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.

Analysis and Experimental Verification of the EMI Signature of Three-Phase Three-Level TCM Soft-Switching Converter Systems

Abstract: This paper investigates the Electromagnetic Interference (EMI) noise signature of three-phase three-level (3L) Triangular Current Mode (TCM)-modulated grid-tied Photovoltaic (PV) inverters that achieve full Zero Voltage Switching (ZVS) and thus minimal switching losses over the entire mains period and/or ensure >99% efficiency. Further required is a very high power density, which facilitates installation and is achieved with high switching frequencies >100kHz. The impact of the characteristic variation of $f_{\mathrm {sw}}$ in all three phases and the therefore different instantaneous switching frequencies in each phase on the overall converter EMI noise signature is analyzed and it is found that the consideration of only one single phase is sufficient to characterize the noise emissions. Numeric approaches to estimate the detector output of EMI test receivers are compared and it turns out that the peak value of the noise voltage envelope is a useful measure to determine the required filter attenuation, provided the phase-shift of the harmonics is considered in the envelope detection. Finally, a hardware demonstrator of a 6.6kW, >99% efficiency three-phase 3L-TCM PV inverter with a power density of 6.2kW/dm3 (102 W/in3) is designed and the theoretical findings are verified. Moreover, the impact of parasitic capacitances from the switch-nodes and from the floating dc link to Protective Earth (PE) is thoroughly studied qualitatively and quantitatively with the result that these capacitances considerably reduce filter attenuation (35dB at 150,kHz in the case at hand), requiring sufficient design margin.

Design of a Test Bench for a Lateral Stator Electrical

Abstract: In a previous study, lateral stator electrical machines have been proposed for micro-machining applications where the space in the tool head is limited. In this paper, the construction of a lateral stator machine merged into a test bench is described. The test bench is used for measuring the standstill torque of the machine in a configuration without bearings, such that only the electromagnetic torque is measured. Moreover, the test bench can be modified to measure the no-load losses and separate mechanical and electromagnetic components of it using a novel method. Further separation of different components of electromagnetic no-load losses is also discussed. Although described on a lateral stator machine, the methodology in this paper can be applied to any electrical machine. I. INTRODUCTION In the last few years, several studies dealing with design, optimization and testing of high-speed electrical drives have been published (1-11). In (12), the authors have grouped the application areas of those high-speed electrical drives into two groups: group of applications with one working point and group of applications where the drive needs to cover a wide torque-speed range. Turbo compressors are a good example of the first group whereas applications like micro-machining spindles belong to the second group. Furthermore, in (12), lateral stator electrical machines are proposed for the second group of applications in order to fit the motor in confined spaces around the rotor, while still maintaining the wide operating range. In the same paper, this wide operating range is characterized by two operating points: a low-speed high-torque operating point where all the high-speed losses such as the core losses in the stator and eddy current losses in the solid bodies are neglected; and a high-speed low-torque operating point, where the copper losses in the windings are neglected. The machine geometry is optimized using a parametric finite element method (FEM) simulation. In this paper, further considerations about building the lateral stator machine are described in detail. Moreover, the lateral stator machine is merged into a test bench which can evaluate the machine performance in the two operating points mentioned above, enabling a direct verification of the FEM simulations. This is done by modifying the test bench into two different setups, one measuring the torque at standstill, the other measuring the no-load losses at higher speeds. The first setup is called the static torque measurement setup and the second one is named as the high-speed loss measurement setup. In the static torque measurement setup, a bearingless configuration is designed, and the torque is measured on the stator side. This allows for the measurement of the electromagnetic torque only, without the bearing friction, which enables a direct verification of the FEM analysis. In the high-speed loss measurement setup, deceleration tests are used to measure the total no-load losses. A novel method of loss segregation is proposed which allows for the separation of the mechanical losses from the electromagnetic losses, overcoming the problem of changing bearing friction loss with changing preload. This is especially important with high-speed, low-torque electrical machines where bearing friction causes an important part of the no-load losses. Moreover, the segregation of the different components of the no-load losses is discussed. Although the test bench design is described for a special electrical machine type, the methodology can be used to test any other electrical machine in similar way.

Non-Isolated Three-Phase Current DC-Link Buck-Boost EV Charger with Virtual Output Midpoint Grounding and Ground Current Control

Abstract: Non-isolated three-phase AC/DC converter concepts facilitate more compact and more efficient realizations of future EV chargers. However, without the galvanic isolation and/or high common-mode (CM) impedance provided by an isolation transformer, non-isolated chargers must employ other means to suppress CM leakage currents to ground sufficiently and to prevent nuisance tripping of mandatory residual current devices (RCDs). Typically, the required EMI filters reduce high-frequency (HF) CM leakage currents to uncritical values. However, low-frequency CM voltages, e.g., generated by third-harmonic injection, may drive significant LF CM currents through the parasitic capacitances of the DC output (including the battery pack) to protective earth (PE). Therefore, considering a non-isolated three-phase buck-boost current DC-link PFC rectifier system that consists of a buck-type current-source rectifier (CSR) stage and a three-level boost-type DC/DC-stage, this paper first proposes a virtual grounding control (VGC) of the DC output voltage midpoint. VGC employs the DC/DC-stage to compensate the LF (third-harmonic) CM voltage inherently generated by the CSR-stage, and thus controls the LF CM voltage between the DC output midpoint and PE to zero. This enables further a direct connection of the DC output midpoint to PE, where an additionally proposed ground current control (GCC) ensures near-zero LF CM leakage current. The proposed concepts are verified with a 10kW hardware demonstrator (power density of 6.4 kW/dm3 or 107.5 W/in3, full-load peak efficiency of 98.5%) considering TT (Terra-Terra) and TN (Terra-Neutral) grounding systems. With a direct connection of the DC output midpoint to PE, GCC limits the LF CM leakage current to < 6mA RMS, i.e., significantly below typical RCD trip levels, and, using the human-body impedance model according to UL 2202, achieves a test voltage of 110mV that is clearly below the most stringent limit (250 mV) of the standard.

Ballast for a gas discharge lamp

Abstract: A ballast for a gas discharge lamp (2) has an inductor in the load circuit (1) and a transformer (14) in a driver circuit (11) for an inverter (7) having high-impedance switch elements (8). In order to reduce the circuit complexity, the primary winding Tp and the secondary winding Ts of the transformer (14) should have a common core (16).

Circuit arrangement for controlling power transistors of a power converter

Abstract: A circuit arrangement for controlling power transistors of a power converter includes a logic circuit configured to generate a pulse-width modulation (PWM) signal and a clock generator configured to generate a clock signal. A first and a second isolator are configured to galvanically isolate transmission of the PWM signal and the clock signal into a high-voltage portion of the power converter so as to produce a galvanically isolated PWM signal and a galvanically isolated clock signal. The first isolator for the PWM signal is configured transmit both DC voltage signals and AC voltage signals. A correction circuit is configured to correct jitter of the galvanically isolated PWM signal based on the galvanically isolated clock signal. The second isolator for the clock signal exhibits a jitter lower than that of the first isolator by a factor of at least two.

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.