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.

A New 3-phase Buck-Boost Unity Power Factor Rectifier with Two Independently Controlled DC Outputs

Abstract: A new 3-phase buck-boost unity power factor rectifier consisting of a 3-phase bridge buck PFC rectifier and two boost dc-dc converters connected in series is proposed for an industrial application where two independent output voltages need to be controlled. This paper presents the proposed topology and the requirements for this application. The proposed and alternative topologies are briefly compared. Through this comparison, it is shown that the proposed topology offers the best solution in terms of simplicity and functionality. The operation of the new topology is described in detail and then the control strategy including PWM calculations to obtain the best performance is given. The validity of the theory and practicality of the new rectifier system is confirmed through simulation and experimental results obtained from a 5 kW prototype.

A novel control concept for reliable operation of a three-phase three-switch buck-type unity power factor rectifier with integrated boost output stage under heavily unbalanced mains condition

Abstract: In this paper the reliable operation of a three-phase three-switch buck-type PWM unity power factor rectifier with integrated boost output stage under heavily unbalanced mains, i.e. mains voltage unbalance, loss of one phase, short circuit of two phases or earth fault of one phase is investigated theoretically and experimentally. The analytical calculation of the relative on-times of the active switching states and of the DC link current reference value is treated in detail for active and deactivated boost output stage. Based on the theoretical considerations a control scheme which allows to control the system for any mains condition without change-over of the control structure is described. Furthermore, digital simulations as well as experimental results are shown which confirm the proposed control concept for different mains failure conditions and for the transition from balanced mains to a failure condition and vice versa. The experimental results are derived from a 5 kW prototype, input voltage range 208-480 V/sub rms/ line-to-line, output voltage 400 V/sub DC/ of the rectifier system, where the control is realized by a 32-bit digital signal processor.

Synchronization of the switching action of hysteresis current controlled parallel connected power electronics systems

Abstract: A method and apparatus for operation of an electrical power conversion system having first and second partial systems connected in parallel. Each partial system includes an inductor and an electronic switch for controlling electrical power transferred through the partial systems. A control circuit controls operation of the electronic switches. The control circuit includes devices for generating a first control signal error and a second control signal error as a function of a reference and current flowing in the inductors. Hysteresis devices receive the first and second control signal errors and provide first and second outputs, respectively, upon intersection of the first and second control signal errors with selected threshold values. Delay devices coupled to the electronic switches receive and delay transmission of the first and second outputs to the electronic switches.

Analysis and Evaluation of Active/Hybrid/Passive dv/dt-Filter Concepts for Next Generation SiC-Based Variable Speed Drive Inverter Systems

Abstract: State-of-the-art variable speed drive inverter systems are typically employing 1200 V Si IGBTs with antiparallel freewheeling diodes, resulting in a large overall semiconductor chip area, relatively high switching losses and/or low switching frequencies, and causing a substantial on-state voltage drop in both current directions, which inherently limits the peak and part-load efficiency. SiC MOSFETs are seen as natural future replacement of Si IGBTs, since they benefit from high switching speeds and low on-state resistances, which drastically reduces switching and conduction losses. However, the high switching speed of SiC devices results in a dv/dt-stress on the motor windings of up to 60...80 V/ns, which must be limited to 3...6 V/ns in order to prevent partial discharge phenomena and/or progressive insulation aging. Full sinewave filtering could solve this issue, but would also reduce the achievable performance improvement, as a higher switching frequency and/or a bulky filter would be required. Therefore, this paper comparatively evaluates different dv/dt-limitation approaches proposed in literature, i.e. active, hybrid and passive filter concepts, for a next generation 10kW SiC PWM inverter supplied from an 800V DC-bus. First, the different filter concepts are described and analyzed, and in a second step their design procedure is explained based on the design space approach. Afterwards, a Pareto optimization is conducted and Pareto optimal designs are selected, evaluated and compared regarding efficiency and power density. All considered filter designs outperform a state-of-the-art typically 98.3% efficient IGBT inverter drive. The hybrid filter enables a part-load (at 8 kW) efficiency of 99.0% for a dv/dt limited to 6 V/ns. If higher dv/dt -values can be tolerated, e.g. 12 V/ns, 99.3% part-load efficiency with a power density above 80 kW/L can be achieved by the active concept.

High-frequency isolated DC/DC converter for input voltage conditioning of a linear power amplifier

Abstract: Conventional linear power amplifiers 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 linear power amplifiers, e.g. for the realization of high power testing voltage sources. In this paper a high-frequency isolated DC/DC converter system for the conditioning of the input voltage of a linear power amplifier. The output voltage of the DC/DC converter is varied according to the output voltage to be formed by the linear power amplifier so that the voltage drop occurring across the power amplifier output transistors is reduced to low values which results in a significant increase of the total system efficiency. The control design of the DC/DC converter is for fast output voltage response according to the high large signal bandwidth of the linear power amplifier. The three-level input stage of the proposed system does allow a direct connection to the output of a three-phase three-level PWM rectifier ensuring low effects on the supplying mains. The operating principle of the proposed system is described and the design of the output voltage control is treated in detail. The resulting dynamic behavior of the system is analyzed by digital simulation. Finally, the theoretical considerations are verified by measurements on a 1.5 kW laboratory prototype.

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.