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.

Comprehensive Design of a Three-Phase Three-Switch Buck-Type PWM Rectifier

Abstract: A three-phase three-switch buck-type pulsewidth modulation rectifier is designed for telecom applications in this paper. The rectifier features a constant 400-V output voltage and 5-kW output power at the three-phase 400-V mains. The principle of operation and the calculation of the relative on-times of the power transistors are described. Based on analytical relationships the stresses of the active and passive components are determined and the accuracy of the given calculations is verified by digital simulations. Exemplarily, a 5-kW power converter is then designed based on the analytical expressions and on switching loss measurements from a hardware prototype constructed with insulated gate bipolar transistor/diode power modules. The loss distribution of the components, the total efficiency, and the junction temperatures of the semiconductors are then evaluated in dependency on the operating point. Finally, the trade-off between the selected switching frequency and the admissible power range for the realized design is shown and a total efficiency of 95.0% is measured on the hardware prototype, where an excellent agreement with the theoretically evaluated efficiency is shown

EMI Filter Design for a 1 MHz, 10 kW Three-Phase/Level PWM Rectifier

Abstract: The attenuation characteristics of electromagnetic interference (EMI) filters in practice often differ from theoretical predictions and minor changes can result in a significant improvement in performance. The performance of the differential-mode (DM) filter stage can usually be well predicted, but the common mode (CM) behavior is more difficult to handle. This is especially true for three-phase pulsewidth modulation (PWM) rectifier systems, which inherently show a large high-frequency CM voltage at the rectifier output. Possible CM noise current paths of a three-phase/level PWM rectifier are analyzed in this paper where parasitic capacitances to the heat sink and to earth are considered. In addition, a concept to significantly reduce CM emissions is discussed in detail. Based on the proposed models, an EMI filter design for a system with 1 MHz switching frequency is shown. Experimental verification of the designed EMI filter is presented by impedance and conducted emission (CE) measurements taken from a 10 kW prototype. Several practical aspects of filter implementation such as component arrangement, shielding layers, magnetic coupling, etc., are discussed and verified by measurements.

Closed-Loop di/dt and dv/dt IGBT Gate Driver

Abstract: This paper proposes a new concept for attaining a defined switching behavior of insulated-gate bipolar transistors (IGBTs) at inductive load (hard) switching, which is a key prerequisite for optimizing the switching behavior in terms of switching losses and electromagnetic interference (EMI). First, state-of-theart gate driver concepts that enable a control of the IGBT’s switching transients are reviewed. Thereafter, a highly dynamic closedloop IGBT gate driver using simple passive diC /dt and dvCE /dt feedbacks and employing a single analog PI-controller is proposed. Contrary to conventional passive gate drivers, this concept enables an individual control of the current and voltage slopes largely independent of the specific parameters or nonlinearities of the IGBT. Accordingly, a means for optimizing the tradeoff between switching losses, switching delay times, reverse recovery current of the freewheeling diode, turn-off overvoltage, and EMI is gained. The operating principle of the new gate driver is described and based on derived control oriented models of the IGBT, a stability analysis of the closed-loop control is carried out for different IGBT modules. Finally, the proposed concept is experimentally verified for different IGBT modules and compared to a conventional resistive gate driver.

Optimized design of medium frequency transformers with high isolation requirements

Abstract: For future DC electric power systems, high-power DC-DC converters will play a major role as they will substitute today's bulky 50/60Hz transformers. One key component within this DC-DC converters is the medium frequency transformer that provides the isolation level and the step up/down of the different voltage levels. As a consequence, an optimized design methodology that considers this high isolation requirements is needed. This paper presents a step-by-step design for medium frequency transformers with high isolation requirements. Each step in the design is carefully discussed and the required design considerations, such as flux density limits, isolation and thermal management, are explained in detail. The proposed design procedure is applied to a core-type transformer analyzing the outcome of the optimization process.

Differential Mode Input Filter Design for a Three-Phase Buck-Type PWM Rectifier Based on Modeling of the EMC Test Receiver

Abstract: For a three-phase buck-type pulsewidth modulation rectifier input stage of a high-power telecommunications power supply module, a differential-mode (DM) electromagnetic compatibility (EMC) filter is designed for compliance to CISPR 22 Class B in the frequency range of 150 kHz-30 MHz. The design is based on a harmonic analysis of the rectifier input current and a mathematical model of the measurement procedure including the line impedance stabilization network (LISN) and the test receiver. Guidelines for a successful filter design are given, and components for a 5-kW rectifier prototype are selected. Furthermore, formulas for the estimation of the quasi-peak detector output based on the LISN output voltage spectrum are provided. The damping of filter resonances is optimized for a given attenuation in order to facilitate a higher stability margin for system control. Furthermore, the dependence of the filter input and output impedances and the attenuation characteristic on the inner mains impedance are discussed. As experimentally verified by using a three-phase common-/Differential-Mode separator, this procedure allows accurate prediction of the converter DM conducted emission levels and therefore could be employed in the design process of the rectifier system to ensure compliance to relevant EMC standards

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.