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 common approach for selecting a suitable EMI filter is detailed based on the example of a realized single-phase 500W PFC rectifier The presented work separates conducted EMI noise into Differential Mode (DM) and Common Mode (CM) components and derives expressions for the DM and CM insertion losses achieved if a given EMI filter is connected to a dedicated power converter With the use of hardware measurement results it is shown that the impedances of the EMI filter and the PFC rectifier have a considerable impact on the realized insertion losses, which, at particular frequencies, may be even less than approximate worst-case estimations proposed in CISPR 17

Practical characterization of EMI filters replacing CISPR 17 approximate worst case measurements

Three-phase rectifiers are widely used in several applications. The main feature desired in these power converters is a satisfying regulation of dc output voltage/current, but this ought to be achieved with high quality ac currents and unitary power factor. The most conventional schemes have unidirectional power flow and a compensation of the ac-side current should be implemented in high-performance systems. A small part of the power converted can be employed to enhance the characteristics in the mains side by using additional passive, active or hybrid circuits. This paper is the first of two parts, where the technology of ac-dc three-phase power converters with compensation techniques to attain ac currents with ohmic behaviour is reviewed. This part reports the passive networks used for this aim, describing the most popular topologies and features.

Three-Phase Rectifiers with Current Compensation Schemes - Part I: Passive Circuits

The paper presents a novel topology for a bearingless permanent magnet motor which is especially qualified for high-torque and yet gentle bioreactor stirring. Both torque and bearing forces are created inside this magnetically levitated disk-shaped motor using a sophisticated control with superimposed coil currents. An optimal design is derived using 3D-FEM analysis and the results are verified with a prototype setup.

Novel bearingless brushless motor in exterior rotor construction for stirred bioreactors

An apparatus for increasing the voltage utilization of a three phase PWM rectifier system (1) with a star connection of filter capacitors connected to the mains phase terminals, star point (5) is connected to the output voltage center point (100). The control of the input currents is done by a current controller (31) in each phase that defines the gate signals for the bridge-leg change over switches (14, 15, 16). The phase current reference value (29) formed by a supervising output voltage controller, is extended according to the invention by adding a phase current reference component that is equal for all three phases. To form this signal, the filter capacitor voltages measured positively against the output voltage center point are added and attenuated by a gain element (36) by a factor of 3. A zero-voltage reference value function generator creates a third harmonic of the mains voltages with defined amplitude and phase position according to the mains voltage.

Apparatus for increasing the voltage utilization of three-phase pwm rectifier systems with connection between output center point and artificial mains star point

This paper introduces a bearingless motor topology with a magnet free rotor, which enables higher rotor torque densities and wider air gap compared to previously published topologies. Flux density in the air gap and therefore torque capability is maximized by a stator in temple configuration, which provides large winding space. The low number of eight stator and six rotor teeth keeps stray flux low, which enables wider air gap ratios at the same time. A challenge of having a low teeth number are large angle dependent force and torque nonlinearities, which are compensated in the control algorithm. A 3D FEM optimized prototype was constructed and put into operation. Measurements of the running system are presented to confirm the feasibility of the introduced topology.

Johann W. Kolar

Papers

Practical characterization of EMI filters replacing CISPR 17 approximate worst case measurements

Three-Phase Rectifiers with Current Compensation Schemes - Part I: Passive Circuits

Novel bearingless brushless motor in exterior rotor construction for stirred bioreactors

Apparatus for increasing the voltage utilization of three-phase pwm rectifier systems with connection between output center point and artificial mains star point

A high torque, wide air gap bearingless motor with permanent magnet free rotor