currents. From the desired real and reactive powers the three-phase currents are generated using a DHC. The DHC avoids the switching interaction between the phases, and when a variable hysteresis band is employed a near constant switching frequency is achieved. The method is also extended for high power inverter applications that include an inductance- capacitance-inductance output filter, where some undesirable characteristic, such as filter resonance, have to be compensated. Theoretical analysis is presented and the performance of the proposed method is experimentally verified.

51 citations

Journal ArticleDOI
TL;DR: A high-frequency isolated boost-type tracking power supply (TPS) system is proposed for the conditioning of the input voltage of an LPA so that the voltage drop across the power amplifier output transistors is reduced to low values, resulting in a significant increase of the total system efficiency.
Abstract: Conventional linear power amplifiers (LPAs) show a high output voltage quality but are characterized by high power losses and/or low power density. Therefore, there is a growing interest in increasing the efficiency of LPAs, e.g., for the realization of high power testing voltage sources. In this paper, a high-frequency isolated boost-type tracking power supply (TPS) system is proposed for the conditioning of the input voltage of an LPA. The output voltage of the TPS is varied according to the voltage to be formed by the LPA so that the voltage drop across the power amplifier output transistors is reduced to low values. This results in a significant increase of the total system efficiency. The operating principle of the proposed system is described. A design method for the output filter using the power supply rejection ratio of the LPA is proposed. This method ensures that the amplifier output voltage has minimal switching frequency components. Furthermore, a control system design method is presented that ensures good performance in the control of the constant inductor current of the switch-mode tracking stage. Finally, the theoretical considerations are verified by measurements on a 1-kW laboratory prototype.

51 citations

Journal ArticleDOI
TL;DR: In this article, a modulation concept for the uni-and bidirectional SWISS rectifier was proposed, which mitigates ac input current distortions at the mains voltage sector boundaries.
Abstract: This paper describes a new modulation concept for the uni- and bidirectional SWISS rectifier, which mitigates ac input current distortions at the mains voltage sector boundaries. An analytical model is derived and compared to simulations, which allows an estimation of the distortion's magnitude from design parameters, showing that these distortions increase the input current total harmonic distortion (THD) significantly. A modification of the original circuit topology is proposed, which decouples the operation of SWISS Rectifier's active third-harmonic current injection network and its dc–dc converter switches. An algorithm is presented which allows the calculation of a temporary pulse width modulation for the SWISS Rectifier's current injection network to mitigating the distortions. The concept is verified for both power flow directions and for operation with unsymmetrical and distorted mains voltages by measurement results taken on a bidirectional 7.5-kW SWISS Rectifier prototype. An ac input current THD of 1.3% results for symmetric sinusoidal mains voltages and 1.4% and 1.6% for operation with distorted and unsymmetrical mains voltages.

51 citations

Proceedings ArticleDOI
09 Mar 2012
TL;DR: In this article, a single-stage dual active bridge (DAB) AC/DC converter with a power factor corrector (PFC) stage in series with a DC/DC isolation stage was compared with a conventional dual-stage concept, where a bidirectional interleaved triangular current mode (TCM) PFC rectifier was chosen in combination with a DAB DC/dc converter.
Abstract: For realizing bidirectional and isolated AC/DC converters, soft-switching techniques/topologies seem to be a favourable choice as they enable a further loss and volume reduction of the system. Contrary to the traditional dual-stage approach, using a power factor corrector (PFC) stage in series with a DC/DC isolation stage, we showed recently that the same functionality can be achieved under full soft-switching operation using a single-stage dual active bridge (DAB) AC/DC converter. This paper investigates the performance of this single-stage approach by comparing it with a state-of-the-art conventional dual-stage concept (both soft-switching converters), where a bidirectional interleaved triangular current mode (TCM) PFC rectifier was chosen in combination with a DAB DC/DC converter. The advantages and drawbacks of each concept are discussed in detail, focusing on the impact of the utilized semiconductor technology and silicon area on the converter efficiency. Furthermore, a comprehensive comparison of power density is allowed by the analytical models that correlate the component losses with their respective volume.

51 citations

Journal ArticleDOI
TL;DR: In this paper, a generic derivation of a passive equivalent circuit that accurately models the converter's terminal behavior is presented, which yields the known analytic results for idealized cases, but additionally allows for a parametrization of the equivalent circuit based on simulated or measured waveforms, thereby facilitating high accuracy also in nonideal cases.
Abstract: The series resonant converter (SRC) operated in the half-cycle discontinuous-conduction-mode (HC-DCM) provides galvanic separation and a tight coupling of its input and output voltages in an open-loop operation, i. e., with minimum control complexity, which renders it suitable for a wide range of applications that require galvanic isolation. This letter first explains the “DC transformer” behavior of the converter and then provides a generic derivation of a passive equivalent circuit that accurately models the converter's terminal behavior. The proposed generic derivation yields the known analytic results for idealized cases, but additionally allows for a parametrization of the equivalent circuit based on simulated or measured waveforms, thereby facilitating high accuracy also in nonideal cases. Furthermore, it is shown that a noninfinite magnetizing inductance results in an additional load-independent difference between the input and the output voltage, and a corresponding extension of the equivalent circuit model is proposed. The considerations are verified by simulations and measurements of a 10 kW/350 V/350 V HC-DCM SRC system.

50 citations


Cited by
More filters
Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
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 …

33,785 citations

Journal ArticleDOI
TL;DR: The most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-Clamped (flying capacitor), and cascaded multicell with separate DC sources are presented and the circuit topology options are presented.
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.

6,472 citations

Journal ArticleDOI
TL;DR: 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.
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.

3,415 citations

01 Sep 2010

2,148 citations