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

A new power amplifier system focused mainly on EMC testing applications is analyzed. The proposed topology consists of a three-level switching power amplifier connected in parallel with a capacitive coupled linear stage which absorbs the output current ripple of the switch-mode stage resulting in an almost ripple-free output voltage of the total amplifier. This concept alternatively can also be interpreted as a switch-mode power amplifier with a hybrid output filter consisting of a passive LC-circuit and of a linear amplifier which compensates the voltage ripple appearing across the filter capacitor (resulting from the ripple current of the switch-mode stage). The design of the linear amplifier has to be performed only regarding the ripple voltage and the ripple current of the passive filter part. Consequently, the rated power of the amplifier and the appearing losses become low as compared to the output power of the total system. A further advantage of the concept is that the output impedance of the total system will be determined mainly by the linear stage. Therefore, contrary to conventional switch-mode amplifiers where the output filter significantly worsens the output impedance, the presented system concerning this property (which especially is important for EMC testing applications) almost is equivalent to a pure linear power amplifier which, however, would show a much lower efficiency. The paper describes the operating principle of the system, specifies the fundamental relationships being relevant to the circuit design and analyzes the control behavior of the switch-mode stage as well as of the linear circuit part.

Dimensioning and Control of a Switch-Mode Power Amplifier Employing a Capacitive Coupled Linear-Mode Ripple Suppression Stage

In order to expedite the development of power electronic systems towards higher power density and efficiency at a lower cost of implementation, Google and IEEE initiated the Google Little Box Challenge (GLBC) aiming for the worldwide smallest 2 kVA/450 VDC/230 VAC single-phase PV inverter with η > 95% CEC weighted efficiency and an air-cooled case temperature of less than 60 °C by using latest power semiconductor technology and innovative topological concepts. This paper, i.e. Part B of a discussion of The Essence of the Little Box Challenge, presents the hardware implementations and novel control concepts of two GaN-based inverter systems selected by the authors to counter the challenge: (i) Little Box 1.0 (LB 1.0), a H-bridge inverter with two interleaved bridge-legs both operated with Triangular Current Mode (TCM) modulation which features a power density of 8.18 kW/dm
 3
 (134 W/in
 3
) and a nominal efficiency of 96.4% and (ii) Little Box 2.0 (LB 2.0), an inverter topology with single bridgeleg DC/|AC| buck-stage operated with constant frequency PWM and a subsequent |AC|/AC H-bridge unfolder, which features a remarkable power density of 14.8 kW/dm
 3
 (243 W/in
 3
) and a nominal efficiency of 97.4% Implemented using latest GaN power semiconductor technology, Zero Voltage Switching (ZVS) throughout the AC period and a variable switching frequency in the range of 200 kHz-1 MHz in order to shrink the size of filter passives, the LB 1.0 was ranked among the top 10 out of 100+ teams actively participating in the GLBC. The LB 2.0 is the result of further research and considers lessons learned from the GLBC and achieves despite moderate 140 kHz constant frequency PWM and hard-switching around the peak of the AC output current a higher power density ρ and a higher efficiency η. For both implemented prototypes experimental results are provided to confirm that all GLBC technical requirements are met. The experimental results include steady-state and step-response waveforms, EMI and ground current measurements, as well as efficiency and operating temperature measurements. The reason for the ηρ-performance improvement of LB 2.0 over LB 1.0 are then discussed in detail. Furthermore, the solutions of other GLBC finalists are described and then compared to the performance achieved with the hardware prototypes presented in this paper. This leads to findings of general importance and provides key guideline for the future development of ultracompact power electronic converters.

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The Essence of the little box challenge-part B: Hardware demonstrators & comparative evaluations

This paper details the weight optimization of the electrical machine required for an Airborne Wind Turbine (AWT) system Presented investigations include the analysis of the power-to-weight ratio versus efficiency limits, γ-η Pareto fronts, of radial and axial flux machine topologies, by making use of analytical models, describing the electromagnetic and thermal behaviour A direct search method is employed rather than a cost function minimization algorithm, as the analytical models allow the evaluation of the whole design space in a computationally efficient manner The results reveal that the best performance in this case is achieved with a radial flux machine with an internal rotor where the magnets are arranged in a Halbach configuration Including the weight of electromagnetically inactive parts, such as bearings, shaft and housing, a power-to-weight ratio of γ ≈ 62 kW/kg (28 kW/lb), at an efficiency of η ≈ 96 %, and a rated speed of 3200 r/min is achieved

Weight optimization of a machine for airborne wind turbines

The paper presents a novel topology for a bearingless permanent magnet motor. This disk-shaped motor can be advantageously employed in delicate bioreactor processes. Both torque and bearing forces originate inside this magnetically levitated motor. Using 3D-FEM analysis, the optimal machine sizing parameters are evaluated with the goal to maximize torque while providing sufficient bearing forces to allow a stable operation.

Design of a novel bearingless permanent magnet motor for bioreactor applications

Low-noise and low-distortion voltage and current acquisition circuits, both analog and digital, are required for the control systems of precision, high-power switch-mode (Class-D) amplifiers used in nanometer-accuracy mechatronic systems. In this paper, the achievable linearity and noise of analog signal processing elements, such as sensors or active filters, is investigated and their performance in a closed-loop control system is demonstrated. Resistive voltage dividers are sufficiently linear but are subject to resistor noise. Nonetheless, a signal-to-noise ratio (SNR) of 130dB is achievable. Shunt resistors can achieve a total harmonic distortion (THD), limited by self-heating, of 110dB while operating at switching frequencies up to 500kHz.

Johann W. Kolar

Papers

Dimensioning and Control of a Switch-Mode Power Amplifier Employing a Capacitive Coupled Linear-Mode Ripple Suppression Stage

The Essence of the little box challenge-part B: Hardware demonstrators & comparative evaluations

Weight optimization of a machine for airborne wind turbines

Design of a novel bearingless permanent magnet motor for bioreactor applications

Voltage/current measurement performance and power supply rejection in all-digital Class-D power amplifiers