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

Phase-modular buck-boost dc/ac inverters extend the voltage conversion range of conventional buck-type inverter topologies, and accordingly offer significant advantages for variable-speed motor drives powered from DC sources with wide-voltage-ranges like fuel cells or batteries. In this Letter, two new modulation schemes are applied to the Six-Switch Buck-Boost Y-Inverter (6YI) topology, with an analysis of the efficiency improvement for the proposed Third Harmonic Injection PWM (TPWM) and Discontinuous PWM (DPWM) schemes relative to conventional Sinusoidal Pulse Width Modulation (SPWM). TPWM substantially reduces conduction losses and DPWM extends this gain by eliminating high-frequency switching for 1/3 of the fundamental period. These gains are validated on a 1kW hardware demonstrator across a DC input voltage from 80V to 240V, with DPWM reducing total converter losses by 31% over SPWM for a peak efficiency at nominal load of 95.6% with a power density of 62.3W/in^3.

Comparative Evaluation of Harmonic Injection Techniques for a Phase-Modular Three-Phase Six-Switch Buck-Boost Y-Inverter

In this paper, a three-phase buck-type unity power factor rectifier is designed for high-power electric vehicle battery charging mains interfaces. The characteristics of the converter, named the SWISS Rectifier (SR), including the principle of opera- tion, modulation strategy, suitable control structure, and dimen- sioning equations are described in detail. Exemplarily, a 7.5 kW hardware prototype is then designed based on the derived ana- lytical expressions and the feasibility of the SR concept is demon- strated by the means of experimental measurements. Finally, the SR is compared with a conventional six-switch buck-type ac-dc power conversion. According to the results, the SR is the topology of choice for a buck-type PFC.

Design and Implementation of a Three-Phase Buck-Type Third Harmonic Current Injection PFC

The “Solar Climber”, a model version of the space elevator, is a great project to introduce students to power electronics. In this project the students are faced with the elementary engineering problem of powering a vehicle (an electromechanical system) from a limited energy source such as a solar panel in this case. Apart from learning about and building a simple buck converter as their first power electronics system, they must also identify the interdependences between a limited energy source, energy conversion efficiency, weight and climbing speed. A buck converter is required to convert a solar panel’s output to a voltage level suitable for the electric motors that drive the elevator towards “space”. This paper describes the motivation, the model space elevator, the learning outcomes and the experiences from this project. Further practical solar power projects, the solar car and mains interface, are presented that have proven to be excellent projects for teaching experimental power electronics.

Modeling the Space Elevator – A Project Oriented Approach for Teaching Experimental Power Electronics

This study explores the upper limits in power-to-weight and torque-to-weight ratios of coreless axial-flux machines with permanent magnets. Moreover, it provides a comprehensive multifunctional optimisation procedure that is utilised for obtaining these limits. The procedure encompasses analytical analysis of electro-magnetic, thermal and structural (mechanical) aspects of axial-flux machines. Obtaining global minima is ensured by considering the whole machine design space, and mapping it into the performance space, where a Pareto front can be easily identified. From it, an optimal motor/generator for airborne wind turbines is identified. The design has a power-to-weight ratio of 6.4 kW/kg (19 Nm/kg at 3200 rpm) including structural (purely mechanical) parts, at an efficiency of 95%. This is a significantly higher ratio than the one in modern commercial machines or designs reported in the literature. Therefore, the resulting machine is manufactured and experimentally tested in order to verify the claimed limits and the optimisation methodology.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-epa.2018.5228

Johann W. Kolar

Papers

Comparative Evaluation of Harmonic Injection Techniques for a Phase-Modular Three-Phase Six-Switch Buck-Boost Y-Inverter

Design and Implementation of a Three-Phase Buck-Type Third Harmonic Current Injection PFC

Modeling the Space Elevator – A Project Oriented Approach for Teaching Experimental Power Electronics

Weight optimisation of coreless axial-flux permanent magnet machines

Solid-State Transformers