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.

Minimization of the DC current ripple of a three-phase buck-boost PWM unity power factor rectifier

Abstract: The modulation of a novel three-phase three-switch buck-type unity power factor rectifier with integrated DC/DC boost converter output stage is optimized concerning the ripple amplitude of the buck-boost inductor current. This is achieved by coordination of the switching operation of the buck input stage and of the boost output stage. A comparative evaluation of different modulation schemes does identify a modulation scheme which simultaneously does provide minimum DC current ripple and minimum input filter capacitor voltage ripple at minimum switching losses and/or maximum pulse frequency. All theoretical considerations are for operation in a wide input voltage range and are verified by simulations and by measurements on a DSP-controlled 5 k W prototype of the system.

Predictive torque and flux control of an induction machine fed by an indirect matrix converter

Abstract: A predictive torque and flux control method for an induction machine fed by an indirect matrix converter is presented in this paper. Simple discrete models of the induction machine and the converter are used to predict the behavior of torque and flux. The control scheme selects the switching state that minimizes the error in the torque and flux predictions according to their reference values. The control objectives are accomplished by using a prediction horizon of one sample time and a very intuitive control law. The proposed control scheme considers the discrete nature of control processors and power converters, presenting a special approach to realize control. The method is validated trough simulation results where it is shown that the predictive approach can be implemented simply with a good tracking of the torque and flux to their respective references.

Analysis of the duality of three phase PWM converters with DC voltage link and DC current link

Abstract: The duality of three-phase pulse-width modulation (PWM) converters with DC current and DC voltage links is analyzed by means of space-vector calculus for the example of a forced commutated rectifier system. The power-invariant transformation of the converter phase voltages or line currents into complex image quantities (space vectors) allows the presentation of the converter system as a complex space-vector voltage source or current source; its initial value is defined by the switching status of the converter system. The modulation principles (e.g., optimized pulse patterns) known from converters using DC voltage link systems, the guidelines concerning the dimensioning of power circuit components, and considerations relating to control are applied to the theory governing DC current link converters. >

High-Bandwidth High-CMRR Current Measurement for a 4.8 MHz Multi-Level GaN Inverter AC Power Source

Abstract: The control of very high switching frequency power electronic converter systems featuring latest generation wide bandgap (WBG) devices requires current measurements with a very high bandwidth (BW) to achieve high closed-loop control dynamics. One example is a ultra-high BW 4.8 MHz parallel-interleaved multi-level GaN inverter AC power source with a target output BW of 100 kHz. This work investigates the combination of state-of-the-art Hall-effect current sensors with a suitable high-frequency (HF) sensor to extend the BW of the commercially available current sensor by a factor of 20 – 50, i.e., up to 10 − 20 MHz. The main focus lies on a small form factor and a low realization effort. HF current sensors based on a Rogowski coil, an inductor integrated voltage sensing and a current transformer (CT) are analyzed and compared. Additionally, their respective performance limitations are highlighted. Furthermore, a precise combiner network to combine the low-frequency (LF) and HF signal is analyzed. The combiner circuit is designed in a way that component tolerances have no influence on the behavior in the transition frequency range from LF to HF. Thereby, also the immunity to Common-Mode (CM) disturbances, i.e., the high dv/dt occurring for the switching transitions of WBG semiconductors is considered. Finally, a hardware demonstrator featuring the two most promising current sensor approaches, i.e., the inductor voltage sensing and the CT, is presented and verified with comprehensive measurements in frequency and time domain. A BW from DC up to 35 MHz is measured. The realized sensors are further tested with a hardware prototype of the aforementioned AC power source switching 600 V at an effective switching frequency of 1.6 MHz. The measurements clearly reveal that both proposed sensor concepts are well suited for accurate measurements in fast switching converter systems with negligible additional volume.

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.