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 …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

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.

Multilevel inverters: a survey of topologies, controls, and applications

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.

/pdf/recent-advances-and-industrial-applications-of-multilevel-26fluutoc9.pdf

Recent Advances and Industrial Applications of Multilevel Converters

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

The control of very high switching frequency power electronic converter systems featuring latest generation wide bandgap devices requires current measurements with a very high bandwidth (BW) to achieve high closed-loop control dynamics. One example is an ultrahigh BW <inline-formula><tex-math notation="LaTeX">$\mathbf {4.8}$</tex-math></inline-formula> MHz parallel-interleaved multilevel GaN inverter ac power source with a target large-signal output BW of <inline-formula><tex-math notation="LaTeX">$\mathbf {100}$</tex-math></inline-formula> kHz. This work investigates the combination of commercially available low-frequency (LF) Hall-effect current sensors (BW<inline-formula><tex-math notation="LaTeX">$\mathbf {\approx 1}$</tex-math></inline-formula> MHz) with suitable high-frequency (HF) sensors to extend the BW above <inline-formula><tex-math notation="LaTeX">$\mathbf {10}$</tex-math></inline-formula> MHz, i.e., enough to measure the HF inductor current. Based on a conventional PCB-integrated Rogowski coil, for the HF sensor, three improved pickup coil (PUC) geometries based on proposals in the literature are investigated. The LF and HF sensor signals are combined with a precision fully differential combiner circuit. Design guidelines for the HF sensors as well as the combiner circuit are presented and thereby the influence of mismatches and tolerances is examined. The performance of the proposed HF sensors is experimentally verified and compared with previous solutions based on galvanically isolated inductor voltage sensing and a current transformer. The PUCs reach a BW <inline-formula><tex-math notation="LaTeX">$\mathbf {>50}$</tex-math></inline-formula> MHz, which is an improvement by more than a factor of <inline-formula><tex-math notation="LaTeX">$\mathbf {50}$</tex-math></inline-formula> compared to the fastest available Hall sensor. Furthermore, it is proven that all investigated sensors are capable to accurately measure the triangular inductor current ripple in a hardware prototype of the aforementioned ac power source. In a final step, the influence of common-mode (CM) disturbances originating from fast <inline-formula><tex-math notation="LaTeX">$\mathbf {{d}v/{d}t}$</tex-math></inline-formula> switching transients on the sensor performance is analyzed. The presented current sensors achieve a CM rejection ratio of almost <inline-formula><tex-math notation="LaTeX">$\mathbf {100}$</tex-math></inline-formula> dB.

Beyond 50 MHz Bandwidth Extension of Commercial DC-Current Measurement Sensors With Ultra-Compact PCB-Integrated Pickup Coils

The Vienna rectifier (VR) is used in applications that require unidirectional, non-isolated, three-phase AC to DC conversion with constant output voltage and sinusoidal input currents. However, because of the unidirectional topology, the input currents become discontinuous at small output power values. As a consequence, the relationship between rectifier input voltage and duty cycle changes compared to continuous conduction mode. Therefore, if no additional measures are taken, the rectifier input currents will be distorted. This work describes a new control scheme that allows operation of the VR with sinusoidal input currents in discontinuous conduction mode (DCM). The limits of operation are described, concerning maximum mains voltage, maximum midpoint current and minimum resistance to the mains in DCM. Further, the noise emission in DCM is compared to continuous conduction mode (CCM) operation. Finally, the proposed scheme is experimentally verified on a hardware prototype.

New Current Control Scheme for the Vienna Rectifier in Discontinuous Conduction Mode

A simple way to improve the line power quality in Electrostatic Precipitator (ESP) applications by using both the characteristics of its electrical installation and the typical ESP high power supply is presented in this work. A multi-pulse system is built by selecting a combination of suitable MV/LV distribution transformers, preserving the simplicity and reliability of the typical ESP installation. In addition, processing only about 10% of the total system apparent power, shunts Active Filters (AFs) are placed on the low voltage side of the transformer (LV) for high order harmonic-current-mitigation (>7th harmonic). In case of imbalance in the transformer loading, the AFs can also act to adjust the current 5th and 7th harmonics, which are then effectively eliminated by the multipulse system. The theory presented in this work is verified experimentally by a 12 pulse system comprising two passive rectifiers and a designed 12kVAr active filter.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/T_Soeiro_2_01.pdf

Line power quality improvement for ESP systems using multi-pulse and active filter concepts

This paper proposes a novel type of watt-range permanent-magnet energy harvester, which harvests energy from a moving conductive body or surface without mechanical contact, as its operation is purely based on eddy-current coupling. The harvester's main advantage over existing solutions is that it allows energy transfer over atypically large (2 … 15 mm) air gaps, which are unavoidable in certain industrial applications. The paper provides a detailed description of the system's operating principle, and elaborates its modeling using 3-D Finite-Element Method (FEM) analysis. Two prototypes are built and tested for verifying the models. A power of 2.42W is harvested from an aluminum surface moving with 10 m/s, over 12mm air gap using a prototype with ≈ 14 cm3 magnet volume. Moreover, the effects of the harvester's placement as well as the speed of the moving conductive surface on the maximum harvested power and the system's efficiency are analyzed, both with FEM simulations and measurements.

Johann W. Kolar

Papers

Beyond 50 MHz Bandwidth Extension of Commercial DC-Current Measurement Sensors With Ultra-Compact PCB-Integrated Pickup Coils

New Current Control Scheme for the Vienna Rectifier in Discontinuous Conduction Mode

Line power quality improvement for ESP systems using multi-pulse and active filter concepts

Novel contactless axial-flux permanent-magnet electromechanical energy harvester

Voltage converter device for a D.C. voltage consumer and a method for supplying the consumer